Dissertations / Theses on the topic 'Tree Water Relations'

There are numerous situations where trees are grown together with herbaceous plants. In these situations there will be some degree of competition between their root zones, depending on the water content of the soils and crop and tree root distribution . Two studies were conducted : the first with maple (Acer platanoides) grown in turf grass, and the second with willow (Salix matsudana) grown in more deeply rooted barley . The objectives of this study were to quantify the effect of herbaceous competition of potential tree water stress under irrigation and when the soil is allowed to dry-down . Soil water uptake was measured in both studies to 1.2 m depth and outwards to 1.2-2.10 m away from the tree . In the maple-turf grass study, water content was measured in a single line away from the tree , while four lines covering a quadrant of the surface area were measured in willow . Water relations stomatal conductance and water potential, and tree growth were also monitored in both studies. Water uptake in turf plots was statistically different from mulch plots by depth and distance during three seasons. Water uptake was greatest at 0-60 cm depth in the turf treatments compared with mulch treatments. Soil water in mulched plots decreased slowly during the growing season. There were no statistical differences between bare soil and barley competition water uptake after soil surface water was depleted. There were marked differences in tree root characteristics as a result of competition from turf or barley roots. The root systems of maples in the mulch and willow in bare soil extended laterally and fine roots were evident. Tree roots extended deeper and fine root were reduced under competition from turf and barley. Trees growing with turf and barley had fewer roots in the top 0.3 m soil surface while trees in mulch and bare soil had more and greater diameter roots at the same depth. Early in the season, when water content is high, root competition for water was not evident, and late in the season after turf roots and barley had depleted the soil water, trees exhibited more negative predawn leaf water potential and less stomatal conductance in response to water stress during a soil dry-down period. Tree growth was measured periodically during 1994, 1995, and 1996. Leaf area and stem growth comparisons showed a significant increase in size as a result of the absence of competition in both species, with mulch and bare soil treatments. Leaf area in mulched trees was twice that in turf treatments. In summary, we found that competition resulted in deeper tree root growth and less top growth in the presence of herbaceous competitors.

Dissertation (PhD (Bosb))--University of Stellenbosch, 2003.<br>ENGLISH ABSTRACT: This study was conducted to evaluate and compare the water and nutrient relations of three indigenous deciduous tree species, viz., Cordia africana Lam., Croton macrostachyus Del., Millettia ferruginea (Hochst.) Baker and two widely planted eucalypts, viz., Eucalyptus camaldulensis Dehnh and Eucalyptus globulus Labill from Ethiopia. The study was organized as glasshouse and field observations in Ethiopia. Owing to the lack of baseline studies on the water and nutrient relations of the deciduous tree species, the glasshouse experiments involved a wide range of water and nutrient applications. Seedlings were grown with the supply of various levels of water and nutrients during which gas exchange, water potential, relative water content, tissue nutrient content and biomass production were measured. The field observations were limited to the study of surface root distribution and leaf nutrient composition of mature trees and their effects on soil nutrient pool. The observations were made on isolated trees and mixed or pure stands of trees in Badessa area, Eastern Ethiopia. The field site was selected because of the availability of the study species and suitability of the trees for the study. In the glasshouse, increased water deficit significantly reduced predawn leaf water potential, relative water content, stomatal conductance, photosynthetic rate, whole plant water use efficiency, plant height, diameter, leaf area and biomass production. Both of the eucalypts did not grow faster than the deciduous species under well-watered conditions unlike under water stress conditions. C. macrostachyus and C. africana had higher transpiration rates and tissue nutrient accumulations than the other species. They also demonstrated higher biomass allocation to roots than all the other species to support the intensive water and nutrient uptake rate. Due to the ability to re-orient its leaves to avoid direct solar irradiance, M. ferruginea maintained higher tissue water potential and relative water content than all the other species under water stress regimes. The impact of imposed drought was quick and more damaging to the eucalypts compared to the deciduous tree species indicating that the eucalypts may not survive extreme drought conditions unlike the deciduous species that drop their leaves and may remain dormant for weeks. The current study gave new experimental proof that E. globulus was more vulnerable to drought than E. camaldulensis. Soil N stress resulted in an overall reduction of tissue N concentration, N:P ratio, photosynthetic rate, stomatal conductance and photosynthetic water use efficiency in all the species studied. Pants with high foliar nitrogen concentration had higher photosynthetic capacities indicating that N plays a key role in photosynthesis and growth of all the studied species. The current study showed that for all the tree species, more attention has to be given to soil N than to P as soil P had minor effects on the photosynthetic activities of plants of all species compared to N.The investigation on tissue nutrient composition confirmed that N:P ratio could be used to detect Plimitation in plants. However, N:P ratio could not distinguish between N-limitation and combined limitations of N and P. The study of isolated C. africana and C. macrostachyus trees on soils in Badessa, Eastern Ethiopia indicated improved soil N, P and K under tree canopies whereas no effects were observed on the other soil nutrients studied. Similar to glasshouse conditions, C. macrostachyus and C. africana produced extensive surface roots, interfering with crops grown in association. Due to their high nutrient cycling potential the net effect on soil was positive. Comparison of E. camaldulensis woodlot and a mixed stand composed of deciduous species indicated that the fine root biomass in the surface soil under E. camaldulensis was about three times that under the mixed stand. The fine root biomass of E. camaldulensis inside the stand and 10 meters away from the stand were comparable in the surface soils showing the presence of root competition with adjacent crops. Therefore, planting of E. camaldulensis in association or adjacent to croplands should be avoided. Nutrient and carbon pool of soil inside the mixed stand was generally higher than that of E. camaldulensis indicating that trees of the mixed stand recycled more nutrients to the soil.<br>AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die verskille tussen water- en voedingstofverhoudings van drie inheemse blaarwisselemde boomsoorte te vergelyk, viz., Cordia africana Lam., Croton macrostachyus Del., Millettia ferruginea (Hochst.) Baker en twee bekende eucalyptus spesies, viz., Eucalyptus camaldulensis Dehnh en Eucalyptus globulus Labil van Etiopië. Die studie het bestaan uit kweekhuis- en veldobservasies in Etiopië. As gevolg van beperkte navorsing ten opsigte van water- en voedingstofverhoudings in bladwisselende boomsoorte, het die kweekhuis-eksperimente bestaan uit 'n wye verkeidenheid water- en voedingstoftoetse. Saailinge is gegroei deur verskillende vlakke van water- en voedingstowwe by te voeg. Gaswisseling, waterpotensiaal, relatiewe hoeveelheid water, hoeveelheid voedingstowwe en produksie van biomassa is gemeet. Die veldobservasies was beperk tot oppervlak-wortelverspreiding en blaarvoedingstof hoeveelhede van volwasse bome, sowel as die effek op grondvoedingstowwe. Observasies was beperk tot geïsoleerde, gemengde en een spesie opstande, in die Badessa area, Oos Etiopië. Die studiearea was gekies op grond van die voorkoms van die gekose boomsoorte, sowel as die toepaslikheid van die bome vir die studie. In die kweekhuis is gevind dat die verhoogte watertekort die pre-sonop blaarwaterpotensiaal, relatiewe hoeveelheid water, stomatiese geleiding, fotosintetiese tempo, heelplant water-gebruikseffektiwiteit, plant hoogte, diameter, blaararea en biomassa produksie beduidend verminder het. Nie een van die eucalyptus spesies het vinniger as die bladwisselende spesies onder voldoende hidrasie gegroei nie. Dit was egter nie die geval onder die waterbeperkte toestande nie. C. macrostachyus en C. africana het ‘n hoër transpirasie tempo sowel as weefselvoedingstof waardes gehad as die ander spesies. Hierdie boomsoorte se wortelbiomassa was ook meer as die ander spesies, om vir die tempo van water- en voedingstofopname te akkomodeer. As gevolg van die vermoë om blare te kan oriënteer om direkte sonlig te vookom, het M. ferruginea ‘n hoër water-weefselpotensiaal