华北落叶松冠层光合生理特性的空间异质性

【目的】森林生产力取决于树冠的整体光合能力,而树冠不同部位的光合作用具有差异性。深入了解华北落叶松冠层内光合作用的差异,为冠层水平模拟和准确估算森林生产力提供依据。【方法】采用Li-6400便携式光合仪对山西省太岳山20年生和40年生华北落叶松不同层次和不同方位的光合生理特性进行研究。【结果】20年生华北落叶松树冠中上层与下层的净光合速率(P_n)差异显著(P<0.05),而不同方位上的P_n差异不显著; 40年生华北落叶松树冠上、中、下3个层次的P_n差异显著(P<0.05),不同方位上的P_n差异也不显著。影响20年生华北落叶松树冠P_n的主要因子是羧化效率(V_c)、胞间CO₂浓度(C_i)、蒸腾速率(T_r); 影响40年生华北落叶松树冠P_n的主要因子是V_c、气孔导度(G_s)、水汽压亏缺(p_VPD)。20年生和40年生华北落叶松树冠不同层次、不同方位叶绿素a、叶绿素b和总叶绿素含量差异不显著。【结论】冠层光合空间异质性是冠层水平模拟和估算森林生产力时必须考虑的因素,这对于从单木到林分的尺度推演和模型拟合具有重要的意义。

Spatial heterogeneity of canopy photosynthesis in Larix principis-rupprechtii Mayr. Plantations

【Objective】The forest primary productivity is determined by canopy photosynthesis. There is a huge spatial heterogeneity of canopy photosynthesis.【Method】To better understand the spatial difference in photosynthesis at the canopy level, a study was conducted on the Larix principis-rupprechtii Mayr plantations with different ages(20-year-old and 40-year-old)in the Taiyue Mountain of Shanxi Province to analyze the photosynthetic characteristics by Li-6400. 【Result】The net photosynthetic rate(P_n)were significantly differences among the crown of upper layer, middle layer and under layer in the 20-year-old plantation, while there were no significant differences in P_n among the various orientations. There was the same true in the 40-year-old plantation. For 20-year-old larch, carboxylation efficiency(V_c), Intercellular CO₂ concentration(C_i), transpiration rate(T_r)were major factors influencing P_n, while for 40-year-old larch, V_c, stomatal conductance(G_s), vapor pressure deficit(p_VPD)were the main factors affecting P_n. There were no significant differences in the chlorophyll a, chlorophyll b and total chlorophyll among the various orientations and level in the 20 and 40-year-old larch. 【Conclusion】This study suggests that the spatial heterogeneity of the photosynthesis in the canopy should be considered when the forest productivity in the canopy level is simulated and estimated. It is important for the deduction from a single tree to stand and simulation.