Academic literature on the topic 'Below ground biomass N (BGB-N)'

The amount of lupin below-ground biomass (BGB), BGB nitrogen (N) content, and utilization of BGB-N by subsequent wheat was estimated from lupins grown in soil columns. Lupin plants were enriched in situ with 15N-labelled urea through a cotton wick inserted through the stem. Of the applied 15N. 92% was recovered in the lupin plant-soil system at maturity: 87% of this 15N was in lupin aboveground biomass and 13% in the soil columns. Total mature lupin dry matter (DM) approximated 11 t/ha, with 3.0 t/ha (27%) of this DM below ground. Total mature lupin N approximated 321 kg/ha, of which 91 kg/ha (28%) resided below ground. In terms of N and DM, BGB was the largest lupin residue component even though only 35% of this was recoverable as root material. About 13% of the BGB-N was in inorganic form at maturity. The net mineralisation of lupin BGB-N after 2 consecutive years of wheat growth was 27%. and wheat assimilated about 74% of this N (i.e. 20% of BGB-N), with equal quantities assimilated in each year. The contribution of lupin BGB-N to the N in wheat tops ranged from 40% for soil columns receiving no fertiliser N to 15-20% for soil columns fertilised with 30 kg N/ha. The net mineralisation of BGB-N and the assimilation of BGB-N by wheat were unaffected by the application of fertiliser N.

Sewage sludge improves agricultural soil and plant growth, but there are hazards associated with its use, including high metal(loid) contents. An experimental study was conducted under greenhouse conditions to examine the effects of sewage sludge on growth of the invasive tree Prosopis glandulosa, as well as to determine its phytoremediation capacity. Plants were established and grown for seven months along a gradient of sewage sludge content. Plant traits, soil properties, and plant and soil concentrations of N, P, K, Cd, Pb, Cu, Ni, Zn, Cr, Co, As, and Fe were recorded. The addition of sewage sludge led to a significant decrease in soil pH, and Ni, Co, and As concentrations, as well as an increase in soil organic matter and the concentrations of N, P, Cu, Zn, and Cr. Increasing sewage sludge content in the growth medium raised the total uptake of most metals by P. glandulosa plants due to higher biomass accumulation (taller plants with more leaves) and higher metal concentrations in the plant tissues. P. glandulosa concentrated more Cd, Pb, Cu, Zn, and Fe in its below-ground biomass (BGB) than in its above-ground biomass (AGB). P. glandulosa concentrated Ni, Co, and As in both BGB and AGB. P. glandulosa has potential as a biotool for the phytoremediation of sewage sludges and sewage-amended soils in arid and semi-arid environments, with a potential accumulation capability for As in plant leaves.

The rapid global plant diversity and productivity loss has resulted in ecosystem functional degeneration in recent decades, and the relationship between plant diversity and productivity is a pressing issue around the world. Here, we sampled six plant communities that have not been grazed for 20 years, i.e., Agropyron mongolicum, Stipa bungeana, Cynanchum komarovii, Glycyrrhiza uralensis, Sophora alopecuroides, Artemisia ordosica, located in a desertified steppe, northwestern China, and tested the relationship between plant diversity and productivity in this region. We found a positive linear relationship between AGB (above-ground biomass) and BGB (below-ground biomass), and the curves between plant diversity and AGB were unimodal (R2 = 0.4572, p < 0.05), indicating that plant productivity increased at a low level of diversity but decreased at a high level of diversity. However, there was no significant relationship between BGB and plant diversity (p > 0.05). Further, RDA (redundancy analysis) indicated that soil factors had a strong effect on plant diversity and productivity. Totally, GAMs (generalized additive models) showed that soil factors (especially total nitrogen TN, total carbon TC, soil microbial biomass nitrogen SMB-N, soil microbial biomass carbon SMB-C) explained more variation in plant diversity and productivity (78.24%), which can be regarded as the key factors driving plant diversity and productivity. Therefore, strategies aiming to increase plant productivity and protect plant diversity may concentrate on promoting soil factors (e.g., increasing TC, TN, SMB-N and SMB-C) and plant species, which can be regarded as an effective and simple strategy to stabilize ecosystems to mitigate aridity in desertified steppes in northwestern China.

