Mulching decreased the abundance of microbial functional genes in phosphorus cycling under maize

Abstract

Microorganisms regulate soil phosphorus (P) cycling in cropping systems. However, the response of microbial functional genes involved in soil P cycling to mulching practices is largely unknown. We used a metagenomic sequencing approach to analyze microbial functional genes related to soil P cycling in a spring maize field that was mulched with crop straw (SM) and plastic film (FM) for ten years and without mulching (CK). Thirty-nine P cycling functional genes were identified. These genes were involved in organic P-mineralization and inorganic P-solubilization, P-uptake and transport, and P-starvation response regulation. Relative abundances of functional genes coding for P-mineralization and solubilization significantly decreased by 8.8 % and 13.9 % in SM and FM (P < 0.05) than in CK, respectively. FM also decreased the total relative abundance of functional genes involved in P-uptake and transport by 13.2 % (P < 0.05) compared to CK. However, mulching practices did not affect the relative abundance of functional genes related to P-starvation response regulation. Random forest analysis suggested eleven key functional genes coding for soil P cycling as determinants of available P in which the gcd gene encoding PQQGDH was dominant. The Proteobacteria and Actinobacteria were two dominant phyla for which P cycling genes were taxonomically attributed. The Mantel test indicated that soil C:P ratio, pH, and available P were closely associated with the relative abundances of functional genes responsible for soil P cycling. Overall, this study demonstrated a decrease in the relative abundance of soil P cycling genes with mulching practices in agroecosystems, irrespective of the mulch type. The mechanism may differ depending on the mulch type.