气候过渡带锐齿栎林土壤呼吸对降雨改变的响应

作为大气与陆地生态系统之间的第二大碳通量,土壤呼吸是评价陆地生态系统碳循环及碳汇能力的不确定性来源之一。降雨格局改变及其导致的土壤水分变化是调节土壤呼吸的重要驱动。气候过渡带的水热状况受全球降雨格局改变的影响更为明显,揭示该区域森林土壤呼吸对降雨改变的响应规律有助于改善碳循环模型的预测精度。然而,气候过渡区的土壤碳排放过程如何响应降雨格局改变尚不清楚。通过在亚热带-暖温带的过渡区(宝天曼)开展降雨改变实验,以阐明锐齿栎林土壤呼吸及其温度敏感性对降雨增加(50%)和减少(50%)的响应规律。结果表明,降雨增加显著提高土壤湿度(+8.92%)而不影响土壤温度。与对照相比,降雨增加导致土壤呼吸显著提高80.5%,其土壤呼吸的温度敏感性(4.07)显著高于对照样地(2.66)。增雨处理下的土壤呼吸与土壤湿度呈负相关。降雨减少则显著降低土壤湿度(-10.25%),并对土壤呼吸有促进趋势,然而,对土壤呼吸的温度敏感性(2.64)无显著影响。减雨处理下的土壤呼吸强度与土壤湿度呈正相关。这意味着在我国亚热带—暖温带过渡区,降雨增加或减少均对土壤呼吸有不同程度的刺激作用,进而很可能减弱该区域森林生态系统土壤的固碳潜力。

Responses of soil respiration to changing precipitation regimes in an oak forest at a climate transitional zone

As the second largest carbon (C) flux between the atmosphere and terrestrial ecosystems, soil respiration remains one of the key sources of uncertainty while assessing terrestrial C cycling and sink strength. Changing precipitation patterns and its corresponding changes in soil water content are critical in regulating soil respiration. Hydrothermal conditions in the climatic transitional zone are more susceptible to changing precipitation patterns than other climatic zones. Determining the responses of soil respiration to changing precipitation regimes in the climatic transitional zone is favor to the improvement of precision of C cycling models. However, there is currently limited information on the response of soil CO₂ emission to changing precipitation regimes in the climatic transitional zone. A field precipitation manipulation experiment was conducted at an oak (Quercus aliena) forest located at a climatic transitional zone (Baotianman), from subtropical to warm temperate, to examine the response of soil respiration and its temperature sensitivity to increased (+50%) and decreased precipitation (-50%). Soil respiration, temperature, and moisture were measured weekly from July to November in 2013. The results showed that increased precipitation significantly elevated soil moisture by 8.92% but had no effect on soil temperature. Soil respiration was substantially enhanced by 80.5% under increased precipitation treatment compared with that in the control plots. Temperature sensitivity of soil respiration under increased precipitation was significantly higher (4.07) than that in control plots (2.66). Soil respiration under increased precipitation showed negative correlations with soil moisture as well as soil temperature. Decreased precipitation substantially reduced soil moisture by 10.25% and tended to increased soil respiration. However, reduced precipitation showed little effect on the temperature sensitivity (2.64) of soil respiration. Soil respiration under the decreased precipitation showed positive correlations with soil moisture and temperature. The results suggest that both increased and decreased precipitation can stimulate soil respiration with different extents. Changing precipitation patterns, therefore, may weaken soil C sequestration in forest ecosystems, and exert a positive feedback on atmosphere CO₂ concentration at the climatic transitional zone from a subtropical to a warm temperate zone.