Dissertations / Theses on the topic 'Seedling traits'

In tropical regions, climate change is predicted to lead to increased drought frequency and intensity. The extent to which this will shift the functional diversity of tropical tree communities is unknown due to a limited understanding about the response of seedlings to variable soil moisture. We addressed this issue using an experimental approach in the Luquillo Experimental Forest, Puerto Rico. We exposed seedlings of eight tree species, representing different successional stages, to an experimental soil moisture gradient. We evaluated (1) How species mean trait values relate to species-specific demographic responses to drought, (2) How intraspecific variation in functional traits relates to a soil moisture gradient, (3) The extent to which demographic response to short-term experimental drought mirrored long-term demographic response of seedlings to natural variation in soil moisture. Growth and survival of species with more `conservative` functional strategies tended to be more sensitive to a change in soil moisture and more tolerant to drought compared to species with more `acquisitive` strategies. In addition, traits of individual seedlings within species varied with respect to soil moisture, suggesting a potential role for phenotypic plasticity in response to drought. Specifically, this response was significant for three species (Inga laurina, Guarea guidonia, Schefflera morototoni) and was primarily associated with relative carbon investment in leaves and roots. Species demographic responses to soil moisture in experimental and long-term studies were weakly positively correlated but more variables are at play under natural conditions, which partly decouples these responses. Overall, our results suggest that tree species with `conservative` functional strategies are likely to become more common under increasing drought frequency and intensity in the Luquillo Mountains of Puerto Rico. However, understanding the broader implications of our findings will require considering the effects of other disturbances, including hurricanes, which may have contrasting effects. Furthermore, intraspecific variation in functional traits is likely to influence how the seedlings of tropical tree species cope with drought.

Alpine and arctic tree line expansion depends on the establishment of tree seedlings above the current tree line, which is expected to occur with climate warming. However, tree lines often fail to respond to higher temperatures. Other environmental factors are therefore likely important for tree seedling establishment. Above the tree line, establishing seedlings encounter existing vegetation such as bryophytes, which often dominate in arctic and alpine tundra. Bryophytes modify their environment in various ways and may mediate climate change effects on establishing tree seedlings, and with that tree line expansion. The aim of this thesis was to understand if and how the environment, in particular bryophytes, mediates the impact of climate change on tree seedling establishment at the alpine and arctic tree line. This was explored by reviewing literature on tree seedling establishment at alpine and arctic tree lines globally. In addition, tree seedling survival and growth of Betula pubescens and Pinus sylvestris were assessed experimentally. Here, individuals were planted into mono-specific mats of different bryophytes species and exposed to warming and different precipitation regimes. The literature review revealed that besides from temperature, tree seedling establishment is affected by a wide range of abiotic and biotic factors including water, snow, nutrients, light, disturbance and surrounding vegetation. Furthermore the review revealed that for example vegetation can change tree seedling responses to climate change. The experiments showed that especially tree seedling survival was adversely affected by the presence of bryophytes and that the impacts of bryophytes were larger than those of the climate treatments. Seedling growth, on the other hand, was not hampered by the presence of bryophytes, which is in line with earlier findings that seedling survival, growth and seed germination do not respond similarly to changes in environmental conditions. Moreover, we found several indications that vegetation above the tree line, including bryophytes, mediated tree seedling responses to warming and precipitation or snow cover. This thesis shows that temperature alone should not be used to predict future tree seedling establishment above the alpine and arctic tree line and that extrapolations from climate envelope models could strongly over or under estimate tree line responses to warming. This underlines the value of multi-factorial studies for understanding the interplay between warming and other environmental factors and their effects on tree seedling establishment across current tree lines.

Human-modified landscapes are ubiquitous and often made up of remnant fragments of natural ecosystems nested within an agricultural or urban matrix. Understanding how species are affected by habitat degradation is a central issue in biodiversity research, yet investigations into the impacts on key ecological interactions have not kept pace. Gaining insight into the responses of ecological processes is vital in order to maximise biodiversity conservation and develop sustainable management practices in a changing world. Herbivory is a fundamental ecosystem process as it mediates the transfer of energy between primary production and higher trophic levels. In tropical rainforests herbivory is primarily carried out by insects. Here, I investigate how leaf damage changes over time by carrying out repeated measures of herbivory following fragmentation. In doing so, I build upon previous ‘snapshot’ studies which have primarily quantified leaf damage at single points in time. An experiment was established within a large-scale manipulation experiment: the Stability of Altered Forest Ecosystems (SAFE) project in the Malaysian state of Sabah, within Borneo. I used seedlings of two species of endemic Dipterocarpaceae as the study system for two main reasons. Firstly, seedlings represent the most vulnerable life stage in a tree’s life cycle, and therefore insect herbivory may be a major determinant of their growth and survival. Secondly, not only do members of the family Dipterocarpaceae dominate in lowland tropical rainforests of Southeast Asia, most are economically valued for their timber and are consequently under pressure from logging which is leading to conservation concern. Five hundred and seventy-six seedlings were planted in 12 recently isolated one hectare fragments and 12 continuous forest control sites. Eight of these control sites were located in an area of continuous forest estimated to be over one million hectares north of the experimental landscape of the SAFE project. Four further control sites were established in a virgin jungle reserve which is over 2,200 hectares and located to the south-west of the experimental area. All leaves were scanned in situ on six occasions over two field seasons (May- October) in 2015 and 2016. At the end of the experiment, traits analyses were performed to quantify three common metrics of leaf defence: total phenolic content, acid detergent fibre and leaf strength. Through this experiment I addressed the following aims; (1) to determine the initial effects of fragmentation on rates of leaf damage, (2) to investigate whether bottom-up control of herbivory was altered by fragmentation through changes in foliar defence, and (3) to assess whether responses were shared among study species or were instead individualistic. I also use data from a key published monograph to create species interaction networks between lepidopteran caterpillars and their known host plants in tropical Asia, with the aim of exploring the importance of members of the Dipterocarpaceae for insect herbivores. I found some evidence that herbivory is disrupted by fragmentation, with both species exhibiting lower levels of herbivory in fragments. Forest type was an important predictor of patterns of leaf area loss in this experiment, but overall differences between herbivory in fragments and control sites were not significant. Instead, herbivory was best explained by seedling traits, and predictors of leaf area loss varied between species indicating species-specific responses. Relaxation of phytochemical defensive traits was also detected in forest fragments, perhaps due to decreased levels of herbivory. A reduction in phytochemical defence may imply an increased vulnerability of seedlings in forest fragments which translates to differences in herbivore damage over time. I highlight the importance of repeated measures experiments when investigating a complex and dynamic ecological process such as herbivory, and propose long term monitoring to fully understand the effects of forest fragmentation. The results of this thesis contribute to understanding the effects of fragmentation on insect herbivory, which remain uncertain, and provide evidence of the extent to which this key ecosystem process is disrupted due to anthropogenic habitat modification<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>School of Environment and Sc<br>Science, Environment, Engineering and Technology<br>Full Text

