Microbial Communities In The Tarim Basin Soil:diversity And Their Roles In Carbon And Nitrogen Cycle

The global desert ecosystem provides people with basic materials for survival and development,and with a stable and extremely important material foundation for economic development,maintaining regional and social maitaining.Its ecologically fragile,single and a large-scale distribution of plants and animals of the ecosytem are limited,So the dynamic distribution of its microbial community are very important to understand the function of desert ecosystem services.Tarim Basin is a very typical desert ecosystem in China.The composition and change of soil microbial community structure and its role in carbon and nitrogen cycle need further elucidation.So,We detected the physicochemical properties of the desert soil in the Tarim Basin,analyzed the changes in the microbial community structure in the soil by high-throughput sequencing,and isolated and cultivated microorganisms,So as to gain insights into the composition of important microbial communities and its roles in carbon and nitrogen cycling in the desert soil.1.Geochemistry of the desert soils in Tarim Basin In this study,18 soil samples were collected from six sites,specifically,three locations in Hotan and another three locations in Xayar.Samples for which the total and dissolved organic carbon,total nitrogen,nitrate nitrogen,ammonium nitrogen,exchangeablepotassium,exchangeablesodium,exchangeablecalcium,exchangeable magnesium,and pH values of the samples were determined.Statistically significant difference was calculated by the ANOVA method,including dissolved organic carbon,total carbon,total nitrogen,and exchangeable calcium.This indicate that soils from Tarim Basin is low nutrient,and of moderate salinity.2.Metagenomic analysis the microbial communities of the desert soils To give a more comprehensive understanding of the structure of the microorganisms,Metagenomic analysis generated about 39–46 million for each sample.After quality filtering,about 85%reads passed the quality threshold and participated in the following analysis for metagenomic samples.By utilizing operational taxonomic units?OTUs?analysis tools embedded in QIIME,for each samples,we obtained 6375 OTUs,25418 Chao1 indices,Alpha diversity by Shannon diversity indices reached over 8 in most samples.This implying that the high species richness and high diversity microbial community.It show no significant difference between locations?p>0.05?or sites?p>0.05?,as well as their interactions?p>0.05?on soil microbial species diversity by ANOVA analysis.In summary,the diversity analysis can conclude that microbial community composition in different locations was not significant difference.Combined with metagenomic sequencing data,We used MetaPlAn2 software to analyze the composition,abundance,and phylogeny of the developmental OTUs of microbial domains,phyloge,classes,orders,families,genera,and species.The data showed that bacterial phylotypes?89.72%on average?dominated the community,with relatively small proportions of Archaea?7.36%?and Eukaryota?2.21%?.Proteobacteria,Firmicutes,Actinobacteria,and Euryarchaeota were most abundant based on metagenomic data.whereas Euryarchaeota of the Archaea domain,Analysis of the sample correlation according to the detected species-level OTUs in metagenomic data showed significant differences?R²=0.6-1.0?,indicating high correlation of species among the soil samples.This showed that there are no reginal differences in microbial community composition in the Tarim Basin.3.Metatranscriptomic analysis the microbial communities of the desert soils.To explored the community composition of transcriptionally active microorganisms by analyzing the metatranscriptomic data using MetaPhl An2.Metatranscriptomic generated 13–37 million 200-nt reads,respectively,for each sample.and 87%reads passed the quality threshold and participated in the following analysis for metatranscriptomic samples.This showed that the transcripts from Archaea,Bacteria,Eukaryota,and Viroid varied largely in different sampleby analyzing the metatranscriptomic data,This showed that the transcripts from Archaea,Bacteria,Eukaryota,and Viroid varied largely in different samples.Bacteria were most active in all samples,Eukaryota and Viroids were least active in these samples,with the exception of viroids in B1sample?77.83%?,the Archaea domain was active in A2,B1,C2,C3,and D3 samples?12.29%³9.07%?,genes associated with Proteobacteria were determined to be most actively transcribed,whereas genes of Actinobacteria were less transcribed in almost all samples.4.Halophiles were the most active species in Tarim soils The 10 most active species-level OTUs from each sample,the 10 most active species represented a large proportion of total active species in all tested soil samples.Moreover,analysis of the sample correlation according to the active species showed significant differences?p-value<0.01?,indicating high diversity of active species among the soil samples.We further analyzed the transcripts of the most active halophilic species that are closely related to Halobacterium sp.DL1 and Halomonas elongate DSM 2581 to yield a understanding of their adaptation to the arid environment of Tarim Basin.This revealed that stress responsive proteins were found to be highly expressed in the Halobacterium species and Halomonas elongate species.Together,these results suggest that these halophilic archaeal and bacterial species are adapted to the thermal and arid conditions probably by elevating the expression levels of stress-responsive proteins.5.Analysis of active nitrogen metabolism pathways Based on the soil metratranscriptome data in the Tarim Basin and enriched the expression of nitrogen cycle-related genes in the KEGG metabolic pathway in each sample.It showed that nitrogen metabolic genes were expressed to a high level in these soils,mainly involved in dissimilatory nitrate reduction,denitrification,and nitrification pathways.Active microbes involved in nitrogen cycle are those belonging to Proteobacteria,Firmicutes,Nitrospirae,Thaumarcheaota,Euryarchaeota,Crenarchaeota,Bacteroidetes,For organisms of the Archaeal domain,Thaumarchaeota were main contributor to the nitrogen cycle in the saline soils of the Tarim Basin.6.Analysis of active CO₂ fixation pathways Based on the soil metratranscriptome data in the Tarim Basin and enriched the expression of CO₂ fixation pathway-related genes in the KEGG metabolic pathway in each sample.It showed that CO₂ fixation pathway gene were expressed to a high level in these soils,mainly involved in C4-dicarboxylic cycle,Calvin cycle,and redcutive TCA cycle.Active microbes involved in the CO₂ fixation pathway are those belonging to Proteobacteria,Bacteridetes,Chloroflexi,Nitrospinae,Fimicutes.Our study reveals that the microbial communities could provide carbon and nitrogen nutrients for higher plants in the sandy saline soils of Tarim Basin.