绿肥配施减量化肥对土壤固氮菌群落的影响

为了探讨绿肥配施减量化肥对土壤固氮菌的影响,以开展八年的紫云英配施减量化肥的长期定位试验站为平台,选取不施肥(CK)、单施化肥(NPK)、紫云英配施80%化肥(MF80)、紫云英配施60%化肥(MF60)和紫云英配施40%化肥(MF40)共5个处理,于水稻分蘖期采集土样,采用荧光定量PCR和Illumina Miseq高通量测序技术,分析了不同施肥制度下土壤固氮菌nif H基因丰度和多样性的变化规律。结果表明:与单施化肥相比,翻压紫云英的减量施肥处理水稻产量与其无显著差异,从化肥用量和产量综合考虑,MF60处理是一种适宜的施肥制度。翻压绿肥处理土壤全氮明显增加;碱解氮含量(除MF60处理)与NPK处理无显著差异。翻压紫云英配施减量化肥的施肥处理(除MF40处理)土壤固氮菌丰度明显高于NPK处理,且固氮菌丰度与土壤碱解氮、硝态氮和p H呈显著正相关。翻压紫云英后土壤固氮菌Shannon指数明显低于NPK处理,各施肥处理间OTU指数差异不明显。各施肥处理的土壤固氮菌均以变形菌门为绝对优势菌门,翻压紫云英的减量施肥处理变形菌门丰度显著低于单施化肥处理。主坐标分析表明,翻压紫云英配施减量化肥的3个施肥处理与CK、NPK处理的土壤固氮菌的群落结构差异较明显。研究表明,紫云英配施减量化肥有利于提升土壤肥力和固氮菌的数量,紫云英的施用和化肥用量都是影响土壤固氮菌群落结构的重要因素。

Effect of green manure and reduced chemical fertilizer load on the community of soil nitrogen-fixing bacteria

Chinese milk vetch (MV) is a type of green manure that has the potential to replace a portion of the chemical fertilizer load; however, it remains unclear how MV would replace N fertilizer. This study was conducted at a long-term field experimental station in Fuzhou, China. The treatments conducted for this study are CK (without fertilization), NPK (chemical fertilizer), MF80 (MV plus 80% NPK), MF60 (MV plus 60% NPK), and MF40 (MV plus 40% NPK). Soil samples were collected from the 0~20 cm soil layer at the rice tillering stage. We determined the soil physicochemical properties. The abundances and community structures of nitrogen-fixing bacteria were assessed using the nifH gene. Quantitative PCR and Illumina MiSeq sequencing were used to determine the abundance and community structure of nitrogen-fixing bacteria in the paddy soil. The results showed that there was no significant difference in the rice yield between the green manure treatments and NPK treatment. MF60 is an appropriate fertilization regime when considering the yield and application rates of chemical fertilizer. Long-term application of green manure combined with a reduced chemical fertilizer load increased the total nitrogen content in comparison with the NPK treatment, and there was no significant difference in the available nitrogen content between the green manure treatments (except for MF60) and NPK treatment. Compared with the NPK treatment, the green manure treatments (except for MF40) increased the abundance of nitrogen-fixing bacteria, and positive correlations between the bacterial abundance and available nitrogen, nitrate nitrogen, and pH were observed. Shannon indices of the nitrogen-fixing bacteria with the green manure treatments were lower than that with the NPK soil, but there was no significant difference in the operational taxonomic unit (OTU) number. Proteobacteria was the dominant phylum for all treatments, and NPK treatment led to a higher relative abundance of Proteobacteria than the green manure treatments. Principal coordinate analysis demonstrated that the community structures of nitrogen-fixing bacteria with the green manure treatments were significantly distinct from that with the NPK treatment. Our results indicated that green manure combined with reduced chemical fertilizer load could increase soil fertility and the abundance of nitrogen-fixing bacteria. Application of MV and application rates of chemical fertilizer are both important factors in shaping the community structure of nitrogen-fixing bacteria in the paddy soil studied.