en relatiewe waterinname gehad in vergelyking met die ander boomsoorte in beperkte water toestande. Die impak van gëinisieerde droogte het vinnig voorgekom en het meer skade aan die eucalyptus aangerig in vergelyking met die bladwisselende boomsoorte. Dit dui aan dat die eucalyptus-spesie nie ekstreme droogte kan oorleef nie, waar bladwisselende spesies hul blare laat afval en vir weke aan een dormant kan bly. Hierdie studie gee eksperimentele bewyse dat E. globulus minder bestand is teen droogte as E. camaldulensis. Beperkte N in die grond het veroorsaak dat daar ‘n algemene vermindering van weefsel Nkonsentrasie, N:P ratio, fotosintetiese tempo, stomatiese geleiding en fotosintetiese watergebruiks effektiwiteit in al die bestudeerde spesies was. Plante wat oor hoër blaar-stikstofkonsentrasiesbeskik, het hoër fotosintetiese kapasiteite wat aandui dat N ‘n belangrike rol in fotosintese en die groei van al die bestudeerde spesies speel. Die oorhoofse bevindings van die studie was, dat daar meer aandag gegee moet word aan grond-N as P omdat grond-P net ‘n kleiner rol speel in die fotosintetiese aktiwiteite van plante van al die spesies in vergelyking met N. Die ondersoek na weefselvoedingstof hoeveelhede het bewys dat die N:P ratio gebruik kan word om P-tekorte in plante aan te dui. Die N:P ratio kan egter nie die verskil in N-tekorte en gekombineerde tekorte van N en P aandui nie. Die studie van die geïsoleerde C. africana en C. macrostachyus bome op grondtipes in Badessa, Oos Etiopië het verbeterde grond-N, P en K onder kroondak gebiede getoon, daar was egter geen verskille in die ander grondvoedingstowwe wat bestudeer is nie. In toestande gelykstaande aan die van die kweekhuis, het C. macrostachyus en C. africana meer oppervlaksswortels ontwikkel. Die toename aan oppervlakswortels het ingedring op gewasse wat in assosiasie gegroei is, dit het egter ‘n positiewe effek op die grond gehad as gevolg van die hoë voedingstof-siklus-potensiaal. Die E. camaldulensis opstand is gevergelyk met ‘n gemengde opstand van bladwisselende spesies waar daar gevind is dat die fynwortel biomassa in die oppervlak grond onder die E. camaldulensis ongeveer drie keer soveel was as die van onder die gemengde opstand. Kompetisie met aangrensende gewasse is aangeui deurdat die fynwortel biomassa van E. camaldulensis binne die opstand en 10 meter weg van die opstand vergelykbaar was in die oppervlakgronde. Dit dui dus aan dat die plant van E. camaldulensis in assosiasie of aangrensend aan gewasse vermy moet word. Die teenwoordigheid van voedingstowwe en koolstof in die grond van die gemengde opstand was oor die algemeen hoër as die van die E. camaldulensis. Dit is ‘n aanduiding dat die bome van die gemengde opstand meer voedingstowwe aan die grond verskaf.

La biodiversité favorise un grand nombre de fonctions et services écosystémiques des écosystèmes forestiers tels que la production de bois ou la résistance aux attaques d’insectes et aux maladies. Cependant l’impact de la diversité sur l’acquisition et l’utilisation de l’eau et du carbone reste largement méconnu dans ces écosystèmes. De plus, dans le contexte actuel de changement climatique, l’influence de la diversité sur la réponse des écosystèmes forestiers à des événements climatiques extrêmes tels que la sécheresse reste à étudier. L’objectif de ce travail est donc de déterminer l’impact de la diversité en espèces d’arbre sur d’importantes fonctions du cycle de l’eau et du carbone telles que la transpiration, la composition isotopique du carbone ou la profondeur d’extraction de l’eau à l’échelle de l’arbre et de l’écosystème sous des conditions contrastées dedisponibilité en eau du sol. Ce travail a été réalisé dans le cadre du projet FunDivEUROPE sur un réseau de parcelles forestières ainsi que dans des plantations expérimentales le long d’un gradient Nord-Sud en Europe afin de couvrir une importante gamme de conditions climatiques. Nos travaux ont montré une importante variabilité de la réponse à la diversité à l’échelle de l’arbre et de l’écosystème en termes de relations hydriques et carbonées à travers l’Europe. La diversité en espèces ne semble pas influencer les relations hydriques et carbonées des espèces et des écosystèmes forestiers dans des conditions non limitantes de disponibilité en eau. Cependant, un fort effet de la diversité a été observé en conditions de sécheresse pour certains types forestiers. A partir de ces résultats, je discute des mécanismes d’interaction entre espèces qui peuvent expliquer les effets observés. Nos données ont montré que l’influence de la diversité en espèces est fortement dépendante du contexte et peut êtremodifiée par les conditions environnementales locales et les conditions climatiques. En terme de gestion forestière, je suggère que pour certaines régions en Europe, promouvoir la diversité en espèces ainsi que contrôler la densité des parcelles doit être recommandé afin d’adapter les écosystèmes forestiers aux futures conditions climatiques<br>Biodiversity is known to support and boost a wide range of forest ecosystem functions and services like productivity and resistance against insect pests and diseases. However, whether tree species diversity also promotes water and carbon acquisition and use in forest ecosystems is still unclear. Furthermore, in the current context of global warming, information on how tree species diversity can influence the response of forest ecosystems to extreme climatic events such as drought are urgently needed. In this framework, the objective of my PhD thesis was to determine how tree species diversity influences important functions of the water and carbon cycle including transpiration, carbon isotope composition and water extraction depth at the tree- and ecosystem-Scale under contrasting soil water conditions. My work was conducted within the FunDivEUROPE project in a network of permanent forest stands and tree plantations across a North-South gradient in Europecovering a wide range of climatic conditions. I found considerable variability among species or forest types in the response of transpiration and carbon isotope composition at the tree- and ecosystem-Scale across Europe. Species diversity did not affect the water and carbon relations of tree species and forest ecosystems under non-Limiting soil water conditions. However, a strong effect of species diversity was observed under drought conditions in some forest types. Based on these data, I discuss the potential mechanisms of species interactions that may explain the observed patterns. I also point out that the influence of species diversity is highly context-Dependent, and changes with local environmental and climatic conditions. In terms of forest management applications, I suggest that, at least in some regions, controlling for tree species diversity along with stand density and total basal area could be recommended to help forests adapt to drier conditions

Hemiepiphytes are important components of tropical forests and are attractive to scientists due to their unique epiphytic growth habit during some period of their life cycle. Unique characteristics in plant water relations and carbon economy have been found in hemiepiphytic plants; however, to further understand this group of species on an evolutionary basis it is necessary to carry out comparative studies between hemiepiphytes and their close relatives. In this dissertation I conduced a comparative study in a suite of functional traits related to plant water relations and photosynthesis between hemiepiphytic and non-hemiepiphytic tree species from a single genus-Ficus. Great differentiation in functional traits has been found between species of the two growth forms both during juvenile and adult stages. Seedlings of hemiepiphytic Ficus species (H) had significantly lower xylem hydraulic conductivity, stomatal conductance, net light saturated CO2 assimilation, and higher water use efficiency than congeneric non-hemiepiphytic species (NH), which are adaptive to a drought-prone epiphytic growth conditions under natural conditions. The conservative water use adaptation in H species is likely crucial to the drought tolerance and survival in the forest canopy but is related to much lower growth rates than NH species. Species of the two growth forms both showed relatively large plasticity in responding to variation in light level as in typical light-demanding species. Surprisingly, the NH species showed characteristics related to higher light demand than H species, which is opposite from the prediction that H species are more light-demanding than NH species. Thus, although commonly accepted, it is likely that light was not the selective pressure for the evolution of hemiepiphytism in Ficus. Using adult trees grown in a common garden, I found that H species showed characteristics of more conservative water use even after they established connections to the soil. Moreover, H species showed significantly different traits in photochemistry compared to NH species due to hydraulic-photosynthetic coordination. The evolution of an epiphytic growth habit during the juvenile stage of a life cycle in the hemiepiphytic Ficus species thus involved changes in a suite of functional traits that persist during their terrestrial growth stages.

