| The source region of the Yangtze River,Yellow River and Lancang River(Sanjiangyuan),located in the hinterland of the Qinghai–Tibetan Plateau,is an important ecological safety and water conservation area in China,and plays an important role in maintaining grassland productivity and ecological services.As an important grassland type in this region,the alpine steppe plays an important role in maintaining its stability.Soil microbes function as a critical factor in the geochemical cycle,material decomposition,soil nutrient cycling promotion and energy flow.The variation in soil microbial community structure and composition reflects soil environmental changes,soil quality and ecological functions.Thus,changes in soil bacterial and fungal composition and their diversity with different altitudes(?,3064 m;?,3227 m;?,3470 m;?,3901 m;?,4200 m)in alpine steppes were invested by using the Illumina MiSeq.And a Biolog-ECO analysis was used to analysis the characteristics of microbial carbon source utilization,and the RT-qPCR was used to analyze the distribution characteristics of functional genes involved in carbon and nitrogen cycle.And the adaption mechanism of soil microbes in alpine steppe to altitude variation was analyzed based on the molecular ecological network pipelines.The results were as follows:1)The plant diversity and coverage were higher at ? and ? of alpine steppe,while the plant height was higher at ?.The altitude change had a great influence on soil physical and chemical properties except the total phosphorus and potassium.The change of altitude resulted in the change of soil enzyme activity.The activities of cellulase and sucrase were higher at ?,while the activities of urease,phosphatase and polyphenol oxidase were higher at ?,? and ?,respectively.The correlation among vegetation,soil physicochemical properties and soil enzyme activity varied,indicating that the influence of altitude variation on them was different.2)The ? diversity of microbes decreased with the increase of altitude,so as to the community structure.The dominant bacterial phylum in alpine steppe under different altitudes was Proteobacterial,Actinobacteria and Acidobacteria,and the dominant fungi groups were Ascomycetes and Basidiomycetes.The linear discriminate analysis(LDA)effect size(LEfSe)analysis found thirty-six biomarkers of bacterium and thirty-two of fungi.The functional profiles(of the bacterial populations predicted by Tax4 FUN,and the fungi was by FUNGuild)revealed that carbonhydrate metabolism and amino acid metabolism were the main metabolism function of bacterium;the fungi community was mainly composed of symbiotic and saprophytic,in addition,pathological types were mainly concentrated in ? and ?.And the microbial communities were mainly correlated with soil pH,phosphatase activity and grassland coverage.3)The results of Biolog-ECO analysis showed that average well color development(AWCD)of alpine steppe under different altitudes increased first and then decreased with the increase of culture time,which was higher at ?.The diversity indexes were higher at ?,which had the same trend with AWCD.Second,principal component analysis showed that altitude changes resulted in the change of alpine steppe microbial community carbon metabolism,sugars and acids were the main carbon sources microoganism utilized.Moreover,there were significant differences in the utilization of 11 carbon sources by microorganism in alpine steppe at different altitudes(p<0.05).These results indicated that the change of altitude resulted in the difference of soil microbial functional diversity,and the microbial survival strategy was adjusted to adapt to the change of altitude.In addition,RDA analysis showed that urease,PPO activity,BD and grassland coverage played a major role in the diversity difference of soil microbial carbon source utilization at different altitudes,among which,BD played a significant role(p<0.05).4)RT-qPCR results showed that the carbon sequestration gene(cbbM and cbbL)was higher at high altitude,which indicated that alpine steppes with high altitude showed larger potential for carbon sequestration.The abundance of the gene(cellulase)with the ability to decompose stubborn carbon abundance increased with the increased altitude,while the gene(amylase)with the ability to decompose labile carbon showed revesed trend,which indicated that microbia in alpine steppe with high altitude showed a greater potential to decompose stubborn carbon,while microbia in alpine steppe with low altitude showed a greater potential to decompose easily decomposed carbon.The ratio of amylase to cellulase first decreased then increased with the increase of altitude,which was higher at ?,that was,microbes in high altitude area showed greater potential to decompose labile carbon.While the ratio of carbon sequestration to carbon decomposition was higher in alpine stepps with low altitudes,which indicated that alpine steppes with high altitude had great ability to decompose carbon,which would be detrimental to the sustainable development of the alpine steppe system.And the nitrogen fixation gene(nifH)increased with the increase of altitude.Correlation analysis showed that the abundance of genes involved in carbon cycle and nitrogen fixation was significantly correlated with vegetation coverage;while soil carbon content was the main factor affecting the decomposition of different types of carbon.The main factors affecting carbon fixation and decomposition in soil were total nitrogen,total carbon and water content.And the nitrogen fixation gene(nifH)was related to soil total carbon content.5)Based on random matrix theory,the molecular ecological network pipelines was constructed between bacteria,fungi,and environmental factors,microbial metabolic function in alpine steppes at different altitudes.The Network parameters showed that,the networks of bacteria and fungi were loose,and unstable.The utilizatiobn of Carbonhydrates and acids were higher.And the network was mainly affected by pho activity,pH and plant coverage. |
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