A New Method to Determine Central Wavelength and Optimal Bandwidth for Predicting Plant Nitrogen Uptake in Winter Wheat

Plant nitrogen （N） uptake is a good indicator of crop N status. In this study, a new method was designed to determine the central wavelength, optimal bandwidth and vegetation indices for predicting plant N uptake （g N m-2） in winter wheat （Triticum aestivum L.）. The data were collected from the ground-based hyperspectral reflectance measurements in eight field experiments on winter wheat of different years, eco-sites, varieties, N rates, sowing dates, and densities. The plant N uptake index （PNUI） based on NDVI of 807 nm combined with 736 nm was selected as the optimal vegetation index, and a linear model was developed with R2 of 0.870 and RMSE of 1.546 g N m-2 for calibration, and R2 of 0.834, RMSE of 1.316 g N m-2, slope of 0.934, and intercept of 0.001 for validation. Then, the effect of the bandwidth of central wavelengths on model performance was determined based on the interaction between central wavelength and bandwidth expansion. The results indicated that the optimal bandwidth varies with the changes of the central wavelength and with the interaction between the two bands in one vegetation index. These findings are important for prediction and diagnosis of plant N uptake more precise and accurate in crop management.

Prediction and Analysis of Total Nitrogen in a Sewage Treatment Plant Effluent

Total nitrogen was an important indicator for characterizing eutrophication of polluted water. Although the use of water quality online monitoring instrument can monitor water quality changes in real time, the degree of intelligence was low, so it was urgent to predict the water quality and take precautions in advance. A predictive model for total nitrogen levels in a sewage treatment plant utilizing the Anaerobic-Anoxic-Oxic (AAO) process was investigated in this paper. This model demonstrated significant practical application value. Based on the ARIMA (Autoregressive Integrated Moving Average) model and taking into account the impact of Biochemical Oxygen Demand (BOD), a prediction model for effluent total nitrogen was developed. However, the initial results exhibited significant deviations. To address this issue, seasonal factors were further considered. Then, the dataset was divided into winter and Non-winter sub-samples, leading to a reconstruction of the prediction model. Additionally, in developing the Non-winter prediction model, life cycle considerations were incorporated, and consequently, a SARIMA (Seasonal Autoregressive Integrated Moving Average) model was established. The predicting deviation associated with both the winter and Non-winter forecasting models showed a significant reduction.

The Effects of Water and Fertilizer Coupling on Plant and Soil Nitrogen Characteristics and Fruit Growth of Rabbiteye Blueberry Plants in a Semi-Arid Region in China

To evaluate the effects of nitrogen(N)and irrigation coupling on the soil N distribution,plant N utilization,and fruit yield of rabbiteye blueberries(Vaccinium virgatum),a field experiment was designed using two factors(water and fertilizer application)with four levels of irrigation and three levels of fertilization,and a control.Under the different water and fertilizer combinations,N primarily accumulated in the leaves.Irrigation and N application within appropriate ranges(pure N≤29 g/plant and irrigation volume≤2.5 L/plant)significantly improved the blueberry fruit yield.Increases in water and N within these ranges promoted the effective accumulation of N in various organs and the absorption and utilization of N in the plants,which ultimately promoted blueberry yield.With increased N application rate,the nitrate N content of the 0–20 cm and 20–50 cm soil layers increased.With increased irrigation volume,the nitrate N content of the 0–20 cm soil layer decreased,while the nitrate content in the 20–50 cm soil layer increased.Low N and moderate water treatments resulted in high fruit yields and reduced nitrate N retention in the soil.Under these conditions,the economic input-output ratio was high and the soil N accumulation was low,and thus the economic and ecological benefits were maximized.

Effects of Plant Density and Nitrogen Application Rate on Grain Yield and Nitrogen Uptake of Super Hybrid Rice

The nitrogen uptake, yield and its components for two super-high-yielding hybrid rice combinations, Guodao 6 and Eryou 7954 were investigated under different plant densities （15, 18, and 21 plants/m^2） and different nitrogen application rates （120, 150, 180, and 210 kg/hm^2）. The experiment was conducted on loam soil during 2004-2006 at the experimental farm of the China National Rice Research Institute in Hangzhou, China. In these years, the two hybrid rice cleady showed higher yield at a plant density of 15 plants/m^2 with a nitrogen application rate of 180 kg/hm^2. Guodao 6 produced an average grain yield of 10 215.6 kg/hm^2 across the three years, while the yield of Eryou 7954 was 9 633.0 kg/hm^2. With fewer plants per unit-area and larger plants in the plots, the two hybrid rice produced more panicles per plant in three years. The highest nitrogen uptake of the two hybrid rice was at a plant density of 15 plants/m^2 with a nitrogen application rate of 180 kg/hm^2. Further increasing nitrogen application rate was not advantageous for nitrogen uptake in super-high-yielding rice under the same plant density.

