广东南岭天然常绿阔叶林林下光环境对林下幼树功能性状的影响

光环境与幼树功能性状的关系对天然林的更新与演替具有重要的生态学意义。以广东南岭区域天然常绿阔叶林下不同林龄(幼龄林,中龄林,老龄林)的森林群落为研究对象,通过监测冠层结构、林下光照数据和林下幼树功能性状等指标,研究林龄梯度下其冠层结构与林下光环境之间的关系,以及林下幼树功能性状对光环境的响应。结果表明:(1)中龄林叶面积指数显著高于幼龄林和老龄林(P0.05),随着林龄的增长,林冠开度和透光率逐渐下降,林龄梯度下透光率、R/FR(红光/远红光比值)、Bw/Rw(宽带蓝光/宽带红光比值)差异极显著(P0.001);(2)天然常绿阔叶林中透光率与光质之间极显著相关(P0.001),R/FR随着透光率的增加而增加,Bw/Rw随着透光率的增加而减少。(3)林下幼树功能性状在光环境之间差异显著(P0.05),老龄林林下幼树叶片氮含量显著高于幼龄林,而叶片重叠率显著低于幼龄林;(4)在本试验地中,R/FR和Bw/Rw的变化对林下幼树的高径比和光合作用并无显著影响,光强对同种植物不同光环境下最大净光合速率的影响较大。总体而言,林龄梯度冠层结构和光环境的差异能在一定程度上解释幼树功能性状的差异,这将有助于我们理解光环境对林下幼树更新的影响机制,同时为天然植被恢复和森林经营提供指导。

Effects of understory light on functional traits of evergreen broad-leaved forest saplings in Nanling Mountains, Guangdong Province

The relationship between light conditions and saplings'' functional traits is of great ecological significance to the regeneration and succession of natural forests. In order to reveal the relationship between canopy structure and understory light, as well as the response of undergrowth saplings'' functional traits to the light, we investigated three natural evergreen broad-leaved forests of different ages (young forest, middle-aged forest, old-growth forest) in the Nanling Mountains of Guangdong Provinces. The results showed that: (1) The leaf area index of the middle-aged forest was significantly higher than that of the young and old-growth forests (P<0.05). Canopy openness and light transmittance gradually decreased with increasing forest age. Light transmittance, R/FR (red/far-red ratio of light) and Bw/Rw (broadband-blue/broadband-red ratio of light) of evergreen broad-leaved forests significantly differed among forest sets (P<0.001). (2) A significant correlation existed between light transmittance and light quality in natural evergreen broad-leaved forests (P<0.001). As light transmittance increased, R/FR increased while Bw/Rw decreased. (3) The functional traits of undergrowth saplings differed significantly among the different light environments (P<0.05). In the old-growth forest, leaves of undergrowth saplings had higher nitrogen content and were less overlapped than that of the young forest. (4) In the experimental plots, the changes of R/FR and Bw/Rw showed no significant effect on the height-diameter ratio and photosynthesis of understory plants, while the light intensity greatly influenced the maximum net photosynthetic rate of the same species. In general, structural differences in canopies and the light environment across the three forests can explain the variation in the functional traits of saplings to some extent, which may facilitate an understanding of the influence of light on understory sapling regeneration, and provide guidance for natural vegetation restoration and forest management.