Nitrogen deep placement mitigates methane emissions by regulating methanogens and methanotrophs in no-tillage paddy fields

Abstract

This study investigated the effects of placement of N at different soil depths on CH4 emissions and related microbial communities in no-tillage paddy soil. Five fertilizing treatments, including no N fertilizer, N surface broadcasting, and N deep placement at the soil depths of 5 cm, 10 cm, and 20 cm were applied in the paddy field. The composition of main microbial groups were determined using phospholipid fatty acid (PLFA) analysis. The absolute real-time quantitative PCR was applied to determine the abundance of the methanogenic and methanotrophic populations with mcrA, pmoA, mmoX, and mxaF as the functional gene markers. Compared with N surface broadcasting, the deep placement of N (i) significantly increased the microbial biomass carbon (C) and dissolved organic C by 7–90% and 6–75%, respectively; (ii) significantly enhanced the amount of the total PLFAs by 12–70% and the bacterial PLFAs by 15–82%; (iii) significantly mitigated the CH4 emissions by 6–39%; and (iv) significantly enhanced the abundance of the methanogenic and methanotrophic populations by 16–55% and 13–210%, respectively. The percent changes varied over a wide range due to different N placement depths as well as the seasonal variations. Moreover, structural equation modeling revealed that N deep placement directly or indirectly affected the CH4-related microbial communities through the increased labile soil organic C fractions by activating plant growth and soil microbial abundance, thereby mitigating the CH4 emissions in no-tillage paddy soil.