土壤中反硝化田间原位测定方法的研究进展

土壤中的反硝化作用由于直接影响到氮肥氮的利用率和环境问题，仍然是氮素研究领域的热点和难点之一，而反硝化作用研究的进展在很大程度上依赖与土壤反硝化的田间测定方法的建立。文章就目前反硝化研究领域常用的^15N平衡差值法、^15示踪气体通量法、乙炔抑制气室法、乙炔抑制土柱法的原理、气体样的采集、测定和计算作了综述，以期为土壤反硝化的研究提供依据。     

土壤氮素反硝化过程研究进展

引用大量文献土壤反硝化过程造成的环境问题及其影响因素。例如，植物（包括根系活动，生长，分泌物，呼吸及植被遮荫等）对氮生物化学转化过程的影响；ＮＯ３活性，微生物民其与根系竞争Ｎ素反硝化水分和氧气容量，有机介含量，施用绿肥及无机肥及无机机械压实，放心纸浆农业利用等对土壤反硝化过程的影响。     

玉米地土壤反硝化速率与N2O排放通量的动态变化

应用乙炔抑制原状土柱培育法测定了4种施肥处理的玉米地N素反硝化损失速率和氧化亚氮（N2O）排放通量，并分析了它们与土壤湿度、土壤温度以及硝态氮（NO3^-－N）含量之间的关系，计算了因反硝化和N2O排放造成的N肥损失率。结果表明，玉米生育期内土壤N素的反硝化损失量为0．67－3．85kg/hm^2，N肥的反硝化损失率为0．5％－1．5％；土壤N2O排放总量为0．55－1．42kg/hm^2，N肥的N2O排放系数为0．2％－0．5％。     

土壤硝化-反硝化作用研究进展

硝化－反硝化作用是氮素循环的重要环节，涉及到气态氮的损失和污染生态环境的影响，是当今氮素研究的热点之一。本文综述了近年来土壤硝化－反硝化作用损失量，机理研究方法及控制对策等方面的研究进展和展望。     

硝化抑制剂对稻田土壤N2O排放和硝化、反硝化菌数量的影响

【目的】本研究旨在明确硝化抑制剂对稻田土壤氮素周转的影响,探讨抑制剂提高氮肥利用率及微生物响应机理。【方法】以草甸黑土发育的水稻土为研究对象,进行了两组培养试验 (25℃),培养周期均为150天。共设4个处理:1) 不施肥 (CK);2) 单施尿素 (Urea);3) 尿素 + 双氰胺 (Urea + DCD);4) 尿素 + 3, 4-二甲基吡唑磷酸盐 (Urea + DMPP)。一组试验从培养第1天起,抽取气体样品,用气相色谱法测定N₂O排放量。另一组试验从培养第1天直到结束,取土样测定氨氧化细菌和氨氧化古菌数量,采用荧光定量PCR等技术测定nirK基因和nirS基因拷贝数,用常规方法测定土壤无机氮含量。【结果】施用尿素显著增加了N₂O排放量,其中85%的N₂O排放发生在培养开始后的前两周内。Urea + DMPP处理土壤NH₄+浓度在前23天稳定在较高水平,与Urea处理相比,N₂O减排率为78.3%,Urea + DCD处理为21.6%。Urea + DMPP处理排放系数为0.05%,Urea + DCD为0.18%,Urea + DMPP处理显著低于Urea + DCD处理。施用尿素培养,土壤氨氧化细菌 (AOB) 数量显著增加而氨氧化古菌 (AOA) 数量则显著减少。添加DCD和DMPP能显著抑制AOB的数量,但对AOA没有影响。培养第3、30和90天,Urea + DMPP处理土壤中的AOB数量显著低于Urea + DCD处理的30%、56%和60%。对于反硝化细菌来说,所有处理中的nirK基因拷贝数均显著高于nirS基因拷贝数。添加DMPP在培养第3和30天显著减少了含nirK和nirS基因的反硝化细菌数量,而添加DCD对两类反硝化细菌数量无明显作用。【结论】东北黑土水稻生产中,硝化抑制剂DMPP降低N₂O排放量和排放系数的效果显著好于DCD,因为DMPP在培养后的30天内,可以显著抑制氨氧化细菌繁衍,降低反硝化细菌数量,从而起到减少N₂O排放、提高肥料利用率的作用。     

