Responses of Soil Bacterial Diversity to Fertilization are Driven by Local Environmental Context Across China

Soil microbial diversity is extremely vulnerable to fertilization, which is one of the main anthropogenic activities associated with global changes. Yet we know little about how and why soil microbial diversity responds to fertilization across contrasting local ecological contexts. This knowledge is fundamental for predicting changes in soil microbial diversity in response to ongoing global changes. We analyzed soils from ten 20-year field fertilization (organic and/or inorganic) experiments across China and found that the national-scale responses of soil bacterial diversity to fertilization are dependent on ecological context. In acidic soils from regions with high precipitation and soil fertility, inorganic fertilization can result in further acidification, resulting in negative impacts on soil bacterial diversity. In comparison, organic fertilization causes a smaller disturbance to soil bacterial diversity. Despite the overall role of environmental contexts in driving soil microbial diversity, a small group of bacterial taxa were found to respond to fertilization in a consistent way across contrasting regions throughout China. Taxa such as Nitrosospira and Nitrososphaera, which benefit from nitrogen fertilizer addition, as well as Chitinophagaceae, Bacilli, and phototrophic bacteria, which respond positively to organic fertilization, could be used as bioindicators for soil fertility in response to fertilization at the national scale. Overall, our work provides new insights into the importance of local environmental context in determining the responses of soil microbial diversity to fertilization, and identifies regions with acidic soils wherein soil microbial diversity is more vulnerable to fertilization at the national scale.