Water management impact on denitrifier community and denitrification activity in a paddy soil at different growth stages of rice

Abstract Rice is one of the largest water-consuming crops. Alternate wetting and drying (AWD) is now an effective water-saving practice for rice cultivation that has been widely applied across the world. AWD may increase denitrification loss. However, the underlying mechanism remains unclear. This study investigated denitrifier activity, abundance and community structure in the rice rhizosphere and bulk soil in response to water management at the internode elongation (IE) and flowering (F) stages. The results revealed that at the IE stage, AWD significantly increased denitrification capacity (DC) in the rhizosphere compared with continuously flooded practice (CF). DC was significantly and positively related to electrical conductivity (EC) and the abundance of nirS-harboring denitrifiers. AWD led to higher EC in the 0–20 cm soil layer than CF. Although AWD lowered nirS abundance by 15 % compared with CF, the activity of nirS-harboring denitrifiers was enhanced by 1.89-folds of CF. At the F stage, AWD significantly decreased DC relative to CF. AWD had lower dissolved organic carbon (DOC) than CF, and DOC was significantly correlated with DC. Compared with CF, AWD also markedly changed the structure and network stability of nirS and nirK communities, resulting in sharp decreases in the total number of links in nirK and nirS networks of rhizosphere. The soil pH and EC were the key factors shaping the structure of nirS and nirK communities. Overall, the increase in denitrification losses due to AWD occurred primarily at the IE rather than F stage, and this increase was attributed to a rise in EC and changes in the activity and structure of nirS community. These findings provide a new insight into the mechanism of impact of the water-saving practice on denitrification loss for rice cultivation.