Interações interespecíficas são consideradas importantes forças estruturadoras da vegetação. Enquanto a competição aparentemente prevalece em ambientes com menor estresse abiótico, a facilitação tende a aumentar em importância em ambientes de maior estresse. Consequentemente, é esperado que a facilitação desempenhe um papel importante em áreas tropicais degradadas, nas quais as condições abióticas, envolvendo altos níveis de irradiação, temperatura e evapotranspiração, são muito distintas das condições ótimas para a maioria das espécies florestais. Além disso, face à complexidade dos processos estruturadores de comunidades florestais tropicais altamente diversas, os ecólogos têm percebido a necessidade de simplificação. Um caminho promissor para isso é por meio do uso de características funcionais, que podem ser medidas para qualquer espécie e comparadas em diferentes sistemas e locais. No entanto, em áreas degradadas ainda é incerta a relação entre as características funcionais e o desempenho das espécies. Neste contexto, planejamos um projeto de restauração na planície costeira do sudeste brasileiro para comparar o crescimento e a sobrevivência de mudas de árvores plantadas em diferentes densidades (sistema isolado ou sistema agregado) em um experimento fatorial com adição de nutrientes. No primeiro capítulo analisamos a sobrevivência, altura, diâmetro ao nível do solo e projeção da copa de 4.132 mudas de 19 espécies de diferentes classificações sucessionais, durante um período de 18 meses. Usamos modelos de efeitos mistos para analisar a relação entre o desempenho de espécies e os tratamentos e selecionamos os melhores modelos utilizando o critério de informação de Akaike (AIC). Verificamos uma maior sobrevivência nos sistemas agregados para as espécies não-pioneiras, indicando o predomínio do processo de facilitação. Em contrapartida, constatamos um menor crescimento em diâmetro nos sistema de plantio agregado, indicando o predomínio de competição. A adição de nutrientes não afetou a sobrevivência nos sistemas agregados, mas, surpreendentemente, teve um efeito negativo sobre as plantas isoladas. Além disso, a adição de nutrientes teve um efeito positivo sobre crescimento, diâmetro e projeção da copa nos sistemas de plantio agregado (indicando a redução da competição), especialmente para espécies pioneiras. Uma vez que o estabelecimento de espécies não-pioneiras em áreas degradadas pode ser bastante difícil, a facilitação para a sobrevivência dessas espécies em sistemas agregados pode ser utilizada como instrumento para melhorar os modelos de restauração. No segundo capítulo utilizamos algumas características funcionais que são facilmente mensuráveis para investigar sua relação com o crescimento e sobrevivência das mudas. Além disso, testamos o efeito das interações interespecíficas na relação das características funcionais com o desempenho das plantas. Para espécies pioneiras, uma maior área foliar específica (SLA - Specific leaf area), foi relacionada com uma maior taxa de sobrevivência. Entretanto, ao considerarmos as relações interespecíficas (sistemas agregados), maior SLA foi relacionada com uma menor taxa de sobrevivência. Em geral, as características funcionais explicaram apenas parcialmente o desempenho de mudas no contexto de restauração de áreas degradadas. Nosso trabalho contribuiu para a discussão sobre o potencial da aplicação prática da abordagem funcional na escolha das espécies para a recuperação de áreas degradadas. O caráter manipulativo da restauração ecológica baseada no plantio de mudas amplia as perspectivas para implementar experimentos que visem testar novas hipóteses em ecologia e refinar modelos de restauração<br>Interspecific interactions are considered to be important structuring forces in early successional vegetation. Whereas competition seems to prevail in less severe environments, facilitation tends to increase in importance in harsh environments. Hence, facilitation is expected to play an important role in degraded tropical areas with high irradiance, heat loads, and evapotranspiration, where conditions are far from optimum for most forest species. Moreover, in order to understand complex structuring process of high diverse tropical forests, ecologists have realized the need for simplification. A promising way to do that is through the use of functional traits, which can be measured for any species and compared in different systems and different locations around the world. However, in these conditions, little is known about the role of species interaction on the relation of functional traits and species performance. In this scenario, we planned a restoration project on the southeastern Brazilian coastal plain to compare growth and survival of tree seedlings planted at two densities (isolated or aggregated) in a factorial experiment with nutrient addition. In the first chapter we analyzed survival, height, ground level diameter, and crown projection of 4,132 saplings from 19 species that ranged along a successional gradient, over an 18-month period. We used mixed-effect models to analyze the relationship between species performance and treatments, and Akaike\'s information criterion (AIC) to select the models. The best model showed higher survival in aggregated plantations (indicating facilitation) for non-pioneer species. In contrast, we found lower diameter growth in aggregated plantation (indicating competition). Fertilizer addition did not affect survival in clusters, but, surprisingly, it had a negative effect on isolated plants of both pioneer and non-pioneer species. On the other hand, fertilizer addition had a positive effect on diameter and crown projection growth in aggregated plantations (reducing competition), especially for pioneer species. Thus, whether facilitation or competition was the predominant interaction depended on the response analyzed. We concluded that, as establishment of non-pioneer species in disturbed sites can be challenging, restoration designs could take advantage of higher survival rates in clusters and use resource addition to ameliorate growth and decrease competition for limited resources. In the second chapter we used the core simple-measurable traits to investigate whether functional traits were related to growth and survival and whether there was a difference in the effect of the functional traits on plant performance of isolated individuals or of individuals subjected to interaction with neighbors. Our main findings were that for pioneer species, the greater the specific leaf areas (SLA), the greater the survival rates, but, under aggregated conditions, the greater the SLA the lower the survival rates. However, functional traits only partially explained saplings performance in a restoration context and more research is needed to understand its role in predicting seedlings outcomes, especially considering the potential applicability of this methodological approach. The manipulative character of ecological restoration broadens perspectives to use experiments to generate and test new hypotheses in ecology and to refine restoration models

