古尔班通古特沙漠不同区域藻类结皮微生物结构和潜在功能

Microbial community structure and potential function of algal crusts in different regions of Gurbantunggut Desert,Xinjiang,China

藻类结皮形成和发育,能够提高土壤稳定性并增加土壤有机质含量,为微生物生长、繁殖和草本植物拓殖创造条件。因此,藻类结皮潜在功能对后续生物结皮及生态系统演替具有重要意义。然而,古尔班通古特沙漠藻类结皮营养循环相关微生物及潜在功能机制尚不清楚。以古尔班通古特沙漠不同区域藻类结皮为研究对象,采用宏基因组测序技术,研究藻类结皮微生物群落及碳氮循环功能基因特征。研究结果表明蓝藻菌门、变形菌门、放线菌门是藻类结皮中主要微生物类群,在沙漠固碳和氮循环中起到重要作用。微生物α多样性结果显示仅物种丰富度指数在三个区域内存在显著差异。β多样性结果显示藻类结皮未因沙漠局部气候及理化因子差异产生微生物群落分化。而微生物群落功能基因对环境变化响应要比微生物群落更为敏感,沙漠东部和西部藻类结皮功能基因产生显著分化。三个区域微生物功能基因中还原型三羧酸循环是自养生物固碳主要途径,而卡尔文循环是光合生物固碳的主要途径,其中rpiA和rbcS基因更易受到降水影响。鞘脂单胞菌属、念珠藻属和伪枝藻属在参与固碳过程中表现出的差异,可能是导致固碳功能基因产生分化的原因之一。氮循环主要途径以硝酸盐还原为主,大部分氮素通过硝酸盐同化作用被土壤微生物转化为铵盐,少量氮素被反硝化为一氧化二氮和一氧化氮流失。沙漠藻类结皮固氮作用较弱,仅有念珠藻属和伪枝藻属参与,且存在nifH、nifD、nifK三个功能基因。这些固氮功能基因更易受到土壤中硝态氮含量的影响。硝化过程仅注释到氨单加氧酶或甲烷单加氧酶编码pmoABC-amoABC基因,而hao和nxrA、nxrB基因均未注释获得。

The formation and development of algal crust improve soil stability and promote the retention of soil organic matter,which create favorable foundational conditions for soil microbial growth,reproduction and herbaceous plant topology.Hence algal crust potential function is of great significance for the subsequent succession of biological crusts.However,the microorganisms and its potential functions of algal crusts nutrient cycling in Gurbantunggut Desert are still unclear.In this paper,the microbial community,the carbon and nitrogen cycling functional gene characteristics of algal crust in different regions of Gurbantunggut Desert were investigated using metagenome sequencing technology.The results showed that.Cyanobacteria,Proteobacteria and Actinobacteria were the dominant microbial communities in algal crusts and play an important role in desert carbon fixation and nitrogen cycling.The microbialα⁃diversity results showed that only the richness indices has significantly different among the three regions.β⁃diversity results showed that microbial communities of algal crusts did not changed due to local climatic and physico⁃chemical differences in the desert.Microbial community functional genes were more sensitive to environmental changes than microbial community structure.The functional genes of algal crusts in the eastern and western deserts show significant differentiation.The Reductive citrate cycle was the primary pathway of autotrophs for carbon fixation in algal crusts.The Calvin cycle served as the primary pathway of photosynthetic organisms for carbon fixation,where rpiA and rbcS genes 58.771 were more susceptible to precipitation.Variances in the contributions of Sphingomonas,Nostoc,and Scytonema to the carbon fixation process may potentially underlie the divergence of genes associated with carbon fixation functions.The primary nitrogen cycling pathway in algal crusts were nitrate reduction,and the most nitrogen were assimilated into ammonium by soil microorganisms through nitrate assimilation,and the small amount of nitrogen emit in the form of nitrous oxide and nitric oxide through denitrification.Nitrogen fixation were relatively weak,which only included Nostoc and Scytonema and three functional genes:nifH,nifD,nifK.Moreover,the expression of functional nitrogen fixation genes appears to be particularly influenced by variations in soil nitrate nitrogen content.The nitrification process only annotated to the ammonia monooxygenase or methane monooxygenase encoding by pmoABC⁃amoABC genes,whereas the hao,nxrA and nxrB genes were not be annotated.