Microbial community structure and function in paddy soil as affected by water-saving irrigation mode

The objective of this study was to understand how the water-saving irrigation mode affected the microbial community structure and function in paddy soil. A field experiment with three irrigation modes (flooding irri-gation FI, alternate wetting and drying irrigation AI and ridge irrigation RI) was conducted, and DNA extracted from the upper 25 cm paddy soils were measured using whole genome sequencing (WGS). The results showed that FI, AI and RI modes were significantly distinct in microbial communities. Compared to FI mode, two water -saving irrigation modes (AI and RI) decreased the relative abundance of Euryarchaeota and showed significant difference in their microbial co-occurrence networks. Compared to FI mode, AI mode increased the relative abundance of Proteobacteria but decreased the relative abundance of Actinobacteria, while RI mode showed opposite effects. Some biomarker species associated with carbon/nitrogen metabolism, such as Cupriavidus tai-wanensis, Gemmatirosa kalamazoonesis, Nitrospira moscoviensis, Pseudomonas tolaasii and Methanosarcina barkeri, were significantly sensitive to different irrigation modes. Meanwhile, two water-saving irrigation modes espe-cially AI mode enhanced the genes involved in carbohydrate decomposition and nitrification pathways, while FI mode significantly enriched the genes involved in methane metabolism, denitrification and nitrogen fixation. Thus two water-saving irrigation modes decreased the main methanogen (Methanosarcina barkeri) and meth-anogenesis genes in paddy soil, while AI mode enhanced potentially beneficial microbes and carbon/nitrogen metabolic-related genes in paddy soil.