Biological nitrogen (N) fixation and organic N degradation are the main sources of soil available N, while microorganisms driving such processes play an important role in soil N supply and the maintenance of soil fertility. In this study, real-time quantitative PCR and amplicon sequencing technology were used to examine the effects of restoration types on the community structure of N2-fixing and chitin-degrading bacteria harboring nifH and chiA genes, respectively, and the gene abundance under four meadows (undisturbed, grazing, fencing, and fencing + reseeding mea-dows) in Qinghai-Tibet Plateau. The results showed that the abundance of nifH and chiA in the four meadows followed the order of undisturbed meadow > grazed meadow > fencing meadow > fencing + reseeding meadow. The abundance of nifH and chiA in the undisturbed meadow was 3.4-6.3 times and 3.3-8.3 times of that in the other three meadows. The α diversity of N2-fixing bacteria in gra-zing, fencing, and fencing + reseeding meadows was significantly higher than that in the undisturbed meadow, while the α diversity of chitin-degrading bacteria was higher in the undisturbed and grazing meadows. Grazing significantly increased the relative abundance of Proteobacteria, but decreased the relative abundance of Cyanobacteria and Actinobacteria. The abundance of nifH and chiA was significantly affected by soil moisture, nutrients, and vegetation characteristics, while the community structure of nifH and chiA was affected by soil moisture, soil organic carbon content, and soil pH. Compared with undisturbed meadow, grazing reduced the potential of N fixation and organic N degradation.The improvement of 10 years grazing prohibition with fencing and reseeding measures on the function of N fixation and organic N degradation was not obvious. The characteristics of functional microbes and their influencing factors should be comprehensively considered during meadow restoration, which might take longer time or take reasonable management measures to restore grazing meadow to undisturbed level.
生物固氮和有机氮降解是土壤有效氮的主要来源,固氮和有机氮降解微生物对土壤氮素供应和地力维持具有重要作用。本研究以青藏高原4种不同利用方式的高寒草甸(未扰动、放牧、围封和围封+补播草甸)为对象,结合荧光实时定量和扩增子测序技术,研究了不同恢复方式对nifH固氮菌和chiA几丁质降解菌基因丰度及其微生物群落结构的影响。结果表明: 4种草甸的nifH和chiA基因丰度大小排序为: 未扰动草甸＞放牧草甸＞围封草甸＞围封+补播草甸,其中未扰动草甸的nifH和chiA基因丰度分别是其他3种草甸的3.4～6.3倍和3.3～8.3倍;固氮菌α多样性在放牧、围封和围封+补播草甸中显著高于未扰动草甸,而几丁质降解菌的α多样性在未扰动和放牧草甸中最高;放牧显著提高了变形菌的丰度而降低了蓝细菌和放线菌丰度;土壤含水量、养分和植被特征对nifH和chiA的基因丰度和群落结构均有显著影响。与未扰动草甸相比,放牧降低了高寒草甸的固氮和有机氮降解潜力,而10年的围封禁牧和补播植草措施对固氮和有机氮降解功能的改善作用不明显。草甸恢复时应综合考虑功能微生物特征及其影响因素,放牧草甸恢复至未扰动水平可能需要更长的封育时间或者采用更加合理的管护措施。.
Keywords:
N2-fixing bacteria;