The morphological and physiological responses of tree seedlings to water stress and the significance of the non-hydraulic influence of root on shoot behaviour of the effects of soil drying were investigated. The experiments were conducted in a glasshouse and growth chamber, using sycamore (<i>Acer pseudoplatanus</i> L.) seedlings rooted in a soil mixture with high water holding capacity. The prime objective of the project was to evaluate the morphological and physiological components of drought tolerance that could be useful for isolation of plants with seedling characteristics acceptable for afforestation in drought-prone environments. Effects of drought on water relations and root growth were studied using long soil columns. Drought resulted in active osmotic adjustment in leaves, with decreases in osmotic potential at full and zero turgor, and it increased bulk elastic modulus and leaf dry weight to turgid weight ratio. Stomatal conductance declined well before any observable change in bulk leaf water potential and was correlated with soil water status. Drought caused changes in the root distribution profile and it increased the root weight. The increase in root weight was mainly due to a substantial shift in assimilates allocated in favour of roots with total biomass being unaffected. Cyclic water stress treatment, induced major changes in sycamore seedlings, including osmotic adjustment, acclimation of photosynthesis and stomatal conductance to water stress, increased water use efficiency, and a substantial shift in biomass allocation pattern in favour of roots, with a consequent increase in root/shoot ratio. The acclimation of photosynthetic machinery was the major factor contributing to the acclimation of photosynthesis to water stress. These modifications were concluded to be important for improvement of seedling drought tolerance. Seedlings grown in soil columns and subjected to drought exhibited substantial reduction in stomatal conductance and a limitation in leaf expansion well in advance of any detectable change in shoot water relations. Root abscisic acid (ABA) concentration increased deeper in the soil profile in concert with the progressive soil drying, and it appeared to be a sensitive indicator of the soil water status around the roots.

This study increases the body of knowledge on the drought response of plant-fungal associations. Hybrid black popular <i>Populus </i>x <i>canadensis</i>, a species commonly seen in shelter belts and small plantations, is tested on its drought response to mycorrhizal colonisation. It also suggests an alternative mechanism for the alteration of plant water relations by arbuscular mycorrhiza. The concept of chemical signalling compounds which control plant response to stress, including drought stress, is topical. This study aims to extend the concept of the plant-fungus symbiosis. The ability of the fungal hyphae to act as an integral part of the root system is tested in its contribution to signalling of drought stress to the host shoot. The response of mycorrhizal poplar to gradients in water availability was tested in two ways. First the effect of changing water availability over time, as drying and wetting cycles, was examined. Second, gradients in water availability across the root-fungal system were considered. The response of poplar to drought stress was tested when inoculated with one of four species of mycorrhizal fungi. These were <i>Glomus intraradices</i>, <i>Glomus mosseae</i>, <i>Gigaspora rosea </i>and <i>Gigaspora margarita</i>. There was no consistent improvement in plant response to drying. However there were variations in plant response over time, and with severity of drought conditions, particularly by plants colonised with <i>G. intraradices </i>and <i>Gi. rosea</i>. Changes in the host plant nutrient status were also found. The concept of hyphal to plant shoot signalling of drought was tested with poplar inoculated with <i>G. intraradices</i>, grown in a specially designed microcosm. Fungal hyphae were able to grow into a separate volume of soil from which plant roots were excluded. The soil water availability around plant roots and adjacent hyphae was altered independently. The plant response in terms of gas exchange was monitored under conditions of varying water availability in each section of the root-hyphal system. In general there were no consistent alterations in plant gas exchange with changing water availability. However during one experiment possible evidence for short-term hyphal signalling to host plants was noticed. This method is suggested as a new concept for further experimentation in plant-fungal water relations.

Dans un contexte de changement global, prédire l’évolution de la productivité de la végétation dans le sud-ouest (SO) Sibérien reste un défi du fait d’incertitudes fortes sur les processus régulant la disponibilité en eau et en nutriments. Nous avons mis en évidence des relations entre cycles biogéochimiques, climat et propriétés du sol sur six sites contrastés.La croissance radiale des tiges de peuplier est principalement sensible au bilan hydrique du sol en forêt de steppe, au sud du SO Sibérien, alors qu’elle est stimulée par de hautes températures estivales en sub-taïga, dans le nord de la région.Des mesures de terrain et des simulations du bilan hydrique du sol ont montré que la fonte des neiges est importante pour la recharge des réserves hydriques du sol au sud. Au nord, ces réserves sont souvent rechargées en automne. La fonte des neiges est alors associée à du drainage. De plus, au nord, une épaisse couverture de neige protège le sol du gel en hiver. La distribution des racines fines est plus profonde en forêt de steppe qu’en sub-taïga, impactée par le déficit hydrique et le gel.L’homogénéité du statut en phosphore (P) des sols dans le SO Sibérien montre qu’il n’est pas encore très impacté par la pédogénèse. Les stocks en P élevés, notammen tles formes disponibles pour les plantes, suggèrent que le P n’est pas et ne sera pas limitant dans le futur.La décomposition des litières aériennes et la libération de l’azote (N) sont plus rapides en sub-taïga qu’en forêt de steppe. Un fort drainage pourrait expliquer un transfert profond du N dans les sols en sub-taïga. Cependant ces sols semblent efficaces pour retenir le N, limitant les pertes pour le système sol–plante<br>Predicting the evolution of vegetation productivity in SW Siberia in the contextof global change remains a challenge because of major uncertainties concerningthe biogeochemical cycling and the plant-availability of water and nutrients. Weprovided insights on their relation to climate and soil properties, investigating sixcontrasting sites.Aspen stem radial growth is mainly sensitive to soil water budget in the foreststeppezone established in the south of SW Siberia while it is enhanced by highsummer temperatures in the sub-taiga, in the north of the region.Field measurements and water budget simulations revealed that snow-melt isimportant re-filling soil water reserves in the south. In the north, these reservesare mostly re-filled in autumn and snow-melt is associated with drainage. A thicksnow-pack also prevents soil from freezing in winter in the sub-taiga. Water deficitand soil freezing largely impact the distribution of fine roots within the soil profilewhich is deeper in forest-steppe than in sub-taiga.The homogeneous soil phosphorus (P) status in the region investigated revealedthis nutrient has not been yet very impacted by contrasting soil processes. High Pstocks, and in particular plant-available forms, suggest P is unlikely to be limitingunder current and future conditions.By contrast, we found differences in nitrogen (N) status. Above-ground litterdecay and the release of N occurs faster in sub-taiga than in forest-steppe. Higherdrainage may explain deeper N transfer in sub-taiga soils. However, sub-taiga soilsalso seem to be efficient in retaining N, limiting losses from the soil–plant system