The objectives of this study were to quantify below-ground nitrogen (BGN) of rainfed fababean (Vicia faba), chickpea (Cicer arietinum), and barley (Hordeum vulgare) and to use the values to determine N balances for the 3 crops. The BGN fraction of legumes in particular represents a potentially important pool of N that has often been grossly underestimated or ignored in calculating such balances. A field experiment was conducted at Breeza on the Liverpool Plains, New South Wales, in which BGN of fababean, chickpea, and barley was estimated using 15N methodologies. Plants were grown in 0.32-m2 microplots and labelled with 15N on 5 occasions during vegetative growth with a total of 1.0 mL of 0.5% 15N urea (98 atom% 15N) using leaf-flap (fababean), leaf-tip (barley), or cut petiole (chickpea) shoot-labelling procedures. At peak biomass (146–170 days after sowing), all plant material and soil to 45 cm depth was sampled from one microplot in each replicate plot and analysed for dry matter (DM), %N, and 15N. At plant maturity, the remaining 3 microplots in each replicate plot were harvested for shoot and grain DM and N. With fababean, 15N enrichments of intact roots and shoots were reasonably uniform at 537‰ and 674‰, respectively. Microplot soil at 0–25 cm depth had a 15N enrichment of 18‰ (natural abundance of 6.1‰). The 25–45 cm soil enrichment was 8.7‰ (natural abundance of 6.3‰). In contrast, 15N enrichment of chickpea shoots was about twice that of recovered roots (685‰ v. 331‰), and the soil enrichment was relatively high (30‰ and 8.8‰ for the 0–25 and 25–45 cm depths, respectively). The 15N enrichments of barley shoots and recovered roots were 2272‰ and 1632‰, respectively, with soil enrichments of 34‰ and 10.7‰ for the 0–25 and 25–45 cm depths, respectively. Estimates of BGN as a percentage of total plant N, after adjusting the 15N shoot-labelling values of fababean and chickpea for uneven distribution of 15N-depleted nodules, were 24% for fababean, 68% for chickpea, and 36% for barley. The BGN values were combined with N2 fixation (fababean and chickpea only) and shoot and grain yield data (all 3 species) to construct N budgets. The inclusion of BGN in the budgets increased N balances by 38 kg N/ha to +36 kg N/ha for fababean and by 93 kg N/ha to +94 kg N/ha for chickpea. As there was no external (N2 fixation) input of N to barley, the inclusion of BGN made no difference to the N balance of the crop of –74 kg N/ha. Such values confirm the importance of BGN of N2-fixing legumes in the N economies of cropping systems.

The time courses of above- and below-ground accumulation of biomass and N were followed in a crop of narrowleaf lupin (Lupinus angustifolius L. cv. Illyarrie) at Geraldton, W.A., and concurrent N2 fixation assessed using the 15N natural abundance technique. Crop biomass peaked at 10 t DM and 231 kg N ha-1 with 13% of this N below ground. The crop accumulated the bulk (90%) of its N through symbiotic N2 fixation. Of the 164 kg total plant N ha-1 remaining in recoverable biomass at maturity 44% was recovered as grain, 49% as other above-ground residues and 7% as roots. Despite a decrease in recoverable N of 67 kg ha-1 between peak biomass and maturity, 96 kg N ha-1 was returned as crop residues after grain harvest. Investigation of six farm crops in the study region gave values for nitrogen accumulation at peak biomass ranging from 199 to 372 kg ha-1 of which, on average, 86% (222 kg ha-1) was fixed from the atmosphere. Predicted N returns to the soil from fixation averaged 65 kg ha-1, though the range (32-96 kg ha-1) indicated that south-west Australian lupin crops provide somewhat variably sized pools of mineralizeable crop residues for following cereal growth.

Growth and nitrogen (N) accumulation relationships based on tree size, rather than age, may provide more generic information that could be used to improve sweet orange [Citrus sinensis (L.) Osbeck] N management. The objectives of this study were to determine how orange trees accumulate and distribute biomass and N as they grow, investigate yearly biomass and N changes in mature orange trees, determine rootstock effect on biomass and N distribution, and to develop simple mathematical models describing these relationships. Eighteen orange trees with canopy volumes ranging between 2 and 43 m3 were dissected into leaf, twig, branch, and root components, and the dry weight and N concentration of each were measured. The N content of each tree part was calculated, and biomass and N distribution throughout each tree were determined. The total dry biomass of large (mature) trees averaged 94 kg and contained 0.79 kg N. Biomass allocation was 13% in leaves, 7% in twigs, 50% in branches/trunk, and 30% in roots. N allocation was 38% in leaves, 8% in twigs, 27% in branches/trunk, and 27% in roots. For the smallest tree, above-/below-ground distribution ratios for biomass and N were 60/40 and 75/25, respectively. All tree components accumulated biomass and N linearly as tree size increased, with the above-ground portion accumulating biomass about 2.5 times faster than the below-ground portion due mostly to branch growth. The growth models developed are currently being integrated in a decision support system for improving fertilizer use efficiency for orange trees, which will provide growers with a management tool to improve long-term N use efficiency in orange orchards.