Despite extensive international acceptance of the critical role of mammalian post-dispersal seed predation in many plant communities, in New Zealand we have limited knowledge of these predators’ influence on plant recruitment in our forests. The principle objective of my thesis was to determine the importance of exotic mammals as post-dispersal seed predators in a New Zealand conifer-broadleaf forest remnant. To address this goal, I used a series of field-based experiments where the actions of different post-dispersal seed predators were separated by wire-mesh exclosures. My study was conducted at Mount Peel Forest Park Scenic Reserve, South Canterbury, New Zealand. Being a human modified conifer forest currently dominated by broadleaf species, it is typical of forest remnants in New Zealand. This presented an opportunity to study a wide range of both potential post-dispersal seed predators and broadleaf tree species. My findings indicate that exotic mammals are not only post-dispersal seed predators at Peel Forest, but are responsible for the majority of post-dispersal predation events observed. Ship rats (Rattus rattus) were the dominant post-dispersal seed predators, while brushtail possums (Trichosurus vulpecula), house mice (Mus musculus) and native invertebrates were also important post-dispersal seed predators for several tree species. Through use of time-lapse video and cafeteria experiments I found that exotic mammalian seed predators, when compared to native invertebrate seed predators, preyed upon larger-seeded plant species and were responsible for considerable seed losses of several tree species. However, exotic mammalian seed predators do share several foraging characteristics with native invertebrate seed predators, as predators foraged in similar habitats and responded in a similar way to changes in seed density. In investigating if post-dispersal seed predation by mammals had a flow-on effect to plant recruitment, I observed natural seedling densities at Peel Forest were significantly higher in the absence of mammalian seed predators, but I found no evidence that the presence of mammals significantly altered the overall species richness. At the community level, I did not find an interaction between habitat and exotic mammals, however I present evidence that for individual plant species a significant mammal : habitat interaction occurred. Consequently, even though my cafeteria experiment implied there was no significant difference in the overall amount of seed preyed upon within different habitats, the less favourable microsite conditions for germination under an intact continuous canopy allows mammals to exacerbate habitat-related patterns of seed mortality and have a noticeable effect on seedling establishment. In an effort to validate the use of manipulative experiments to predict the long-term effect of post-dispersal seed predation on plant dynamics, I attempted to link results of my cafeteria experiment with observed seedling abundance at Peel Forest. Seven tree species were used in this comparison and a strong correlation was observed. This result shows that the level of post-dispersal seed predation determined in the cafeteria experiment provided a good predictor of the effect of mammalian post-dispersal seed predation on seedling establishment. To fully gauge the impact of mammalian post-dispersal seed predators on seedling establishment, the relationship between these seed predators and the type of recruitment limitation experienced by a plant species was also investigated. By using a combination of seed addition, plot manipulations and seed predator exclusion I was able to investigate this relationship. I found evidence that seed limitation at Peel Forest is positively correlated with seed size, and that while mammalian post-dispersal seed predators can further reduce plant recruitment of plant species experiencing seed limitation, the influence of mammals in determining plant recruitment was limited for plant species experiencing microsite limitation. My study has proven that exotic mammals are now the dominant post-dispersal seed predators at Peel Forest, the amount of seed preyed upon varies among plant species, and post-dispersal seed predation by mammalian species can lead to differences in seedling richness and abundance. I proved that the influence of exotic mammals on seedling establishment is also linked to habitat structure and recruitment limitations. When combined these observations suggest that exotic mammalian post-dispersal seed predators may play an important role in determining landscape abundance and distribution of plants at Peel Forest.

Thesis (M.S.)--Miami University, Dept. of Botany, 2005.<br>Title from first page of PDF document. Document formatted into pages; contains [1], v, 38 p. : ill. Includes bibliographical references (p. 35-38).