Response of grain yield to plant density and nitrogen rate in spring maize hybrids released from 1970 to 2010 in Northeast China

The objective of this study was to identify the response of grain yield to plant density and nitrogen rate in spring maize hybrids released from 1970 to 2010 and grown extensively in Northeast China.Twenty-one hybrids were grown for 2 years in Northeast China at densities of 30,000,52,500,75,000,and 97,500 plants ha^(-1)and N application levels of 0,150,300,and 450 kg N ha^(-1).Irrespective of density or nitrogen application rate,grain yields both per plant and per unit area were significantly higher for newer than older hybrids.As plant density increased from 30,000 to 97,500 plant ha^(-1),yield per plant of 1970 s,1980 s,1990 s,and 2000 s hybrids decreased by 50%,45%,46%,and 52%,respectively.The response of grain yield per unit area to plant density was curvilinear.The estimated optimum plant densities were about 58,000,49,000,65,000,and 65,000 plants ha^(-1)for hybrids released in the 1970 s,1980s,1990 s,and 2000 s,respectively.The theoretical optimum densities for the hybrids released from the 1970 s to the 2000 s increased by 1750 plants ha^(-1)decade^(-1).Nitrogen fertilization significantly increased grain yields per plant and per unit area for all hybrids.The theoretical optimum N application rates for high yield for hybrids released in the 1970 s and 1980 s were about 280 and 360 kg ha^(-1),and the hybrids from the 1990 s and 2000 s showed highest yield at 330 kg ha^(-1)N.No significant difference in the grain yields of 2000 s hybrids between the N levels of 150 to 450 kg ha^(-1)was found.Significant yield gains per plant and per unit area were found,with average increases of 17.9 g plant^(-1)decade^(-1)and936 kg ha^(-1)decade^(-1)over the period 1970–2010,respectively.Yield gains were attributed mainly to increased yield per plant,contributed by increases in kernel number per ear and1000-kernel weight.The rates of lodging and barren plants of newer hybrids were significantly lower than those of older ones,especially at high plant density.

Response of nitrogen mineralization dynamics and biochemical properties to litter amendments to soils of a poplar plantation

Understanding the impact of plant litters on soil nitrogen （N） dynamics could facilitate development of management strategies that promote plantation ecosystem function. Our objective was to evaluate the effects of different litter types on N mineralization and availability, microbial biomass, and activities of L-asparaginase and odiphenol oxidase （o-DPO） in soils of a poplar （Populus deltoides） plantation through 24 weeks of incubation experiments. The tested litters included foliage （F）, branch （B）, or root （R） of poplar trees, and understory vegetation （U） or a mixture of F, B, and U （M）. Litter amendments led to rapid N immobilization during the first 4 weeks of incubation, while net N mineralization was detected in all tested soils from 6 to 24 weeks of incubation, with zero-order reaction rate constants （k） ranging from 7.7 to 9.6 mg N released kg-1 soil wk-1. Moreover, litter addition led to increased （C） 49-128% and increased microbial biomass carbon MBC：MBN ratio by 5-92%, strengthened activities of L-aspaxaginase and o-DPO by 14-74%; Up to about 37 kg N ha-1 net increase in mineralized N in litter added soils during 24 weeks of incubation suggests that adequate poplar and understory litter management could lead to reduced inputs while facilitate sustainable and economic viable plantation production.

Effects of Nitrogen Application on Plant Growth and Soil Inorganic Nitrogen Content in Alpine Grasslands

In order to further determine the nitrogen demand of plants in alpine grassland ecosystem,different nitrogen levels( 0,1,2,4,8,16,24,32 g/m2)were designed through field control to study the responses of different plant functional groups( grass,sedge and weed) to different nitrogen application levels in the aboveground biomass and soil inorganic nitrogen( nitrate nitrogen and ammonium nitrogen).The results showed that with the increase of nitrogen application rate,the aboveground biomass of different functional groups increased linearly,and the soil inorganic nitrogen content increased with the increase of nitrogen application rate,among which treatments N16,N24 and N32 increased significantly in soil nitrate nitrogen content( P < 0.05).The results showed that the optimal nitrogen content in alpine grasslands was 8 g/m^2,which could not only promote plant growth,but also effectively control soil nitrate nitrogen content.

