永定河沿河沙地杨树人工林生态系统呼吸特征

杨树是世界上广泛采用的人工造林树种之一,也是中国人工林面积最大的树种。研究杨树人工林生态系统呼吸(Re)及其分量土壤呼吸(Rs)的时间动态格局以及强度特征,分析两者对环境因子的响应是提高人工林生态系统净生产力和促进固碳减排等人工林经营管理中考虑的首要问题。采用开路式涡度相关系统、Licor-8150土壤呼吸测定系统以及小气候测定系统连续测定了位于北京大兴区永定河沿河沙地杨树人工林的生态系统呼吸、土壤呼吸和小气候特征。研究结果表明:(1)2007-2009年该生态系统的Re年总量分别为946.68、863.58、817.30gCm^-2a^-1,其中Rs年总量分别为642.11、629.29,609.05gCm^-2a^-1, Rs年总量约占Re年总量的70%;(2)Re和Rs月总量一般在7或者8月份达到最大值,Rs的变化趋势与土壤5cm温度(Ts5)相一致;(3)Ts5是Re和Rs两者的显著影响因子,但Re与空气相对湿度(RH)的相关性最显著。此外,Rs更容易受到Ts5和0-20cm土壤平均体积含水量(vwc)两者耦合效应的限制。

Ecosystem and soil respiration of a poplar plantation on a sandy floodplain in Northern China

Poplar is one of the most widely planted tree species through China's ambitious reforestation effort especially in the northern China since the 1970s. Among various pressing issues related to this plantation, the magnitude and dynamics as well as the biophysical regulation of carbon loss through respiration are critical information needed in the context of wood productivity and carbon sequestration. Ecosystem respiration(Re), soil respiration(Rs), and meteorological conditions of a Populus × euramericana cv. "74/76" plantation located on the floodplain of the Yongding River in Daxing District of Beijing, were measured through an eddy-covariance system, a four-channel soil respiration measurement system(Li-8150, Li-Cor, NE), and a microclimate measurement system from 2007 through 2009. The variation of Re and Rs in the different time scales and their responses to environmental factors including soil temperature and soil water content were analyzed and discussed in this paper. Energy balance closure was evaluated by statistical regression between turbulent energy fluxes of sensible (Hs) and latent heat (LE) against the difference etween available energy of net radiation (Rn) and the soil heat flux (G), which excluded the heat storage from the ground to the height of measurement. The ratio of turbulent energy fluxes to available energy was 0.78, with an average intercept of 18.95 Wm^-2s^-1 at half-hourly scale in all three years indicating that the flux data were reliable in general. The total annual Re was 946.68, 863.58, and 817.30gCm^-2a^-1 for 2007, 2008, and 2009, respectively; and the total annual Rs was 642.11, 629.29, and 609.05gCm^-2a^-1.Rs was the dominant component of Re, accounting for about 70% of Re on an annual basis. The annual Rscan be used to estimate the annual Re in the future studies. The monthly Re and Rs reached the maximum in July or August, and Rs showed a similar seasonal variation in all three years. The similar temporal variation was observed for the monthly Rs and the averaged soil temperature at 5cm depth (Ts5) from 2007 to 2009. The maximum daily Rs and Re were 5.285 and 7.781 gCm^-2d^-1, compared with the minimum value of 0.330 and 0.504 gCm^-2d^-1for 2007,2008, and 2009, respectively.Re and Rs were significantly correlated with Ts5, however, we found that Re was mostcontrolled by air relative humidity (RH) among all the climate and soil moisture conditions. In addition, Rs was more determined than Re by the coupling factor of volumetric soil water content (vwc) and Ts 5.