季节性干旱对中亚热带人工林显热和潜热通量日变化的影响

The diurnal trends of sensible and latent heat fluxes of a subtropical evergreen coniferous plantation subjected to seasonal drought

植被与大气间的显热和潜热通量的日变化是大气过程和植被生理过程的显著标志。本研究利用ChinaFLUX千烟洲站典型的夏季雨热不同季的季节性干旱的试验条件,探讨了2003年季节性干旱对该生态系统显热和潜热通量日变化变异幅度和峰值时间的影响。研究表明:显热通量的日变化变异幅度年平均值为176 W/m2。潜热通量的日变化变异幅度年平均值为171W/m2。显热通量到达日变化峰值的时间平均为11∶57。全年潜热通量的日变化都在午后达到峰值,平均值为12:33。季节性干旱造成显热通量的日变异幅度明显增大,从144W/m2增加到321 W/m2。而潜热通量的日变异幅度明显降低,从324 W/m2减小到198 W/m2。,显热和潜热通量日变异幅度的相对变化明显增大,从-165 W/m2增加到76 W/m2,气温和饱和水汽压差是影响显热和显热日变异幅度及其相对变化的主要控制因素。干旱胁迫期,深层水对显热通量日变化变异幅度及其与潜热通量日变化变异幅度的相对变化的作用更显著,而潜热通量日变化变异幅度与气象要素关系不显著。季节性干旱造成显热通量日变化的峰值时间和显热和潜热通量日变化峰值时间的相对变化明显向下午偏移,显热通量日变化的峰值从11:31到12:17,相对变化从1小时到1小时20分钟。季节性干旱对潜热通量日变化峰值时间没有显著的影响。非干旱胁迫期,显热通量日变化峰值时间和显热及潜热通量日变化峰值时间的相对变化均与气温负相关,而干旱胁迫期,则与气温正相关。潜热通量日变化峰值时间与气象要素关系均不显著。该生态系统显热和潜热通量日变化峰值的相对变化主要受降水量的季节分配控制,在干旱胁迫期降水的作用更加明显。潜热和显热通量日变化峰值时间的相对变化总体上都受植被与大气间的耦合程度控制。

Evidence of global climate change is well-documented, with long-term increases observed in average global surface temperature, the atmosphere＇s carbon dioxide （CO2） concentration, precipitation, and runoff. SPAC system is the strongest active layer in surface energy and mass exchanges. The diurnal trends of sensible and latent heat fluxes are signatures of atmospheric and physiological processes that control biophysical fluxes at the surface. The diurnal trends of sensible and latent heat fluxes depends on temporally evolving interactions between atmospheric demand, the net radiation, temperature, and atmospheric vapor pressure deficit, and the ability of the vegetation to supply available water. Droucht canchange the diurnal trends and the energy partitioning between sensible and latent heat fluxes. And that may affect the surface energy and water exchanges cycle. Continuous measurements of the influence on diurnal variation range and diurnal centroids for sensible and latent heat fluxes during seasonal drought were recorded at Qianyanzhou in 2003. The mean diurnal variation of sensible heat flux was 176 W/m^2 and that of latent heat flux was 171 W/m^2. The mean diurnal centroid for sensible heat flux was 11：57 and that of latent heat flux was 12：33. Seasonal drought led to increases in the mean diurnal variation range of sensible heat flux from 144 W/m^2 to 321 W/m^2, whereas the mean diurnal variation range of latent heat flux decreased from 324 W/m^2 to 198 W/m^2. The relative change between sensible heat flux and latent heat flux increased from -165 W/m^2 to 76 W/m^2. Temperature and water vapor pressure deficit were the major factors controlling the diurnal variation range of sensible heat flux and relative change between sensible heat flux and latent heat flux. During seasonal drought, the change in deep water content had a more significant effect on the diurnal variation range of sensible heat flux and relative change between sensible heat flux and latent heat flux, whereas the diurnal variation range of latent heat flux showed no relationship with meteorological factors. Seasonal drought weighted the diurnal centroid for sensible heat flux toward the afternoon, from 11：31 to 12： 17. The relative change between sensible heat and latent heat flux changed from I h to 80 min. Seasonal drought had no impact on the diurnal centroid for latent heat flux. During the non-drought period, the diurnal centroid for sensible heat flux and relative change between sensible heat flux and latent heat were negatively correlated with air temperature, and positively correlated with air temperature during seasonal drought. Meteorological factors had no impact on the diurnal centroid for latent heat flux. The seasonal distribution of precipitation dominated the relative change between the diurnal centroids for sensible heat flux and latent heat flux. Precipitation may be more important during seasonal drought. It is suggested that relative change between the diurnal centroids for sensible heat and latent heat flux might be subject to the coupling between vegetation and the atmosphere. From this study, it was clear that these environmental variables, especially air temperature and water condictions regulated the diurnal trends of sensible and latent heat fluxes over the planted coniferous ecosystem.