云南文山石漠化区车桑子叶脉密度与叶氮含量关系对生境的响应

植物叶脉特征和叶氮含量的变化影响着叶片经济谱的形成,为验证叶片结构中叶脉网络构建提供了理论依据。该文以单位质量叶氮含量(N_(mass))和单位面积叶氮含量(N_(area))分别表示叶氮含量,采取主成分分析、线性回归分析的方法,研究了云南文山石漠化区旷地(Ⅰ)、林缘(Ⅱ)和林下(Ⅲ)3种自然生境下车桑子的叶脉密度(Vein density,VD)与N_(mass)和N_(area)的异速关系。结果表明:从乔灌群落的旷地到林下,车桑子的比叶面积、叶绿素总含量、光能利用率和N_(mass)逐渐增大,光饱和点、光补偿点、水分利用效率、VD、N_(area)逐渐减小,净光合速率、蒸腾速率、气孔导度呈先增大后减小的趋势。VD与叶氮含量呈不同程度的相关性,在生境I和III,VD与N_(mass)和N_(area)分别具有显著的负相关(P0.05)和正相关(P0.05);在生境Ⅱ,VD与N_(mass)和N_(area)分别呈不显著负相关(P0.05)和正相关(P0.05)。车桑子在旷地强光生境,高VD的叶片含有低N_(mass)高N_(area),而林下荫蔽生境偏向于相反的配置模式,反映了石漠化区植物较强的叶脉可塑性及其与氮利用性状的权衡机制。

Relationship between vein density and leaf nitrogen concentration of Dodonaea viscose in response to habitat changes in rocky desertification area, Wenshan, Yunnan

Changes of vein traits and leaf nitrogen concentration of plant affect the formation of leaf economic spectrum, which provides a theoretical basis for verifying the construction of leaf vein network function in leaf structure. The mass-based nitrogen content (N_mass) and area-based nitrogen content (N_area) were used as leaf nitrogen concentration in this study. Principal component analysis and linear regressions were used to determine the relationships of vein density with leaf nitrogen concentration of Dodonaea viscose in three natural habitats. The study area was located in the rocky desertification area in Dongshan Township, Wenshan City, Yunnan (23°54''N, 104°58''E). According to the light condition of forest community, D. viscosa population was divided into 3 microenvironments including open areas of forest (I), forest edge (II), and forest understory (III). We sampled 10 (10 m×10 m) D. viscose plots from each microenvironment and investigated photosynthesis of the plants and environmental factors at three gradients. Three individuals of D. viscose were selected in each plot. The leaf area, leaf dry weight, chlorophyll content, vein density (VD), N_mass and N_area of 12 healthy leaves from 4 directions in each individual were measured at laboratory. The results indicated that specific leaf area, total chlorophyll content, light use efficiency, and N_mass of D. viscosa increased gradually along the gradient from I to III in arbor-shrub community, while the light saturation point, light compensation point, water use efficiency, VD, and N_area decreased gradually. The net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance, and photosynthetic nitrogen use efficiency increased firstly and then decreased. There were varying correlations between VD and leaf nitrogen content. VD was significantly negatively correlated with N_mass (P<0.05), but had a significantly positive correlation with N_area in I and III (P<0.05). The correlation was not significant between VD both N_mass and N_area in II (P>0.05). In the open areas of forest habitats, which were characterized by strong light intensity, D. viscosa had a higher VD, N_area and lower N_mass than those growing on forest edge and forest understory habitats. While the opposite patterns were seen in the shady habitats, reflecting the strong leaf vein plasticity of plants in rocky desertification areas and its balance mechanism with nitrogen utilization traits.