外源碳对旱地土壤硝态氮同化速率的影响及其作用机理

土壤硝态氮的累积与否是硝态氮产生和消耗过程彼此竞争的结果。已有研究通过抑制硝态氮的产生（如施入硝化抑制剂）减少土壤硝态氮的累积，但是国内外较少有研究关注硝态氮同化过程。硝态氮同化过程可以将硝态氮转化为微生物生物量氮，兼有保氮功能且环境友好。已有少量研究表明，加入优质碳源如葡萄糖可以提高硝态氮同化速率，然而目前尚不清楚有机物料作为碳源是否可以促进农田土壤硝态氮同化作用？本项目以我国粮食主产区易发生硝酸盐累积的农田旱作土壤为研究对象，采用15N稀释技术、选择性抑制剂和现代分子生物学技术相结合的方法，阐明不同C/N比的有机物料及其加入量对土壤微生物硝态氮同化作用的影响，明确铵态氮存在是否影响有机物料对土壤微生物硝态氮同化作用的刺激作用，揭示土壤细菌和真菌对硝态氮同化作用的相对贡献，以期为减少农田土壤硝酸盐累积和提高农田土壤保氮能力提供理论依据和技术支持。

Control of soil NO3- accumulation is of particular importance to reduce N losses in agricultural soil. Many previous studies have demonstrated that the application of nitrification inhibitor can inhibit the NO3- formation and thus reduce NO3- accumulation in soil. However, NO3- accumulation in soil is the result of competition between nitrification and NO3- consumption (NO3- immobilization and denitrification) processes. Thus, enhancing microbial immobilization of NO3- would also be vital in controlling soil NO3- concentrations. However, few studies have quantified microbial immobilization of NO3- and its controlling factors. It was found that the addition of sufficient glucose-C might stimulate microbial immobilization of NO3-. However, it is largely unknown whether the input of organic material (as C source) would enhance soil microbial immobilization of NO3-. In this project, 15N dilution techniques in combination with selective biomass inhibitors and modern molecular biotechnology were employed to calculate the NO3- immobilization rates and related mechanism of microbiology. The purposes are to 1) characterize the effects of the added organic material differing in C/N ratio on microbial assimilation of NO3- under a gradient of available-C conditions in upland soils prone to NO3- accumulation from the major grain producing areas in China, 2) evaluate whether the stimulation of microbial assimilation of NO3- following the input of organic material depends on soil NH4+ concentrations, 3) quantify the contribution of bacteria and fungi to microbial assimilation of NO3-. These results will provide deep insights into the reducing NO3- accumulation and enhancing N retention capacity in agricultural upland soils.