长期施肥下双季稻田土壤氮素生物转化特征研究

Rice is China's most important food crop, and double rice cropping system plays an important role in grain production. Soil microbial diversity influenced ecosystem stability, soil production potential, soil ecosystem functioning and resilience towards stress and disturbance. This study was carried out on a long-term experiment at Nanchang County of Jiangxi Province, subtropical China, established in 1984 on reddish paddy soil under double rice cropping system with different fertilization regimes. Five treatments were selected for this study: no fertilizer(CK), balanced chemical fertilizers (NPK), chemical fertilizers substituted by organic manure from 30% to 70% (70%F+30%M, 50%F+50%M, 30%F+70%M). The aim of this study was to evaluate the effect of long term fertilizer application on the soil nitrogen transformation and soil microbial genetic diversity. Therefore, the field and laboratory incubation experiments were carried out, and soil microbial biomass nitrogen(SMBN), soil enzymatic activities were detected. Effects of long-term fertilization on abundance and community composition of ammonia oxidizing bacteria(AOB), ammonia oxidizing archaea(AOA) and denitrifier communities were studied with targeting amoA, nosZ, narG, nirK and nirS genes using quantitative real-time polymerase chain reaction (qPCR) and denaturing gradient gel electrophoresis (DGGE) , respectively. The overall objectives of this study are as: ⅰ) to examine the effect of long-term application of organic manure and mineral fertilizers on the soil enzymatic activities, soil microbial biomass nitrogen and functional gene diversity, ⅱ) to investigate the microbial community succession and dynamic of soil microorganisms at different crop growth stages, ⅲ) to show the influence of nitrifying and denitrifying bacterial communities on nitrogen transformation, and their relationship with soil nitrogen. In addition, with this study, we can enhance the research contents on the key processes and microbial mechanisms of soil nitrogen transformation, and to provide theoretical basis and scientific guidance for scientific fertilization of double rice cropping system and sustainable use of farmland.

双季稻种植在我国粮食生产中具有重要地位，稻田土壤微生物多样性对于土壤生产潜力、土壤生态功能稳定和生态环境安全等具有重要意义。本项目拟以持续了30年的红壤性水稻土双季稻连作定位试验为基础，研究长期施肥对土壤氮库、微生物生物量氮、土壤酶活性和功能微生物多样性的影响，探明作物关键生育期土壤功能微生物群落演替以及氮转化相关功能微生物与土壤氮素的关系，阐明长期有机无机配施下土壤功能微生物多样性特征及对土壤氮素转化的影响。研究成果可揭示长期不同施肥措施对土壤功能微生物多样性的影响以及双季稻田土壤氮生物转化特征，对于指导双季稻田合理施肥和农田可持续利用具有重要意义。

本项目以持续了30年的红壤性水稻土双季稻连作定位试验为基础，研究了长期施肥下土壤碱解氮、无机氮、微生物生物量氮、土壤酶活性、功能基因和微生物多样性的变化，探讨了长期施肥引起土壤理化性质变化对土壤微生物群落结构和氮转化的影响。研究结果表明：长期有机无机配施土壤全氮、碱解氮和有机质显著提高，并且随着有机肥用量增加而增加。土壤碱解氮在早稻和晚稻不同生育期含量较稳定，各生育期碱解氮氮、微生物生物量氮和微生物生物量碳有机无机配施处理(70F+30M、50F+50M、30F+70M)>NPK处理>对照，而土壤硝态氮和铵态氮早晚稻不同生育期变异较大。长期施肥显著影响了红壤性水稻土养分状况和微生物生物量碳氮，从而影响土壤胞外酶活性（EEAs），其中土壤全氮（TN）和微生物量碳（MBC）是关键的决定因子，分别解释了酶活性变异的34.3%和20.9%。红壤稻田优势菌门主要包括变形菌门、绿弯菌门、酸杆菌门、硝化螺旋菌门、拟杆菌门、疣微菌门、绿菌门、浮霉菌门、放线菌门、芽单胞菌门、后壁菌门，占细菌总数的79.4%~84.8%。有机无机配施处理增加了变形菌门、拟杆菌门、浮霉菌门、放线菌门、芽单胞菌门和后壁菌门的微生物丰度，降低了硝化螺旋菌门的丰度，绿弯菌门和疣微菌门有所下降，但对酸杆菌门和绿菌门的影响不显著。相关分析结果显示变形菌门、拟杆菌门、浮霉菌门、放线菌门、芽单胞菌门和后壁菌门主要与土壤养分呈正相关关系，而硝化螺旋菌门和绿弯菌门与土壤养分负相关，酸杆菌门主要与土壤pH和硝态氮含量呈显著负相关，而疣微菌门与土壤理化指标之间相关性均不显著。典型相关分析表明，土壤pH和有机质分别解释了微生物总体变异的13.7%和5.16%，是影响红壤稻田土壤微生物群落结构的关键指标。有机无机配施有利于水稻增产，并提高土壤养分、微生物生物量和土壤碳、氮、磷循环相关水解酶活性，并调节土壤微生物群落结构，是维持作物高产和提升土壤质量最优的施肥管理措施。