Role of minerals in regulating the mineralization of cover crop residue and native organic matter and the community and necromass of microbes in flooded paddy soils

The application of cover crop residue is an important means in managing paddy soil. This study was to investigate the influences of minerals on the mineralization of organic matter and the community and necromass of microbes in paddy soils amended with cover crop residue. 13C-labelled cover crop residue (Astragalus sinicus L.) was prepared using a pulse labeling method. The mineralization of cover crop residue and native soil organic matter and the community and necromass of microbes in two flooded paddy soils amended with or without illite, goethite and ferrihydrite was investigated by incubation experiments. The released CO2/CH4 was analyzed by gas chromatography. Amino sugar was used as the biomarker of microbial residue carbon. Soil microbial communities were analyzed by high-throughput sequencing and quantitative polymerase chain reaction. Illite, goethite and ferrihydrite significantly decreased the amounts of both CO2 and CH4 emissions from native soil organic carbon in both paddy soils. Moreover, the inhibition efficiency followed the same sequence of ferrihydrite > goethite > illite for both CO2 and CH4 emissions. However, ferrihydrite significantly stimulated the mineralization of cover crop residue in both paddy soils. The examined minerals, especially ferrihydrite, also tended to decrease bacterial and fungal abundance and diversity in both paddy soils. Moreover, the contents of both bacterial and fungal residue carbon were significantly decreased by the examined minerals in alkaline paddy soil. Examined minerals tended to decrease total mineralization of cover crop residue and native organic matter, the microbial abundance, diversity, and necromass in flooded paddy soils.