地形和土壤特性对亚热带常绿阔叶林内植物功能性状的影响

Effects of topographic variations and soil characteristics on plant functional traits in a subtropical evergreen broad-leaved forest

植物功能性状与环境之间的关系是功能性状研究的核心问题。为了探讨地形和土壤特性的差异对亚热带常绿阔叶林植物功能性状的影响,并找到影响古田山亚热带常绿阔叶林植物形态和生理性状的主要环境驱动因子,我们于2008年和2009年夏天在古田山国家级自然保护区内24ha大型监测样地测定了147个样方中115种常见木本植物的功能性状。所测性状包括3个生理生态性状(叶绿素含量、叶绿素荧光参数Fv/Fm和PIABS和枝条比导率)和4个形态性状(气孔密度、叶厚度、比叶面积和叶长/宽比)。结合地形数据(平均海拔、凹凸度、坡度和坡向)和土壤数据(含水量、全氮含量、全磷含量、全碳含量和pH值),分析影响这些功能性状的主要驱动因子。排序结果显示,叶绿素含量随海拔和凹凸度的上升而下降,但与土壤中的氮含量和水分含量呈现正相关关系。由于古田山土壤呈酸性,土壤磷素缺乏,叶绿素荧光参数Fv/Fm和PIABS与土壤氮、磷含量呈现显著的负相关。枝条比导率与土壤含水量具有较为显著的正相关关系。比叶面积与海拔呈现正相关关系。研究结果表明,在小尺度上,海拔和凹凸度是影响亚热带常绿阔叶林植物功能性状最关键的两个地形因子,而土壤含水量和全氮含量是影响该地植物功能性状最主要的土壤因子。然而,由于土壤中磷的缺乏,诸如植物光合作用等一些重要的生理过程受到影响,使得某些性状与环境因子之间呈现出不同寻常的相关关系。

To elucidate the driving factors behind plant functional traits, especially in mountainous areas, we explored how variation in topography and soil characteristics affects ecophysiological and morphological traits of woody plants within the Gutianshan 24-ha plot in Zhejiang Province. This site is in a typical subtropical broad-leaved forest. During the summers of 2008 and 2009, we measured three ecophysiological traits （chlorophyll content, chlorophyll fluorescence parameters Fv/Fm and PIABS, and stem sapwood xylem specific hydraulic conductivity） and four morphological traits （stomata density, specific leaf area, leaf thickness, and ratio of leaf length to leaf width） among 115 woody species in the field. Redundancy analysis was conducted to identify the most influential environmental factors from our topographical factors （mean elevation, convexity, slope, and aspect） and five soil parameters （moisture, total nitrogen content, total phosphorus content, total carbon content, and pH）. Leaf chlorophyll content was negatively correlated with elevation and convexity, but positively correlated with soil moisture and total nitrogen content. The two chlorophyll fluorescence parameters （Fv/Fm and PIABS） were strongly negatively correlated with soil total nitrogen and phosphorus content; these variables were likely interrelated with low soil pH values. Stem sapwood xylem specific hydraulic conductivity was positively correlated with soil moisture and specific leaf area was positively correlated with elevation. Topographical variables explained 10.4% of total variation in functional traits; mean elevation was the most powerful explanatory variable, followed by convexity, slope and finally, aspect. Soil parameters explained 13.9% of the total functional trait variation; and soil moisture was the most pow-erful factor, followed by total nitrogen content, pH value, total phosphorous content, total carbon content and the ratio of nitrogen and phosphorous. At this scale and at this site elevation and convexity were the two most influential topographical factors, and moisture and nitrogen were the most influential soil factors, on plant functional traits. However, because of a lack of phosphorous in the soil, some important physiological processes including photosynthesis may have been limited, thereby leading to some confusing trait/environment relationships.