不同干旱强度下气候过渡带典型森林土壤呼吸各组分对降雨脉冲的响应

Soil respiration plays a key role in terrestrial ecosystem carbon (C) cycling. Episodic precipitation often leads to a higher and continuous soil respiration than normal level in a period after a rainfall, which strongly increases the uncertainty of soil CO2 emission in terrestrial ecosystems C cycling. Currently, our understanding in the response soil respiration to precipitation pulse remains unclear, especially in the following two aspects: 1) whether response of soil respiration to precipitation pulse relates to drought intensity and does hetero- or auto-trophic respiration show the same response patterns to precipitation pulse? 2) are the regulations of soil biotic and abiotic factors on soil respiration depend on precipitation size. The lack information limits our ability in quantifying and assessing the importance of soil CO2 emission in terrestrial ecosystem C cycling. A field experiment with simulated drought and precipitation pulse will be conducted in a deciduous forest at transitional climatic zone; so as to investigate the responses of soil respiration and its components to precipitation pulse with different drought intensities and to determine the driving mechanism of biotic and abiotic factors on soil respiration in respond to precipitation pulse. The results will expand our understanding on the impacts of precipitation on soil CO2 emission at transitional climatic zone, and enhance the prediction accuracy of soil CO2 emission under changing precipitation patterns in the further.

土壤呼吸是陆地生态系统碳循环的重要途径之一。脉冲式的降雨事件导致土壤呼吸在瞬间内极速增加并持续一段时间，土壤呼吸这种短期激发效应增加了陆地生态系统碳循环的不确定性。目前对土壤呼吸响应降雨脉冲的认识仍不全面，主要问题有：ⅰ土壤呼吸对降雨脉冲的响应是否与土壤干旱程度有关，不同呼吸组分对降雨脉冲的响应是否一致？ⅱ土壤生物及非生物因素对土壤呼吸响应降雨脉冲的调节作用是否因降雨强度而异？对这两方面认识的不足严重限制了人们对陆地土壤碳排放格局的精确量化和科学评价。本项目拟在我国亚热带-暖温带过渡带落叶阔叶林中开展干旱及降雨脉冲实验，揭示不同干旱强度下土壤呼吸各组分对降雨脉冲的响应规律，阐明土壤呼吸对降雨脉冲响应的生物/非生物调控机制。本项目的开展将有助于深入理解降雨对气候过渡带森林土壤碳排放的影响，以及提高未来降雨格局改变情景下土壤碳排放的预测精度。

土壤呼吸是陆地生态系统碳循环的重要途径之一，脉冲式的降雨事件导致土壤呼吸在瞬间内极速增加并持续一段时间，土壤呼吸这种短期激发效应增加了陆地生态系统碳循环的不确定性。本项目在我国亚热带－暖温带过渡带落叶阔叶林中开展干旱及降雨脉冲实验，以探讨不同干旱强度后土壤碳排放对降雨脉冲的响应规律。研究表明，落叶阔叶林中春季土壤碳排放对降雨脉冲的响应程度依赖于干旱强度，严重干旱(30天)下的土壤呼吸对降雨脉冲的响应量级显著高于轻度和中度干旱状况的土壤。与对照(0mm)相比，降雨脉冲(5mm, 10mm和20 mm)事件可分别显著提高土壤呼吸86%到175%。与轻度和中度干旱相比，极端干旱显著提高异养呼吸在总呼吸中的贡献。春季以总呼吸和异养呼吸形式排放的碳对降雨脉冲的响应程度要高于干旱强度。通过对四个季节降雨脉冲过程的研究发现，土壤呼吸均随着降雨脉冲强度的提高而增加，夏季和秋季降雨脉冲导致的土壤碳排放量显著高于春季和冬季。降雨脉冲对土壤异养呼吸和自养呼吸的影响因季节而异，降雨脉冲显著提高冬季的异养呼吸及夏季自养呼吸组分。此外，降雨脉冲显著降低夏季和秋季土壤异养呼吸在总呼吸中的比例。降雨脉冲后的土壤温度，降雨前的土壤湿度和土壤无机氮是影响土壤呼吸对降雨脉冲响应方式的主要环境驱动。本研究强调在评价陆地生态系统碳循环过程时要同时考虑干旱强度和降雨脉冲对土壤碳排放的交互影响。