Transfer of Symbiotically Fixed Nitrogen in an Alfalfa-Grass Mixture Studied Through Isotope Dilution in a Pot Experiment

Abstract

The nitrogen transfer between alfalfa and ryegrass was studied through isotope dilution at three different levels of N fertilization (20 mg N/pot, 200 mg N/pot, 400 mg N/pot) in a pot experiment using quartz sand as a substrate. An isogenic, nodulating, but non nitrogen fixing alfalfa line was used as a reference crop. Fixed N was transferred to the grass in the 20 mg N treatment and contributed markedly to the N nutrition of the grass (about 50% of the N in the plants). No transfer of fixed N could be detected in the higher fertilized treatments, although nitrogen fixation was only slightly inhibited by the presence of the fertilized mineral N. It is concluded that N transfer is strongly influenced by the N concentration in the substrate and transferred N contributes only slightly to the productivity of the legume/grass mixture under the given experimental conditions.     

Transfer of symbiotically fixed nitrogen in an alfalfa-grass mixture studied through isotope dilution in a pot experiment

The nitrogen transfer between alfalfa and ryegrass was studied through isotope dilution at three different levels of N fertilization (20 mg N/pot, 200 mg N/pot, 400 mg N/pot) in a pot experiment using quartz sand as a substrate. An isogenic, nodulating, but non nitrogen fixing alfalfa line was used as a reference crop. Fixed N was transferred to the grass in the 20 mg N treatment and contributed markedly to the N nutrition of the grass (about 50% of the N in the plants). No transfer of fixed N could be detected in the higher fertilized treatments, although nitrogen fixation was only slightly inhibited by the presence of the fertilized mineral N. It is concluded that N transfer is strongly influenced by the N concentration in the substrate and transferred N contributes only slightly to the productivity of the legume/grass mixture under the given experimental conditions.     

Independence of alpine meadow plants from soil organic matter for nitrogen supply: evidence from stable nitrogen isotopes

Stable nitrogen isotope signatures of major sources of mineral nitrogen (mineralization of soil organic nitrogen, biological N(2) fixation by legumes, annual precipitation and plant litter decomposition) were measured to relatively define their individual contribution to grass assimilation at the Haibei Alpine Meadow Ecosystem, Qinghai, China. The results indicated that delta(15)N values (-2.40 per thousand to 0.97 per thousand) of all grasses were much lower than those of soil organic matter (3.4+/-0.18 per thousand) and mineral nitrogen (ammonium and nitrate together, 7.8+/-0.57 per thousand). Based on the patterns of stable nitrogen isotopes, soil organic matter (3.4+/-0.18 per thousand), biological N(2) fixation (0 per thousand), and precipitation (-6.34+/-0.24 per thousand) only contributed to a small fraction of nitrogen requirements of grasses, but plant litter decomposition (-1.31+/-1.01 per thousand) accounted for 67 %.     

