Effects of nitrogen and phosphorus inputs on the diversity of carbon-, nitrogen-, and phosphorus- mineralization microbial communities in subtropical Chinese fir plantations

The regulation of N and P input on microbial communities is related to the bottom-up effects of soil resources (i.e., nutrients), and the top-down effects of predators (i.e., protists). However, it is not clear how exogenous N, P, and NP inputs effect on the bottom-up (pH, soil nutrients, and eco-stoichiometry ratio of C: N: P), and top-down (abundance and diversity of protist community) factors to estimate soil microbial community involved in C-, N-, and P- mineralization. In this study, we explored the effects of a 7-years N, P, and NP inputs on the bottom-up and top-down controls on the abundance and diversity of functional microbial communities in the subtropical Chinese fir plantations using metagenomic sequencing. The results showed that N and NP inputs decreased soil pH and soil acidifying cause a reduction in the alpha diversity of microbial function. Exacerbated soil microbial C limitation under N, P, and NP inputs was negatively correlated with the alpha diversity of metagenomic function. The alpha diversity of bacteria was negatively correlated with the ratios of soil total and available N: P, due to increasing available P content. Regarding top-down effects of protists on the abundance and diversity of microbial C-, N-, and P- mineralization community, P and NP inputs increased alpha diversity of protist, thus, selectively increased the relative abundances of Calditrichaeota involved in C-mineralization, and decreased the relative abundances of Elusimicrobia and Marinimicrobia involved in N-mineralization. Although protozoa feed on both bacteria and fungi, changes in protists under N, P, and NP inputs mainly affected bacterial diversity and abundance, with no significant changes in fungi. Overall, the present results provide important knowledge on bottom-up (pH, soil nutrients, and eco-stoichiometry ratio of C: N: P), and top-down (abundance and diversity of protist community) factors of the abundance and diversity of the microbial community involved in C, N and P mineralization in the context of elevated N and P input.