Holz aus Kurzumtriebsplantagen (KUP) mit Pappeln (Populus spp.) kann eine bedeutende Rolle im Mix der Bioenergieressourcen in Deutschland spielen. Trotz eines günstigen Energieinput-Energieoutput-Verhältnisses ist das Erreichen wirtschaftlich zufriedenstellender Ergebnisse mit KUP jedoch auf den meisten potenziellen Anbauflächen durch hohe Ansprüche der Pappeln an die Wasserversorgung erschwert. Hohe Produktivitätsraten der Pappeln sind an einen hohen Wasserverbrauch gebunden und viele Trockenheitsanpassungen führen zu deutlichen Ertragsrückgängen. In der vorgestellten Arbeit wurde eine sechsjährige Vollgeschwister-F1-Kartierungspopulation der Europäischen Zitter Pappel (Aspe, Populus tremula L., Wuchsperiode 1998-2003) physiologisch und genetisch untersucht, um mögliche Wege zu einer züchterischen Verbesserung der Trockenheitstoleranz von Pappeln diskutieren zu können. Dabei wurde das Zuchtziel der Trockenheitstoleranz als Minimierung der Ertragsrückgänge unter trockenen Bedingungen definiert. Neben wuchsleistungsbezogenen Größen (Biomassegesamtleistung (BM, oberirdische Dendromasse), Biomassezuwachs (iBM), Radialzuwachs (ir), Baumhöhe (h)) wurden physiologisch holzanatomische Eigenschaften untersucht, die retrospektiv anhand der Jahrringe messbar sind und zur nicht direkt messbaren Eigenschaft der Trockenheitstoleranz in einer Beziehung stehen. Diese waren die Kohlenstoff- und Sauerstoffisotopsignatur (δ13C, δ18O), die Faser- und Gefäßgliedlänge (FL, GL), die Gefäßlumenquerschnittsfläche (AG), die Gefäßdichte (GD), der potenziell Saftstrom leitende Querschnittsflächenanteil (LQ), der hydraulisch gewichtete Gefäßlumendurchmesser (Dh) und die röntgendensitometrische Holzdichte (RD). Um trockenheitsbedingte physiologische Reaktionen vom Einfluss der Juvenilität der Kartierungspopulation unterscheiden zu können, wurden regionaltypische Juvenilitätstrends der RD, FL, GL, und des ir anhand eines zweiten, für das östliche Deutschland repräsentativen Aspen-Kollektivs aus natürlicher Sukzession ermittelt. Bedingt durch Trockenheitsanpassungen bzw. eine bevorzugte Wurzelentwicklung nach dem Verpflanzen zeigte die Kartierungspopulation in den ersten drei Jahrringen Abweichungen von den regionaltypischen Juvenilitätstrends. In den Trendverläufen der Kartierungspopulation heben sich die beiden Trockenvegetationsperioden 2000 und 2003 ab, wobei bis zum Sommer 2003 infolge des Starkniederschlages 2002 (Flut) ein außergewöhnlich gutes Grundwasserangebot herrschte. Alle untersuchten phänotypischen Eigenschaften zeigten 2000 starke trockenheitsbedingte Abweichungen. Im Jahrring 2003 wichen nur die GL und die RD von ihren Juvenilitätstrends ab. Außerdem konnte anhand der δ13C und δ18O Werte eine signifikante Abnahme der Wassernutzungseffizienz bzw. eine Zunahme der Transpiration im Jahr 2003 gezeigt werden. Die übrigen Größen folgten ihren Juvenilitätstrends und stiegen an. Die Jahrringdatensätze 2000 und 2003 der RD waren nicht signifikant mit der BM korreliert, dagegen zeigten die δ13C Datensätze 2002 und 2003 schwach positive Korrelationen mit der BM. Der trockenheitstoleranteste Genotyp verband seine überdurchschnittliche BM mit einer hohen Wassernutzungseffizienz (angezeigt durch überdurchschnittliche δ13C Werte), mit einer überdurchschnittlichen AG und mit einer nicht unterdurchschnittlichen RD in Höhe des Populationsmittels. Aufgrund des Fehlens negativer Korrelationen zwischen BM und δ13C bzw. BM und RD in der vorliegenden Arbeit können δ13C und RD als nützliche Weiser für die Unterscheidung der Trockenheitstoleranz verschiedener Aspen zu züchterischen Zwecken vorgeschlagen werden. Außer der BM unter trockenen Bedingungen kann keine der untersuchten Eigenschaften als alleiniger Trockenheitstoleranzweiser empfohlen werden. Zu einer Trockenheitstoleranzbewertung sollten Merkmalspaare verwendet werden, von denen ein Merkmal positiv mit dem Ertrag korreliert ist und das andere eine Trockenheitsanpassung verkörpert. Dadurch werden sowohl das primäre Zuchtziel eines höchstmöglichen Ertrages als auch eine bessere Trockenheitsangepasstheit berücksichtigt. Zwei verschiedene Trockenheitstoleranzindizierungen wurden angewendet, um die Kartierungsnachkommen entsprechend ihrer Trockenheitstoleranz einem Ranking zu unterziehen. Dabei wurden in beiden Fällen Bäume mit einem höheren Ertrag besser platziert. Der zweite Schwerpunkt der Arbeit lag auf der genetischen Kartierung von Quantitative Trait Loci (QTL) für die untersuchten phänotypischen Jahrringeigenschaften mit Bezug zur Trockenheitstoleranz. Als Basis für das QTL Mapping wurden, der Pseudo-Testcross-Mapping-Strategie folgend, genetische Kopplungskarten für die Elternbäume der Kartierungspopulation konstruiert. Die maternale Karte (P. tremula, „Schandau 4“) deckte mit 157 Markern (144 AFLP, 13 SSR) in 30 Kopplungsgruppen 1.369 cM ab, die 21 paternalen Kopplungsgruppen mit 148 Markern (132 AFLP, 16 SSR) überspannten 1.079 cM des Genoms (P. tremula, „Lichtenhain 1“). Die im Vergleich zur haploiden Chromosomenzahl der Pappeln (19) hohen Zahlen an Kopplungsgruppen sowie die hohen Zahlen an Doublets und unkartierten Markern zeigten eine geringe Genomabdeckung an. So konnte nur eine begrenzte Zahl, höchstens zwei QTL für die untersuchten phänotypischen Jahrringeigenschaften mit Bezug zur Trockenheitstoleranz, kartiert werden. Ein QTL Bereich mit pleiotropem Effekt auf mehrere wachstumsbezogene Größen wurde auf der maternalen Kopplungsgruppe 1 (dem Populus Chromosom I zuzuordnen) detektiert. Die Signifikanz der Effekte dieses QTL auf den Radialzuwachs entwickelte sich steigend mit zunehmendem Baumalter<br>Wood production in short rotation coppices (SRC) with poplar (Populus spp.) can contribute significantly to the future bio energy supply mix in Germany. Although the energy-input to energy-output ratio is rather good, SRC often do not meet cost effectiveness due to high water demand of poplar species. High biomass productivity depends on optimal water supply. Also, numerous adaptations to water deficits result in an undesirable decrease of yield. Combined physiological and genetic investigations were conducted within a six-year old F1-full-sib crossbred population of European aspen (Populus tremula L., growing period 1998-2003). Possible implications on selection, breeding or improvement of poplar cultivars showing a high tolerance to water deficits are discussed. For the work presented here, the breeding goal of higher water deficit tolerance was defined as the minimisation of yield losses under dry conditions. Beyond growth related traits (aggregate yield (BM), aboveground woody biomass), biomass increment (iBM) and radial increment (ir), physiological and wood anatomical traits were included; these are related to reactions to water deficit and are measurable on tree rings retrospectively. These traits were the Carbon- and Oxygen isotope ratios (δ13C, δ18O), the fibre length and vessel element length (FL, GL), the vessel lumen cross sectional area (AG), the vessel density (GD), the cumulative vessel lumen area to cross sectional area ratio (LQ), the hydraulically weighted mean vessel lumen diameter (Dh) and wood density assessed by X-ray densitometry (RD). To distinguish the drought induced physiologic reactions from juvenile developmental patterns of the mapping population, juvenile trends of RD, FL, GL, and ir, which are representative of habitats in south-eastern Germany, were investigated in a second aspen collective that was selected from natural succession. During the first three years, the mapping population showed deviations from the juvenile trends due to water deficit adaptations or preferential root development, respectively. Due to drought