Le brachypode rameux (Brachypodium retusum) est une espèce herbacée pérenne qui domine les pelouses sèches de Méditerranée occidentale. Dans notre zone d’étude du Sud de la France, la recolonisation spontanée est très faible après perturbation du sol. Cette observation ne correspond pas aux résultats d'études menées dans d'autres régions montrant une capacité de colonisation élevée. L'objectif principal de cette thèse était donc de tester les différentes hypothèses pouvant expliquer les différents patrons de colonisation.Dans un premier chapitre, nous avons testé si ces différents patrons de colonisation résultent d'une différenciation génétique entre les populations. Des marqueurs AFLP ont été utilisés pour analyser la structure génétique de 17 populations de Méditerranée occidentale dont la différenciation neutre entre populations. Dans un sous-échantillon de 13 populations françaises, la différenciation de traits phénotypiques sous sélection a été testée dans un jardin commun et comparée à la différenciation neutre. Dans le deuxième chapitre, nous présentons une étude sur la différenciation adaptative des traits phénotypiques et avons testé une potentielle réponse différentielle à la manipulation de facteurs environnementaux clés. Les deux derniers chapitres de la thèse ont analysé les facteurs environnementaux qui limitent la recolonisation in situ, indépendamment du génotype ou de la population. Dans le troisième chapitre, nous avons testé l’effet du pâturage et du feu sur le recouvrement végétatif ainsi que sur la reproduction sexuée de B. retusum installé. Enfin, dans le quatrième chapitre, nous avons mesuré l’effet de l’arrosage initial et du pâturage sur l’installation de plantules transplantées initialement germées en serre et de plantules issues de semis in situ. Nos résultats ont montré que les populations de B. retusum sont génétiquement différenciées pour les marqueurs neutres mais également pour les traits phénotypiques. Cette différenciation est supérieure à la dérive seule et suggère une adaptation aux conditions environnementales, en particulier aux températures estivales et à la fréquence du gel en hiver. Une réponse différentielle à la manipulation expérimentale de facteurs environnementaux (sol, pâturage, humidité du sol) a confirmé le caractère adaptatif de la différenciation génétique. Les expériences in situ ont montré que le feu a un effet positif sur la reproduction de B. retusum et sur la communauté végétale associée, alors que son recouvrement végétatif n’était pas supérieur à la moyenne de la communauté. L'exclusion du pâturage pendant deux saisons n'a eu d'incidence sur aucun des paramètres mesurés chez les populations adultes. L'arrosage initial a affecté l’installation des plantules au cours de la première saison. Au cours de la deuxième saison, l'effet seul de l’arrosage n'était pas significatif, cependant son effet est resté positif sur la survie uniquement dans les parcelles pâturées. Le pâturage, au début du cycle de vie de B. retusum, a eu un effet négatif sur le recrutement et la croissance des plantules. En conclusion, la différenciation adaptative entre les populations peut avoir contribué aux différences régionales en termes de capacité de colonisation et doit être prise en compte lors du ciblage des populations sources pour l'introduction de plantes en restauration écologique. La réponse positive de B. retusum a indiqué que le feu était une force sélective importante dans le passé qui pourrait être utilisée pour favoriser l'espèce et la communauté végétale associée dans des opérations de conservation et de restauration. L'exclusion du pâturage à court terme est tolérée par les populations adultes de B. retusum, mais l'abandon à long terme entraîne une diminution de son recouvrement par rapport aux graminées pérennes à croissance rapide<br>Ramose false brome (Brachypodium retusum) is a perennial herbaceous species that dominates dry grasslands of the Western Mediterranean. In our southern French study area, spontaneous re-colonisation is very low after soil disturbance. This observation does not correspond to the results of studies from other regions showing a high colonisation capacity. The major objective of this PhD thesis was to test different hypotheses potentially explaining the different colonisation patterns.In the first chapter, we tested whether these different colonisation patterns are the result of genetic differentiation among populations. AFLP markers were used to analyse genetic structure including neutral population differentiation in 17 Western Mediterranean populations. In a sub-sample of 13 French populations, differentiation in phenotypic traits under selection was tested in a common garden and compared to neutral differentiation. In the second chapter, we present a study on adaptive differentiation in phenotypic traits testing a potentially differential response to the manipulation of key environmental factors. The last two chapters of the PhD analysed environmental factors that limit re-colonisation in the field independent of genotype or population. In the third chapter, we tested the effect of grazing and fire on vegetative recovery as well as on sexual reproduction of established B. retusum and in the fourth chapter we measured the effect of initial watering and grazing on the establishment of transplanted seedlings pre-grown in a greenhouse and of field-sown seedlings.Our results showed that populations of B. retusum are genetically differentiated in neutral markers but also in phenotypic traits. This differentiation is superior to drift alone and suggests adaptation to environmental conditions, particularly to summer temperature and winter frost frequency. A differential response to experimental manipulation of environmental factors (soil, pasture, soil moisture) confirmed the adaptive character of genetic differentiation. The field experiments showed that fire has a positive effect on B. retusum reproduction and on the associated community whereas vegetative recovery was not higher than community average. Two seasons of grazing exclosure did not affect any of the measured parameters in adult populations. Initial watering affected seedling establishment in the first season. In the second season, the watering main effect was not significant but interestingly the effect remained positive on survival in grazed plots whereas no such effect was observed in exclosures. Grazing in early life cycle stages of B. retusum had a negative effect on seedling recruitment and growth.In conclusion, adaptive differentiation between populations may have contributed to regional differences in colonisation capacity and needs to be taken into account in targeting source populations for plant introduction in ecological restoration. The positive response of B. retusum indicated that fire was an important selective force in the past which may be used to favour the species and its associated plant community in current conservation and restoration management. Short-term grazing exclosure is tolerated by mature B. retusum populations but long-term abandonment results in a decrease of cover relative to high-growing perennial grasses. In early stages of seedling establishment grazing should be avoided to guarantee introduction success - or grazing stress needs to be compensated by watering

