长期绿肥轮作对稻田反硝化脱氮速率影响及其机制研究

Nitrogen fertilizer efficiency of paddy field is low in our country, and denitrification is an important way of N loss in paddy field. Previous researches show that the long-term application of green manure can cultivate soil, improve soil N availability, reduce the application of nitrogen fertilizer and the negative effects on ecological environment. Meanwhile, the long-term green manure rotation changed the soil structure and bacteria and fungi community diversity, increased microbial community structure, and so on. The changes of these factors will inevitably affect the soil denitrification process. However, due to the difficulty in denitrification rate measurements, the effect of long-term green manure rotation on denitrification process is less. This project is to study the effect of long-term green manure rotation effect on the denitrification rate and its mechanism by using the high precision of Membrane inlet mass spectrometer method and the isotope pairing technique. This study will be expected to clarify the effect of long-term different green manure rotation on denitrification in paddy field, explain the mechanism of the effect on denitrification, in order to better understand the mechanism of long-term green manure rotation on nitrogen loss and make reasonable measures to reduce nitrogen fertilizer losses.

我国稻田氮肥利用率低下，反硝化是稻田氮素损失的一个重要途径。前期研究结果证明长期施用绿肥可培育土壤、提高土壤氮素有效性、减少稻季氮肥用量、降低对生态环境负面效应。同时，长期绿肥轮作改变了土壤结构、增加微生物群落结构、改变土壤细菌和真菌的群落多样性等。这些因子的改变，必然对土壤反硝化过程产生影响。然而，由于反硝化测定方法的限制，长期绿肥轮作对反硝化过程的影响报道较少。本项目拟应用高精度的膜进样质谱法，结合同位素配对技术，研究长期绿肥轮作效应对稻田反硝化速率的影响及其机制。这一研究将有望明确长期不同绿肥轮作对稻田反硝化影响规律，解释对反硝化影响的内在机理，以便更好的理解长期绿肥轮作对稻田脱氮机制与制定合理减少氮肥损失的措施。

稻田是土壤氮素转化过程研究的热点区域，本项目通过布置田间试验，重点开展不同绿肥与水稻轮作对稻季反硝化脱氮过程影响及内在机理研究，不同轮作方式对稻季温室气体排放的影响研究。项目开展过程中得到如下重要结果：1）得到长期绿肥与水稻轮作下稻季各脱氮过程的速率，其中长期实行紫云英-水稻轮作下反硝化脱氮速率为0.5599 kg N ha-1 d-1，氨挥发速率为0.2175 kg N ha-1 d-1，N2O排放速率为0.0137 kg N ha-1 d-1，长期实行蚕豆-水稻轮作下反硝化脱氮速率为0.6445 kg N ha-1 d-1，氨挥发速率为0.1740 kg N ha-1 d-1，N2O排放速率为0.0124 kg N ha-1 d-1；2）与传统种植冬小麦和水稻轮作相比，实行绿肥-水稻轮作能增加稻季反硝化脱氮速率，主要原因是实行长期绿肥与水稻轮作，增加了稻季氮素转化功能功能基因(nirK, nirS, and nosZ )拷贝数，提高了氮素转化效率。其中实行蚕豆-水稻轮作稻季反硝化脱氮速率高于紫云英-水稻轮作稻季反硝化脱氮速率，主要由于该轮作下土壤nirK、nirS和nosZ功能基因拷贝数高于紫云英-水稻轮作，利于反硝化各个过程进行，尤其是nosZ功能基因拷贝数的增加，使N2O更多的还原成N2,利于反硝化更彻底的进行，实行紫云英-水稻轮作稻季N2O排放量高于蚕豆-水稻轮作和冬小麦-水稻轮作，同样由于该轮作下nosZ功能基因拷贝数少，限制了N2O还原成N2；3）对比了太湖地区紫云英-水稻、油菜-水稻和休耕-水稻三种轮作方式对CH4和N2O温室气体排放的影响，发现实行紫云英-水稻轮作降低了稻季温室气体全球增温潜势（GWP）和单位水稻产量温室气体排放强度（GHGI），对提高水稻产量，降低温室气体排放效果最好；田间试验结果发现，添加生物质炭可以提高谷物产量和氮肥利用率（NUE），同时增加了稻田土壤GWP，会导致更高的潜在环境成本，但生物炭添加能增强土壤的外源碳固存，从而抵消温室气体排放的增加。以上结论为太湖地区推行轮作休耕制度提供了科学依据和数据支撑。