FACE环境下不同秸秆与氮肥管理对稻田土壤硝化和反硝化菌的影响

利用位于江都市小记镇的中国稻-麦轮作FACE平台,采用最大可能(MPN)法,在2004年水稻生长季研究了不同施肥情况(施常规N量UN和低N量LN)、不同秸秆还田情况(秸秆全还田HR和秸秆不还田NR)下,土壤中硝化和反硝化细菌数量在FACE条件下随时间的变化。结果表明,FACE条件下,土壤硝化菌数普遍在抽穗期或乳熟期达到最大值,而对照土壤的硝化菌数普遍到成熟期才达到最大值,并且显著高于FACE处理的相应值(P<0.05)。在HR条件下,LN和UN小区FACE处理的土壤硝化细菌数量较对照减少6%~10%。FACE条件LN小区的反硝化菌数在成熟期达到最大值,而对照处理则在乳熟期达到最大值,并显著高于FACE处理(P<0.05);而UN小区的反硝化菌数二者均在抽穗期达到最大值。在LN小区HR和NR情况下,FACE处理土壤反硝化细菌数量分别低于对照处理的相应值8%和13%。在HR情况下,土壤反硝化潜势FACE处理显著低于对照。在LN和UN小区,FACE处理土壤的反硝化作用潜势分别是对照的83.7%和95.4%。     

氢醌、双氰胺组合影响稻田甲烷和氧化亚氮排放研究进展

稻田是大气中CH4和N2O的重要来源。大量氮肥的施入不仅影响稻田CH4和N2O排放,且易造成NH3挥发、NO2-和NO3-淋溶及N2O、N2等形式的氮损失。脲酶抑制剂和硝化抑制剂通过缓解尿素水解及抑制硝化反硝化反应减少稻田N2O排放量,但对稻田CH4产生排放的影响报道不一。脲酶抑制剂氢醌(HQ)和硝化抑制剂双氰胺(DCD)是近年来研究较多的组合。本文试图在前人研究的基础上,综述HQ和DCD的基本性质及作用机理,总结HQ/DCD组合在稻田生态系统的应用状况、使用效果及存在问题,并特别讨论了HQ/DCD施用对稻田CH4排放的影响机理,旨在为合理使用脲酶/硝化抑制剂、有效减缓稻田温室气体排放和提高氮肥利用率等方面提供理论依据。     

反硝化测定方法的评述

反硝化作用是氮循环的重要环节,对生态系统的初级生产力、水体质量、大气环境具有重要影响。然而由于大气中N2的背景值很高,使得准确量化反硝化产生的微量N2存在一定的困难;此外,不同研究者在反硝化研究方面缺乏交流,限制了对反硝化测定方法的改进以及对反硝化过程的深入研究。本文综述了目前在陆地和水体生态系统中常用的7种测定反硝化的方法,并对这些方法的优缺点进行了讨论,以期为反硝化测定方法的综合改进提供参考。已有的反硝化测定方法往往只针对于某一种特定的生态系统,具有一定的局限性,未来应加强对已有研究方法的改进,扩大其适用范围,同时加强研制精密度更高的质谱仪和气相色谱仪,以促进反硝化研究的进一步发展。     

