水稻在生长过程中不断向土壤分泌大量的根冠细胞，当其中的有机氮被氨化转变为氨以后，就会促使硝化反应。氨氧化作用是硝化过程的关键限制反应，主要由氨氧化微生物驱动。氧化亚氮是硝化过程中的一种附带产物，亦能由硝化产物硝酸根的反硝化作用而产生。氧化亚氮是一种很重要的温室气体，它的温室效应潜能是二氧化碳的298倍。本研究拟以水稻愈伤组织为根冠细胞的模型，采用实验室培养的方法，运用稳定同位素跟踪氮元素的转化走向，在分析土壤氮含量、硝化速率以及氧化亚氮的释放量等基础上，明确根冠细胞对各种形式氮素转化的相对贡献；结合稳定性同位素核酸探针技术、变性梯度凝胶电泳和实时荧光定量PCR技术等分子生物学手段分析土壤氨氧化微生物群落组成，研究根冠细胞对氨氧化菌群落结构、数量与功能特性的影响及氨氧化菌对根冠细胞氮素转化的驱动作用，为加深了解稻田生态系统氮元素循环模式，正确量化各种氮源对温室气体的贡献提供科学依据。

Root cap cells from growing rice roots release organic nitrogen (N) compounds, which upon ammonification, produce ammonium (NH4+). Ammonium in then oxidized by ammonia oxidizing microbes in the soil which leads to the production of nitrate(NO3-) and the greenhouse gas nitrous oxide (N2O). Ammonia oxidation is a key rate-limiting step of the nitrification process, and is driven by ammonia oxidizing microbes in the soil. N2O is a by-product of ammonia oxidation and is also produced from denitrification of NO3-. N2O is a potent greenhouse gas with a long-term global warming potential 298 times that of CO2. In this research program, we will study the transformations of N compounds from rice root cap cells by tracing N flows during decomposition of root cap cells, using 15N-labeled rice callus as the model of root cap cells in laboratory incubation experiments. The contribution of root cap cells to nitrification and nitrous oxide emissions in the soil will be quantified. The impact of root cap cells on soil ammonia oxidizing community composition, abundance and activity will be determined using soil molecular biology techniques, such as DNA-Stable isotope probing, Denatured Gradient Gel Electrophoresis and Real-time Polymerase Chain Reaction. Results from this research will significantly improve our fundamental understanding of root cap cell impacts on the microbial community composition, abundance and functions, on N cycling and on the production of nitrous oxide in the paddy field ecosystem.