微生物活性对紫色土坡耕地硝酸盐淋失的影响

Sloping croplands of purple soil widely distributed in the upper Yangtze River play an important role in the local agriculture. A large amount of nitrate loss from hillslope agriculture in the purple soil areas due to low utilization efficiency of fertilizer and heavy soil and water erosion, thus, pose a severe threat to the water quality of the Yangtze River. Previous studies mostly concentrated on paths, flux and models of nitrate leaching, but how microbial activity affects nitrate formation and transformation is not clear. So we proposed to conduct research on transcription activity of amoA, narG and napA , nitrification rate and denitrification rate, and nitrate leaching and try to figure out the relationship among them. In this research, fux of nitrate leaching will be monitored and sampled in the hillslope free-drain lysimeters, rates of nitrification and denitrification are determined using 15N pool dilution technique and acetylene block method respectively, and some modern molecular biology technique including quantitative real-time PCR,DGGE and high-throughput sequencing technique are employed to examine microbial transcription activity. Impact of amnonia-oxidizing microbes and denitrifier on rate of nitrification and denitrification will be analyzed, then relationship between microbial activity and nitrate formation and transformation and nitrate leaching are further illustrated, and basic scientific supports will be provided for both effective nitrogen management and decreasing nitrate leaching.

紫色土坡耕地氮肥投入高，利用率低，硝酸盐淋失问题突出，但以往研究多集中在硝酸盐淋失路径、通量、估算模型等方面，影响紫色土硝酸盐形成和转化的微生物活性并不清楚，针对上述问题，利用紫色土坡地lysimeter装置观测紫色土硝酸盐淋失通量，采用15N同位素稀释技术和乙炔抑制培养法分别测定硝化速率、反硝化速率，并结合实时定量PCR、DGGE及高通量测序等现代分子生物学技术，测定氨氧化微生物、反硝化微生物功能基因转录活性，研究紫色土氨氧化及反硝化微生物活性与硝化-反硝化速率的关系，进而阐明其对硝酸盐形成与转化及硝酸盐的淋失的影响，为紫色土坡耕地氮素的有效管理及硝酸盐淋失的减控提供科学依据。

紫色土坡耕地氮肥投入高，利用率低，硝酸盐淋失问题突出，但以往研究多集中在硝酸盐 淋失路径、通量、估算模型等方面，影响紫色土硝酸盐形成和转化的微生物内在机制并不清楚。针对上述问题，在本项目支持下，我们利用紫色土坡耕地lysimeter平台获取了整个作物生物期硝酸盐累积及淋失动态，紫色土硝酸盐淋失是氮素淋失的主要形态，紫色土硝酸盐淋失主要发生在降雨量集中的玉米季；采用qPCR方法研究了整个作物生育期紫色土氮转化相关功能微生物基因数量，采用PCR-DGGE方法对紫色土氨氧化微生物群落结构进行了分析，并基于RNA水平测定了紫色土微生物多样性特征，结合测定的硝化、反硝化速率，对紫色土硝酸盐淋失机制进行了深入探讨，研究了肥料施用对紫色土坡耕地氨氧化、反硝化微生物群落结构功能的影响，研究发现在麦季，雨水较少，水孔隙度较低，紫色土硝化作用剧烈，累积大量NO3- (r=0.530, P=0.014)，紫色土硝化作用主要驱动者是氨氧化细菌(r=0.785, P<0.0001)，在玉米季暴雨冲刷下累积的硝酸盐大量淋失。研究发现秸秆还田或施用有机肥可降低硝酸盐淋失量，这主要与有机质的添加促进异养细菌的活性，一方面促进氮素的固定，持续向作物提供养分，一方面增强反硝化作用，降低硝酸盐淋失风险。本研究为该区减控硝酸盐污染提供理论支持，对保障粮食生产、有效减低面源污染、改善长江中上游水质安全也具重要意义。截至目前，已发表SCI论文1篇，申请专利2项，协助培养研究生2名。