Accumulation Laws of Nitrogen and Phosphorus in Wetland Plants

To study the accumulation regularity of nitrogen and phosphorus in typical constructive plants in coastal wetland,samples of Suaeda glauca(Bunge) Bunge,Phragmites austrahs and Tamarix chinensis Lour,were taken from the Yellow River Delta National Coast Wetland Nature Reserve,nitrogen and phosphorus content in plants was measured and analyzed.The results showed that ① nitrogen and phosphorus content in different wetland plants is correlated;② different species in the same place and the same species in different spaces show different accumulation regularity of nitrogen and phosphorus;③ nitrogen and phosphorus content in plants is closely related to nitrogen and phosphorus content in the habitat;④ nitrogen content in T.chinensis Lour,is the highest,the mean is 11.63 g/kg,and phosphorus content in S glauca(Bunge) Bunge is the highest,the mean is 1.38 g/kg;⑤ nitrogen content in the 3 species:T.chinensis Lour.> S.glauca(Bunge) Bunge > P.australis;⑥ nitrogen content in aboveground parts of all plants is significantly higher than that in underground parts,and phosphorus content in aboveground parts of all plants except S.glauca(Bunge) Bunge is significantly higher than that in underground parts;⑦ nitrogen content in the 3 species in the study area is significantly higher than phosphorus content in these species.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

Experimental analysis of a nitrogen removal process simulation of wastewater land treatment under three different wheat planting densities

Nitrogen contaminant transport, transformation and uptake simulation experiments were conducted in green house under three different planting density of winter wheat. They were Group A, planting density of 0.0208 plants/cm 2, Group B, 0.1042 plants /cm 2, and Group C, 0.1415 plants/cm 2. The capacity and ratio of nitrogen removal were different on three kinds of conditions of wastewater land treatment. From analysis of wastewater treatment capacity, wastewater concentration and irrigation intensity for Group C were suitable and nitrogen quantity added was 2 times of that for Group B, 2.6 times for Group A while nitrogen residue was only 7.06%. Hence, wastewater irrigation and treatment design with purpose of waste water treatment should select the design with maximum capacity, optimal removal ratio and least residue in soil, which was closely related to crop planting density, crop growth status and also background nitrogen quantity in soil.

Advances in Nitrogen Loss Leached by Precipitation from Plant Canopy

Function of canopy in changing nutrient cycle and flux is one of the focuses in recent years. On the basis of comprehensively appraising published research, we analyzed the nitrogen loss leaching from plant canopy and several factors which affected it. We pointed out the disadvantages of the published researches and the key issues that ought to be solved： （1） The menstruation need to be advanced, and the research should be carried out on nitrogen loss leaching from the canopy of the field plant. （2） If the nitrogen is leached from the plant canopy, the research on the type of nitrogen loss should be carried out, and the nitrogen use efficiency of different varieties should be dealt on a research perspective with regard to the nitrogen leaching. （3） The research should be conducted on the mechanism and pathway, and the progress of nitrogen leaching; and the factors affecting nitrogen leaching should be included in the research, such as the leaf area of different growth stages, stomata densities, stomata conductance, and the apparent free space, which are beneficial to explain the mechanism of nitrogen leaching from the plant canopy.

Water,Nitrogen and Plant Density Affect the Response of Leaf Appearance of Direct Seeded Rice to Thermal Time

Field experiments were conducted in the Ebro Delta area （Spain）, from 2007 to 2009 with two rice varieties： Gleva and Tebre. The experimental treatments included a series of seed rates, two different water management systems and two different nitrogen fertilization times. The number of leaves on the main stems and their emergence time were periodically tagged. The results indicated that the final leaf number on the main stems in the two rice varieties was quite stable over a three-year period despite of the differences in their respective growth cycles. Interaction between nitrogen fertilization and water management influenced the final leaf number on the main stems. Plant density also had a significant influence on the rate of leaf appearance by extending the phyllochron and postponing the onset of intraspecific competition after the emergence of the 7th leaf on the main stems. Final leaf number on the main stems was negatively related to plant density. A relationship between leaf appearance and thermal time was established with a strong nonlinear function. In direct-seeded rice, the length of the phyllochron increases exponentially in line with the advance of plant development. A general model, derived from 2-year experimental data, was developed and satisfactorily validated; it had a root mean square error of 0.3 leaf. An exponential model can be used to predict leaf emergence in direct-seeded rice.

