Soil microbial community composition and its role in carbon mineralization in long-term fertilization paddy soils

Microbial communities are critical in mediating soil biological processes, including C mineralization; yet, the mechanism of microbial mediation for soil C mineralization remains poorly understood under the long-term fertilization. To identify the relative roles of microbes in C mineralization in the soil of rice paddies, we investigated the long-term (11years) effects of repeated N, P, and K fertilization on crop yield, soil properties and microbial communities and their relationships with C mineralization. The treatments included: no fertilization (control); normal fertilization (NPK); doubling the amount of N, P or K fertilizer (2NPK, N2PK, or NP2K); and doubling the amount of all three (2(NPK)). Long-term fertilization significantly increased rice yields by 3.4 to 4.8 times, and yield significantly improved by 23-32% with higher N fertilization. Increasing N fertilization significantly decreased total N and total P concentrations, while increasing P fertilization significantly increased soil pH, Olsen-P and total P concentrations. Increasing N and P fertilization changed soil microbial community compositions; pH and ratio of SOC and TN (C:N) were the most important contributors to the variance in microbial community composition. Increasing P fertilization decreased the abundance of Gram-positive and actinomycetes phospholipid fatty acid (PLFA) and significantly increased the ratio of fungal to bacterial PLFA. However, the alterations in soil microbial abundance and community composition did not significantly influence the C mineralization, while it significantly was determined by C:N ratio and marginally by crop yield. The results suggest that substrate quality (C:N ratio) and availability (crop yield), having a closer relationship with C mineralization compared to soil microbial communities, should be preferentially considered to predicting C mineralization under long-term fertilization.