高原喀斯特土壤有机碳短期稳定的温度作用机制

Short-term Mechanism of Warming-induced Stability for Organic Carbon in the Karst Plateau Soil

探明有机碳稳定的温度作用机制,是评估全球变化背景下土壤碳源/汇演变趋势的关键.应用土壤密度分组和酸水解技术,采用红外线辐射增温法,对比研究不同升温情景下高原喀斯特土壤及其物理和生化组分中有机碳密度的短期(4a)变化特征.升温情景包括不升温(对照)、对称升温(全年同步升温2.0℃)和非对称升温(冬春/夏秋季升温幅度为2.5℃/1.5℃、3.0℃/1.0℃、3.5℃/0.5℃和4.0℃/0℃,低度、中度、高度和极端非对称升温),其中中度非对称升温与该区域多年升温情景类似.结果表明,不同升温情景下表层(0~15 cm)土壤有机碳密度在1.95~2.02 kg·m-2之间,其差异不显著,且与对照(1.94 kg·m-2)差异不显著.升温处理间土壤轻组和重组碳密度、重组顽固性碳密度差异不显著,且与对照差异不显著.5个升温处理轻组顽固性碳平均密度是对照的1.18倍,其中对称升温、低度和中度非对称升温处理显著高于对照.轻组顽固性碳密度和轻组顽固性碳指数随升温的非对称性增加而降低,其中对称升温处理均显著高于中度、高度和极端非对称升温.亚表层(15~30 cm)土壤及其物理和生化组分中有机碳密度对短期升温均不敏感.研究揭示:短期内,升温提高了高原喀斯特土壤非保护组分中有机碳顽固性.基于对称升温情景并不一定会误估全球变暖对土壤有机碳数量和土壤碳物理保护能力的影响,但可能会高估表层土壤(0~15 cm)非保护组分有机碳顽固性.

Elucidating the mechanisms of warming-induced stability for soil organic C is one of the keys for evaluating the tendency of soil C sources/sinks in projected global warming models. Organic C densities in soil,and soil physical and biochemical fractions,under different warming scenarios in the Karst Plateau were investigated following a 4-yr continuous warming using infrared radiators,via density fractionation and acid hydrolysis. Six treatments were arranged： no warming（ ambient temp,CK）; symmetric warming（ ambient ＋ 2. 0℃ full year）; and lowly,moderately,highly,and extremely asymmetric warming（ ambient ＋ 2. 5℃/1. 5℃,3. 0℃/1. 0℃,3. 5℃/0. 5℃,and 4. 0℃/0℃ in winter-spring/summer-autumn seasons,respectively; LAW,MAW,HAW,and EAW）.The moderately asymmetric warming was highly similar to a multi-year warming scenario in the study region. The results showed there were no significant differences in soil organic C densities in the surface layer（ 0-15 cm） among the warming treatments,with a range of 1. 95 kg·m^-2 to 2. 02 kg·m^-2,which is insignificantly different to the CK（ 1. 94 kg·m^-2）. There were no significant differences in the C density of light and heavy fractions,and the recalcitrant heavy-fraction among the warming treatments,and between the warming and no warming treatments. The average recalcitrant C density of the light fraction in the warming treatments was 1. 18 times higher than the CK,with a significantly higher recalcitrant C density of the light fraction in the symmetric warming,and lowly and moderately asymmetric warming treatments,compared to that of the CK. The recalcitrant C density and recalcitrant C index of the light fraction showed a tendency to decrease as the asymmetry of warming increased under the five warming scenarios. Warming had negligible effects on the organic C density in soil,and soil physical and biochemical fractions in the subsurface layer（ 15-30 cm）. The results revealed that in the short-term,warming may increase the recalcitrance of non-protected C in the Karst Plateau soil. This is not necessarily an over-or underestimation of the effects of global warming on soil organic C density and the capacity of soil to protect C when subjected to symmetric warming,but may potentially overestimate the recalcitrance of organic C in the non-protected fraction of the surface layer（ 0-15 cm）.