我国北方山地灌丛土壤呼吸对降水量增减变化的响应及其机制

Soil respiration is the second largest carbon flux in terrestrial ecosystems, and plays a critical role in global carbon cycling. Precipitation, which acts as an important disturbance to soil respiration, leads to large uncertainties in estimating carbon exchange between the soil and the atmosphere. Shrublands are a widespread vegetation type that often have high carbon sequestration potential value. However, only a few of researches have studied the carbon flux of shrublands in the scenario of global climate change. To indentify the effect of changing precipitation on soil respiration in montane shrubland, three precipitation-manipulation treatments were designed to reflect potential changes in precipitation regimens: +30% precipitation water supplementation; -30% precipitation water droughting; and current conditions (no manipulation of water availability). The objective of the present research is to quantify the impact of precipitation changes on soil respiration and its components. Furthermore, response of soil respiration and its components to abiotic and biotic drivers are assessed. At last, the combined effects of environmental variables on soil respiration are analyzed by the use of Structural Equation Modeling (SEM). The present study considering precipitation changes are needed to properly assess future trends in soil CO2 fluxes under scenarios of global climate change.

土壤呼吸作为陆地生态系统碳循环的重要环节，对调控全球气候变化发挥着重要作用。土壤呼吸对降水量变化响应的不确定性，影响着气候变化条件下碳平衡的准确评估。灌丛是未来固碳增汇的潜力区，但全球气候变化情景下的碳循环研究却较薄弱。本研究将围绕降水量增减变化与土壤呼吸的关系这一问题，选择我国北方山地荆条灌丛作为研究对象，采用野外控制降水试验（自然状态、自然状态增加30 %和自然状态减少30 %），研究降水量增减变化条件下土壤呼吸及其组分以及相关环境因子的动态规律，确定自养呼吸和异养呼吸对土壤呼吸的相对贡献率，并通过建立土壤呼吸的结构方程模型来探讨影响土壤呼吸的各环境因子之间的相互作用关系，旨在阐明降水量增减变化对灌丛土壤呼吸的影响机制，以期为全球气候变化背景下灌丛土壤CO2排放响应研究提供基础数据。

全球气候变化带来降水格局的改变。土壤呼吸是土壤碳库向大气释放CO2的重要途径，其对降水变化的响应对陆地生态系统碳循环和全球气候变化进程有着重要的意义。本研究选择我国北方山区荆条灌丛为研究对象，采用野外控制降水实验，研究降水量变化对土壤呼吸的的影响及其与环境因子关系，得出如下主要结论：（1）研究期内，不同处理条件下月平均土壤呼吸速率的变化范围为1.35 ~ 1.57 µmol m-2 s-1，呈明显的季节动态。降水量减少30 %显著抑制了土壤呼吸速率，使平均土壤呼吸速率减少了9.0 %；降水量增加30 % 显著提高了土壤呼吸速率，使土壤呼吸速率增加了6.4 %；（2）在一定范围内，土壤湿度比土壤温度更好的解释土壤呼吸速率变化；土壤温湿度的双因素模型对土壤呼吸变化规律的解释效果提升不明显；（3）月平均土壤自养呼吸速率和月平均异养呼吸速率的变化范围分别为0.37 ~ 0.47 µmol m-2 s-1和0.99 ~ 1.10 µmol m-2 s-1，并且表现出季节性波动规律；（4）观测期内，自养呼吸对土壤总呼吸贡献率的均值为27.1 % ~ 29.8 %，异养呼吸对总呼吸贡献率的均值为70.2 % ~ 72.9 %。