不同氮肥处理下小麦冠层和叶片光谱特征及产量分析

利用遥感光谱无损、快速分析出氮肥的施用时期和施用模式,对于保护环境、产量及氮肥利用率的提高具有重要意义。利用FieldSpec 4 Wide-Res Field Spectrum radiometer便携式地物光谱仪,测定了不同氮水平下小麦冠层和叶片两种模式光谱特征及红边参数变化规律;提出一个新指数--归一化差异最大指数（normalized difference maximum index,NDMI）,并分析其与叶面积指数（leaf area index,LAI）、SPAD（soil and plant analyzer development）值、MDA（malondialdehyde）含量、旗叶氮含量和产量的相关性。结果表明,小麦叶片原始光谱在开花后26 d起800～1 330 nm区间的光谱反射率以N3（1/3底施+1/3冬前追肥+1/3拔节期追肥）处理为最高,N1处理（1/2底施+1/2冬前追肥）次之。主要原因是由冬前和拔节期两个时期均施三分之一氮肥,增强了叶片光合能力。小麦冠层原始光谱,在400～700 nm波段,N2（1/2底施+1/2拔节期追肥）处理最低;在760~1 368 nm波段区间,由于群体结构不同,在开花期至灌浆中期N1处理的光谱反射率最高,N3处理次之;N3处理的冠层光谱反射率在开花后26和33 d最高。建议用400～700和760～1 368 nm波段的冠层原始光谱数据,分别来辨别小麦旗叶含氮量的高低及施肥模式。叶片模式下一阶微分光谱在500～750 nm区间出现两个“峰”,通过峰的位置偏移程度和偏移时期来估测施氮的模式。在670～740 nm区间冠层一阶微分光谱值在开花期最高,开花后10 d的一阶微分光谱值最低。在开花期至开花后10 d N1处理的一阶微分光谱值高于N3处理;灌浆中期至开花后33 d N3处理的一阶微分光谱值高于N1处理。可以通过一阶微分最大值来推测小麦所处的生育期和施肥的方式及施肥时期。在开花期至灌浆中期,冠层反射率一阶导数最大值（FD-Max）N1处理最高,N3处理次之;在开花后26～33 d,N3处理的群体结构较其他处理密,导致其一阶导数最大值一直最高。四个处理叶片一阶导数最大值变化趋势不如冠层显著。四个处理的反射率一阶导数最大值对应的红边位置（REP_FD-Max）中,N1和N3冠层REP_FD-Max在灌浆中期后偏移显著;在开花后26～33 d,N3处理的群体上层结构密,叶片宽且厚,冬前追施氮肥影响REP_FD-Max偏移程度。基于NDVI基础上,筛选出一个新指数--归一化差异最大指数。冠层归一化差异最大指数（CNDMI）与农化参数的相关系数高于叶片归一化差异最大指数（LNDMI）,且CNDMI与产量的相关性比LNDMI显著。冠层归一化差异最大指数与旗叶氮含量、SPAD值和MDA含量有着显著的相关性,相关系数r分别为0.812 88,0.928 21和-0.722 17。综上所述,借助光谱数据和红边参数可以推测小麦含氮量的高低,所处的生育期和施氮肥的模式,进而为田间施肥管理及施肥诊断提供依据。CNDMI与小麦产量有着更好的相关性,符合我国资源卫星的光谱波段范围,具有可实际操作性。     

Dinitrogen fixation of microbe-plant associations as affected by nitrate and ammonium supply

Abstract The dinitrogen fixation activity of Azospirillum sp., and Pantoea agglomerans strains was determined by (15)N(2) incorporation after incubation with (15)N(2) labeled air or/and by acetylene reduction. These bacterial strains were able to fix N(2) both in pure culture and in association with wheat plants in hydroponics. Nitrogenase activity of Azospirillum sp., in pure culture was more rapidly inhibited by the addition of NH(4) (+) than NO(3) (-). The N(2) fixation of P. agglomerans decreased only by NH(4) (+) -addition, but was stimulated by NO(3) (-). Nitrogen fixation in association with wheat plants remained unaffected by both N compounds. However, nitrogen derived from the atmosphere (N(dfa)) contributed only very little to the overall nitrogen nutrition of the plants.     

Nutrient cycling responses to fire frequency in the Kruger National Park (South Africa) as indicated by stable isotope analysis

Fires, which are an intrinsic feature of southern African ecosystems, produce biogenic and pyrogenic losses of nitrogen (N) from plants and soils. Because of the long history of fires in these savannas, it was hypothesized that N2 fixation by legumes balances the N losses caused by fires. In this study, the N2 fixation activity of woody legumes was estimated by analyzing foliar delta15N and proportional basal area of N2 fixing species along experimental fire gradients in the Kruger National Park (South Africa). In addition, soil carbon (C) and N pools, foliar phosphorus (P) and gross N mineralization and nitrification rates were measured, to indicate the effects of fires on nutrient stocks and the possible N cycling processes modified by fires. Although observations of increased soil C/N and mineralization rates in frequently burned plots support previous reports of N losses caused by fires, soil %N did not decrease with increasing fire frequency (except in 1 plot), suggesting that N losses are replenished in burned areas. However, relative abundance and N2 fixation of woody legumes decreased with fire frequency in two of the three fire gradients analyzed, suggesting that woody legume N2 fixation is not the mechanism that balances N losses. The relatively constant %N along fire gradients suggests that these ecosystems have other mechanisms to balance the N lost by fires, which could include inputs by atmospheric deposition and N2 fixation by forbs, grasses and soil cyanobacteria. Soil isotopic signatures have been previously used to infer patterns of fire history. However, the lack of a relationship between soil delta15N and fire frequency found in this study indicates that the effects of fires on ecosystem delta15N are unpredictable. Similar soil delta15N along fire gradients may reflect the contrasting effects of increased N gaseous emissions (which increases delta15N) and N2 fixation other than that associated with woody legumes (which lowers delta15N) on isotopic signatures.     

