Lusk C H, Reich P B
Departamento de Botánica, Universidad de Concepción, Casilla 160-C, Concepción, Chile, (e-mail:
Department of Forest Resources, University of Minnesota, St. Paul, MN 55108, USA, , , , , , US.
Oecologia. 2000 May;123(3):318-329. doi: 10.1007/s004420051018.
It has been argued that plants adapted to low light should have lower carbon losses via dark respiration (Rd) than those not so adapted, and similarly, all species would be expected to down-regulate Rd in deep shade, because the associated advantages of high metabolic potential cannot be realized in such habitats. In order to test these hypotheses, and to explore the determinants of intraspecific variation in respiration rates, we measured Rd, leaf mass per unit area (LMA), and nitrogen content of mature foliage in juveniles of 11 cold-temperate tree species (angiosperms and conifers), growing in diverse light environments in forest understories in northern Minnesota. Among the seven angiosperm species, respiration on mass, area, and nitrogen bases showed significant negative overall relationships with shade tolerance level. Mass-based respiration rates (Rd ) of angiosperms as a group showed a significant positive overall relationship with an index of light availability (percentage canopy openness, %CO). Rd of most conifers also showed evidence of acclimation of Rd to light availability. LMA of all species also increased with increasing %CO, but this response was generally much stronger in angiosperms than in conifers. As a result, the response of area-based respiration (Rd ) to %CO was dominated by ΔRd for conifers, and by ΔLMA for most angiosperms, i.e., functional types differed in the components of acclimation of Rd to light availability. Among the seven angiosperm species, the relationships of leaf N on a mass basis (N ) with %CO were modulated by shade tolerance: negative slopes in shade-tolerant species may be related to the steep increases in LMA of these taxa along gradients of increasing light intensity, and associated dilution of N-rich, metabolically active tissue by increasing investment in leaf structural components. Although N was therefore an unreliable predictor of variation in Rd along light gradients, respiration per unit leaf N (Rd/N) was significantly positively correlated with %CO for most species. This probably reflects variation in the proportion of leaf N allocated to protein and/or the influence of leaf carbohydrate status on Rd. Species shade tolerance differences were not significantly correlated with the magnitude of either ΔRd or ΔRd , indicating that variation in acclimation potential of Rd is much less important than inherent differences in this trait. Acclimation of Rd to light availability appears to be a generalized feature of juvenile trees, and the important ecological trade-off is likely between high metabolic capacity in high light and low respiratory losses in low light.
有人认为，适应弱光环境的植物通过暗呼吸（Rd）损失的碳应该比未适应的植物少，同样，所有物种在深层阴影中都有望下调Rd，因为在这种栖息地无法实现高代谢潜力的相关优势。为了验证这些假设，并探究呼吸速率种内变异的决定因素，我们测量了明尼苏达州北部森林林下不同光照环境中生长的11种寒温带树种（被子植物和针叶树）幼树的Rd、单位面积叶质量（LMA）和成熟叶片的氮含量。在七种被子植物中，基于质量、面积和氮的呼吸与耐荫性水平呈现出显著的负相关关系。作为一个群体，被子植物基于质量的呼吸速率（Rd）与光照可利用指数（树冠开放度百分比，%CO）呈现出显著的正相关关系。大多数针叶树的Rd也显示出对光照可利用性的适应性证据。所有物种的LMA也随着%CO的增加而增加，但这种响应在被子植物中通常比在针叶树中要强得多。因此，基于面积的呼吸（Rd）对%CO的响应在针叶树中以ΔRd为主，而在大多数被子植物中以ΔLMA为主，即功能类型在Rd对光照可利用性的适应性组成部分上存在差异。在七种被子植物中，基于质量的叶片氮含量（N）与%CO的关系受耐荫性调节：耐荫物种的负斜率可能与这些类群沿着光照强度增加梯度的LMA急剧增加有关，以及随着对叶片结构成分投资的增加，富含氮的、代谢活跃的组织被稀释。因此，尽管N不是沿光照梯度Rd变异的可靠预测指标，但大多数物种单位叶氮呼吸（Rd/N）与%CO显著正相关。这可能反映了分配给蛋白质的叶片氮比例的变化和/或叶片碳水化合物状态对Rd的影响。物种耐荫性差异与ΔRd或ΔRd的大小均无显著相关性，这表明Rd适应潜力的变异在该性状中比固有差异的重要性要小得多。Rd对光照可利用性的适应似乎是幼树的一个普遍特征，重要的生态权衡可能存在于强光下的高代谢能力和弱光下的低呼吸损失之间。