The tropical rainforests of the Peruvian Andes are some of the most biodiverse and most vulnerable to climate warming in the world. The Andes are predicted to experience substantial increases in warming of between +2 °C to +5 °C by the end of the century, in addition to an increases in the frequency of high temperature extremes, drought and flood events. The response of these forests to climate change over the next century has global relevance, due to the high levels of endemic species present and the potential role these areas will play as refugia for lowland species. Despite this, the response of tropical montane forests (TMCFs) to climate change remains under-studied. Our current understanding of how Andean species will respond to climate change is based on studies of past compositional changes. Upslope shifts in plant communities of approximately 1.2 - 2.0 m·y-1 have been observed along elevational gradients within Central and South America over the last decade. Based on these migration rates, it has been estimated that the majority of communities will lag behind increases in temperature by 5.5 °C by the end of the century. The implications of this for populations at the trailing range edge is unclear, due to a lack of mechanistic data concerning the acclimatory limits of rainforest species. When faced with rapid warming plant species will need to rapidly adapt, acclimate or migrate in order to survive. In the case of Andean species, migration rates may not be sufficient for a species to remain within its optimal thermal niche and adaptive responses will likely be too slow to be effective, hence individuals will have to acclimate in situ to prevent a decline in performance. The acclimatory ability of species can be quantified by measuring changes in performance, leaf physiology and anatomy in response to experimental manipulations of climate, however such studies are rare within the tropics. Here we carried out a seedling transplant experiment, utilising an extensive 400-3500 m asl elevational gradient in the Peruvian Andes, to simulate climate warming and upslope migration of tree seedlings under real-world conditions. To provide context for the transplant study, natural variation in leaf anatomical traits and physiological stress were explored for twelve species belonging to lowland (LF), mid-elevation (LMF) and tropical montane cloud forest communities. Adults and seedlings from the centre and furthest-most extent of each species' elevational range were studied and compared. Seedlings of each elevational forest community were transplanted downslope and upslope of their local elevational range by the equivalent of ±2 °C and ±4 °C in mean annual temperature. The experiment followed the transplanted seedlings of eleven species over a one year period, monitoring survival, growth and physiological stress (Fv/Fm) of individuals. The acclimatory ability of a subset of these species was quantified by measuring changes in photosynthetic capacity (Vcmax and Jmax), respiratory capacity (Rd) and anatomical traits (Na, Pa, LMA, LDMC) in response to transplantation. The results showed that within the natural population there was little evidence of leaf trait acclimation to elevational shifts in climate, but also little evidence of physiological stress at the trailing range edge. There were however differences in the leaf trait strategies employed by each elevational community, increasing in abiotic stress-tolerance with elevation. Physiological stress was greatest in the seedling population and, unlike the adult population, increased slightly at the trailing edge. This indicated that seedlings were more vulnerable to warming than their adult counterparts and at mid-elevations TMCF seedlings were more vulnerable than LMF seedlings. Seedling survival and growth declined in response to transplantation away from the home elevation for the majority of species, with upslope declines as a result of abiotic limitations, and downslope declines due to biotic limitations. All seedlings were found to be able to acclimate their respiratory capacity in response to transplantation, however this was not the case for photosynthetic capacity. LMF species performed significantly better than TMCF seedlings with transplantation, demonstrating a greater acclimatory capacity for photosynthesis. LMF species were able to adjust Jmax in order to maintain rates at ambient temperatures, but were not able to upregulate Vcmax upslope, whereas TMCF species were not able to respond in either transplant direction. Overall, these findings suggest that under moderate warming scenarios LMF species will have a competitive advantage over TMCF species at mid-elevations, gradually expanding their range into TMCF species' habitat over the next century. As a result of this and due to the slow pace of upslope migration, we predict that TMCF species will undergo range retractions and possible extinctions. The speed of this response will be determined by the trajectory of future warming and the frequency of extreme climatic events.

碩士<br>國立臺灣大學<br>農藝學研究所<br>102<br>Rice is one of the major crops in the world. Because human population grows, increasing rice production is necessary to meet human’s need. Salinity is a common abiotic stress to affect crop production, and rice is one of salt sensitive crops, therefore maintaining rice growth vigor under salt condition is an important issue. Root system is a major physical interaction between plants and soil substrates, it affects nutrients and salt absorption. In this research, we used two populations as study materials, one is recombinant inbred lines population derived from a cross between indica and temperate japonica, and a global diversity panel with 196 accessions. We measured root length under normal and salt condition at seedling stage, and found out degree of root growth vigor inhibited by salinity stress differs by root types. We used high density SNP markers to map QTLs controlling shoot and root growth in response to salt stress, many QTLs in RILs and in global diversity panel were mapped in this study. Although there was positive correlation between root and shoot traits under salinity stress, no identical QTLs were mapped. We selected accessions with good performance under salinity stress, these accessions will be good breeding materials to improve root vigor in elite cultivars, and through molecular assisted selection, QTLs with positive effect can be introduced to elite cultivars efficiently.

碩士<br>國立臺灣師範大學<br>生命科學研究所<br>101<br>Plant functional traits are usually defined as morphological and physiological traits of plants that may influence their survival, growth, reproduction and fitness. Identifying key functional traits to predict the survival and growth of plants in a given habitat and provides an effective approach to understand the strategies of resource exploitation. Such understand may serve as a basis to construct community assembly rules. In this study, I applied a trait-based approach to compare the survival and growth of seven shade-tolerant species during their seedling stage in the Kenting karst forest. Niche differentiation among seven intermediate and shade-tolerant species and mechanisms of species coexistence were studied. In this study, three questions were addressed. (1) Which environment factors may cause interspecific differences in seedling survival and growth? Do seedling survival and growth vary with light availability and soil depth? (2) Which functional traits are the best predictors to model seedling survival and growth? (3)Are there trade-offs between seedling survival and growth? This study was carried out in the Kenting Karst Forest Dynamics Plot. Seedling censuses were executed every three months during July, 2007 - January, 2013. The survival status and height of seedlings were measured in 144 seedling plots. Proportional hazard mixed models were used to explore the relationships between seedling survival and various functional traits, such as seed mass and specific leaf area. Seedling growth was analyzed by generalized linear mixed models. Our results indicated that seedlings could survived for 185~469 days on average. The survival intervals were significantly influenced by soil depth and light availability during the dry season. In the survival model, the interactions between species and two environmental factors, light availability and soil depth, were significant. Seedling survival was significantly correlated with seed mass, specific leaf area (SLA) and leaf thickness. Meanwhile, relative growth rates of seedling were significantly correlated with SLA and photosynthetic capacity. This study indicated that interspecific variability in seedling survival was critical for these seven species in Kenting karst forest, which may be highly influenced by light availability during the dry season and soil depth. Such results suggested that soil water availability may be the most critical limiting factor in the karst forest.

Exotic and invasive species have threatened the integrity of many ecosystems in the world. They not only harm the native species diversity but also disturb the biological integrity and functioning of an ecosystem. Although these species cause huge economic and social impacts in most of its non-native ranges, one of the most significant impact includes its allelopathic effect on native vegetationand crop species. In India, several invasive and exotic species have been reported some of which are Parthenium hysterophorous, Lantana camara, Crotalaria pallida, Eucalyptus globulus, Acacia auriculiformis. These species are native to tropical America or Australia and are known to proliferate in varied landscapes causing harm to a lot of forest and agricultural regions, replacing the native vegetation and crops. This study aims to understand the allelopathic effects of leaf litter of these invasive and exotic species on the germination and seedling traits of Pisum sativum (common pea plant), a widely grown crop species in India. Using a randomized complete block design, this study estimated the effects of lead litter type and amount on the productivity and root traits of pea plants It was observed that both leaf litter type and amount significantly affected the productivity and seedling traits in pea and among all the species, the lead litter of Parthenium hysterphorous proved to be the most detrimental to the germination and seedling traits of pea seedlings.