Abstract. Global climate change has generally modified net primary production (NPP) which leads to increasing litter inputs in some ecosystems. Therefore, assessing the impacts of increasing litter inputs on soil nutrients, plant growth and ecological carbon (C) : nitrogen (N) : phosphorus (P) stoichiometry is critical for an understanding of C, N and P cycling and their feedback processes to climate change. In this study, we added plant above-ground litter, harvested near the experimental plots, to the 10–20 cm subsoil layer of a steppe community at rates equivalent to annual litter input of 0, 15, 30, 60 and 120%, respectively, covering the entire range of the expected NPP increases in this region due to climate change (10–60%). We measured the resulting C, N and P content of different pools (above- and below-ground plant biomass, litter, microbial biomass). Small litter additions, which are more plausible compared to the expected increase predicted by Earth system models, had no effect on the variables examined. Nevertheless, high litter addition (120% of the annual litter inputs) significantly increased soil inorganic N and available P, above-ground biomass, below-ground biomass and litter. Our results suggest that while very high litter addition can strongly affect C : N : P stoichiometry, the grassland studied here is resilient to more plausible inputs in terms of stoichiometric functioning.

A leaf-feeding technique for in situ 15N-labelling of intact soil–pasture plant systems was assessed, using subterranean clover (Trifolium subterraneum L.) and serradella (Ornithopus compressus L.) grown under glasshouse conditions. Total recoveries of fed 15N were 87–100% following leaf-feeding of plants at flowering but were lower (74–84%) following the feed at the vegetative stage. Below-ground recovery of fed 15N ranged from 7 to 26%, with serradella partitioning a greater proportion of labelled N below ground than subterranean clover. Additionally, plants of both species fed at the vegetative stage accumulated a greater proportion of the 15N label below ground than did those fed at flowering. Dry sampling procedures, which utilised freeze-drying, enabled fractionation of the below-ground portion of the system into ‘clean’ nodulated macro-roots with no adhering soil, residual uncleaned root, rhizosphere, and bulk soil. Calculated specific enrichment for the ‘clean’ roots at different depths demonstrated a relatively uniform distribution of 15N label in the subterranean clover roots, whereas the presence of large indeterminate nodules in the crown region of serradella roots contributed to apparent uneven distribution of label. Approximately half of the N in the residual fraction of both species consisted of labelled material, postulated to be mostly fine root. Additionally, 5–20% of the rhizosphere N and 0·5–3% of the N in bulk soil was legume root-derived, with some 15N detected in the extractable total soluble N and microbial N pools. Rhizodeposition of N represented approximately 10% of total plant N and 17–24% of total below-ground N for subterranean clover, whereas values for serradella were 20 and 34–37%, respectively. Estimated total below-ground N of subterranean clover reached a maximum value of 177 mg N/plant at 98 days after sowing, which corresponded with a peak shoot N of 243 mg N. Maximum below-ground N for serradella attained 196 mg N/plant 84 days after sowing with a corresponding shoot biomass of 225 mg N. There was a decline in the total below-ground N of serradella at maturity. Overall, recovered clean root N represented 30–62% of estimated total below-ground N, so it was concluded that standard root recovery procedures might be likely to underestimate severely the total below-ground N accretion and N turnover by legumes. The implications of these results for field estimation of total legume N yield, biological N fixation, and the N benefit from legumes in rotations are discussed.

Abstract Aims Global change factors (e.g. warming and nitrogen deposition) may influence biological invasions, but how these factors may influence the performance of invasive species and further mediate the interactions with native competitors remain still unknown. Methods Here, we conducted a 5-month greenhouse experiment to examine the effects of warming (using open-top chambers, +0.62°C) and N addition (adding NH4NO3 at a rate of 4.2 g m−2) on the performance of the native and invasive populations of an invasive species Plantago virginica in competition with a native Plantago asiatica. Important Findings Under warming treatment and its interaction with nitrogen addition treatment (W × N), invasive and native populations of P. virginica had different biomass allocation strategies to compete with native competitor P. asiatica. Native population of P. virginica (PV-Na) increased more below-ground biomass, whereas those from the invasive population (PV-In) increased more above-ground biomass. We also found that invasive species P. virginica had stronger responses to warming and N addition than the native species P. asiatica. The competitive ability of the invasive plants was significantly reduced by warming which indicated that the invasive plant were much stronger sensitivity to elevated temperature than native plant. Similarly, N addition and W × N reduced the competitive response of PV-In in below-ground biomass, but increased the competitive response of PV-Na in above-ground and total biomass when they grew with the P. asiatica. The results show that P. virginica have occurred differential biomass allocation strategies during its invasions and invasive population exhibit flexible competition ability to adapt to environmental changes (especially warming). These findings may potentially help to predict plant invasions and make management strategies in a world with changing climate.