Comparison of Carbon, Nitrogen, and Sulfur in Coastal Wetlands Dominated by Native and Invasive Plants in the Yancheng National Nature Reserve, China

The rapid invasion of the plant Spartina alterniflora in coastal wetland areas can threaten the capacity of their soils to store carbon(C),nitrogen(N),and sulfur(S).In this study,we investigated the spatial and temporal distribution patterns of C,N and S of both soil and(native and invasive)plants in four typical coastal wetlands in the core area of the Yancheng National Nature Reserve,China.The results show that the invasive S.alterniflora greatly influenced soil properties and increased soil C,N and S storage capacity:the stock(mean±standard error)of soil organic carbon(SOC,(3.56±0.36)kg/m^3),total nitrogen(TN,(0.43±0.02)kg/m^3),and total sulfur(TS,(0.69±0.11)kg/m^3)in the S.alterniflora marsh exceeded those in the adjacent bare mudflat,Suaeda salsa marsh,and Phragmites australis marsh.Because of its greater biomass,plant C((1193.7±133.6)g/m^2),N((18.8±2.4)g/m^2),and S((9.4±1.5)g/m^2)storage of S.alterniflora was also larger than those of co-occurring native plants.More biogenic elements circulated in the soil-plant system of the S.alterniflora marsh,and their spatial and temporal distribution patterns were also changed by the S.alterniflora invasion.Soil properties changed by S.alterniflora’s invasion thereby indirectly affected the accumulation of soil C,N and S in this wetland ecosystem.The SOC,TN,and TS contents were positively correlated with soil electrical conductivity and moisture,but negatively correlated with the pH and bulk density of soil.Together,these results indicate that S.alterniflora invasion altered ecosystem processes,resulted in changes in net primary production and litter decomposition,and increased the soil C,N and S storage capacity in the invaded ecosystems in comparison to those with native tallgrass communities in the coastal wetlands of East China.

Effect of Plant Growth-Promoting Rhizobacteria at Various Nitrogen Rates on Corn Growth

Plant growth-promoting rhizobacteria (PGPR) colonize plant roots and promote plant growth by producing and secreting various chemical regulators in the rhizosphere. With the recent interest in sustainable agriculture, an increasing number of researchers are investigating ways to improve the efficiency of PGPR use to reduce chemical fertilizer inputs needed for crop production. Accordingly, greenhouse studies were conducted to evaluate the impact of PGPR inoculants on biomass production and nitrogen (N) content of corn (Zea mays L.) under different N levels. Treatments included three PGPR inoculants (two mixtures of PGPR strains and one control without PGPR) and five N application levels (0%, 25%, 50%, 75%, and 100% of the recommended N rate of 135 kg N ha&#8722;1). Results showed that inoculation of PGPR significantly increased plant height, stem diameter, leaf area, and root morphology of corn compared to no PGPR application under the same N levels at the V6 growth stage, but few differences were observed at the V4 stage. PGPR with 50% of the full N rate produced corn biomass and N concentrations equivalent to or greater than that of the full N rate without inoculants at the VT stage. In conclusion, mixtures of PGPR can potentially reduce inorganic N fertilization without affecting corn plant growth parameters. Future research is needed under field conditions to determine if these PGPR inoculants can be integrated as a bio-fertilizer in crop production nutrient management strategies.

Effect of Industrial Sludge Application on Soil Nitrogen and Wheat Plant Response

Wazirpur industrial area of Delhi generates a huge quantity of sludge per day, which is highly acidic in nature (pH 2.7 to 4.4) and contains macronutrients, micronutrients as well as toxic metals. A pot-culture experiment was conducted by taking the two soils (JNU and Chhattarpur) amended with sludge (0%, 10%, 20%, 30%), pretreated with lime (0%, 0.5% and 1%). Two wheat seedlings were planted per pot containing 3 kg sludge amended or control soil and the experiment was carried out till harvesting (four months) in a glass house. Lime treatments enhanced the N content in wheat plant in almost all cases. Sludge and lime treatments enhanced dry weight in wheat plants grown in Chhattarpur soil and dry weight increased with time. Maximum growth was observed in 0.5 lime treated and 20% sludge amended soils. But we have to take an account about any kind of metal toxicity before disposal of this waste to land.