区分土壤中硝化与反硝化对N2O产生贡献的方法

土壤是产生N2O的最主要来源之一。硝化和反硝化反应是产生N2O的主要机理,由于硝化和反硝化微生物同时存在于土壤中,因而硝化和反硝化作用能同时产生N2O。N2O的来源可通过使用选择性抑制剂,杀菌剂以及加入的标记底物确定。通过对生成N2O反应的每一步分析,主要从抑制反应发生的催化酶和细菌着手,总结了测量区分硝化、反硝化和DNRA反应对N2O产生的贡献方法。并对15N标记底物法,乙炔抑制法和环境因子抑制法作了详细介绍。     

Denitrification potential in a grassland subsoil: effect of carbon substrates

We examined the potential of a subsoil to denitrify nitrate under optimal anaerobic conditions in a laboratory-based incubation when supplied with a range of C substrates of increasing recalcitrance. Both topsoil and its associated subsoil were supplied with nitrate and either glucose, starch or cellulose. Microbial respiration and the evolution of N₂O and N₂ were measured. The subsoil supported low amounts of microbial activity and responded only to the glucose treatment; with less than one-fifth of the N₂O production measured in the top soil. Overall, our findings demonstrated that the denitrification potential of this particular subsoil is relatively low and that only simple carbohydrates could be utilised readily by the resident microorganisms.     

Denitrification,N2-fixation and fermentation during anaerobic incubation of soils amended with glucose and nitrate

Nitrate and glucose additions were investigated for their role in the C and N dynamics during anaerobic incubation of soil. A gas-flow soil core method was used, in which the net production of N₂, N₂O, NO, CO₂, and CH₄ under a He atmosphere could be monitored both accurately and frequently. In all experiments clayey silt loam soil samples were incubated for 9 days at 25 °C. Addition of nitrate (50 mg KNO₃-N kg^-1 soil) had no effect on total denitrification and CO₂ production rates, while the N₂O/N₂ ratio was affected considerably. The cumulative N₂O production exceeded the cumulative N₂ production for 6 days in the treatment with nitrate addition, compared to 1.2 days in the unamended treatment. Glucose addition stimulated the microbial activity considerably. The denitrification rates were limited by the growth rate of the denitrifying population. During denitrification no significant differences were observed between the treatments with 700 mg glucose-C kg^-1 and 4200 mg glucose-C kg^-1, both in combination with 50 mg KNO₃-N kg^-1. The N₂ production rates were remarkably low, until NO _inf3 ^sup- exhaustion caused rapid reduction of N₂O to N₂ at day 2. During the denitrification period 15–18 mg N kg^-1 was immobilised in the growing biomass. After NO _inf3 ^sup- shortage, a second microbial population, capable of N₂-fixation, became increasingly important. This change was clearly reflected in the CO₂ production rates. Net volatile fatty acid (VFA) production was monitored during the net N₂-fixation period with acetate as the dominant product. N₂-fixation faded out, probably due to N₂ shortage, followed by increased VFA production. In the high C treatment butyrate became the most important VFA, while in the low C treatment acetate and butyrate were produced at equal rates. During denitrification no VFA accumulation occurred; this does not prove, however, that denitrification and fermentation appeared sequentially. The experiments illustrate clearly the interactions of C-availability, microbial population and nitrate availability as influencing factors on denitrification and fermentation.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

不同利用方式红壤反硝化势和气态产物排放特征

采用厌氧培养-乙炔抑制法测定了4种不同利用方式红壤的反硝化势和气态产物N₂O和N₂的排放速率。结果表明，不同利用方式红壤反硝化势和N₂O和N₂的排放速率差异明显，土壤反硝化势强弱顺序依次为：竹林>茶园>林地>旱地。反硝化势与土壤有机碳(P<0.05)、厌氧培养期间土壤CO₂累积排放量(P<0.01)、nirS基因丰度( P<0.05)和nirK基因丰度(P<0.05) 呈显著正相关关系。逐步回归分析结果表明，CO₂累积排放量表征的易矿化碳是造成不同利用方式红壤反硝化势差异的主要原因，可以解释反硝化势变化的66%(P<0.01)。不同利用方式红壤N₂O和N₂排放速率差异明显，旱地红壤N₂O和N₂排放速率均最低，表明土壤pH的提升并没有增加旱地红壤的反硝化损失风险和N₂O排放速率。土壤易矿化有机碳含量也是影响不同利用方式红壤N₂O和N₂排放速率的主要因素。反硝化功能基因nirS、nirK和nosZ的丰度均与CO₂累积排放量呈显著正相关关系，进一步支持了土壤易矿化有机碳含量是影响不同利用方式红壤反硝化势和气态产物排放的主要因子。土壤pH是影响不同利用方式红壤反硝化气态产物N₂/N₂O的主要因素，但是pH影响红壤N₂/N₂O的微生物机制仍需要进一步研究。     

