退耕对民勤绿洲土壤碳氮循环关键微生物及功能基因的影响

采用时空互代法，以巴丹吉林沙漠东南缘民勤绿洲不同退耕年限样地土壤为研究对象，利用微生物宏基因组测序技术，以KEGG数据库碳固定、氮代谢途径为工具，研究长期退耕对参与区域土壤碳固定和氮代谢途径的主要微生物群落组成及其功能基因变化的影响。试验共设置9个退耕年限梯度样地：未退耕耕地、退耕1年样地、退耕2年样地、退耕4年样地、退耕8年样地、退耕13年样地、退耕20年样地、退耕30年样地和退耕40年样地。结果表明：退耕明显改变了碳固定、氮代谢土壤微生物和功能基因丰度，细菌在碳固定和氮代谢两个过程中均起到主导作用；还原三羧酸循环途径、还原乙酰辅酶A途径以及3-羟基丙酸/4-羟基丁酸循环途径等为研究区土壤微生物主要碳固定途径，厌氧氨氧化途径、硝酸盐异化还原途径、硝酸盐同化还原途径、反硝化途径以及硝化途径等为研究区土壤微生物主要氮代谢途径；芽单胞菌属（Gemmatimonas）、未分类绿弯菌属（unclassified_Chloroflexi）和链霉菌属（Streptomyces）等是区域土壤微生物碳固定主要菌属，氮代谢则以腈基降解菌属（Nitriliruptor）、芽单胞菌属（Gemmatimonas）、土壤红杆菌属（Solirubrobacter）、未分类绿弯菌属（unclassified_Chloroflexi）和链霉菌属（Streptomyces）等为主；Gemmatirosa、未分类绿弯菌属（unclassified_Conexibacter）、未分类念珠菌门（unclassified_Candidatus Rokubacteria）、Gaiella和Geminicoccus等5个属分类土壤微生物可作为研究区退耕地碳固定途径标记性微生物种群，coxL.cutL和ACO.acnA等是研究区退耕地土壤微生物碳固定途径主要响应功能基因；腈基降解菌属（Nitriliruptor）、未分类念珠菌门（unclassified_Candidatus Rokubacteria）、Geminicoccus、未分类绿弯菌属（unclassified_Conexibacter）、土壤红杆菌属（Solirubrobacter）、未分类酸杆菌门（unclassified_Acidobacteria）和红色杆菌属（Rubrobacter）等7个属分类土壤微生物可作为研究区退耕地氮代谢途径标记性微生物种群，GDH2和E1.4.7.1是研究区退耕地土壤微生物氮代谢途径主要响应功能基因。该结果对于明确退耕影响下民勤绿洲土壤碳氮循环过程具有重要意义。

Effects of abandoned farmland on key microorganisms and functional genes of soil carbon and nitrogen cycles in Minqin Oasis

Utilizing the spatio-temporal intergenerational methodology, we conducted an investigation into the impacts of prolonged fallowing on the composition and functional genetic alterations of the primary microbial communities engaged in the carbon fixation and nitrogen metabolism pathways within the regional soil. To accomplish this, we employed microbial metagenome sequencing technology and utilized the carbon fixation and nitrogen metabolism pathways from the KEGG database as a tool. The study was carried out in sample plots located in the Minqin Oasis, situated at the southeastern edge of the Badan Girin Desert. These plots were categorized into nine groups based on the duration of fallowing:plots with no fallowing, 1-year fallowing, 2-year fallowing, 4-year fallowing, 8-year fallowing, 13-year fallowing, 20-year fallowing, 30-year fallowing, and 40-year fallowing. The findings revealed significant alterations in the abundance of soil microorganisms and functional genes related to carbon fixation and nitrogen metabolism due to fallowing. Bacteria played a predominant role in both carbon fixation and nitrogen metabolism. The primary carbon fixation pathways of soil microorganisms in the study area were the reductive tricarboxylic acid cycle pathway, reductive acetyl-CoA pathway, and the 3-Hydroxypropionate/4-hydroxybutylate cycle pathway. As for nitrogen metabolism, the main pathways identified were anaerobic ammonium oxidation, dissimilatory nitrate reduction, assimilatory nitrate reduction, denitrification, and nitrification. Gemmatimonas, unclassified Chloroflexi, and Streptomyces were main bacteria for carbon fixation of regional soil microorganisms, while the nitrogen metabolism relied mainly on Nitriliruptor, Gemmatimonas, Solirubrobacter, unclassified Chloroflexi, and Streptomyces. Gemmatirosa, unclassified Conexibacter, unclassified Candidatus Rokubacteria, Gaiella, and Geminicoccus could be used as marker microbial populations of the pathways of carbon fixation in the cultivated land in the study area, and coxL.cutL and ACO.acnA were main response function genes of the pathways of carbon fixation in the cultivated land in the study area. Seven genera of classified soil microorganisms, including Nitriliruptor, unclassified Candidatus Rokubacteria, Geminicoccus, unclassified Conexibacter, Solirubrobacter, unclassified Acidobacteria, and Rubrobacter, could be used as the marker microbial population of the pathways of nitrogen metabolism in the study area, and GDH2 and E1.4.7.1 were main response function genes of the pathways of nitrogen metabolism in the study area. These results hold significant importance in elucidating the processes of carbon and nitrogen cycling in the soils of Minqin Oasis under the influence of fallowing.