Symbiotic N2 Fixation and N Uptake of Yellow and White Lupines Influenced by Spontaneous Rhizobia Infection and Substrate

Abstract

By using soil as substrate, white and yellow lupines (Lupinus albus L., Lupinus luteus L.) assimilated higher N amounts than under quartz sand conditions. This was caused by spontaneous infection of lupines with wild Rhizobia strains and also by an additional N uptake from the soil. In yellow lupines without inoculation in non-sterile soil, only the additional N uptake played a role. Differences in P and K supply as the cause of different N acquisition from soil and quartz sand could be excluded. As compared with white lupines, yellow lupines inoculated with Rhizobia had a high N₂ fixation that exceeded the effect of spontaneous infections. This result as well as the positive effect of spontaneous infections with soil-borne Rhizobia on white lupines indicates insufficient effectiveness of the strains used for inoculation on this plant species.     

Nutrient cycling responses to fire frequency in the Kruger National Park (South Africa) as indicated by Stable Isotope analysis

Fires, which are an intrinsic feature of southern African ecosystems, produce biogenic and pyrogenic losses of nitrogen (N) from plants and soils. Because of the long history of fires in these savannas, it was hypothesized that N 2 fixation by legumes balances the N losses caused by fires. In this study, the N 2 fixation activity of woody legumes was estimated by analyzing foliar i 15 N and proportional basal area of N 2 fixing species along experimental fire gradients in the Kruger National Park (South Africa). In addition, soil carbon (C) and N pools, foliar phosphorus (P) and gross N mineralization and nitrification rates were measured, to indicate the effects of fires on nutrient stocks and the possible N cycling processes modified by fires. Although observations of increased soil C/N and mineralization rates in frequently burned plots support previous reports of N losses caused by fires, soil %N did not decrease with increasing fire frequency (except in 1 plot), suggesting that N losses are replenished in burned areas. However, relative abundance and N 2 fixation of woody legumes decreased with fire frequency in two of the three fire gradients analyzed, suggesting that woody legume N 2 fixation is not the mechanism that balances N losses. The relatively constant %N along fire gradients suggests that these ecosystems have other mechanisms to balance the N lost by fires, which could include inputs by atmospheric deposition and N 2 fixation by forbs, grasses and soil cyanobacteria. Soil isotopic signatures have been previously used to infer patterns of fire history. However, the lack of a relationship between soil i 15 N and fire frequency found in this study indicates that the effects of fires on ecosystem i 15 N are unpredictable. Similar soil i 15 N along fire gradients may reflect the contrasting effects of increased N gaseous emissions (which increases i 15 N) and N 2 fixation other than that associated with woody legumes (which lowers i 15 N) on isotopic signatures.     

Using the natural 15N abundance to assess the main nitrogen inputs into the sand dune area of the north-western Negev Desert (Israel)

The variation of the natural 15N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system: i. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N2-fixing vascular plants (e.g. the shrub Retama raetam); ii. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition. Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90 cm), N2-fixing and non-N2-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The delta15N values measured were in the following ranges: grass -2.5/1000 to +1.5/1000; R. reatam: +0.5/1000 to +4.5/1000; non-N2-fixing shrubs +1/1000 to +7/1000; sand beneath the biological crusts +4/1000 to +20/1000 (soil depth 2-90 cm); and arable land to the north up to 10/1000. Thus, the natural 15N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various 15N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the 15N abundances measured were calculated to be 46-86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative 15N values (-3/1000 to -0.5/1000), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to -10/1000. The atmospheric N bulk deposition, which amounts to 1.9-3.8 kg N/hayr, has a 15N abundance between 4.4/1000 and 11.6/1000 and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative delta15N values, e.g. gaseous N forms (NOx, NH3). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric deposition of nitrogen.     