碩士<br>國立臺灣大學<br>農藝學研究所<br>104<br>To increase the yield production, the crops may have to grow in the harsh environment. Salinity is one of the major abiotic stresses, and rice is very sensitive to increasing salts. In this study, we evaluated three different root types performance in South East Asia rice varieties, total sixteen loci were detected using genome-wide association mapping (GWAS), and two were found in previous study. In addition, chlorophyll fluorescence was used to measure the leaf photosynthesis rate under salt stress. The pilot experiment showed the effective PSII quantum yield (ΦPSII) on day 9 and Injury score (IS) on day 11 was moderately correlated (r = -0.588), suggesting the damage level of leaf photosynthesis rate and its repairing mechanism may be crucial for salinity tolerance in rice. Total 32 significant loci were detected by GWAS in five chlorophyll fluorescence related traits. Among these loci, two genes OsNHX3 and OsCBL4 related to salinity tolerance mechanisms were detected in the candidate regions. Finally, we analyzed root and shoot traits in diverse accessions and found that performance of shoot and root is independent under salt stress We expect these varieties could be used to improve salt tolerance through QTLs pyramiding approach in rice breeding program.

The overall objective of the thesis was to estimate the amount and distribution of genetic and environmental variation, and correlations between genetic variability and seed source origin, of yellow-cedar (Chamaecyparisnootkatensis (D. Don) Spach). Variation was measured for traits of seed, and for morphological and physiological traits of seedlings grown in a common garden, and in differing greenhouse environments. The study focused on traits that sampled the developmental sequence of events that influence a population’s adaptation to its environment. These included growth rate, phenology, drought resistance, cold acclimation, and dormancy. Significant variability was evident at both the population and family within population level in most traits measured. Substantially more genetic variability (2 to 16 times) was found at the family within population level as opposed to the population level in all but two traits. Narrow-sense heritabilities varied from 0.16 for growth during third-year shoot initiation to 0.64 for first-year height in the nursery bed. There was little evidence of adaptive variation for seed and germination traits: however, growth traits and cold-hardiness were moderately to strongly correlated with latitude and elevation of seed origin. Seedlings from more southerly and high elevation populations were taller, had greater diameter, grew later into the growing season, and were more susceptible to cold injury during acclimation and at maximum hardiness, than more northern populations. The above trends were not apparent if southern populations (Oregon) were excluded. Environments had a large effect on growth and morphology of yellow-cedar. Shoot elongation was extremely plastic, responding to both decreased photoperiod and water-stress through decreased shoot growth. Upon release of the stress treatments, growth increased to relative rates greater than the non-stressed trees. In all growth and morphology traits, there was minimal evidence for significant genotype by environment interactions at either the population or family within population level, with both photoperiod treatments and water regimes. Genetic variation in gas exchange, water relation parameters, and morphological traits, in response to a drought, was evident with 2-year-old yellow-cedar seedlings among and within populations. Seedlings from Coquihalla, a xeric habitat, had less shoot and lateral branch extension, and less biomass allocated to branches and more to roots, as compared to mesic sources, under both well-watered and drought conditions. As well, these seedlings maintained greater rates of net photosynthesis and higher levels of stomatal conductance under both well-watered and droughty conditions. Yellow-cedar populations at the extremes of environment for the species, i.e. southern and continental populations, have responded to environmental selection pressures by changes in gene frequencies. The changes most likely have been aided by reduced gene flow due to spatial isolation and poor sexual reproduction (Russell et al. 1990). At the same time, however, the species has maintained a substantial amount of both genetic variation and phenotypic plasticity within populations. Yellow-cedar seems to have evolved an intermediate mode of adaptation with less genetic differentiation associated with geography than Douglas-fir, Sitka spruce, and western hemlock, but more genetic differentiation than western white pine and western red cedar.

The issue of alien species, especially invasive aliens (IAS), is the current focus of the international scientific debate owing to the negative effects that such species have caused and continue to cause to ecosystems, economic activities and human health. In Italy, there was an increase of 96% of alien species (over 3,000) over the last thirty years. The reason for the widespread diffusion of alien species lies in some features that make them particularly competitive, such as the resistance to pests, the ability to adapt to different environmental conditions, including anthropized habitats, and the competitive superiority in gaining resources compared to native species. Climate change and biological invasions are two important drivers affecting biodiversity and ecosystem services. However, their effect on biodiversity has usually been assessed independently, despite good scientific reasons to expect the rate and extent of biological invasions to be influenced by climate change. Resident species can become increasingly poorly adapted to the local environment, whereas newcomers might be better adapted and, thus, more competitive under the new conditions. Populations of alien plants are considered more likely to survive if they are introduced to areas with climatic conditions similar to those in their native distribution range. Changes in climatic conditions resulting in a prolonged growing and reproductive period often provide alien species with exploitable opportunities. Indeed, there is increasing evidence that global warming can enable expasion into areas where the species were previously kept in check by climate. Over recent decades, an increasing number of studies have analysed patterns of biological invasions to disentangle the underlying ecophysiological processes. Under this perspective, the recent focus on the functional traits or the syndrome of traits enhancing the invasive potential of IAS, holds promise to develop predictions on which species are more likely to become successful invaders in different habitats. Functional trait ecology represents a relatively novel approach to investigate this phenomenon. Functional traits provide tools for measuring functional diversity, as they impact plant fitness via effects on growth, reproduction and survival, and reflect the trade-offs among different physiological and ecological functions. In particular, through the ecophysiological processes it is possible to understand how the different processes of growth, reproduction and distribution of IAS are influenced by the interaction with ecological factors (abiotic and biotic). Many factors may contribute to the invasion success, including seed production and germination, high relative growth rate (RGR), seedling recruitment, carbon allocation, life history characteristics of species, and susceptibility to disease and/or herbivores. The aim of the present thesis was to identify the functional traits that underline the invasion process of three widespread IAS in Italy: Ailanthus altissima (Mill.) Swingle, Robinia pseudoacacia L. and Phytolacca americana L.. In particular, the focus has been directed to three fundamental aspects, i.e., seed germination traits, seedlings growth dynamics and physiological and morphological traits of seedlings under drought condition. The focus was to understand which traits allow a better performance to IAS and if there are common strategies of considered species. The results presented through the three Chapters of the thesis provide a significant contribution to characterize ecophysiological behaviour of three important IAS to expand knowledge on functional traits underline the invasion process of IAS. In particular, the results from: - Chapter 2 demonstrate that a global temperature increase could be considerably increase germination percentages of some species and future warmer conditions could naturally break seed dormancy, extending the favourable period for seedling establishment; - Chapter 3 provide compelling evidence that certain traits, such as rapid growth, high leaf production rate and high leaf area production rate are considered intrinsic characteristics that can give species some advantages for the colonization of new sites and therefore increase their distribution; in addition, it highlights not all invasive species respond in the same way at temperature and seedling growth reflects the climatic conditions of the native habitat. The considered traits can be useful to help disentangle the trait dimensions by which IAS cope with air temperature change; - Chapter 4 explore how water stress affect the functional traits related to gas exchange in each considered species. The results shows a species dependent effect of the water stress at a physiological and morphological level as well as an interaction between species and stress duration. In particular, the study reveal the considered IAS differ mainly in their capacity to control photosynthesis through stomatal control, highlighting a different species responsiveness in coping with water stress. Overall, the present PhD Thesis by analysing the response to temperature and water availability variations at different plant life stages (i.e., germination and seedling) contribute to the scientific debate on the IAS capacity to face the current climatic changes. In particular, the results reveal that the extent of the response to environmental factor variations, differs among IAS due to different capacity to maximize their performance under limiting environmental conditions. Accordingly, the results highlight the importance of integrating physiological functional information to better understand the invasion strategies of these IAS in the perspective of planning more effective measures of their management and control.

