How does water management impact the effects of straw returning on biological nitrogen fixation and diazotrophs?

Abstract

Background and aims Both straw incorporation and water management affect biological nitrogen fixation (BNF), but it is unclear how water management impact the effects of straw returning on BNF and diazotrophs in rice fields. Methods A 15N2-labelling system was used to determine BNF under straw returning with continuous or intermittent flooding in rice field for 90 days. The nitrogenase nifH gene and nifH RNA gene (cDNA) were amplified by qPCR and the community structure of diazotroph was studied by high-throughput sequencing of nifH DNA gene. Results Combined continuous flooding and straw incorporation, BNF was 14.29 kg ha-1, which was much higher than 6.62 kg ha-1 under straw incorporation and intermittent flooding. Straw incorporation and continuous flooding showed an obvious synergistic effects on BNF, nifH DNA gene copy number and nifH cDNA gene copy number. The increased effects were mainly attributed to the increase of heterotrophic diazotrophs Desulfovibrionaceae, Azonexus and Azotobacter. Conclusions In conclusion, straw incorporation under continuous flooding could increase BNF greatly than under intermittent flooding. The results indicated that combined straw incorporation and continuous water flooding could build soil fertility faster.