in the growing seasons of 2000 and 2003, the juvenile trends show outstanding values for both years, although ground water supply in 2003 was exceptionally good following the intense rain event of 2002 (Elbe flood 2002). The tree ring traits of both years stand out from the juvenile trends due to drought adaptations. In 2000, all phenotypic traits showed a significant deviation from their respective trends. In 2003, only GL and RD showed an adaptation to drought as observable by a deviation from their juvenile trends. A significant decrease in water use efficiency (WUE) and an increase in net transpiration, respectively, were shown for 2003 by means of δ13C or δ18O values. All other traits showed an increase following their juvenile trends. RD data for 2000 and 2003 were not significantly correlated with BM, but δ13C data (and therefore WUE) for 2002 and 2003 revealed a weakly positive correlation with BM. The genotype that was most tolerant to water deficits showed a combination of a superior growth with a superior WUE (by means of δ13C), a superior AG, and an RD close to but not less than the population average. Due to the lack of negative correlation between BM and δ13C or BM and RD in the present work, δ13C and RD can be valuable proxies for the determination of drought tolerance of aspen trees for tree improvement purposes. Aside from BM under dry conditions, no other traits that were investigated can be recommended as a stand-alone proxy for water deficit tolerance. For a water deficit tolerance evaluation, pairs of traits should be used, of which one trait is positively correlated with yield and the other represents a water deficit adaptation. Both the primary breeding goal of the highest possible yield as well as a better water deficit tolerance should always be considered in this context. Two different drought tolerance indices were used to rank the individuals of the mapping population according to their water deficit tolerance. In both cases, trees with higher BM were ranked better. The second focus of the present work is on genetic mapping of Quantitative Trait Loci (QTL) for the investigated tree-ring traits that refer to water deficit reaction. As a basis for the QTL-mapping approach, genetic linkage maps were constructed for each parental tree of the F1-full-sib crossbred mapping-population following the two-way pseudo-testcross mapping strategy. The maternal map (P. tremula, “Schandau 4”) consisted of 157 markers (144 AFLP, 13 SSR) in 30 linkage groups and covered 1,369 cM. The 21 linkage groups of the paternal map (P. tremula, “Lichtenhain 1”) covered 1,079 cM of the genome (144 AFLP, 13 SSR). Compared with the haploid chromosome number (19) of the Populus genome, the high number of linkage groups, doublets and unlinked markers indicated low genome coverage. Only a low number of QTL was detected, maximal two per in¬vesti¬gated phenotypic trait with a relation to water deficit tolerance. One QTL having a pleiotropic effect on several growth related traits was detected on the maternal linkage group 1 (corresponding to the Populus Chromosome I). The significance of the QTL effects seemed to increase with tree age

The Australian macadamia industry faces two significant challenges; high levels of fruit abscission during early fruit development, and declining average yields from orchards. The decline in average yield is occurring despite the maturing of an industry where production and plant husbandry methods have been considerably refined since the early days of macadamia farming in Australia. In terms of the high early fruit drop, it has previously been estimated that approximately 1 to 3 percent of the initial fruit set reaches maturity. Plant reproduction imposes significant resource costs to trees; these include water, carbohydrates and nutrients. The potential causes of the declining yield or the high fruit drop are likely to be complex and involve many factors. The research presented in this thesis is based on a physiological understanding of reproductive water relations and within tree interactions. The primary aim of the research was to identify factors other than soil water content that influence reproductive water relations under field conditions, and whether these factors affect reproductive success and yield in macadamia. Research was undertaken at two locations in the Bundaberg region; a commercial macadamia orchard and research blocks of macadamia trees (DAFF Research Station) managed in the same way as a commercial orchard. Tree water status was assessed through water potential and transpiration measurements. Trees and branches were manipulated to investigate reproductive and vegetative interactions, reproductive water relations, and vascular hydration pathways. A small number of detached stem experiments were also undertaken to investigate water relations and reproductive interactions. The interaction discovered between leaves and racemes in macadamia is perhaps the most significant in terms of future research and the potential to increase commercial macadamia production. The interaction identified means that as floral or fruit load increases, leaf stomatal conductance in macadamia declines. This is in contrast to many other tree crops, which increase leaf stomatal conductance and photosynthesis in response to fruit presence and load. The potential effect in macadamia is to limit photosynthesis and carbohydrate production, which imposes a significant limit on reproductive development and therefore fruit set. Results from this study provide a mechanism that explains why macadamia have such a high level of early fruit drop. This reproductive load response in macadamia could be related to the maintenance of plant water relations and conservation of limited soil water under natural forest conditions and seasonally dry periods. Another important interaction was the source-sink ratio, that is, changing the ratio in favour of the sink (flowers and fruit) lowered the leaf stomatal conductance rate. This response is counter-intuitive as many plants typically increase leaf stomatal conductance and photosynthesis as the number of fruit increase. However, macadamia appear to be unusual and the reverse occurs as fruit load increases. Results from this part of the study showed that fruit drop will increase and yield will be significantly lower when the source-sink ratio favours fruit. Branch angle in macadamia trees also appears to be important, with the angle of branches influencing floral load and density, leaf stomatal conductance, and leaf water potential. Horizontal branches had the most positive influence on floral load in macadamia. An important aspect of branch angle was the influence of flushing and the potential for vertical branches to dominate the canopy. Flushing resulted in a significantly lower leaf stomatal conductance rate on horizontal branches compared with vertical branches. This is likely to lead to lower vegetative growth on horizontal branches and comparatively more on vertical branches. The other aspect of flushing was a lower leaf stomatal conductance (indicative of a lower photosynthesic rate in macadamia), which has already been shown to negatively impact on fruit set. This thesis also investigated reproductive hydration pathways by measuring water potential gradients, cincturing and histology studies. Xylem hydration of flowers and fruit appears important in macadamia, however results indicate that water entering flowers and fruit via the phloem ranges between 5 and 13 percent. Results also indicated that macadamia florets have a diurnal transpiration pattern. Floral transpiration varies throughout the day and appears to follow a similar pattern to leaves. The final area investigated in this thesis was the effect of vapour pressure deficit on fruit set under field conditions. The microclimate surrounding macadamia racemes appears to be important, with a small change in the mean daily vapour pressure deficit significantly decreasing the initial fruit set (1.6 kPa compared with1.3 kPa). The findings from this PhD project identified a number of important physiological interactions between leaves and racemes in macadamia. One of these interactions was a lower leaf stomatal conductance rate in response to reproductive load, which potentially explains the high level of early fruit drop in macadamia.<p></p>

