紫云英季土壤固氮微生物对外源碳氮投入的响应

【目的】分析不同外源有机物料(稻草、葡萄糖)及氮素投入对紫云英季土壤固氮微生物的调控作用,为我国南方紫云英-水稻轮作体系中秸秆还田及化肥减施增效提供支持。【方法】采用盆栽试验,共设7个处理,即CK(对照,不添加有机物料和氮)、稻草等量添加并配施不同量氮素(分别表示为Rs、RsN1和RsN2,对应C/N比分别为66、25和13);等秸秆碳量添加葡萄糖并配施不同量氮素(即Glc、GlcN1、GlcN2)、调整C/N比与秸秆添加相应处理保持一致。采集紫云英快速生长期土壤样品,利用Illumina Miseq PE300高通量测序和绝对定量PCR技术分析固氮功能基因nifH及固氮微生物群落特征。【结果】单独添加外源秸秆或葡萄糖处理的土壤C/N与对照无明显差异,但增施氮肥后C/N比呈下降趋势,GlcN2处理土壤C/N显著低于对照;对于土壤速效养分,Rs和RsN1处理土壤NO3--N含量与CK类似,但RsN2处理明显增加了60%;而添加葡萄糖处理土壤NO3--N含量整体较高(增幅为35%—79%);稻草单独添加或与氮素配施对土壤速效磷含量无明显影响,添加葡萄糖处理则显著降低其含量,降幅为16%—2...

Responses of Soil Diazotroph Community to Rice Straw,Glucose and Nitrogen Addition During Chinese Milk Vetch Growth

【Objective】This study was to reveal the regulating roles of carbon (C) sources (rice straw vs. glucose) and nitrogen (N) addition in soil diazotroph community during growth of Chinese milk vetch (Astragalus sinicus L.), which is crucial for the management of crop residue and mineral fertilizer application in Chinese milk vetch - rice rotation system in southern China. 【Method】A pot experiment was conducted with seven treatments, including CK (no exogenous C and N addition), rice straw (Rs) plus various rates of N inputs (Rs, RsN₁ and RsN₂, corresponding to C/N ratios of 66, 25 and 13, respectively), and glucose (Glc) addition plus different N rates (Glc, GlcN₁, and GlcN₂) with same C quantity and C/N ratios in Rs-included treatments. Soils were sampled during the fast-growing phase of Chinese milk vetch, and destined for characterization of nifH gene marker and diazotroph community by using the Illumina Miseq PE300 sequencing and PCR techniques.【Result】Soil C/N ratios were similar between the CK and the treatments with straw or glucose addition alone, while tended to decrease with increasing N input, and significant decrease was observed in the GlcN₂ relative to CK. Regarding to the available nutrients, comparable soil NO₃ ^--N contents were observed under treatments of CK, Rs, and RsN₁, but it was significantly increased by 60% under the RsN₂ treatment. Compared to the CK, Glc-included treatments increased soil NO₃ ^--N content by 35%-79%. There were limited variations of soil available phosphorous (P) content under the CK and Rs-included treatments. 16%-24% decrease of soil available P content was found in the Glc-included treatments than that under CK, but not affected by N rates. The copy number of nifH gene ranged from 80.4×10 ⁶—140.5×10 ⁶ g ^-1soil under all treatments. Compared to the CK, nifH gene copy number tended to increase under treatments with both Rs and Glc addition, while a downward trend was observed with increasing N inputs. Exogenous C and N addition resulted in an overall decrease of diazotroph α-diversity than that under the CK. The responses of diazotroph α-diversity to N supply differed between C sources (Rs vs. Glc). Compared to Rs alone, RsN₁ and RsN₂ had less observed species (decreased by 6%-11%) and Chao 1 index (decreased by 13%-15%), however, GlcN₁ and GlcN₂ enhanced α-diversity to some extent relative to Glc alone. PCoA showed that diazotroph community structure was clustered into different groups depending upon C sources, and was marginally affected by N inputs. Bradyrhizobium was the most abundant genus in all treatments, and its relative abundance was significantly reduced by C and N addition in comparison with CK, however, the magnitude of reduction was obviously less in Rs-included treatments than in Glc-included treatments (12.3%-19.7% vs. 31.6%-40.5%). In contrasting to Bradyrhizobium, the relative abundance of the second most dominant genus (Geobacter) was markedly increased by C addition relative to the CK, with greater magnitude observed in Glc-included vs. Rs-included treatments (by 170%-270% vs. 25.0%-54.6%, respectively). Meanwhile, Multivariate regression tree analysis, RDA, and Mantel analysis revealed that the diazotroph abundance, diversity and community structure were closely associated with soil NO₃ ^--N and available P concentrations. 【Conclusion】The results suggested that effects of N supply on soil diazotroph abundance, diversity and structure were regulated by C sources or the C availability of rice straw and glucose amendments. Meanwhile, the resulted differences of soil available P availability by various C additions might be a key driving factor of reshaping soil diazotroph community during Chinese milk vetch growth.