Long-term rice cultivation promoted microbial mineralization of organic P in a black soil

Information on the microbiological process in paddy soil is essential to understand phosphorus (P) transformation, due to the special biogeochemical change of P in flooded rice (Oryza sativa L.)-growing environment. However, relatively few references have been focused on this process in long-term cultivation of black paddy soil. In this study, we investigated the effect of microbial community and phoD gene on changes in soil P fractions in a black paddy soil. The results showed that, compared with 1-yr soil, long-term cultivation (35-yr rice growth) significantly increased the concentration of soil P pool (P < .05). In detail, the soil available-P increased from 15.4 to 34.8 mg kg(-1), and primary-P, secondary-P, occluded-P and organic-P increased from 41.4 to 73.6 mg kg(-1), 7.60 to 18.9 mg kg(-1), 57.6 to 106.1 mg kg(-1), and 13.7 to 29.1 mg kg(-1), respectively. Notably, the microbial biomass C/P ratio decreased from 190.8 (1-yr) to 56.2 (35-yr), indicating that the mineralization of organic P (Po) by microorganisms played a dominant role in long-term cultivation. The results were further verified by significantly increased soil microorganism concentration, copy number of phoD gene, and strong interaction in phoD-harboring bacteria. The change of soil P pool was significantly affected by soil properties and phoD gene community through variance partitioning analysis, and Streptomyces and Cupriavidus were the main biomarkers affecting Po mineralization through linear discriminant analysis effect size (LEfSe) analysis. The results will be helpful to understand the microbial process of P transformation (especially for Po) and to guide the management of P fertilizer in black soil area.

Automated summary

Information on the microbiological process in paddy soil is crucial for understanding phosphorus transformation. This study focused on the long-term cultivation of black paddy soil and found that microbial community and phoD gene significantly influenced the changes in soil phosphorus fractions. The results showed an increase in soil phosphorus concentration after 35 years of rice growth, with microorganisms playing a dominant role in organic phosphorus mineralization. Soil properties and phoD gene community were identified as important factors affecting soil phosphorus pool changes.