城市林地叶片与冠层尺度CO2浓度、水汽密度比较

为了定量评价城市公园林地的小气候作用,在北京市海淀公园架设涡度相关系统连续观测林地的冠层尺度数据,利用光合作用仪Licor 6400观测林地较大面积树种的叶片尺度数据,比较夏季日间叶片尺度与冠层尺度CO2浓度和水汽密度.结果表明,两个尺度观测的CO2浓度和水汽密度的日变化趋势基本相同,但叶片尺度CO2浓度高于冠层尺度数据10％ ～20％,叶片尺度水汽密度高于冠层尺度数据40％ ～70％.冠层尺度数据的双峰"午休现象"不明显,或弱于叶片尺度数据和存在时间上的滞后.叶片尺度CO2浓度与净辐射、净光合速率呈显著的负相关关系,叶片尺度水汽密度与蒸腾速率呈显著的正相关关系、与空气温度呈显著的负相关关系.冠层尺度CO2浓度和水汽密度数据均与垂直风速呈显著的正相关关系.研究结果有助于了解城市林地冠层与叶片之间CO2和水汽的湍流输送.

Comparison of CO2 concentration and vapor density at leaf scale and at canopy scale in urban woodland

In order to quantitatively evaluate the microclimate effects of urban woodland, eddy covariance system was installed to measure gas and energy fluxes at canopy scale in Haidian Park, Beijing, and Licor 6400 portable photosynthesis system was used to measure gas exchange and chlorophyll fluorescence of tree species with large area at leaf scale. CO2 concentrations at leaf scale are compared with those at canopy scale, so are vapor densities at leaf scale with those at canopy scale. Result shows the diurnal variations of CO2 concentrations and vapor densities at both leaf scale and canopy scale are basically similar. However, CO2 concentrations at leaf scale are 10~20% higher than those at canopy scale, and vapor densities at leaf scale are 40~70% higher than those at canopy scale. The midday depression of photosynthesis with double peaks in diurnal variations is not obvious at canopy scale, or is weaker than that at leaf scale and there is a time lag. There is a significant negative relation between CO2 concentration at leaf scale and net radiation, net photosynthetic rate. Vapor density at leaf scale has a significant positive correlation with transpiration rate, a significant negative relationship with air temperature. Both CO2 concentration and vapor density at canopy scale show positive correlation with vertical wind speed. The results are helpful for understanding the turbulent transfer of CO2 concentration and vapor between leaf and canopy in urban area.