Denitrification losses from puddled rice soils in the tropics

Summary Although denitrification has long been considered a major loss mechanism for N fertilizer applied to lowland rice (Oryza sativa L.) soils, direct field measurements of denitrification losses from puddled rice soils in the tropics have only been made recently. This paper summarizes the results of direct measurement and indirect estimation of denitrification losses from puddled rice fields and reviews the status of research methodology for measurement of denitrification in rice fields. The direct recovery of (N₂+N₂O)-¹⁵N from ¹⁵N-enriched urea has recently been measured at sites in the Philippines, Thailand, and Indonesia. In all 12 studies, recoveries of (N₂+N₂O)-¹⁵N ranged from less than 0.1 to 2.2% of the applied N. Total gaseous N losses, estimated by the ¹⁵N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-N. Denitrification was limited by the nitrate supply rather than by available C, as indicated by the values for water-soluble soil organic C, floodwater (nitrate+nitrite)-N, and evolved (N₂+N₂O)-¹⁵N from added nitrate. In the absence of runoff and leaching losses, the amount of (N₂+N₂O)-¹⁵N evolved from ¹⁵N-labeled nitrate was consistently less than the unrecovered ¹⁵N in ¹⁵N balances with labeled nitrate, which presumably represented total denitrification losses. This finding indicates that the measured recoveries of (N₂+N₂O)-¹⁵N had underestimated the denitrification losses from urea. Even with a probable two-or threefold underestimation, direct measurements of (N₂+N₂O)-¹⁵N failed to confirm the appreciable denitrification losses often estimated by the indirect difference method. This method, which determines denitrification losses by the difference between total ¹⁵N loss and determined ammonia loss, is prone to high variability. Measurements of nitrate disappearance and ¹⁵N-balance studies suggest that nitrification-denitrification occurs under alternate soil drying and wetting conditions both during the rice cropping period and between rice crops. Research is needed to determine the magnitude of denitrification losses when soils are flooded and puddled for production of rice.     

Measuring the rhizodeposition of carbon by rice: an approach based on carbon flux observations

ABSTRACT

Rhizodeposition is an important component of carbon cycling in terrestrial ecosystems. However, there remains tremendous uncertainty in its quantification due to the methodological limitations. In the present study, we propose a method to evaluate the rhizodeposition by plants by observing carbon flux. We investigated the ecosystem CO₂ flux variability and calculated the rhizodeposition of carbon by the rice rhizosphere, by using the carbon flux, meteorological data, and biomass observation from 2003 to 2011 at the Taoyuan Agro-ecological Experimental Station, a representative subtropical paddy ecosystem. Our data indicated that the process of rhizodeposition is the major reason for the discrepancy between the biomass and net primary productivity of the paddy ecosystem under intensive human interference. Both the amount and ratio of rhizodeposition of carbon in this paddy ecosystem were assessed; this provides important theoretical and methodological support for further investigating rhizodeposition by rice under field conditions. The rhizodeposition amount in the growing season of early rice, late rice, and for the entire planting period was 0.52–2.56, 0.74–3.75, and 1.61–5.24 t ha^?1, respectively, with the corresponding mean (±SD) rhizodeposition ratios of 23.16 ± 8.87%, 28.16 ± 12.94%, and 27.00 ± 9.3%. This method enabled us to calculate rhizodeposition under in situ conditions, and the results showed that the growing season of late rice was the primary period for rhizodeposition in rice ecosystem.     