长期定位施肥对黑土养分平衡和胡敏素分子结构动态变化的影响

以黑土长期定位试验(始于1979年)为基础,根据土壤养分的输入和输出分析长期不同施肥处理的土壤养分收支状况。利用红外光谱和核磁共振光谱分析胡敏素(Humin,Hu)分子结构的动态变化特征并分析土壤养分收支状况与Hu结构变化之间的关系。结果表明：不同施肥措施在改变黑土养分含量的同时,影响了土壤中惰性组分Hu的分子结构。1980年-2014年有机无机肥配施(MNPK)处理可以满足作物对养分的吸收,土壤总养分含量有盈余,且较不施肥(CK)处理增加土壤有机碳含量,降低土壤C/N比,同时土壤Hu的2 920/1 620和2 920/2 850、脂族C/芳香C、烷基C/烷氧C和疏水C/亲水C比值均增加,表明黑土Hu分子结构变得脂族化、简单化,施肥可以增加土壤活性有机碳,减少惰性有机碳组分含量。有机肥(M)和氮磷钾化肥(NPK)处理不能满足作物对养分的吸收,土壤养分出现亏缺状况。红外光谱显示,施肥年限增加,有机肥(M)和氮磷钾化肥(NPK)处理土壤Hu的2 920/1 620下降,表明其脂族C含量降低;核磁共振光谱显示,氮磷钾化肥(NPK)和不施肥(CK)处理烷基C/烷氧C降低,表明其活性有机碳含量下降。虽然各施肥处理较不施肥(CK)处理整体增加土壤Hu的脂族C含量,降低芳香C含量,但随着施肥年限的增加,氮磷钾化肥(NPK)处理使土壤Hu结构有变复杂化的趋势。各养分盈亏量与土壤Hu的结构特征参数之间具有相关性,N,P₂O₅和K₂O养分盈亏量和总养分盈亏量与2 920/1 620、脂族C呈正相关,与芳香C呈负相关,表明养分状况可以影响土壤Hu的结构。节约经济成本情况下,轮作周期内施入一次有机肥,每年结合氮磷钾化肥的施入可以满足作物对养分的吸收,在提高作物产量的同时,改善土壤腐殖质惰性组分结构,培肥地力。     

15N allocation into wheat grains (Triticum aestivum L.) influenced by sowing rate and water supply at flowering under a Mediterranean climate

This study examined the effects of a reduced wheat sowing rate (250 vs. 500 grains m^–2) on grain yield, uptake of ¹⁵N into grains, and the incorporation into gluten and non-gluten proteins of wheat under field conditions in the Aegean region. A single ¹⁵N application was applied at stem elongation, at flowering, or at both developmental stages. Each ¹⁵N treatment included either additional water supply, or no additional water supply at flowering. Sowing rate (either 250 or 500 grains m^–2) had no impact on grain yield. Grain yield increased with additional water supply, but at the expense of protein quality, because of a decrease in the protein content of gluten. The ¹⁵N content of the gluten and non-gluten proteins at grain maturity was not different among cultivars. ¹⁵N applied at both stem elongation and flowering was found in comparable amounts in grains and protein fractions, irrespective of sowing rate.     

