中文摘要：

植物温度是森林生态系统能量平衡和植被呼吸估算的重要参数.采用T型热电偶监测树皮和木材特性各异的2个阔叶树种（白桦和水曲柳）不同深度、高度和方位的树干温度（Ts）,探索Ts日变化的空间变异及其影响因素.结果表明：Ts月平均日变化格局与空气温度呈相似的正弦曲线,但Ts变化滞后于空气温度,时滞从树皮表面处的0 h增加到6 cm深度处的4 h.随测定深度的增加和高度的降低,Ts日变化的峰值和日较差均逐渐减小.Ts周向差异不大,休眠季节白天南向、西向Ts日峰值略高.两树种树皮和木材的热学特性（比热容和导热系数）的差异,会通过影响树干表面与外界的热交换和树干内部热扩散而造成Ts径向变化的种间差异.白桦树皮较高的反射率削弱了太阳辐射对Ts的影响.多元逐步回归分析表明,环境因子可以很好地估测Ts日动态（R^2〉0.85）,影响程度依次为空气温度〉水汽压〉净辐射〉风速.估算生物量热储和树干表面CO2通量时应考虑Ts径向、纵向和种间差异.

英文摘要：

Plant temperature is an important parameter for estimating energy balance and vegetation respiration of forest ecosystem. To examine spatial variation in diurnal courses of stem temperatures（ Ts） and its influencing factors,we measured the Ts with copper-constantan thermocouples at different depths,heights and azimuths within the stems of two broadleaved tree species with contrasting bark and wood properties,Betula platyphylla and Fraxinus mandshurica. The results showed that the monthly mean diurnal courses of the Ts largely followed that of air temperature with a ‘sinusoidal＇pattern,but the Ts lagged behind the air temperature by 0 h at the stem surface to 4 h at 6 cm depth. The daily maximal values and ranges of the diurnal course of Ts decreased gradually with increasing measuring depth across the stem and decreasing measuring height along the stem. The circumferential variation in Ts was marginal,with slightly higher daily maximal values in the south and west directions during the daytime of the dormant season. Differences in thermal properties（ i. e.,specific heat capacity and thermal conductivity） of both bark and wood tissue between the two species contributed to the inter-specific variations in the radial variation in Ts through influencing the heat exchange between the stem surface and ambient air as well as heat diffusion within the stem.The higher reflectance of the bark of B. platyphylla decreased the influence of solar radiation on Ts.The stepwise regression showed that the diurnal courses of Ts could be well predicted by the environmental factors（ R^2〉 0.85） with an order of influence ranking as air temperature〉 water vapor pressure〉 net radiation 〉wind speed. It is necessary to take the radial,vertical and inter-specific variations in Ts into account when estimating biomass heat storage and stem CO2 efflux.