The Proportion of Soil-Borne Fungal Pathogens Increases with Elevated Organic Carbon in Agricultural Soils

Soil-borne fungal phytopathogens are important threats to soil and crop health. However, their community composition and environmental determinants remain unclear. Here, we explored the effects of agricultural fertilization regime (i.e., organic material application) on soil fungal phytopathogens, using data sets from a combination of field survey and long-term experiment. We found that soil organic carbon was the key factor that affected the diversity and relative abundance of fungal phytopathogens in agricultural soils. The dominant genera of phytopathogens including Monographella was also strongly associated with soil organic carbon. In addition, the elevated soil organic carbon enhanced the node proportion of phytopathogens and the positive interactions within the fungal community in the network. Results of the long-term experiment revealed that applications of crop straw and fresh livestock manure significantly increased the proportion of phytopathogens, which were associated with the elevated soil organic carbon. This work offers new insights into the occurrence and environmental factors of fungal phytopathogens in agricultural soils, which are fundamental to control their impacts on the soil and crop systems. IMPORTANCE Fungal phytopathogens are important threats to soil and crop health, but their community composition and environmental determinants remain unclear. We found that soil organic carbon is the key factor of the prevalence of fungal phytopathogens through a field survey, which is also supported by our long-term (6-year) experiment showing the applications of crop straw and fresh livestock manure significantly increased the proportion of fungal phytopathogens. These findings advance our understanding of the occurrence and environmental drivers of soil-borne fungal phytopathogens under agricultural fertilization regime and have important implications for the control of soil-borne pathogens.