Global Change Biology：我国稻田和旱地土壤有机碳固持途径研究
中国科学院亚热带农业生态研究所研究员苏以荣团队在我国东部四个水稻分布气候区随机采集了240对稻田和旱地表层土壤，以解析稻田和旱地土壤有机碳来源和稳定性、阐明两类土壤有机碳固持途径。相关成果发表于Global Change Biology（IF=8.555）。
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Paddy soils make up the largest anthropogenic wetlands on earth, and are characterized by a prominent potential for organic carbon (C) sequestration. By quantifying the plant‐ and microbial‐derived C in soils across four climate zones, we identified that organic C accrual is achieved via contrasting pathways in paddy and upland soils. Paddies are 39%–127% more efficient in soil organic C (SOC) sequestration than their adjacent upland counterparts, with greater differences in warmer than cooler climates. Upland soils are more replenished by microbial‐derived C, whereas paddy soils are enriched with a greater proportion of plant‐derived C, because of the retarded microbial decomposition under anaerobic conditions induced by the flooding of paddies. Under both land‐use types, the maximal contribution of plant residues to SOC is at intermediate mean annual temperature (15–20 °C), neutral soil (pH~7.3) and low clay/sand ratio. By contrast, high temperature (~24 °C), low soil pH (~5) and large clay/sand ratio are favorable for strengthening the contribution of microbial necromass. The greater contribution of microbial necromass to SOC in water‐logged paddies in warmer climates is likely due to the fast anabolism from bacteria, whereas fungi are unlikely to be involved as they are aerobic. In the scenario of land‐use conversion from paddy to upland, a total of 504 Tg C may be lost as CO2 from paddy soils (0–15 cm) solely in eastern China, with 90% released from the less protected plant‐derived C. Hence, preserving paddy systems and other anthropogenic wetlands and increasing their C storage through sustainable management are critical for maintaining global soil C stock and mitigating climate change.
稻田和旱地土壤有机碳形成途径概念图
稻田是地球上最大的人工湿地生态系统。同一个小的地貌单元内，稻田和旱地错落分布，具有相似的母质和气候条件。通常，旱地土壤有机碳含量较低，而相邻稻田土壤却具有突出的有机碳固持能力。解析稻田和旱地土壤有机碳来源和稳定性、阐明两类土壤有机碳固持途径，可为农田土壤有机碳库管理提供有力科学依据。
中国科学院亚热带农业生态研究所研究员苏以荣团队在我国东部四个水稻分布气候区（中温带-黑土、暖温带-潮土、亚热带-红壤和热带-砖红壤）采用配对采样原则，随机采集了240对稻田和旱地表层土壤。分析发现，四个区域稻田土壤有机碳固持效率比相邻旱地土壤高39%~127%，且温暖区（亚热带和热带）差异大于寒冷区（中温带和暖温带）。进一步随机选择40对土壤，基于生物标识物木质素酚和氨基糖分析，量化植物残体和微生物残留物来源有机碳对土壤有机碳积累的贡献，结果表明，长期耕作以来，稻田土壤固持的有机碳中植物残体来源碳占33%~54%、微生物残体来源碳占28%~36%，而旱地土壤中积累的有机碳植物残体贡献19%~42%，微生物残留物贡献40%~59%。绝对值来看，稻田土壤中植物残体来源碳库大小是旱地土壤的3.3倍。因此，稻田土壤突出的碳固持能力主要由于淹水限制了微生物活性、抑制植物残体微生物分解过程，促进有机碳以植物残体直接积累。从木质素酚和氨基糖的化学组成来看，相较旱地土壤，稻田土壤木质素单体中C/V（木质素单体中肉桂基酚类/香草基酚类）高、S类（紫丁香基酚类）单体的酸醛比低，且真菌和细菌残留物比值低，说明稻田土壤中积累的有机碳稳定性低、易受环境变化或人为干扰而丢失。情景分析表明，若我国东部所有稻田转变为旱地，将造成稻田表层土壤（0~15 cm）中504 Tg有机碳丢失（相当于中国所有农田表层土壤有机碳库的13%），且98%以上发生在亚热带和热带，这些丢失的碳90%以上为植物残体来源碳。研究结果提示了保护亚热带、热带地区稻田和其他人工湿地生态系统的重要性，强调合理的水分管理是减少稻田土壤有机碳丢失的关键。
研究工作得到国家自然科学基金、国家重点研发计划等的支持。
责任编辑：宋潇
校对和审核：张阳 王农