碩士<br>國立臺灣大學<br>生物產業機電工程學研究所<br>105<br>Roots are important organs of plants. Root system architecture (RSA), the spatial configuration of roots, of rice (Oryza sativa L.) has shown a high degree of diversity. RSA needs to be quantified with high accuracy to understand the relationship between RSA and functionality of rice roots. This study developed a three-dimensional (3D) imaging system to quantify the RSA of rice seedling roots of 15 varieties. In this work, rice seedlings were cultivated in glass tubes filled with transparent jelly culture medium for ten days. The two-dimensional (2D) side-view images of the seedlings were acquired using the imaging system. Silhouettes of rice roots were then identified from the 2D side-view images using image recognition technology. Three-dimensional images of the rice roots were next reconstructed using the silhouettes and space-carving algorithm. A ground truth was used to validate the accuracy of the system. Last, RSA traits of rice seedling root of 15 varieties were quantified.

碩士<br>國立臺灣大學<br>農藝學研究所<br>107<br>Rice is an important staple food feeding half of the world population. Drought as the major abiotic stress for rice greatly affects the yield production both in upland and lowland fields. In particular, with the increasing frequencies and severity of drought stress, breeding for drought-tolerant rice is necessary nowadays. Root system architecture (RSA) has been considered as a critical component in drought tolerance because of the important role of roots in water uptake from soil. Various traits contribute together to RSA, such as root morphology including root length, root growth angle and root dry weight, therefore, genetic improvement for an appropriate root system is another promising strategy to elevate drought resistance in rice. In this study, two bi-parental crosses-derived populations: a recombinant inbred lines (RILs) and a F2 population, and a diverse panel were evaluated for their root and drought-tolerant related traits at seedling stage under a hydroponic system with and without an osmotic-associated drought stress induced by polyethylene glycol 6000 (PEG-6000) treatment. Low water potential imposed by PEG in Kimura solution provided a relatively stable experimental condition and allowed us to measure the root-related traits. Single nucleotide polymorphism (SNP) markers of the three populations were obtained following the genotyping-by-sequencing (GBS) approach. With the high-density SNPs, traditional interval mapping (IM), single marker analysis (SMA), and genome wide association study (GWAS) were performed in respective population to identify the genotype-phenotype associations. Our mapping results showed the power of SMA in detecting associations in bi-parental population as compared to the resolution which simple interval mapping can achieve when using the high-density markers. Total 13 genomic regions associated with root-related traits were identified in the three populations, ten of them were searched for candidate genes using three online databases. According to the gene functions, one gene was predicted to be involved in root development and three were characterized to regulate root growth. These four genes are the candidates for future functional analysis to confirm their roles in controlling the root length. Several genomic regions associated with seedling height (SH), rolling score (RS), and heading date (HD) were detected in our F2 populations and diverse panel. We hope the significant regions and SNP markers identified in this study can be utilized in the breeding for drought-tolerant rice cultivars.