The wood anatomy, hydraulic properties and leaf water status of five sub-tropical plant species were studied. The specimens studied were growing in a private, irrigated garden. Consequently, any differences in xylem anatomy would be a result of phylogenetic and not environmental factors. Podocarpus latifolius, being a gymnosperm, had only narrow, short tracheids as the conducting conduits. The size of the vessels of the four angiosperms increased in the following order: Tecomaria capensis, followed by Cinnamomum camphora, Trichilia dregeana and finally Barringtonia racemosa had the widest vessels. T. capensis and T. dregeana had the shortest vessel lengths. Those of C. camphora were slightly longer and the vessels of B. racemosa were the longest. Measurements of hydraulic conductance (Kh), twig specific conductivity (TSC) and xylem specific conductivity (XSC) followed similar trends to those of conduit diameters. The measurements of leaf specific conductivity (LSC) , however, did not follow these trends. T. dregeana, which had a far higher Kh than P. latifolius, did not have a significantly different LSC. This is because the twigs of T. dregeana supported a far greater leaf area than did the twigs of P. latifolius. There was also no significant difference in LSC among T. capensis, C. camphora and B. racemosa, although their LSC's were all significantly higher than those of P. latifolius and T. dregeana. The consequence of efficient xylem anatomy thus seems to be, not only a greater supply of water to the leaf but also, and perhaps more importantly, it allows a greater leaf area to be produced. The length of the vessels was also shown to have a large effect on the hydraulic conductivity of the twigs. The Kh values measured on excised twigs were found to range between 40% and 87% of the Kh calculated using the Hagen- Poiseuille equation. Conduit size distributions were also found to be important in calculating the Kh. The more efficent xylem anatomy of B. racemosa resulted in little decrease in plant water potential even with large increases in transpiration. P. latifolius on the other hand showed a considerable decrease in leaf water potential with just a slight increase in transpiration. The other three species showed decreases in leaf water potential inter-mediate to these two extremes. The inferred root-to-leaf condutivity, shown by the inverse of the slopes of the water potential versus transpiration curves, were lower than the LSC measurements taken on excised twigs in the laboratory. The difference between the inferred and the measured LSC's could give an indication of resistances such as those within the root and at the soil-root interface.<br>Thesis (M.Sc.)-University of Natal, Durban, 1991.

The growth and recovery of trees from disturbances such as fire and browsing is driven by the intensity of the disturbances and the availability of resources. In savannas, resprouting has become recognized as a key functional trait in plant ecology over the past decade. Although this may indeed be the case, there is still limited information about the physiology and growth strategies of resprouting trees. Available information about the influence of disturbance comes from ecosystems that are in many ways different from tropical and sub-tropical savannas. Therefore it is important to know and understand post-disturbance tree responses and limitations so as to establish sustainable use and management practices. This thesis reports the findings of a study, conducted in the Mpumalanga province of South Africa, aimed at achieving a better understanding of the influences of resource availability (water and nutrients) and disturbances (herbivory and repeated cutting) on the coppicing of a widely distributed savanna tree species that is both ecologically and economically important; Terminalia sericea. To investigate the effects of resource availability, cut trees were exposed to different levels of water and nutrient (nitrogen and phosphorus) supplementation over a period of two years in a factorial experimental design. A number of coppice regrowth variables (e.g. shoot production, resprout shoot diameter and shoot length) were measured monthly, while the phenological responses (e.g. timing of leaf discolouration and fruit presence) were monitored every two weeks. The effects of disturbances were investigated in two separate experiments, in which cut trees were exposed to a five month browsing period and different cutting frequencies, respectively. Coppice regrowth variables were monitored for 12 months in trees exposed to browsing and for five months in trees exposed to different cutting frequencies. The effect of multiple cutting cycles on total non-structural carbohydrates and leaf chemistry (carbon, nitrogen and phosphorus) was measured. There was evidence of self-thinning of coppice shoots within cut trees in all experiments in the second year of growth, with supplemented trees also recording lower shoot numbers. With shoot production higher in trees that received no resource addition, water and nutrients interacted synergistically, doubling shoot diameter and shoot length for supplemented trees after 12-months of addition. The majority of the phenophases monitored peaked in the wet growing season. Supplemented trees changed colour from the typical green to senescent yellow later in the growing season than unsupplemented trees. Fruit presence occurred in the second year after cutting for supplemented trees. Shoot length and shoot diameter for unbrowsed trees were twice those for browsed trees, with leaf nitrogen and phosphorus content significantly higher for browsed trees compared to unbrowsed trees. Trees subjected to multiple cutting cycles recorded half the TNC levels, and half the resprout shoot diameter and shoot length of trees cut only once. Results from this study demonstrate that self-thinning (i.e., negative change in shoot number) is not primarily under resource control. By contrast, the findings suggest that shoot growth characteristics, the timing and duration of phenological stages in coppicing trees are resource-limited in savannas. Browsing induces an initial compensatory response through higher shoot production in browsed trees and should be kept minimal because, in the long run, browsed cut trees would take longer to recover lost biomass compared to unbrowsed cut trees. Repeated cutting significantly depleted non-structural carbohydrate reserves in stems, implying that repeatedly cut trees rely heavily on non-structural carbohydrate reserves for regrowth. The significantly lower shoot diameter and shoot length in repeatedly cut trees imply that the coppicing ability of a tree reduces as the cutting frequencies increase. Such information can be vital in establishing the competitive growth ability of T. sericea in a multiple-species ecosystem affected by changes in resource availability as well as natural disturbances. With reference to multiple cut trees, a form of cutting or harvesting strategy should be in place that allows for sustainable regeneration of the study species. A threshold in terms of number of cutting cycles a tree can tolerate based on either maximum or minimum levels of reserve carbohydrates should also be established, as this has a direct effect on the coppice growth and survival.