Assessment of slow release fertilizers and nitrification inhibitors in flooded rice

This work evaluates the effect of different slow-release fertilizers and nitrification inhibitors (NI) on N-use efficiency, grain yield and N₂ fixation in rice fields of Valencia (Spain) during three consecutive crop seasons (1998–2000). Eight N sources [ammonium sulphate, urea, polymer-coated urea (PCU 32% and 40% N), sulphur coated urea, isobutylidene diurea (IBDU), ammonium sulphate nitrate (ASN) plus dicyandiamide and ASN plus dimethyl pyrazole phosphate, were applied at 120 kg N ha^–1 and at 2 or 15 days before flooding (DBF) during 1998. Another experiment was based on the use of urea blended with PCU (40% N) at four ratios (1:0, 3:1, 1:1, 1:3) and applied at 15 DBF and at four rates (70, 95, 120 and 145 kg N ha-1) during 1999 and at only one rate (120 kg N ha^–1) during 2000. Both experiments also included a control (no N). The results showed that, when applied shortly before flooding, PCU (32% and 40% N) and IBDU application improved biological N₂ fixation compared to the conventional fertilizer application, with or without NI, reaching similar values to those observed in the absence of N fertilizer. Slow release fertilizers, particularly PCU 40% N applied basally before flooding, were the best N source for grain yield and improved recovery efficiency. Differences among N sources were only significant when the flooding was delayed for 15 days after fertilizer application.     

Methods for measuring N2O flux from water surface and N2O dissolved in water from agricultural land

A new chamber method and a stripping method were developed for field measurements of the rate of N₂O emission from the water surface and for determinations of dissolved N₂O in water from agricultural land.

These methods were used for the measurement of drainage canal water and flooded water of rice fields during the period of June 1982 to January 1983. The results demonstrate that aquatic systems of agricultural land may provide both source and sink for atmospheric N₂O.     

Short-term effects of clearfelling on soil CO2, CH4, and N2O fluxes in a Sitka spruce plantation

We examined the effects of forest clearfelling on the fluxes of soil CO₂, CH₄, and N₂O in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO₂, CH₄, N₂O as well as environmental factors such as soil temperature, soil water content, and depth to the water table were recorded in two mature stands for one growing season, at the end of which one of the two stands was felled and one was left as control. Monitoring of the same parameters continued thereafter for a second growing season. For the first 10 months after clearfelling, there was a significant decrease in soil CO₂ efflux, with an average efflux rate of 4.0 g m⁻² d⁻¹ in the mature stand (40-year) and 2.7 g m⁻² d⁻¹ in clearfelled site (CF). Clearfelling turned the soil from a sink (−0.37 mg m⁻² d⁻¹) for CH₄ to a net source (2.01 mg m⁻² d⁻¹). For the same period, soil N₂O fluxes averaged 0.57 mg m⁻² d⁻¹ in the CF and 0.23 mg m⁻² d⁻¹ in the 40-year stand. Clearfelling affected environmental factors and lead to higher daily soil temperatures during the summer period, while it caused an increase in the soil water content and a rise in the water table depth. Despite clearfelling, CO₂ remained the dominant greenhouse gas in terms of its greenhouse warming potential.     

土壤含水量测定方法研究进展

综述了国内外近20a来测定土壤含水量的研究情况,总结了国内外常用的测定土壤含水量的方法及其原理, 比较分析了各种测定方法的优缺点,介绍了一些新兴的土壤含水量测试技术,提出了本领域中存在的主要问题及研究展望,指出未来的土壤含水量测定方法应当是朝着高精度、低成本、非破坏、自动化等方向发展。