半干旱区草地土壤团聚体磷组分对氮添加响应的微生物机理

Nitrogen input (e.g. atmospheric nitrogen deposition) has significant effect on the phosphorus components transformations in the soil of semi-arid grassland, and microorganisms are the key regulatory factors in this effect process. Due to the large difference of soil microbial characteristics in soil aggregate sizes, the microbial mechanisms of phosphorus components response to nitrogen addition in various aggregate sizes may be different. However, such research is still lacking. Based on previous experimental studies, this study will carry out a nitrogen addition experiment on the grassland of Loess Plateau. The 31P NMR technology and functional gene sequencing analysis methods were used to reveal the characteristics of phosphorus components (e.g. phosphate, polyphosphate phosphate, phospholipid and phosphine) in different aggregates sizes responded to nitrogen addition in grassland soil. The microbial community, biomass and extracellular enzymes related to phosphorus transformation in soil aggregates after nitrogen addition will be studied. Based on this, we will build a response model between phosphorus components and microbial pathways in different soil aggregate sizes after nitrogen addition. By quantifying the relative importance of different microbial pathways and their relationships, the microbial mechanism of N addition affect P components in grassland soil aggregates can be clarified. The finding of this study can provide a more in-depth theoretical understanding of the soil phosphorus cycling process in semiarid areas and contribute to the sustainable nutrient management of grassland ecosystems.

外源氮输入（如大气氮沉降）会改变半干旱区草地土壤磷组分转化过程，微生物在磷转化中扮演重要角色。由于不同粒级土壤团聚体中微生物群落的差异，导致团聚体水平土壤磷组分对氮添加响应的微生物机理存在不确定性，但相关研究依然缺乏。本项目选择黄土高原半干旱草地，在氮添加定位试验研究基础上，以不同粒级土壤团聚体为研究对象，采用31P核磁共振技术、功能基因测序等方法，研究草地土壤不同粒级团聚体磷组分(正磷酸盐、多聚磷酸盐、磷脂、膦酸盐等)对氮添加的响应特征；阐明氮添加后土壤团聚体中磷转化相关功能微生物群落结构、生物量和胞外酶变化规律；建立氮添加后草地土壤团聚体磷组分和微生物间的响应模型，利用结构方程模型解析不同调控途径的作用大小和关系，以揭示团聚体水平草地土壤磷组分对氮添加响应机理。研究可为半干旱区草地土壤磷循环过程提供更深入的认识，也有助于草地生态系统养分管理。

磷是半干旱地区草地生长的主要限制因子之一，氮添加对草地土壤磷含量及其有效性有显著影响，但目前关于团聚体水平上氮添加对草地磷组分的影响及其微生物途径尚不清楚。研究基于长期定位试验，揭示了氮添加对半干旱区草地土壤不同粒级团聚体磷组分调控及其微生物机理。结果表明：（1）高浓度氮添加提高了土壤大、中团聚体Resin-Pi、NaHCO3-Pi以及NaHCO3-Pi等高活性磷组分的含量和比例，而降低了土壤小团聚体中高活性磷组分比例，即高浓度氮添加促进了小团聚体磷组分的稳定性和大、中粒级团聚体的活性。（2）氮添加对不同团聚体磷酸单酯酶、磷酸二酯酶和植酸酶活性有显著影响，总体上高浓度氮添加导致了土壤团聚体中三种酶活性的显著增加；小粒级和中粒级团聚体中酶活性高于大粒级；不同粒级团聚体中微生物生物量对氮添加的响应有所差异，其中不同粒级土壤团聚体中MBC、MBC:MBN、MBC:MBP均对氮添加表现为非线性响应特征。（3）氮添加显著改变了土壤团聚体磷转化功能微生物群落的多样性特征，随着氮添加浓度的增加，微生物α多样性呈现先降低后升高的趋势；氮添加引起了土壤团聚体中不同分类水平微生物群落构成变化，但各粒级团聚体中群落变化规律有差异，氮添加处理下大团聚体中变化显著的门类为Actinobacteria、Firmicutes、Gemmatimonadetes和Deinococcus-Thermus、中团聚体中变化显著的门类为Actinobacteria和Cyanobacteria、小团聚体中为Actinobacteria和Deinococcus-Thermus。（4）氮添加处理下团聚体磷组分与微生物多样性、关键门类和土壤基础理化性质之间具有较强的相关性；基于偏最小二乘回归的结构方程模型分析结果表明氮添加对草地土壤磷组分的影响机理在不同粒级团聚体中存在较大差异，pH是其关键调控路径，可以直接或通过改变微生物特征对磷组分产生影响；尤其是在大粒级团聚中，磷转化功能微生物及其分泌的磷转化胞外酶活性是氮添加调控团聚体磷转化的关键途径。研究结果加深了对氮沉降背景下半干旱地区草地磷循环过程的理解，也有助于草地养分可持续管理。