红外光谱法测定肥料施用26年土壤的腐殖质组分特征

采用红外光谱法探讨了有机肥以及有机肥与化学肥料配合施用26年对棕壤腐殖质及其组分富里酸和胡敏酸的结构变化。结果表明,采用红外光谱仪测定肥料施用对腐殖质及腐殖质组分富里酸和胡敏酸结构的影响是可行的。施肥26年后,不同处理肥料施用后腐殖质具有基本一致的结构;在某些特征峰吸收强度上有不同程度的差异,反映了不同肥料处理对土壤腐殖质的结构单元和官能团数量及组成有明显的影响。不同施肥处理胡敏酸也存在一些差别。红外光谱解析表明,与CK相比,施用有机肥或氮磷钾配合施用后,土壤腐殖质中小分子糖类物质减少,芳族类物质增加。试验结果证实,施用有机肥可明显增加土壤水溶性有机物芳构化程度。利用不同肥料处理腐殖质的红外光谱,可以判断土壤有机质的演变程度。     

Distribution and utilization of 15N in cowpeas injected into the stem under influence of water deficit

Investigations were carried out on Vigna unguiculata L. Walp. to estimate the distribution and utilization of 15N in different organs after stem injection during vegetative, flowering and pod filling stage. During flowering effects of water deficit were also examined. In well watered plants, within 4 days after injection, 65% of 15N accumulated in leaves. This was drastically reduced to 42% by water deficit. 15N accumulation in stems increased under water deficit. The translocation of 15N from the stem base to roots were not altered by water deficit. During pod filling 62% of recovered 15N in the plants had accumulated in seeds, 24% in leaves and 11% in stems within 4 days, whereas the uptake of nitrogen in pod walls and roots remained low (2%). These results demonstrate that the method of injecting very small quantities (1 mg/plant) of 15N into the stem base allows an exact and detailed quantitative assessment of N translocation/distribution with regard to different organs, different growth stages and different treatments.     

Using the natural 15N abundance to assess the main nitrogen inputs into the sand dune area of the North-Western Negev desert (ISRAEL)

The variation of the natural ¹⁵N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system:

1. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N₂-fixing vascular plants (e.g. the shrub Retama raetam);

2. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition.

Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90?cm), N₂-fixing and non-N₂-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The δ¹⁵N values measured were in the following ranges: grass ?2.5‰ to +1.5‰; R. reatam: +0.5‰ to +4.5‰; non-N₂-fixing shrubs +1‰ to +7‰; sand beneath the biological crusts +4‰ to +20‰ (soil depth 2–90?cm); and arable land to the north up to 10‰. Thus, the natural ¹⁵N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various ¹⁵N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the ¹⁵N abundances measured were calculated to be 46–86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative ¹⁵N values (?3‰ to ?0.5‰), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to ?10‰. The atmospheric N bulk deposition, which amounts to 1.9–3.8?kg?N/ha?yr, has a ¹⁵N abundance between 4.4‰ and 11.6‰ and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative δ¹⁵N values, e.g. gaseous N forms (NO _x , NH₃). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric deposition of nitrogen.     

15N-Dynamics of Cucumber (Cucumis sativus L.) in Field Trials on Sandy Loam in Brandenburg (Germany)

Abstract

Field experiments were conducted to study the ¹⁵N-utilization of cucumbers (Cucumis sativus L.) grown on sandy loam under black mulch film. With the progress of the ontogenetic development the plants took up rising ¹⁵N-amounts, which were increasingly transferred to the fruits after the beginning of flowering. At the end of the vegetation period more than 55% of the applied ¹⁵N-labelled fertilizer was found in the plants, and from this portion more than 70% in the fruits. Up to 13% of the total plant nitrogen were derived from the fertilizer. In the top soil layer (0–30 cm) the ¹⁵N-content was strongly reduced during plant growth. Though most of the ¹⁵N was taken up by the plants, a ¹⁵N transfer to deeper soil layers (30–60 cm, 60–90 cm) was observed. Balancing the amount of applied ¹⁵N-fertilizer indicates a loss of 11% during the experimental period.     

