南亚热带针阔叶混交林生态系统水分利用效率

Water-use efficiency in a mixed conifer-broadleaf forest ecosystem in lower subtropical China

针阔叶混交林是我国南亚热带针叶林向地带性常绿阔叶林演替的中间林分类型,研究其生态系统水分利用效率有利于预测环境变化对生态系统碳水过程的影响。基于我国南亚热带鼎湖山站2005—2010年涡度相关法通量数据及相应气象观测数据,分析了演替中期针阔叶混交林的生态系统水分利用效率的变化特征和主要环境因子对其影响作用。结果表明:(1)年尺度上,鼎湖山针阔叶混交林生态系统年平均水分利用效率为(2.85±0.22)g C·kg^-1H2O,季节尺度上呈单峰变化,夏季低,春冬高,秋季次之,最低月均水分利用效率出现于2009年7月,为1.45 g C·kg^-1H2O,最高月2006年1月平均水分利用效率为4.75 g C·kg^-1H2O,研究期间,系统水分利用效率呈现出降低的波动趋势。(2)与环境因子的相关分析表明,年尺度上,生态系统水分利用效率变化的主要驱动因子为光合有效辐射(PAR)、水汽压亏缺(VPD)及气温。气温、VPD对干季的典型月份(11月—翌年1月)WUE影响显著(P<0.001),PAR对湿季的典型月份(6—9月)影响显著(P<0.001)。研究结果有助于明晰南亚热带地区森林生态系统碳水耦合程度,为气候变化下生态系统的管理提供服务。

Mixed conifer-broadleaf forest is a transitional type from coniferous forest to zonal evergreen broad-leaved forest in subtropical area of southern China.Research on water use efficiency(WUE)of forest ecosystem is helpful in predicting the impacts of environmental change on water and carbon processes in lower subtropical China.In this study,the changes of WUE and the effects of main environmental factors in the mixed conifer-broadleaf forest ecosystem during 2005to 2010 were analyzed based on the eddy covariance system installed at the Dinghushan Forest Ecosystem Research Station.The results showed that,at the annual scale,mean annual WUE of the mixed conifer-broadleaf forest was(2.85±0.22)g C·kg^-1H2O.The seasonal trend of WUE presented a typical single-peak curve,with the highest values occurring in spring and winter,followed by autumn,and the lowest values in summer.The highest monthly WUE was 4.75 g C·kg^-1H2O in January 2006,while the lowest was 1.45 g C·kg^-1H2O in July 2007.WUE showed a decreasing trend during the study period(2005-2010).The annual WUE was significantly correlated with air temperature and vapor pressure deficit(VPD)during the dry season(NovemberJanuary of the next year),while WUE was significantly correlated with photosynthetically active radiation(PAR)in the wet season(from June to September)(P<0.001).These results are helpful to clarify carbon-water coupling in forest ecosystems in lower subtropical China and provide scientific basis for ecosystem management in the context of climate change.