Organic fertilizations alter the abundance and diversity of soil microbial genes involved in C, N, P mineralization in a coastal poplar plantation

Organic fertilization supports the sustainability of managed ecosystems; however, investigations into how microbial-driven mineralization processes of carbon (C), nitrogen (N), and phosphorus (P) interact with soil functions under the application of organic fertilizers remain limited. We investigated the impacts of six years of applying biogas-slurry and biochar on the abundance and diversity of soil microbial genes involved in C, N, and P mineralization in a poplar plantation. Our findings indicated that the addition of biogas-slurry alone, as well as in combination with biochar, reduced the diversity of microbial genes involved in C, N, and P mineralization. The addition of biogas-slurry increased the abundance of these genes, but the application of biochar decreased it. Using thresholds from the eco-enzyme vector model, we found that the addition of biogas-slurry, either alone or in combination with biochar, alleviated microbial P limitation by decreasing the N:P ratio of microbial biomass and increasing soil dissolved organic C (DOC). Additionally, linear regression indicated that the alleviation of microbial P limitation suppressed the diversity of genes and promoted the abundance of genes involved in C mineralization. Random forest and partial dependence analyses showed that increased DOC was the major factor responsible for the decreased diversity of microbial genes and increased abundance of genes involved in N mineralization. The SOC: TN ratio was negatively correlated with the abundance of genes involved in N and P mineralization. These findings highlight the inconsistent responses of the abundance and diversity of microbial genes involved in C, N, and P mineralization to the application of organic fertilizers in managed ecosystems. Additionally, these varying responses are regulated by increasing nutrient supplies and alleviating microbial P limitation. Our findings provide a new understanding of soil carbon and nutrient cycling and suggest the application of organic fertilizers to facilitate the sustainable management of ecosystems in the future.