This paper describes the use of a cotton-wick method to enrich lupin plants with 15N. The method involved the insertion of a cotton thread through the stem and the submergence of the ends of the cotton thread in a solution of highly enriched 15N urea. The distribution of 15N in lupin plant components during pre-reproductive growth and pod filling. and in relation to the frequency of labelling, was determined. The recovery of applied 15N within plant tissues was close to 100% for lupins grown in solution culture, but 15N was not distributed between plant components in the proportions observed for total plant N. Stems and leaves were preferentially labelled with 15N irrespective of the phase of lupin growth when the 15N was applied. Pre-reproductive and mature lupin root biomass was depleted in 15N because of the poor assimilation of 15N within lupin nodules. More applied 15N was found in the root biomass of lupin plants that received fortnightly, compared with weekly, applications of 15N. The distribution of 15N between lupin components was reproducible when 15N-urea was wick-applied to plants of the same age. Recovery of 15N was incomplete when urea was fed to lupins grown in sand culture. Incomplete recovery of root material and loss of 15N associated with root exudates probably contributed to the lower recoveries of 15N in root material in sand compared with solution culture. The ability to manipulate the 15N solution concentration, the volume of solution fed to plants, time of application, and frequency of 15N application underscore the usefulness of the wick technique to label woody legumes with 15N.

The incorporation of legumes into crop rotations has been suggested as a strategy to address declining soil fertility, especially of nitrogen (N), in Central Queensland cropping systems. However, traditional methods to determine the contribution made by legumes to soil N are flawed in that usually only the above ground biomass (AGB) or at best macro root tissues are assessed. Furthermore crops regularly experience soil water deficits in this environment, but the impact this has on the contribution made to soil fertility by legumes is poorly documented.

A published ¹⁵N foliar labelling methodology that accurately estimates legume below ground biomass N (BGB-N), was adapted under polyhouse conditions and verified in the field for lab lab, lucerne and siratro. For the legumes investigated, labelled macro root tissue at a depth of 10-20 cm was representative of recoverable root tissue (all > 500 um) throughout a 60 cm soil profile. A protocol was established that reliably estimated the ¹⁵N content of soil enriched by the labelled root system to within a 95% confidence interval.

N₂ fixation in symbioses which translocate fixed N as amides from their nodules are reported to have a greater tolerance to water stress than that in symbioses which export ureides. The impact of water stress on N₂ fixation and the distribution of biomass and N between above and below ground compartments was therefore studied for two commercially important legumes: mungbean (a ureide exporter) and peanut (an amide exporter). Under glasshouse conditions, drought had no effect on mungbean BGB-N as a proportion of legume N (AGB-N + BGB-N) (35%) whereas the proportion of peanut N as BGB-N increased from 33 % under optimal conditions to 44% (P<0.05) under terminal drought. Legume N and N derived from atmospheric N2 (Ndfa), including BGB-N and BGB Ndfa was significantly greater than estimates based on AGB-N alone. Under drought, whole plant Ndfa was twice that of values based on AGB-N alone. The proportion of cereal crop N derived from legume BGB-N (27%) was significantly greater than that derived from AGB-N (20%). The proportion of mungbean N derived from atmospheric N₂ (%Ndfa) was 51% under optimal soil water conditions but declined to 20 and 12% under the moderate and terminal droughts, respectively. Severe drought produced a small but significant reduction in N₂ fixation activity compared to optimally watered plants (%Ndfa decreased to 67 from 78%; P<0.05). Moderate drought had not significant effect on %Ndfa compared to optimally watered plants (78 and 75%Ndfa, respectively).

Similar trends to those reported in the glasshouse trial were observed under field conditions, with significantly greater contributions by mungbean and peanut to soil N fertility and cereal crops documented than reported previously for a range of grain and pasture legumes used in Central Queensland cropping systems. Droughted legumes increased the proportion of BGB-N at depth (20-60 cm), with greater increases by peanut. Despite drought induced decreases in mungbean and peanut %Ndfa (at 59 and 32%, respectively, of irrigated plants), droughted mungbean and peanut %Ndfa was still substantial (30 and 53%, respectively). Droughted whole mungbean and peanut Ndfa was estimated at 10 and 21 kg N/ha, respectively. However, net N balance was nevertheless neutral to negative for mungbean when N exported in harvested grain was considered. The estimates of Ndfa were three fold higher than that based on AGB-N only, and were consistent with the thesis that legumes possessing an amide exporting symbiosis offer significantly greater potential to improve soil N fertility in the region. The drought survival mechanisms exhibited by legumes is also a factor determining whether or not accumulated N and N₂ fixation were maintained under increased soil water deficit and when a net contribution to soil N stores was likely.