城市绿地冠层导度季节变化及其环境调控

冠层导度(canopy conductance,gc)是生态系统对环境响应的敏感性指标,探讨冠层导度对环境因素的响应模式对了解生态系统生产力的变化模式至关重要。城市绿地作为人为设计的复合生态系统,其冠层导度变化规律及其对环境因子的响应亟待明确。基于涡度相关方法,本研究调查了北京奥林匹克森林公园2012-2016年连续5年的冠层导度的季节动态变化及其对空气温度(Ta)、光合有效辐射(PAR)、饱和水汽压差(VPD)以及土壤含水量(VWC)等环境因子的响应,利用统计回归方法分析了环境因子对冠层导度的影响,最后分析了冠层导度对总生态系统生产力(GEP)的影响。结果表明:2012-2016年的冠层导度依次为3.97、3.28、2.13、3.95和5.07 mm·s^-1,5年平均值为3.69±1.99 mm·s^-1;季节变化表现为从4月开始逐渐升高,在7、8月达到最大值后逐渐降低;在季节尺度上,VWC和Ta是影响冠层导度的主要环境因子,冠层导度随它们的增加而增大;而PAR和VPD对冠层导度的影响存在年际间的差异;5年间,GEP随着冠层导度的升高显著增大;城市绿地中,季节尺度上土壤水分的增加和气温的升高显著增加冠层导度,从而促进GEP。

Seasonal variation in canopy conductance of urban green land and its environmental control

Canopy conductance(gc) is a sensitive index indicating ecosystem response to environment. Understanding the response of canopy conductance to environmental factors is crucial for modelling ecosystem processes. We analyzed the seasonal dynamics of canopy conductance and its relationship with daily mean air temperature(Ta),photosynthetically active radiation(PAR),vapor pressure deficit(VPD) and soil water content(VWC) in Beijing Olympic Forest Park in the growing season from April to October 2012-2016 using eddy covariance technique. Regressions were used to test the effects of environmental factors on canopy conductance and the effects of canopy conductance on gross ecosystem productivity(GEP). The results showed that mean annual gcwas 3.97,3.28,2.13,3.95 and 5.071 mm·s^-1 in 2012-2016,respectively,with a mean value of 3.69 ± 1. 99 mm·s^-1. The gcstarted to increase in April and peaked in July or August,then gradually decreased at intra-annual scale. VWC and Tawere the main factors affecting seasonal variation in gc,which increased as increasing VWC and Ta. The effects of PAR and VPD on gcvaried yearly. GEP significantly increased with increasing gcduring the five years. Ele-vated soil water content and air temperature enhanced canopy conductance,and thus promoted GEP on a seasonal scale in urban green land.