Aims

Grasslands are experiencing severe degradation globally, impacting aboveground vegetation and soil properties. The influences of grassland degradation on bacterial communities in soil are not well-understood.

Methods

The normalized difference vegetation index (NDVI) was calculated to represent grassland status and indicate grassland degradation (decreasing NDVI). Soil ph, bacterial communities, as well as nutrient and organic carbon concentrations were measured.

Results

Bacterial alpha diversity had negative relationships with soil moisture, soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP). Bacterial community structure was significantly associated with NDVI, the change rate of NDVI, moisture, ph, SOC, TN, as well as soil C:N and C:P ratios. Bacterial phyla were differentially related with these environmental variables. Moreover, network analysis showed that the network of soil bacteria had strong cooperation relationships (positive correlations between taxa) and was grouped into three modules. According to modularity, 71 keystone taxa were detected as network connectors and module hubs. All the modules had close relationships with environmental variables, and many keystone taxa were negatively associated with soil moisture and SOC.

Conclusions

These results suggest that grassland degradation might be responsible for shifts in soil bacterial communities in terms of alpha diversity and community structure through changes in soil moisture, SOC, nutrients, and C:nutrient ratios. Moreover, in the network analyses, the strong co-occurrence relationships between taxa as well as close relationships between environmental variables and module structures and keystone taxa suggest low stability and high vulnerability of bacterial communities to the influences of grassland degradation.

中文翻译：

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青海湖流域土壤细菌群落随草地退化而变化。

目的

全球草原正在严重退化，影响到地上植被和土壤特性。草地退化对土壤中细菌群落的影响尚不清楚。

方法

计算归一化差异植被指数（NDVI）以代表草地状况并指示草地退化（NDVI减少）。测量了土壤的酸碱度，细菌群落以及养分和有机碳浓度。

结果

细菌的α多样性与土壤水分，土壤有机碳（SOC），总氮（TN）和总磷（TP）呈负相关。细菌群落结构与NDVI，NDVI，水分，ph，SOC，TN的变化率以及土壤C：N和C：P比率显着相关。细菌菌群与这些环境变量差异相关。此外，网络分析表明，土壤细菌网络具有很强的合作关系（分类单元之间呈正相关），并分为三个模块。根据模块性，检测到71个主要分类单元作为网络连接器和模块集线器。所有模块均与环境变量密切相关，许多基石分类群与土壤水分和SOC呈负相关。

结论

这些结果表明，草地退化可能通过土壤水分，SOC，养分和C：养分比的变化而导致土壤细菌群落在α多样性和群落结构方面发生变化。此外，在网络分析中，分类单元之间强烈的共现关系，以及环境变量与模块结构与基石分类单元之间的密切关系表明，细菌群落的稳定性较低，并且对草地退化的影响易感性较高。