Modeling the Effect of Planting Dates and Nitrogen Application Rates on Potatoes Water Productivity in Jordan Valley

Agricultural sector in Jordan is facing serious challenges in meeting the growing needs of food security because of its low water availability. Maintaining and enhancing agricultural water productivity under such prevailing environmental constraints are hard to achieve. Potatoes water productively in Jordan Valley was modeled using Decision Support System for Agrotechnology Transfer (DSSAT) under six nitrogen applications (0, 60, 80, 100, 120 and 140 kg/ha) and twelve planting dates every two weeks from October 1 to March 15 scenarios. The potatoes yield increased from 0% to 100% nitrogen treatment and then no considerable increase occurred. The potatoes’ crop yield increased from October 1st to January 15 and then decreased after which until the last day of planting date. The seasonal cumulative crop evapotranspiration for potatoes about doubled from 0% to 60% nitrogen treatment and then kept increasing gradually until the last treatment. The growing season cumulative crop evapotranspiration for potatoes increased gradually from October 1 to March 1. The water productivity increased from 0% nitrogen treatment to 100% and then decreased. The potatoes’ water productivity increased from October 1 until November 15 and then decreased to the end. From these results, we recommend that 100% of nitrogen requirements should be applied. The best window for potatoes’ planting date is the last two weeks in November.

有机肥替代化肥氮对谷子氮素累积、产量及品质的影响

有机肥部分替代化肥是一种实现化肥减量的可持续农业生产措施。本研究于2020和2021连续2年以“沁黄2号”为供试材料,设不施氮(CK)、常量化肥氮(NPK)、有机肥替代25%化肥氮(25%M)、有机肥替代50%化肥氮(50%M)、有机肥替代75%化肥氮(75%M)和有机肥替代100%化肥氮(100%M) 6个处理,研究不同替代率对谷子产量构成和氮素吸收的影响,并分析氮素吸收调控小米米色、糊化特性和类胡萝卜素组分的效应,明确谷子生产中有机肥最佳替代率。结果表明,2年中较低的有机肥替代化肥氮率显著提高了谷子植株氮素累积,但随着替代率的持续增加,植株氮素累积量呈降低趋势,最终影响谷子产量和小米品质。2020年, 25%M处理显著提高了谷子地上部氮素累积量,较NPK处理提高9.6%;2021年,25%M处理谷子地上部氮素累积量、生物量、穗粒数和产量达到最高,较NPK处理分别提高6.1%、12.0%、15.4%和12.0%。50%M处理显著影响了小米的米色、糊化特征和类胡萝卜素含量,与NPK相比,小米籽粒红绿值、橘色值、支链淀粉含量、总淀粉含量、小米糊化最终黏度、叶黄素含量、玉米黄质含量和黄色素含量的增幅分别可达6.0%、6.0%、7.4%、4.3%、7.8%、20.7%、17.4%和2.8%。但有机肥完全替代化肥降低了谷子地上部氮素吸收、地上部生物量、穗粒数及谷子产量,也抑制了小米叶黄素和玉米黄质含量的提升。2年均表现出谷子地上部氮吸收量与小米单粒重、直链淀粉含量和小米糊化回升值呈显著的负相关。且2021年谷子地上部氮吸收量还与小米总淀粉含量、蛋白质含量、小米粉糊化峰值黏度和小米黄色素含量呈显著的负相关,与小米糊化峰谷黏度呈显著的正相关。综上,施氮总量120 kg hm^(–2)下,有机肥替代25%~50%化肥氮能通过促进植株氮素的吸收,实现产量、米色、蒸煮特性及类胡萝卜素的协同提升,为谷子化肥减量和提质增效生产提供技术支撑。