Current mining methods used to extract coal from underground mine workings disturb the natural environment and the existing stable geological structures. As a result, the ingress of water into the mines increases and the quality of the water passing through the mine workings deteriorates, irrespective of the operational status of the mines. Water ingress is generated by regional aquifers, local aquifers, recharge from the surface through rainfall, natural drainage paths on the surface, and surface water bodies. The quality of water in the mines deteriorates as a result of contact with the remaining coal in the mine workings. Mining can therefore cause an increased influx of water into a mine and the degradation of this water. The solution to reducing the impact of mines on the environment is to prevent, or at least reduce, the amount of water entering the mines, and to manage this water to prevent further degradation in water quality. This study focused on afforestation with Eucalyptus viminalis trees to manage or inhibit ingress of water into underground mine workings. The hypothesis of this study was that a change in vegetation, from grassland to fast-growing and potentially high water-using trees like Eucalyptus. could possibly reduce the drainage of water below the root-zone and into the mine workings. The hypothesis was tested by estimating the components of the soil water balance for a grassland site and a Eucalyptus tree site. The research site was situated in Mpumalanga, (260 36' Sand 290 08' E, 1650 m a.m.s.l.), one of South Africa's major coal bearing areas. Although the Secunda area is a treeless environment and conditions are not optimal for forestry, some Eucalyptus species are suited for conditions (frost and periodic droughts) encountered in this area. The soil water balance of grassland and E. viminalis trees were studied through a field experiment and a long-term (30 years) modelling exercise. Total evaporation of the grassland site was estimated using the Bowen ratio energy balance technique. The transpiration of six representative E. viminalis trees were estimated using the heat pulse velocity technique. The soil water storage changes at both sites were determined from the soil water content, estimated using water content reflectometers. Measurements were performed in a smectic clay soil which resulted in measurements difficulties. Vertical cracks were formed under soil drying. To establish the importance of climate and plant growth on the drainage beyond the root-zone, the soil water balance of a grassland and an E. viminalis site were simulated over a 30-year period with the Soil Water Atmosphere Plant (SWAP) model. It was concluded from the comparative field experiment and modelling, that a change in vegetation from grassland to E. viminalis will reduce the drainage of water below the root-zone, especially under above-average rainfall conditions. The reduction in drainage beyond the root-zone at the E. viminalis sites, compared to the grassland site, was demonstrated in the modelling exercise and can be deduced from the total evaporation and soil water storage estimated at both sites. The results from the field experiment confirmed the modelling results and showed that usually there were higher transpiration rates for the E. viminalis tree site, compared to the grassland site. The higher transpiration rates for E. viminalis trees resulted in lower relative saturation of soil layers and lower profile soil water contents at the E. viminalis site, and higher daily soil water storage changes at the E. viminalis site compared to the grassland site. These differences were more pronounced during winter when the grassland was dormant. The results from the modelling exercise showed that an E. viminalis tree stand, with a closed canopy, reduced drainage below the root-zone compared to a grassland. The drainage at the grassland site contributed to up to 54 % of the rainfall, compared to the 43 % at the E. viminalis site. However, under below-average rainfall conditions the annual drainage at both sites, were similar. Further, the absolute magnitude of the drainage was similar to the total evaporation at the grassland site under certain conditions. The results not only suggest that a change in vegetation, from grassland to E. viminalis trees, would reduce the drainage beyond the root-zone, but that it may delay the onset of drainage. Under above-average rainfall conditions, the modelled drainage at the E. viminalis site only exceeded 20 mm, a month later than at the grassland site. The simulation results also showed that under conditions of aboveaverage rainfall, drainage occurs whenever the rainfall exceeds the long-term average rainfall, irrespective of the existing vegetation. However, when the rainfall is belowaverage drainage at both sites are limited to large rainfall events. This simulation showed that over a period of eight years, E. viminalis trees could potentially reduce the drainage by 1235 mm more than grassland, which is equivalent to 1540 m3 ha- I a-I, or 1.54 Me ha- I a-I. The annual average reduction in drainage below the root-zone caused by E. viminalis trees (1.79 Mf ha-1 a-\ is a small reduction when compared to the influx of water into mineworkings. E.g. the influx of water into a bord-and-pillar mine range between 0.5 and 4 Mt d-I per area mined and up to 17000 Mt d-I per area mined under high extraction mining (Hodgson and Krantz, 1998; Hodgson et aI., 2001). This work gave a comprehensive account of the differences in the soil water relations of grassland and E. viminalis trees overlying coal mine working. Few other studies in South Africa compared the total evaporation and soil water relations of grassland and E. viminalis trees in so much detail. State of the art monitoring techniques were used and produced valuable comparison of their use in expansive clay profiles. The work should contribute to management decisions focussed on limiting ingress of water into mine workings.<br>Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.

Holz aus Kurzumtriebsplantagen (KUP) mit Pappeln (Populus spp.) kann eine bedeutende Rolle im Mix der Bioenergieressourcen in Deutschland spielen. Trotz eines günstigen Energieinput-Energieoutput-Verhältnisses ist das Erreichen wirtschaftlich zufriedenstellender Ergebnisse mit KUP jedoch auf den meisten potenziellen Anbauflächen durch hohe Ansprüche der Pappeln an die Wasserversorgung erschwert. Hohe Produktivitätsraten der Pappeln sind an einen hohen Wasserverbrauch gebunden und viele Trockenheitsanpassungen führen zu deutlichen Ertragsrückgängen. In der vorgestellten Arbeit wurde eine sechsjährige Vollgeschwister-F1-Kartierungspopulation der Europäischen Zitter Pappel (Aspe, Populus tremula L., Wuchsperiode 1998-2003) physiologisch und genetisch untersucht, um mögliche Wege zu einer züchterischen Verbesserung der Trockenheitstoleranz von Pappeln diskutieren zu können. Dabei wurde das Zuchtziel der Trockenheitstoleranz als Minimierung der Ertragsrückgänge unter trockenen Bedingungen definiert. Neben wuchsleistungsbezogenen Größen (Biomassegesamtleistung (BM, oberirdische Dendromasse), Biomassezuwachs (iBM), Radialzuwachs (ir), Baumhöhe (h)) wurden physiologisch holzanatomische Eigenschaften untersucht, die retrospektiv anhand der Jahrringe messbar sind und zur nicht direkt messbaren Eigenschaft der Trockenheitstoleranz in einer Beziehung stehen. Diese waren die Kohlenstoff- und Sauerstoffisotopsignatur (δ13C, δ18O), die Faser- und Gefäßgliedlänge (FL, GL), die Gefäßlumenquerschnittsfläche (AG), die Gefäßdichte (GD), der potenziell Saftstrom leitende Querschnittsflächenanteil (LQ), der hydraulisch gewichtete Gefäßlumendurchmesser (Dh) und die röntgendensitometrische Holzdichte (RD). Um trockenheitsbedingte physiologische Reaktionen vom Einfluss der Juvenilität der Kartierungspopulation unterscheiden zu können, wurden regionaltypische Juvenilitätstrends der RD, FL, GL, und des ir anhand eines zweiten, für das östliche Deutschland repräsentativen Aspen-Kollektivs aus natürlicher Sukzession ermittelt. Bedingt durch Trockenheitsanpassungen bzw. eine bevorzugte Wurzelentwicklung nach dem Verpflanzen zeigte die Kartierungspopulation in den ersten drei Jahrringen Abweichungen von den regionaltypischen Juvenilitätstrends. In den Trendverläufen der Kartierungspopulation heben sich die beiden Trockenvegetationsperioden 2000 und 2003 ab, wobei bis zum Sommer 2003 infolge des Starkniederschlages 2002 (Flut) ein außergewöhnlich gutes Grundwasserangebot herrschte. Alle untersuchten phänotypischen Eigenschaften zeigten 2000 starke trockenheitsbedingte Abweichungen. Im Jahrring 2003 wichen nur die GL und die RD von ihren Juvenilitätstrends ab. Außerdem konnte anhand der δ13C und δ18O Werte eine signifikante Abnahme der Wassernutzungseffizienz bzw. eine Zunahme der Transpiration im Jahr 2003 gezeigt werden. Die übrigen Größen folgten ihren Juvenilitätstrends und stiegen an. Die Jahrringdatensätze 2000 und 