Livestock grazing in grasslands regulates the multifunctionality of those ecosystems and has an adverse effect on soil carbon (C) dynamics and fractions. However, our understanding of grazing-induced changes in soil microbial community and their links to soil organic C (SOC) fractions is limited. By using a long-term grazing experiment in desert steppe, we examined impacts of different grazing intensity on the diversity and composition of soil microbial community and their potential contribution to SOC content and fractions. The results showed that 15-year grazing reduced total SOC (TSOC), albeit not significant, but induced a notable decrease in both labile and recalcitrant SOC fractions, especially under high grazing intensity. Soil prokaryotic communities were not significantly impacted by grazing intensity. However, we observed that sensitive operational taxonomic units (OTUs), identified by indicator taxa analysis, grouped in distinct modules that reflected the different grazing intensities, suggesting that groups of microbes may cluster together and respond to grazing intensity. Association networks of prokaryotic OTUs and organic C fractions showed that SOC fractions were significantly related to rare taxa, indicating that grazing practice may act as a kind of environmental filtering and strongly affected soil microbial rare taxa and thereafter SOC fractions. Together, our findings suggest that grazing intensity did not change total microbial community and TSOC but affected SOC fractions by altering rare taxa. Overall, our results indicated that soil C fractions and rare microbial taxa were more sensitive to grazing intensity, which could act as indicator of variations in ecosystem functions in the semi-arid desert steppe.

中文翻译：

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放牧加速了沙漠草原中稀有微生物类群驱动的不稳定和顽固的土壤碳流失

草原上的牲畜放牧调节了这些生态系统的多功能性，并对土壤碳 (C) 动态和分数产生了不利影响。然而，我们对放牧引起的土壤微生物群落变化及其与土壤有机碳 (SOC) 部分的联系的了解是有限的。通过在沙漠草原进行长期放牧实验，我们研究了不同放牧强度对土壤微生物群落多样性和组成的影响及其对 SOC 含量和分数的潜在贡献。结果表明，15 年的放牧降低了总 SOC (TSOC)，尽管不显着，但导致不稳定和顽固的 SOC 部分显着降低，尤其是在高放牧强度下。土壤原核生物群落不受放牧强度的显着影响。然而，我们观察到，通过指标类群分析确定的敏感操作分类单元 (OTU) 分组为反映不同放牧强度的不同模块，这表明微生物群可能聚集在一起并对放牧强度做出反应。原核生物 OTU 和有机 C 组分的关联网络表明 SOC 组分与稀有类群显着相关，表明放牧实践可能作为一种环境过滤，强烈影响土壤微生物稀有类群以及随后的 SOC 组分。总之，我们的研究结果表明，放牧强度不会改变总微生物群落和 TSOC，但会通过改变稀有分类群来影响 SOC 比例。总体而言，我们的结果表明土壤碳组分和稀有微生物类群对放牧强度更敏感，