浙江天童太白山不同群落植物构型比较

植物构型是植株构件在空间上的分配方式,反映了植物对环境的响应策略。通过对浙江天童太白山海拔差异很小的栲树(Castanopsis fargesii)、小叶青冈(Cyclobalanopsis gracilis)和云山青冈(Cyclobalanopsis sessilifolia)群落类型中所有植株的树高、树冠厚度、树冠面积、叶片聚集度、枝下高和距地45 cm基径等植物构型性状,以及树冠曝光指数、土壤含水率、空气温湿度、土壤p H值和风速6个环境因子的测定,分别分析乔灌木层植物构型性状及性状关系在3个群落间的变化规律。结果表明:(1)从栲树到小叶青冈至云山青冈群落,灌木层的树高、树冠厚度、枝下高和距地45 cm基径增加,叶片聚集度减小;乔木层的树高、树冠厚度、树冠面积、枝下高和距地45 cm基径均减小,叶片聚集度增大;(2)3个群落灌木层构型性状间显著相关(P0.001),而乔木层只在中低海拔群落存在相关性;(3)从栲树到小叶青冈至云山青冈群落,乔灌木层的冠层曝光指数显著增加(P0.05);(4)多元逐步回归表明,树冠曝光指数对灌木层构型性状变异的贡献最大,而风速、土壤含水率和p H值对乔木构型性状的变异起主导作用。综上得知,天童太白山乔灌木植物在不同群落间存在构型分异,植物对光资源的竞争是引起灌木构型在不同群落间变化的主要驱动因子,而对乔木植物,其构型变化更多受到风速和土壤含水量的影响。

Comparison of plant architecture among communities in taibai mountain of tiantong region, Zhejiang Province

Plant architecture, reflecting ecologically adaptive strategy of plants in response to changing environment, refers to the overall shape and size of the wood plants and the spatial arrangement of its components such as crowns, stems, branches and leaves. For mechanical and hydraulic reasons, architecture of a plant can greatly affect whole-plant function such as photosynthesis, transpiration and energy balance. As one of the leading dimensions in shaping plant function, plant architecture is also fundamental to influence species demographics, and consequently species coexistence. Therefore, variation in plant architecture among communities that differ in site properties is considered to indicate relationship between plant architecture and environmental stress. Linking spatial pattern of plant architecture with changes in altitude is important for understanding plant adaptive strategies in relation to biomass allocation. However, little is currently understood whether plant architectural traits correlate to the site properties with changing altitude in the evergreen broad-leaved forests. In this study, our objectives were to elucidate variation in plant architectural traits among communities, and to explain the mechanical relationships between plant architectural traits and environmental conditions. Specifically, three community types, i.e., Castanopsis fargesii community, Cyclobalanopsis gracilis community and Cyclobalanopsis sessilifolia community, differing in altitude, were selected in Taibai Mountain in Tiantong region, Zhejiang Province, to examine plant architectural traits including tree height, crown depth and area, leaf convergence, the lowest branch height (LBH) and basal diameter at the 45 cm aboveground (D₄₅). In addition, crown exposure index, soil moisture content, air humidity, air temperature, soil pH, and windy velocity in each of three communities were determined. Then variation in architectural traits for plants in each of tree and shrub layers among communities, and their relationships with environmental factors were analysized. The results shown that, for plants in shrub layer, plant height, crown depth, the lowest branch height and basal diameter at the 45 cm aboveground increased, but proportion of leaf convergence decreased gradually from Castanopsis fargesii to Cyclobalanopsis sessilifolia community with increasing altitude. However, for plants in tree layer, tree height, crown depth, crown area, LBH and D₄₅ decreased, while leaf convergence increased. Significant correlations among architectural traits (P<0.01) was found in three altitudinal communities for plants in shrub layer, but for plants in tree layer, architectural traits correlated significantly in the lowest and intermediate altitudinal communities only. Crown exposure index in both shrub and tree layers increased significantly from Castanopsis fargesii to Cyclobalanopsis sessilifolia community with increasing elevation (P < 0.05). Multiple stepwise regression demonstrated that, for plants in the shrub layer, crown exposure index was mainly responsible for variation in plant architecture, whereas, soil moisture content, wind velocity, and soil pH were the determinant factors influencing plant architecture for plants in the tree layer. In conclusion, plant architectural traits vary differently with community change for plants in each of shrub and tree layers in Taibai Mountain in Tiantong region. Variability of plant architecture in shrub layer results largely from light competition, while plant architecture in tree layer was driven by wind velocity and soil moisture content.