碩士<br>國立臺灣大學<br>農藝學研究所<br>88<br>Low temperature occurs frequently at the rice seedling and leads to chilling injuries. To reveal the genetic control of chilling tolerance-related physiological traits in rice seedlings , a chilling-resistant rice cultivar ( Oryza sativa L., cv. Tainung 67 ) and a chilling-sensitive rive cultivar ( Oryza sativa L., cv. Taichung Native 1 ) were treated with low temperature ( 5℃) for 1 day at both 3-leaf stage and 4-leaf stage. After chilling treatment, the seedlings were transferred to a 30/25℃ greenhouse and rewarming for 5 days. The changes of several physiological responses, including electrolyte leakage and antioxidant enzyme activities, were analyzed at 1, 3, 5 days after rewarming. Chlorophyll fluorescence ( Fv/Fm value ) of rice seedlings was also measured at 1, 2, 3 days after rewarming. The results showed that the differences of these physiological traits between Taichung Native 1 and Tainung 67 were significant both at 3-leaf stage and 4-leaf stage. Chilling caused a decrease in fresh weight, soluble protein level and chlorophyll fluorescence, and an increase in leakage and MDA content in seedlings of Taichung Native 1. As regards to the antioxidant enzyme activities, there was an increase in the activities of ascorbate peroxidase and glutathione reductase but a decrease in catalase activity. However, such significant effects were not shown in seedlings of Tainung 67. The further experiment was to analyze the effects of chilling treatment on the physiological traits for the F2 offsprings of reciprocal crosses ( TN1 × TNG67, TNG67 × TN1 ) between Taichung Native 1 and Tainung 67 at 4-leaf stage, and estimate the genetic characteristics of the physiological traits. Most of the frequency distributions of the F2 individuals for the tested traits were continuous except Fv / Fm value. The physiological traits with continuous frequency distributions were revealed to be quantitative, suggesting that they may be controlled by polygenetic systems. The frequency distribution of Fv / Fm value showed binomial. Chi-square analyses were calculated for chilling injury scale and Fv / Fm value to test the fitness of hypothesized 3:1 genetic ratio. Only the chilling scale fitted the ratio in the cross between Tainung 67 and Taichung Native 1 ( TNG67 × TN1 ), indicating that the chilling injury scale may be controlled by a dominant gene. Also, from the different results of the tests in the reciprocal crosses of chilling injury scale, we inferred that a cytoplasm effect may exist. Three physiological traits, leakage rate、MDA content and GR activity were positively correlated to the chilling injury scale in ( TNG67 × TN1 )F2 population, indicating that these three physiological traits may have more contribution to the expression of chilling injury for rice seedlings.

碩士<br>臺灣大學<br>森林環境暨資源學研究所<br>98<br>Leaf life-span (LLS) could be affected by the photosynthetic ability of a plant, light availability and herbivory, and thus regarded as an indicator of a plant’s adaptation to the environment. In this study, I investigated the leaf dynamics and the related physiological traits of 6 hardwood species (Cyclobalanopsis glauca, Cyclobalanopsis stenophylloides, Pasania hancei, Quercus variabilis, Beilschmiedia erythrophloia and Lindera megaphylla) in a Cryptomeria japonica plantation in Chitou district, the Experimental Forest, National Taiwan University, central Taiwan to understand the relationships of leaf life-span with light availability, leaf chemical traits and herbivory. The main results were as follows: According to Kikuzawa (1983), 6 species have a common leaf emergence type --Flush type. However, the patterns of leaf fall were more diverse in these species, belonging to three types--Intermittent, Continuous and L-shaped. LLS, leaf nitrogen concentrations and leaf total phenols concentrations did not differ significantly among 4 sampling lines with different canopy openness. By contrast, herbivory (percentage of leaf area loss) of some species differed significantly between sampling lines, but the patterns were inconsistent. Leaf life-spans differed significantly among species within the same cohorts. By contrast, LLS differed significantly among cohorts only in C. glauca, with significantly longer LLS in the 1st cohort than in the 2nd and 3rd. LLS was somewhat negatively correlated with leaf nitrogen concentrations, but the relationship was insignificant. With Q. variabilis excluded, LLS was positively correlated with leaf total phenols concentrations. Within the 1st cohort of 5 species (except Q. variabilis), there was a significantly positive correlation between LLS and leaf total phenols concentrations. Leaf nitrogen concentrations differed significantly among species. In addition, leaf nitrogen concentrations differed significantly among cohorts in C. glauca, with the concentration higher in the 1st cohort than in the 2nd and 3rd. Leaf total phenols concentrations differed significantly among species, with significantly higher concentration in Q. variabilis than in the other 5 species. Leaf total phenols significantly differed among cohorts in some species, but the patterns were inconsistent. Herbivory differed significantly among species. With B. erythrophloia excluded, herbivory differed significantly among cohorts. Within the 5 species (except B. erythrophloia), the herbivory was significantly higher in the 2nd cohort. There was no significant correlations between herbivory and leaf nitrogen concentrations, leaf total phenols concentrations and leaf toughness. By contrast, leaf nitrogen concentration was in significantly negative correlation with total phenols concentration. The results of this study suggest that LLS could be associated with light availability, leaf nitrogen concentrations, leaf total phenols concentrations and herbivory. Beyond the scope of this study, there are many more biotic and abiotic factors which can have influenced LLS. The complexity of LLS demands further studies to help elucidate the mechanisms affecting LLS.

Junipers and pines exhibit contrasting patterns of growth decline and mortality with climate change-type warming and drought; yet, the underlying physiological mechanisms are not fully understood. Does warming exacerbate the effects of drought on gas exchange physiology and growth? Do the combined effects of drought and warming differ for pines and junipers? To what extent do isohydric vs. anisohydric responses to water limitation in pines and junipers constrain net leaf CO2 exchange and plant growth response to drought and warming? To address these questions, we compared responses of leaf gas exchange and growth in seedlings of juniper (Juniperus scopulorum, J. virginiana) and pine (Pinus edulis, P. taeda) species of contrasting arid and mesic origin in a study of combined warming (ambient, +1.8 °C) and enhanced summer drought (long-term mean, -40%). Warming and enhanced summer drought each reduced photosynthesis and growth and effects were largely independent, suggesting that warming exacerbates drought effects on growth. Enhanced summer drought and warming had distinct impacts on photosynthetic carbon gain that were differentially revealed depending upon soil water content. Warming reduced light-saturated net photosynthesis (Asat) under low soil water contents, whereas carry-over effects of drought treatment were evident under well-watered conditions. Short-term soil drying led to greater reduction of Asat in pines (-51%) rather than junipers (-30%). Under short-term water-limited conditions, Asat and gs were about two-times higher for junipers compared to pines. Relative growth rate of junipers declined with warming (-28%) and drought (-50%) treatments. In contrast, pine growth and Asat declined more with warming than drought. Only P. edulis exhibited increased mortality in response to warming and drought, reaching 75% in the combined warming and drought treatment. Diminished sensitivity of R to water limitations, coupled with steeper reductions in Asat with decreasing soil water content in isohydric pines compared to anisohydric junipers could account for the greater sensitivity of pines to warming and drought under climate change.