珠三角城市绿地CO_2通量的环境响应特征

Environmental response characteristics of CO_2 flux above urban green space in Pearl River Delta

城市绿地的净生态系统CO2交换量(NEE)受多种环境因素控制,定量分析NEE的环境响应机制对评估绿地生态系统固碳效益、优化城市绿地布局有重要意义。本文应用2009、2010年位于东莞市植物园内的涡度相关CO2通量定位观测资料,分析了光合有效辐射(PAR)、土壤温度(Ts)、饱和水汽压差(VPD)、降水及周边不同下垫面类型对NEE的影响。结果表明:NEE绝对值随PAR的升高而增加,PAR超过光饱和点(约为1500μmol photons·m-2·s-1)后,NEE绝对值呈回落趋势;生态系统呼吸(Reco)随Ts升高而增加,在温度较低时,Reco对Ts的敏感性较强(10℃时,Lloyd-Taylor方程的Q10=1.8),随着温度升高,敏感性下降(30℃时,Q10=1.43);VPD通过影响植物气孔导度对CO2交换产生作用,相同温度下,随着VPD升高,气孔导度增大,呼吸释放与光合固定的CO2量均增加;降水能增加土壤湿度进而使Reco增大,25℃时,降水后的Reco比降水前增加15.8%;测站东北和西南方的绿地范围较大,当东北和西南部是主要贡献区时,NEE绝对值较大,表明增加城市绿地能有效提高城市固碳效益。

The net ecosystem exchange （NEE） of CO2 above urban green space is controlled by various environmental factors. To quantitatively analyze the environmental response of the NEE can provide valuable basis for the evaluation of carbon fixation effect of green space ecosystem and the optimization of urban green space distribution. Based on the CO2 flux data of Dongguan Botanical Garden in 2009 and 2010 measured by eddy-covariance method, this paper analyzed the relationships between the NEE and the environmental factors （photosynthetic active radiation （PAR）, soil temperature （Ts）, saturation vapor pressure differential （VPD）, precipitation, and land cover distribution）. The results showed that the absolute value of NEE increased with increasing PAR when the PAR was less than the light saturation point （1500 μmol photons·m^-2·s^-1）, but presented a decreasing trend when the PAR was higher than the light saturation point. The ecosystem respiration （Reco） increased with rising Ts, and was more sensitive to the Ts when the temperature was low （the Q10 of Lloyd-Taylor equation was 1.8 at 10 ℃）, compared with that at high temperature （Q10 was 1.43 at 30 ℃）. The VPD could act on CO2 exchange by affecting plant stomata conductance. When the VPD rose, both the CO2 release and the CO2 fixation increased. Precipitation had significant effect on the Reco through increasing soil moisture content. After precipitation, the Reco at 25 ℃ was 15.8% higher than that before precipitation. There was a wider green space in northeast and southwest directions around the observation station. When these directions were the main contribution areas, the absolute value of NEE was larger, indicating that increasing urban green space could improve urban carbon fixation effect.