The Fate of [(15)N]Ammonium and [(15)N]Nitrate in the Soil of a 140-Year-Old Spruce Stand (Picea Abies) in the Fichtelgebirge (NE-Bavaria)

Abstract A (15)N tracer-experiment was carried out in a 140-year-old spruce stand (Picea abies (L.) Karst.) in the Fichtelgebirge (NE-Bavaria, Germany). Highly enriched (98 at%) [(15)N]ammonium and [(15)N]nitrate were applied as tracers by simulation of a deposition of 41.3 mol N ha(-1) with 11 water m(-2). To examine seasonal variations of uptake by spruce and understorey vegetation, different plots were labelled in spring, summer and autumn 1994. One aim of the present study was to perfect a method of preparation of soil extracts for isotope ratio mass spectrometry (IRMS) measurements. Ammonium and nitrate from soil extracts were prepared for IRMS measurements by steam distillation and subsequent freeze drying. Additionally, tracer distribution and transformations in the soil nitrogen pools were examined. Ammonium, nitrate and total nitrogen were examined in the organic layer and the upper 10 cm of the mineral soil during 3 months after the first tracer application in spring 1994. In July 1994, three months after tracer application, 40% of the [(15)N]ammonium label and 29% of the [(15)N]nitrate label, respectively, were recovered in the total N pool of the investigated soil horizons. In the organic layer the L/Of horizon retained most of the recovered tracers. Nitrification, immobilisation and mineralisation occurred even under the conditions of high soil acidity at the study site.     

基于无人机多光谱影像的冬小麦返青期变量施氮决策模型研究

氮素是影响冬小麦生长的重要元素,如何根据冬小麦需求适时变量施用氮肥是现代农业精准施肥研究需要解决的关键问题之一。无人机遥感技术在冬小麦生长情况监测中具有高分辨率、高时效性、低成本等优势,为解决施肥需求监测问题提供了重要数据源。因此研究无人机多光谱影像数据,构建其与冬小麦产量与施肥量之间的关系模型对于精准施肥研究十分重要。选择冬小麦典型生产区山东省桓台县为实验区,布置4种不同施氮水平的田间实验。利用无人机搭载Sequoia多光谱传感器,采集实验区不同氮素施肥水平的冬小麦返青初期多光谱影像,同时测得冬小麦冠层叶绿素含量（soil and plant analyzer development,SPAD）数据及产量数据。通过多光谱影像数据计算获得归一化植被指数（normalized difference vegetation index,NDVI）、叶绿素吸收指数（modified chlorophyll absorption ratio index,MCARI2）等6种形式植被指数,建立无人机多光谱影像植被指数与小麦冠层SPAD值的线性、二阶多项式、对数、指数和幂函数模型,优选地面氮素状况最优植被指数模型,反演冬小麦不同施氮水平的状况,进而根据不同施氮水平与敏感植被指数和冬小麦产量的关系,构建了基于植被指数指标的氮肥变量施肥模型,并将模型应用于同时期小麦多光谱影像。结果如下：（1）地面实测的SPAD值能较好的反映冬小麦施氮水平及生长状况。无人机多光谱数据分区统计结果表明不同施氮水平冬小麦冠层反射率有较大差异性。（2）结构性植被指数与SPAD拟合效果优于其他类型指数。MCARI2的二阶多项式模型精度最优（R2=0.790,RMSE=0.22）,其能较好的移除冬小麦返青初期土壤背景等因素的影响,为氮肥敏感植被指数。（3）基于产量-施氮量模型和产量-敏感植被指数模型,构建敏感植被指数的氮肥变量施肥模型为N_r=10 707.63×MCARI22-5 992.36×MCARI2+715.27。通过模型应用生成了实验区冬小麦氮肥变量施肥图,与实际情况具有较高一致性。该研究提出了利用无人机多光谱数据进行冬小麦施氮决策的模型及方法,为冬小麦精准施肥的进一步研究提供了依据。     

