土地利用驱动的土壤性状变化影响微生物群落结构和功能

微生物在调节陆地生态系统地球化学循环过程中具有重要作用。土地利用方式改变显著影响土壤微生物群落结构和功能，但对土地利用驱动的土壤性状变化与微生物群落结构和功能关系的研究相对匮乏。依托长期定位监测试验（始于1984年），通过16S rRNA基因片段和ITS高通量测序，研究了土地利用方式（裸地、农田、草地）驱动的土壤碳氮变化对微生物群落结构和功能的影响。结果表明：对于细菌群落而言，裸地中α-多样性最高、其次是草地、农田中最低，农田和草地中细菌优势菌群变形菌（Proteobacteria）和放线菌门（Actinobacteria）相对丰度较裸地低4.5%、3.9%和5.5%、3.8%；对于真菌群落而言，裸地子囊菌门（Ascomycota）相对丰度最高、农田次之、草地最低；化能异养型、好氧化能异养型细菌相对丰度裸地显著高于农田和草地（P<0.05），而硝化型和好氧氨氧化型细菌裸地显著低于农田和草地（P<0.05）；腐生型真菌相对丰度大小排序为：裸地>农田>草地。细菌群落变化主要与土壤容重、全氮、矿质氮、C ： N比和微生物量碳有关，而真菌群落与土壤矿质氮有关。细菌和真菌功能菌群主要受土壤容重、土壤有机碳、土壤全氮、C ： N比和微生物量碳影响。因此，土壤容重、土壤全氮、土壤有机碳、C ： N比、微生物量碳、矿质氮差异可能是影响不同土地利用方式中微生物群落和功能变化的主要因素。

Variations of soil properties effect on microbial community structure and functional structure under land uses

Microorganisms play an important role in regulating biogeochemical cycling in terrestrial ecosystems. Microbial functional structure and related processes are determined by the microbial community. Soil physiochemistry properties affect microbial community structure. Land uses affect soil properties and microbial communities, whereas most of the researches at home and abroad focus on the effect of different land uses on soil properties, and how effect of soil properties variations on microbial community and functional structure under land uses were unclear. In this study, land uses (i.e., bare-land, farmland, and grassland) were selected from the long-field experiment (established in 1984). The experimental plot is located at the Changwu National Field Scientific Observation and Research Station of Farmland Ecosystem in the highland and gully region of Shaanxi Province, which is a dry-farming and rain-fed agricultural area. Soil microbial community structure (16S rRNA and ITS), soil physiochemistry properties have been determined, such as soil bulk density (BD), soil organic carbon (SOC), soil total nitrogen (TN), soil microbial biomass carbon (SMBC), and soil mineral nitrogen (mineral N). We found that there was a significant difference in the relative abundance of microbial communities and functional structure under different land uses. Alpha diversity of soil bacterial community was the highest in bare-land, and followed by grassland and farmland. The relative abundance of Proteobacteria, Actinobacteria, and Ascomycota in the farmland (29.7%, 17.3%, 9.2%) and grassland (29.9%, 17.6%, 5.5%) were lower than in bare-land (31.1%, 18.3%, 27.0%). The relative abundance of chemoheterotrophy and aerobic chemoheterotrophy in the bare-land were significantly higher than those in the farmland and grassland, where nitrification and aerobic ammonia oxidation were significantly lower than those in the farmland and grassland (P<0.05). Saprotrophic fungi were the highest in bare-land, followed by farmland and grassland. Variation of bacterial community structure was influenced by BD, TN, mineral N, C:N ratio, and soil microbial biomass carbon (SMBC), while variation of fungal community structure was mainly influenced by mineral nitrogen. In addition, the functional community structure of both bacteria and fungi were mainly affected by BD, SOC, TN, C:N ratio, and SMBC. Specifically, Proteobacteria, Actinomycetes, Ascomycetes, and Basidiomycetes were more suitable to live in the farmland soil than in grassland. Chemical heterotrophic, aerobic chemical heterotrophic bacteria, and saprophytic fungi, which participated in soil carbon cycle, were mainly enriched in the farmland. Nitrification and aerobic ammonia oxidizing bacteria involved in the nitrogen cycle were mainly concentrated in the grassland. Therefore, the change of soil physiochemistry properties driven by land uses affected the community structure and function of microorganisms. In conclusion, variations of BD, TN, SOC, C:N ratio, SMBC, and mineral N under land uses change dominated the microbial community and functional structure.