2003 der RD waren nicht signifikant mit der BM korreliert, dagegen zeigten die δ13C Datensätze 2002 und 2003 schwach positive Korrelationen mit der BM. Der trockenheitstoleranteste Genotyp verband seine überdurchschnittliche BM mit einer hohen Wassernutzungseffizienz (angezeigt durch überdurchschnittliche δ13C Werte), mit einer überdurchschnittlichen AG und mit einer nicht unterdurchschnittlichen RD in Höhe des Populationsmittels. Aufgrund des Fehlens negativer Korrelationen zwischen BM und δ13C bzw. BM und RD in der vorliegenden Arbeit können δ13C und RD als nützliche Weiser für die Unterscheidung der Trockenheitstoleranz verschiedener Aspen zu züchterischen Zwecken vorgeschlagen werden. Außer der BM unter trockenen Bedingungen kann keine der untersuchten Eigenschaften als alleiniger Trockenheitstoleranzweiser empfohlen werden. Zu einer Trockenheitstoleranzbewertung sollten Merkmalspaare verwendet werden, von denen ein Merkmal positiv mit dem Ertrag korreliert ist und das andere eine Trockenheitsanpassung verkörpert. Dadurch werden sowohl das primäre Zuchtziel eines höchstmöglichen Ertrages als auch eine bessere Trockenheitsangepasstheit berücksichtigt. Zwei verschiedene Trockenheitstoleranzindizierungen wurden angewendet, um die Kartierungsnachkommen entsprechend ihrer Trockenheitstoleranz einem Ranking zu unterziehen. Dabei wurden in beiden Fällen Bäume mit einem höheren Ertrag besser platziert. Der zweite Schwerpunkt der Arbeit lag auf der genetischen Kartierung von Quantitative Trait Loci (QTL) für die untersuchten phänotypischen Jahrringeigenschaften mit Bezug zur Trockenheitstoleranz. Als Basis für das QTL Mapping wurden, der Pseudo-Testcross-Mapping-Strategie folgend, genetische Kopplungskarten für die Elternbäume der Kartierungspopulation konstruiert. Die maternale Karte (P. tremula, „Schandau 4“) deckte mit 157 Markern (144 AFLP, 13 SSR) in 30 Kopplungsgruppen 1.369 cM ab, die 21 paternalen Kopplungsgruppen mit 148 Markern (132 AFLP, 16 SSR) überspannten 1.079 cM des Genoms (P. tremula, „Lichtenhain 1“). Die im Vergleich zur haploiden Chromosomenzahl der Pappeln (19) hohen Zahlen an Kopplungsgruppen sowie die hohen Zahlen an Doublets und unkartierten Markern zeigten eine geringe Genomabdeckung an. So konnte nur eine begrenzte Zahl, höchstens zwei QTL für die untersuchten phänotypischen Jahrringeigenschaften mit Bezug zur Trockenheitstoleranz, kartiert werden. Ein QTL Bereich mit pleiotropem Effekt auf mehrere wachstumsbezogene Größen wurde auf der maternalen Kopplungsgruppe 1 (dem Populus Chromosom I zuzuordnen) detektiert. Die Signifikanz der Effekte dieses QTL auf den Radialzuwachs entwickelte sich steigend mit zunehmendem Baumalter.<br>Wood production in short rotation coppices (SRC) with poplar (Populus spp.) can contribute significantly to the future bio energy supply mix in Germany. Although the energy-input to energy-output ratio is rather good, SRC often do not meet cost effectiveness due to high water demand of poplar species. High biomass productivity depends on optimal water supply. Also, numerous adaptations to water deficits result in an undesirable decrease of yield. Combined physiological and genetic investigations were conducted within a six-year old F1-full-sib crossbred population of European aspen (Populus tremula L., growing period 1998-2003). Possible implications on selection, breeding or improvement of poplar cultivars showing a high tolerance to water deficits are discussed. For the work presented here, the breeding goal of higher water deficit tolerance was defined as the minimisation of yield losses under dry conditions. Beyond growth related traits (aggregate yield (BM), aboveground woody biomass), biomass increment (iBM) and radial increment (ir), physiological and wood anatomical traits were included; these are related to reactions to water deficit and are measurable on tree rings retrospectively. These traits were the Carbon- and Oxygen isotope ratios (δ13C, δ18O), the fibre length and vessel element length (FL, GL), the vessel lumen cross sectional area (AG), the vessel density (GD), the cumulative vessel lumen area to cross sectional area ratio (LQ), the hydraulically weighted mean vessel lumen diameter (Dh) and wood density assessed by X-ray densitometry (RD). To distinguish the drought induced physiologic reactions from juvenile developmental patterns of the mapping population, juvenile trends of RD, FL, GL, and ir, which are representative of habitats in south-eastern Germany, were investigated in a second aspen collective that was selected from natural succession. During the first three years, the mapping population showed deviations from the juvenile trends due to water deficit adaptations or preferential root development, respectively. Due to drought in the growing seasons of 2000 and 2003, the juvenile trends show outstanding values for both years, although ground water supply in 2003 was exceptionally good following the intense rain event of 2002 (Elbe flood 2002). The tree ring traits of both years stand out from the juvenile trends due to drought adaptations. In 2000, all phenotypic traits showed a significant deviation from their respective trends. In 2003, only GL and RD showed an adaptation to drought as observable by a deviation from their juvenile trends. A significant decrease in water use efficiency (WUE) and an increase in net transpiration, respectively, were shown for 2003 by means of δ13C or δ18O values. All other traits showed an increase following their juvenile trends. RD data for 2000 and 2003 were not significantly correlated with BM, but δ13C data (and therefore WUE) for 2002 and 2003 revealed a weakly positive correlation with BM. The genotype that was most tolerant to water deficits showed a combination of a superior growth with a superior WUE (by means of δ13C), a superior AG, and an RD close to but not less than the population average. Due to the lack of negative correlation between BM and δ13C or BM and RD in the present work, δ13C and RD can be valuable proxies for the determination of drought tolerance of aspen trees for tree improvement purposes. Aside from BM under dry conditions, no other traits that were investigated can be recommended as a stand-alone proxy for water deficit tolerance. For a water deficit tolerance evaluation, pairs of traits should be used, of which one trait is positively correlated with yield and the other represents a water deficit adaptation. Both the primary breeding goal of the highest possible yield as well as a better water deficit tolerance should always be considered in this context. Two different drought tolerance indices were used to rank the individuals of the mapping population according to their water deficit tolerance. In both cases, trees with higher BM were ranked better. The second focus of the present work is on genetic mapping of Quantitative Trait Loci (QTL) for the investigated tree-ring traits that refer to water deficit reaction. As a basis for the QTL-mapping approach, genetic linkage maps were constructed for each parental tree of the F1-full-sib crossbred mapping-population following the two-way pseudo-testcross mapping strategy. The maternal map (P. tremula, “Schandau 4”) consisted of 157 markers (144 AFLP, 13 SSR) in 30 linkage groups and covered 1,369 cM. The 21 linkage groups of the paternal map (P. tremula, “Lichtenhain 1”) covered 1,079 cM of the genome (144 AFLP, 13 SSR). Compared with the haploid chromosome number (19) of the Populus genome, the high number of linkage groups, doublets and unlinked markers indicated low genome coverage. Only a low number of QTL was detected, maximal two per in¬vesti¬gated phenotypic trait with a relation to water deficit tolerance. One QTL having a pleiotropic effect on several growth related traits was detected on the maternal linkage group 1 (corresponding to the Populus Chromosome I). The significance of the QTL effects seemed to increase with tree age.

The genus Populus is ideally suited to investigate questions related to the interplay between an individual’s environmental history and its capacity to respond to external stimuli. In order to dissect the influence of individual history on subsequent plant responses, transcriptome level changes due to water deficit were assessed in clonal populations of Populus hybrids. Results indicate variation in the drought transcriptomes of genetically identical clones originating from different locations can be shaped by the individual history of the clone. Additionally, yearly variations in drought transcriptome patterns showed specific trends associated with a clonal population that were not related to an unknown influence at a location, nor with the biological source of cuttings. Despite these sources of transcriptome variation, a common shared response was identified across all populations. The findings hint at the influence of the environment and epigenetic factors in the dynamic regulation of transcriptome level responses in clonal individuals.