哀牢山亚热带常绿阔叶林冠层温度变化特征

Characteristics of canopy temperature in a subtropical evergreen broadleaf forest in Ailao Mountain

冠层温度是衡量植物体内水分变化的重要指标之一.为探明哀牢山亚热带常绿阔叶林冠层温度变化特征,利用冠层红外温度探测方法,测定云南省哀牢山亚热带常绿阔叶林冠层红外温度,并定量评价环境因子净辐射(R_(n))、风速(W_(s))和饱和水汽压差(VPD)对冠层温度(T_(c))与大气温度(T_(a))差值(即冠-气温差)的相对贡献.结果表明:(1)哀牢山亚热带常绿阔叶林冠层温度的日变化和年变化特征都呈现出单峰变化趋势;(2)雨季冠层温度和空气温度变化较干季平缓,昼夜温差(5.51℃)比干季(8.86℃)低37.8%,且雨季(0.51℃)的冠-气温差比干季(1.34℃)低62.3%;(3)受降雨影响,雨季日平均T_(c)与T_(a)的变异程度小于干季(雨季T_(c)与T_(a)变异系数分别为1.0%、1.1%;干季Tc与Ta变异系数分别为1.8%、1.8%);(4)净辐射、饱和水汽压差和风速是影响亚热带常绿阔叶林冠层温度变化的重要因子,而且不同环境因子在不同季节对冠-气温差的贡献程度差异较大.本研究预示冠层小气候的变化可能会对哀牢山亚热带常绿阔叶林的冠层热量交换产生重要影响,结果可为建立有明确生理生态学机理的森林碳水通量模型提供基础.(图6表2参41)

Canopy temperature(T_(c))is one of the most important indices for measuring changes in the water content of plants.To reveal the characteristics of T_(c)change in a subtropical evergreen broadleaf forest of Ailao Mountain in Southwest China,we measured T_(c)in the subtropical forest via an infrared temperature sensor.We further assessed the relative contributions of the key environmental factors of net radiation(R_(n)),wind speed(WS),and vapor pressure deficit(VPD)to T_(c)with respect to air temperature(T_(a)).We found that:(1)the diurnal and annual variations in T_(c)of the subtropical evergreen broadleaf forest in Ailao Mountain showed a single-peak trend;(2)T_(c)changes were more smooth in the rainy season than in the dry season.The diurnal temperature difference was 37.8%lower in the rainy season(5.51℃)than in the dry season(8.86℃),and the T_(c)difference(0.51℃)was 62.3%lower in the rainy season than in the dry season(1.34℃);(3)under the influence of rainfall,the overall variation degree of T_(c)and T_(a)was smaller in the rainy season than in the dry season(the coefficients of variation of T_(c)and T_(a)were 1.0%and 1.1%in the rainy season and 1.8%and 1.8%in the dry season,respectively);and(4)R_(n),VPD,and WS were the important drivers of T_(c)in the subtropical evergreen broadleaf forest,with the different environmental factors significantly contributing to the T_(c)difference in the different seasons.These results indicate that changes in the microclimate in the canopy layer appeared to exert an important effect on the canopy heat exchange of the subtropical evergreen broadleaf forest in Ailao Mountain.This study paves the way for establishing the models of forest carbon and water fluxes based on clear physiological and ecological mechanisms.