基于^(15)N示踪技术的甘蔗不同季节播种对氮肥利用效率影响研究

为促进甘蔗(Saccharum spp.)氮肥高效利用,以甘蔗品种桂糖42号为材料,采用田间微区^(15)N示踪技术分析秋季(8月20日)、春季(2月20日)和夏季(5月20日)播种甘蔗的氮肥利用效率及去向。结果表明,3个播期新植蔗吸收的N有21.56%~33.93%来自当季施用的氮肥,氮肥利用率、残留率和损失率分别为16.84%~21.50%、42.71%~47.45%和31.05%~39.43%;宿根蔗吸收的N来自上季施用氮肥的比率为6.65%~9.16%,上季氮肥在宿根季的利用率、残留率和损失率分别为4.15%~6.58%、30.25%~31.26%和8.31%~9.61%。3个播期两季甘蔗氮肥残留均随土层深度的增加而大幅递减,但0~40 cm土层残留以夏季播种较多,40~60 cm土层残留以秋季播种较多。秋季播种两季蔗茎干物质积累量为59693.69 kg·hm^(-2),较春季、夏季播种增加2.74%和34.43%;夏季播种两季甘蔗的氮肥利用率为28.08%,较秋季、春季播种提高4.63和6.58个百分点;春季播种两季甘蔗的氮肥损失率为47.85%,较秋季、夏季播种增加1.54和7.19个百分点。可见,甘蔗秋季播种产量较高,夏季播种氮肥吸收较多、损失较少,但夏季播种新植蔗吸收的大量氮肥未能转化为增产效应。本研究结果可为优化广西甘蔗氮肥施用提供科学依据。

Nitrogen transfer between N_2-fixing plant and non-N_2-fixing plant

The transfer mechanisms. calculating methods and ecological significance of nitrogen transfer between legumes and non-legumes are briefly reviewed. There are three pathways 0f nitrogen transf6r from legumes to neighboring non-legumes: (1) the nitrogen pass in soluble form from the donor legume root into the soil solution, move by diffusion or/and mass flow to the receiver root and be taken up by the latter, (2) nitrogen pass into the soil solution as before, be taken up and transported by mycorrhizal hyphae attached to the receiver roots,(3) if mycorrhizal hyphae form connections (bridges) between the two root systems, the nitrogen could pass into the fungus within the donor root and be transported into the receiver root without ever being in the soil solution. The mechanisms of nitrogen transfer between N2-fixing plants and non-N2-fixing plants are reviewed in terms of indirect and direct pathways. The indirect N-transfer process is related to the release of nitrogen from legumes(donor plants), the possible interaction of this nitrogen with soil, the decomposition and mineralization of legumes and tumover of nitrogen, the nitrogen absorbing and competing abilities of the legume and the non-legume (receiver plant). The direCt nitrogen transfer process is generally considered to be related to the nitrogen gradient and physiological imbalance between legumes and non-legumes, and when the donor legume lies in stressful stage (i.e. removal of shoots or attacked by insects), the nitrogen transfer can be improved significantly. Themethods of deterrnining nitrogen transfer (lndirect 15N-isotope. dilution method and direct 15N determination method) are evaluated, and their advantages and shortcomings are shown in this review.

How do nitrogen-limited alpine coniferous forests acquire nitrogen?A rhizosphere perspective

Background:Alpine coniferous forest ecosystems dominated by ectomycorrhizal(ECM)tree species are generally characterized by low soil nitrogen(N)availability but stabilized plant productivity.Thus,elucidating potential mechanisms by which plants maintain efficient N acquisition is crucial for formulating optimized management practices in these ecosystems.Methods:We summarize empirical studies conducted at a long-term field monitoring station in the alpine coniferous forests on the eastern Tibetan Plateau,China.We propose a root-soil interaction-based framework encompassing key components including soil N supply,microbial N transformation,and root N uptake in the rhizosphere.Results:We highlight that,(i)a considerable size of soil dissolved organic N pool mitigates plant dependence on inorganic N supply;(ii)ectomycorrhizal roots regulate soil N transformations through both rhizosphere and hyphosphere effects,providing a driving force for scavenging soil N;(iii)a complementary pattern of plant uptake of different soil N forms via root-and mycorrhizal mycelium-pathways enables efficient N acquisitions in response to changing soil N availability.Conclusions:Multiple rhizosphere processes abovementioned collaboratively contribute to efficient plant N acquisition in alpine coniferous forests.Finally,we identify several research outlooks and directions to improve the understanding and prediction of ecosystem functions in alpine coniferous forests under on-going global changes.