具有硝化抑制功能牧草及其制成粪肥减缓土壤N2O排放潜力和机制研究

Global atmospheric N2O concentration has been increasing at an annual rate of about 0.26%. Agricultural soils contribute approximately 60% of the global anthropogenic N2O emission due to fertilizer application. It is estimated that N2O emissions will increase by four times by year 2100, especially in China where inorganic N fertilizer applied accounts for 30% of the total global use. Thus there is a global concern over N2O emissions from agricultural soils. Nitrification and denitrification are biological drivers for N2O production. Nearly 70% of the annually applied 150 Tg N as N fertilizer to agricultural systems in the world is lost either through nitrate leaching or gaseous N emissions and most of the leached nitrate will eventually denitrified, generating N2O and NO. It has been found that some plants not only contain components but also excrete organic materials as exudates that could inhibit the growth and activity of ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA), resulting in lower rates of soil nitrification and low N2O emission. Our hypothesis is that lower N2O will be emitted from a tropical grass excreting organic materials with high biological nitrification inhibition (BNI) potential compared to the grass with no/low BNI, and that applying manures derived from ruminants fed forage grass with BNI and containing plant secondary metabolites with BNI could suppress the activity of AOB and/or AOA, and then reduce N2O emission while increasing C sequestration in agricultural soils. The component of exudates and secondary metabolites in manures will be analyzed. The influence of manures on the abundance and community structure of AOB and AOA will be measured by qPCR and PCR-DGGE. The inhibition effect on the nitrification rate and N2O production will be determined using 15N trace technology. N2O and NO emissions will be monitored during the growth of grass with high BNI and grass with low BNI and from soils amended with manures with high and low BNI. The purpose of the proposed project is (1) to determine whether there are lower N2O and NO emissions from pasture grass with high BNI compared to grass with no/low BNI, and (2) to evaluate how large amounts of manures with BNI applied to soils will reduce N2O and NO emissions while increasing C sequestration potential in agricultural soils. The project will provide a cornerstone for the production of pasture grasses in the tropical region and using plant secondary metabolites in manures to reduce N2O and NO emissions and meanwhile increase soil organic carbon in agricultural ecosystems.

大气N2O浓度以年均0.26%速率增长，土壤是大气N2O重要排放源，占全球人为排放的60%。新近发现部分热带牧草能够分泌有机物抑制硝化作用，减少土壤N2O排放。我们假设：与常规牧草相比，具有硝化抑制功能牧草生长土壤将排放更少N2O，此类牧草制成的动物粪便含有硝化抑制功能次生代谢产物，也可以抑制硝化作用，减少N2O产生。项目将建立牧草田间试验，监测土壤N2O和NO排放，明确硝化抑制功能牧草减缓排放N2O和NO的潜力；采用15N示踪、液相色谱-质谱等技术，研究植物分泌物和粪便的硝化抑制效应，解析具有硝化抑制功能的有机物种类；利用分子生物学等技术，研究氨氧化菌和古菌群落结构变化，揭示分泌物和粪便抑制硝化作用的机制；布设田间试验，监测不同牧草制成粪肥对土壤N2O/NO和CO2排放影响，明确硝化抑制功能牧草制成粪肥减缓土壤N2O/NO排放和提高有机质潜力，为农田温室气体减排提供新思路和新技术。

项目围绕具有硝化抑制功能牧草对土壤N2O排放的影响及机制展开研究，重点研究了：（1）种植不同硝化抑制功能牧草对土壤N2O排放的影响；（2）不同硝化抑制功能牧草种植下土壤氮素转化过程及N2O产生来源的差异；（3）不同硝化抑制能力牧草种植对土壤氮素转化关联微生物的影响。取得的主要进展如下：（1）建立为期两年野外试验发现，随施肥量增加，两种牧草产量均增加而氮肥利用率下降，其中臂型草产量、氮肥利用率均显著高于假俭草。牧草产量与牧草氮素吸收能力、土壤铵态氮强度、土壤硝态氮强度线性相关。（2）利用静态箱法检测种植臂型草和假俭草的土壤N2O排放发现，土壤N2O排放通量与土壤铵态氮、硝态氮浓度和土壤含水量显著相关。土壤N2O累积排放量随施氮量增加而增加，且与牧草产量呈显著正相关。相同施氮水下，臂型草处理土壤N2O累积排放、N2O排放系数显著高于假俭草处理，而单位生物量N2O排放反之。（3）利用15N示踪技术，种植臂型草和假俭草土壤的N2O排放均主要来自于硝化过程，但臂型草处理反硝化过程对N2O排放的贡献率（16.6%）大于假俭草处理（7.1%）。与假俭草处理相比，臂型草种植显著促进土壤矿化速率而降低土壤硝化能力，并延迟N2O排放速率峰值的出现。而且随N2O排放速率的增加，臂型草处理自养硝化和反硝化对N2O排放的贡献增加。（4）利用荧光定量PCR技术，发现牧草种植显著提高土壤AOB-amoA、AOA-amoA、nirK和nosZ基因的丰度，但降低nirS基因的丰度。相同施氮水平下，臂型草处理土壤中AOA-amoA、nirK和nosZ基因丰度均高于假俭草处理，但AOB-amoA基因丰度仅在低氮水平下如此。