This study investigated the effects of placement of N at different soil depths on CH 4 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 CH 4 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 CH 4 -related microbial communities through the increased labile soil organic C fractions by activating plant growth and soil microbial abundance, thereby mitigating the CH 4 emissions in no-tillage paddy soil.

中文翻译：

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深施氮肥通过调节免耕稻田产甲烷菌和甲烷氧化菌来减少甲烷排放

本研究调查了不同土壤深度施氮对免耕水稻土中 CH 4 排放和相关微生物群落的影响。稻田采用不施氮肥、表施氮肥、深施氮肥5 cm、10 cm、20 cm土层5种施肥处理。使用磷脂脂肪酸（PLFA）分析确定主要微生物群的组成。应用绝对实时定量 PCR 来确定产甲烷和甲烷氧化种群的丰度，其中 mcrA、pmoA、mmoX 和 mxaF 作为功能基因标记。与表面施氮相比，深施氮（i）显着增加了微生物生物量碳（C）和溶解有机碳，分别增加了 7-90% 和 6-75%；(ii) 使总 PLFAs 的数量显着增加了 12-70%，细菌 PLFAs 的数量增加了 15-82%；(iii) 显着减少了 6-39% 的 CH 4 排放；(iv) 使产甲烷和甲烷氧化种群的丰度分别显着提高了 16-55% 和 13-210%。由于不同的 N 放置深度以及季节性变化，百分比变化在很大范围内变化。此外，结构方程模型表明，深施氮通过激活植物生长和土壤微生物丰度，通过增加不稳定的土壤有机碳组分直接或间接影响 CH 4 相关微生物群落，从而减少免耕稻田中的 CH 4 排放. (iv) 使产甲烷和甲烷氧化种群的丰度分别显着提高了 16-55% 和 13-210%。由于不同的 N 放置深度以及季节性变化，百分比变化在很大范围内变化。此外，结构方程模型表明，深施氮通过激活植物生长和土壤微生物丰度，通过增加不稳定的土壤有机碳组分直接或间接影响 CH 4 相关微生物群落，从而减少免耕稻田中的 CH 4 排放. (iv) 使产甲烷和甲烷氧化种群的丰度分别显着提高了 16-55% 和 13-210%。由于不同的 N 放置深度以及季节性变化，百分比变化在很大范围内变化。此外，结构方程模型表明，深施氮通过激活植物生长和土壤微生物丰度，通过增加不稳定的土壤有机碳组分直接或间接影响 CH 4 相关微生物群落，从而减少免耕稻田中的 CH 4 排放.