夏季石灰土CO_2昼夜动态及其影响因素

Diurnal dynamics and constraints of soil CO_2 concentration in a limestone site during summer

土壤呼吸是土壤释放CO_2的过程,土壤CO_2动态及其控制因素的研究对于陆地生态系统碳收支核算和气候变化研究具有重要意义。本研究以喀斯特地区石灰土为对象,利用红外传感器(Vaisala GMP252)和自动装置高频次观测手段,测定了夏季土壤CO_2浓度和表观土壤呼吸速率(即土壤表面CO_2通量)的昼夜动态变化及其对集中降雨的响应特征,并分析了土壤CO_2浓度、表观土壤呼吸速率与土壤温度和湿度之间的关系。结果表明,土壤CO_2浓度的昼夜变化总体上呈现单峰变化趋势,峰值出现在正午(12:00—13:00)。此外,土壤CO_2浓度在集中降雨过程中呈"V"字型快速响应特征。土壤CO_2浓度与土壤温度呈正相关,而与土壤湿度呈负相关,石灰土偏碱性的环境使降雨时充填于土壤孔隙的水体中HCO_3^-、CO_3^(2-)及CO_2的平衡对土壤CO_2浓度变化具有重要影响。表观土壤呼吸速率的整体变化趋势与土壤温度和CO_2浓度变化一致,但前二者的变化与CO_2浓度相比略为滞后。表观土壤呼吸速率与土壤温度呈显著相关,而与土壤CO_2浓度的相关性不明显。土壤温度和湿度可以解释45%的表观土壤呼吸速率变化。因此,集中降雨影响下的石灰土表观土壤呼吸在短时间尺度上的变化主要受降雨、温湿度等环境因子影响下的土壤CO_2与空气交换过程的控制。

Soil respiration is the process of soil releasing COz. It is important to explore the dynamics of soil CO2 and its controls for mechanistic understanding of the terrestrial carbon budget and global climate change. Using infrared sensors （Vaisala GMP252） and an automatic device, we monitored CO2 concentration and apparent respiration rate （i.e., soil surface CO2 flux） of a limestone soil profile with high frequency, aiming to capture the diurnal dynamics of soil CO2 and its relationship with soil temperature, soil moisture and intense rainfall during summar. The resuits showed that the diurnal dynamics of soil CO2 concentration generally exhibited single-peak curves, with a maximum during 12： 00-13：00 each day. Moreover, soil CO2 concentration showed a V-shaped response to intense rainfall. Soil CO2 had a positive correlation with soil temperature, but had a negative correlation with soil moisture. The equilibrium of HCO3-, CO32- and CO2 in the water filling in soil pore-space during rainfall may have impacts on the CO： concentration dynamics in limestone soil due to its alkaline property. The apparent soil respiration rate hada similar diurnal variation trend as soil temperature and CO2 concentration, showing significant correlation with temperature, while the poor correlation with soil CO2 concentration. Soil tempera- ture and moisture explained 45% of the variation of apparent soil respiration rate. Our results indicated that with the impacts of intense rainfall events, short-term apparent soil respiration of limestone was mainly controlled by CO2 exchange between soil and atmosphere, which was largely dependent on environmental factors such as rainfall, soil temperature and moisture.