南亚热带针阔混交林土壤热通量研究

Soil heat fluxes of mixed coniferous and broad-leaf forest in the south subtropics in China

运用土壤热通量板、常规微气象观测系统等设施对鼎湖山针阔混交林的土壤热通量和微气象因子进行了系统研究,结果表明,不同热通量板测值之间的差异可达10%以上.在中小时间尺度(≤1月)上,土壤热通量板上方土壤贮热均不能忽略,否则所测算的表层土壤热通量会产生较大误差,甚至发生热通量传递方向逆转的情况.5 cm深度处和表层土壤热通量的日变化均呈'S'形,且前者相位后移0.5～1 h.旱季土壤为热源而雨季为热汇,表层土壤年总热通量为-0.44 MJ·m-2,说明就全年尺度而言,土壤是热源.表层土壤热贮量月变动范围为-0.14～0.20 MJ·m-2,是5 cm深度处土壤热通量的-11.0%～1.3%.表层土壤热通量月总值占净辐射的比例变动范围为-12.0%～3.3%,由于能量平衡大多在较小时间尺度上进行比较,故必须准确考察土壤热通量的变化,否则会极大地影响能量平衡.在0.5 h尺度上,表层土壤热通量与2.5 h前的冠层净辐射回归方程相关性最好,达极显著水平,说明鼎湖山针阔混交林土壤热通量对冠层净辐射的反馈要延滞约2.5 h.

Soil heat fluxes and meteorology of a mixed conifer and broad leaf forest in Dinghushan, Southern China were monitored by soil heat flux plates (SHFP) and a meteorological monitoring system, respectively. The results showed that measurement discrep-ancy of soil heat flux by different SHFP might be more than 10%. If the soil heat storage above the SHFP was neglected, especially in middle and short temporal scales(≤1 month), the surface soil heat flux data would be inaccurate, and the direction of heat transfer might reverse sometimes. The diurnal changes of both soil heat fluxes at the surface and at the 5cm depth had an “S” shape. The fluctuation of soil heat flux at the 5 cm depth lagged about 0.5 h to 1 h than that of the surface. In dry seasons, the soil was a heat source, however, it was a heat sink in rainy seasons. The total surface soil heat flux was -0.44 MJ·m-2 per year, indicating that the soil was a heat source at the annual temporal scale. The monthly changes of heat storage of the surface soil above the SHFP ranged from -0.14 MJ·m-2 to 0.20 MJ·m-2, about -11.0% to 1.3% of that at the 5cm depth. The proportion of monthly surface soil heat flux to net radiation above the canopy ranged from -12.0% to 3.3%. Since most studies on the energy balance were carried out in a short tempo-ral time scale, it is important to measure or calculate the short-term soil heat flux as well. Significant correlations between the surface soil heat flux and net radiation above the canopy measured 2.5 h earlier were found, suggesting that response of the soil heat flux to the net radiation above the canopy could lag 2.5 h.