同步辐射软X射线近边吸收谱方法研究长期施肥对黑土有机氮官能团的影响

有机态氮是土壤氮素的主要存在形式,在农田生态系统氮循环中占有重要地位。了解土壤有机氮官能团组成,可为制定合理的农田管理措施提供科学依据。同步辐射软X射线近边吸收谱(N K-edge XANES)技术,是原位测定土壤有机氮官能团组成最有效的方法,但利用该技术对长期施肥条件下土壤有机氮官能团组成的研究尚未见报道。本试验利用N K-edge XANES方法,研究了长期(18年)不同施肥措施[即休闲(Fallow)、不施肥(CK)、施氮磷钾化肥(NPK)、有机肥配施化肥(NPKM)、1.5倍量的有机肥配施化肥(1.5NPKM)和玉米秸秆配施化肥(NPKS)]对黑土全土及粘粒中有机氮官能团的影响。结果表明：各处理均在401.2～401.6和402.7～403.1 eV范围内出现特征吸收峰,分别归属为酰胺/胺和吡咯类化合物,粘粒中特征吸收峰通常较全土更为明显。半定量分析结果指出,全土和粘粒均以酰胺/胺的相对比例最高,是有机氮官能团的主要存在形态;与休闲处理相比,对照处理中酰胺/胺的相对比例较低,而吡咯类氮的相对比例较高;有机无机配施条件下,酰胺/胺的相对比例随有机肥量的增加而下降,而吡咯类氮的相对比例则呈相反的变化趋势;全土中以NPKS处理的酰胺/胺相对比例最高,而粘粒中则以休闲处理的腈类/芳香氮相对比例最高。利用N K-edge XANES方法原位测定不同施肥措施下土壤有机氮官能团组成的变化是可行的。     

Latitudinal distribution of nitrogen isotopic composition in suspended particulate organic matter in tropical/subtropical seas

Natural nitrogen isotopic composition (δ(15)N) of suspended particulate organic matter (POM) and nitrogen fixation rates via (15)N(2) assay were measured in surface waters along 120° E from 30° N to 30° S in the Asian marginal seas (the East/South China Seas and the Sulu/Celebes/Java Seas) and the northeastern Indian Ocean in November-December 2005 and March 2006. The POM δ(15)N values ranged from-1.8 to 12.2‰ with an average of 3.6‰ and showed a decreasing trend towards the equator in both hemispheres. In parallel, the measured N(2) fixation rates showed an increase from the subtropical to the tropical seas. This implies that a higher contribution of (15)N-depleted POM was derived from enhanced N(2) fixation. Water temperature and the stability of water column were partly responsible for the observed variations in nitrogen fixation. The large-scale spatial variations in suspended POM δ(15)N and N(2) fixation rates suggest that the suspended POM δ(15)N may be a potential indicator of nitrogen fixation in surface waters in tropical/subtropical seas.     

化学氮肥有机替代条件下黑土DOC荧光光谱特征

有机无机肥配施是实现土壤培肥、减少无机肥施用的有效措施。为探讨黑土区有机肥替代无机肥(氮肥)对土壤溶解性有机碳（DOC）含量及结构的影响,本研究采用有机肥不同比例替代化学氮肥,分析土壤DOC的含量及荧光光谱特征。结果表明,M(100%有机替代化学氮肥)处理土壤DOC显著高于其他处理,其含量为325.97 mg·kg-1。与CK(不施肥)处理相比,各施肥处理荧光峰各波长均有不同程度蓝移,各处理土壤DOC的荧光指数(FI)分布在1.54~1.59范围内,腐殖化指数(HIX)均小于0.85,表明DOC来源受自生源和陆生源共同作用的影响,土壤腐质化程度均较低。平行因子分析法分析识别出3个荧光组分,分别为2个腐殖质类组分（富里酸类物质和腐殖酸类物质) 及1个类蛋白组分(类酪氨酸蛋白质物质)。各施肥处理3个组分荧光强度均高于CK处理,其中M和M₂N₂(25%有机替代化学氮肥)处理下土壤DOC总荧光强度较高,C3组分荧光强度以M₂N₂处理最高,土壤DOC中3个有机组分的相对比重以荧光组分C1最高,接近50%,表明该地区土壤中小分子物质占有较大比例,施肥能够提高土壤腐质化程度,有利于土壤DOC固定,合理的有机肥配施化学氮肥能增加DOC的有效性,提升土壤供肥能力。