天然林中不同径级新疆野苹果的光合能力

研究新疆天山野果林建群种新疆野苹果（Malus sieversii）光合生理特性，对于该种群保育及其生态功能评价具有重要意义。通过野外测定新疆新源天然野果林中不同径级64株新疆野苹果南向枝条上部叶和下部叶饱和光强下的净光合速率（A）、气孔导度（g_s）和比叶面积（SLA）。结果表明：随着径级增加，上部叶和下部叶的A_area、A_mass显著增加。g_s随径级的增加先增加再降低，在径级Ⅲ（树干0.5 m高处直径25~35 cm）时达最大。上部叶比下部叶有着高的A_area、A_mass和g_s。回归分析表明：随着树干直径增加，A_area和g_s呈二次多项式增加，A_mass呈线性增加。SLA随径级增加变化不显著，上部叶SLA显著低于下部叶。上部叶的A_area高于下部叶，但由于SLA显著减小，在A_mass上两者差异减小。随g_s增加，上部叶Aarea呈幂函数增加，下部叶A_area呈二次多项式增加。 

Photosynthetic Capacity of Malus sieversii Trees in Natural Forest

Photosynthesis is a basic eco-physiological process for the functioning of ecosystems. Malus sieversii(Ledeb.) Roem. is the most important dominant species in the wild fruit forest on the northern slope of the Tianshan Mountains in northwest China. M. sieversi population has been declining rapidly due to more and more intensive anthropogenic disturbances. Research on the photosynthetic characteristics of M. sieversii of different size classes is critical to understand the functions of its dominated ecosystems and to take proper measures to conserve this endangered species. Net assimilation rate (A), stomotal conductance (g_s)and specific leaf area (SLA) of sun-facing M. sieversii leaves at upper and lower parts of 64 adult trees were measured in a natural wild fruit forest in Xinyuan County on the northern slope of the Tianshan Mountains in Xinjiang, northwest China. The results showed that there was a significant effect of stem diameter class on photosynthetic characteristics of M. sieversii. Both A_area and A_mass were increased with the increase of diameter class, whereas g_s was increased at first and then decreased, and the maximum values appeared at the main stem diameter of 25-35 cm at 0.5 m height. There was a significant effect of leaf position on photosynthetic characteristics. A_area, A_mass and g_s of the leaves on the upper part of branches were significantly higher than those on the lower part. The results of regression analysis revealed that A_area and g_s were increased in a quadratic polynomial way with the increase of stem diameter, whereas Amass was increased in a linear relation. With the increase of diameter class, the change of SLA was not significant. There was a significant effect of leaf position on SLA. SLA of the leaves on the upper part of crown was significantly lower than that on lower part, and the differences of A_mass between the leaves on the upper and lower parts was low. A_area of the leaves on both upper and lower parts was increased with the increase of g_s, but the regression equations were different. A_area of upper leaves was increased in a power function with the increase of g_s, where as A_area of lower leaves was increased in a quadratic polynomial way with the increase of g_s.