State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences
the National Natural Science Foundation of China（No. 41877325），the Youth Innovation Promotion Association of the Chinese Academy of Sciences（No.2018349）and the National Key Research and Development Program of China（No.2017YFD0300105）
甲烷的减排问题早已成为各国政府和科研人员关注的焦点。稻田是温室气体甲烷的重要排放源，甲烷产生是排放的前提条件，主要有乙酸发酵和CO2/H2还原两条途径。常年淹水稻田甲烷排放量高，减排潜力大，但关于这类稻田甲烷产生途径的季节变化规律尚缺乏研究报道。于四川省资阳市的常年淹水稻田，采集水稻4个重要生育期（分蘖期、孕穗期、抽穗期、成熟期）的新鲜土样，通过室内厌氧培养试验观测了甲烷产生潜力，并采用稳定性碳同位素方法和氟甲烷（CH3F，2%）抑制法，量化了CO2/H2产甲烷的碳同位素分馏系数（α（CO2/CH4）），从而定量评估了乙酸产甲烷途径的相对贡献率（?乙酸）。结果表明：添加CH3F显著降低甲烷产生，甲烷产生潜力在成熟期最大，变化范围为3.22 ~ 12.71 μg·g-1·d-1 ；产生CH4的δ13C值（δ13CH4）为-66.83‰ ~ -59.62‰，较添加CH3F的δ13CH4显著偏正（-90.83‰ ~ -82.26‰）；α（CO2/CH4）在分蘖期最大，孕穗期最小，变化范围为1.064 ~ 1.076；?乙酸由分蘖期的54% ~ 61%急剧下降到孕穗期的30% ~ 35%，在成熟期又上升到54% ~ 61%。进一步分析发现：甲烷产生潜力的季节变化与土壤溶解性有机碳（DOC）含量的季节变化显著正相关，?乙酸的季节变化与土壤乙酸含量的季节变化显著正相关。综上，常年淹水稻田的甲烷产生潜力和产生途径均存在明显的季节变化，且分别主要受土壤DOC和乙酸含量的影响。
[Objective] The mitigation of methane (CH4) emission has long been the focus of governments and researchers worldwide. Rice fields are an important source of CH4 emission, and CH4 production is the precondition of CH4 emission. It is mainly produced by acetate fermentation and CO2/H2 reduction. Substantial CH4 emissions are observed from the permanently flooded rice fields, thus leaving a high mitigation potential of emission. However, reports on the seasonal variation of the methanogenic pathway in these rice fields are limited. [Method] Fresh soil samples from four rice growth stages (tillering stage, booting stage, heading stage, and maturity stage) were collected from a permanently flooded rice field in Ziyang City, Sichuan Province, China. The CH4 production potential (MPP) was observed through anaerobic incubation experiments. Both stable carbon isotope technique and methyl fluoride (CH3F, 2%) inhibition method were used to quantify the carbon isotopic fractionation factor for the conversion of CO2 to CH4 (α (CO2/CH4)), as well as to quantitatively estimate the relative contribution of acetate-dependent methanogenesis (? acetate). [Result] The addition of CH3F significantly decreased the CH4 production, and the MPP reached the highest value at the maturity stage, ranging from 3.22 to 12.71 μg·g-1·d-1. The δ13C-value of produced CH4 (δ13CH4) varied in the range -66.83‰ ~ -59.62‰, which was much more positive than that of produced CH4 with CH3F addition (-90.83‰ ~ -82.26‰). The α (CO2/CH4) reached its maximum and minimum values at tillering and booting stages, respectively, which was between 1.064 and 1.076. The ? acetate (30% ~ 61%) decreased sharply from 54% ~ 61% at the tillering stage to 30% ~ 35% at the booting stage and then increased to 54% ~ 61% at the maturity stage. Further analysis showed that the seasonal variation of MPP was positively correlated with the variation of soil dissolved organic carbon (DOC) content, and the seasonal variation of ? acetate was significantly related to variations of acetate content. [Conclusion] Distinct seasonal variations were observed in both MPP and methanogenic pathways of the permanently flooded rice fields, which was mainly affected by soil DOC content and acetate content, respectively.
ZHU Xiaoli, HUANG Qiong, SONG Kaifu, MA Jing, ZHANG Guangbin, XU Hua. Seasonal Variations in Methane Production Potential and Methanogenic Pathway in a Permanently Flooded Rice Field[J]. Acta Pedologica Sinica,,[In Press]