Scaling of leaf area with biomass in trees reconsidered: Constant metabolically active sapwood volume per unit leaf area with height growth

Hypoallometric (slope&lt;1) scaling between metabolic rate and body mass is often regarded as near-universal across organisms. However, there are compelling reasons to question hypoallometric scaling in woody plants, where metabolic rate=leaf area. This leaf area must provide carbon to the metabolically active sapwood volume (VMASW). Within populations of a species, variants in which VMASW increases per unit leaf area with height growth (e.g. ⅔ or ¾ scaling) would have proportionally less carbon for growth and reproduction as they grow taller. Therefore, selection should favor individuals in which, as they grow taller, leaf area scales isometrically with shoot VMASW (slope=1). Using tetrazolium staining, we measured total VMASW and total leaf area (LAtot) across 22 individuals of Ricinus communis and confirmed that leaf area scales isometrically with VMASW, and that VMASW is much smaller than total sapwood volume. With the potential of the LAtot-VMASW relationship to shape factors as di..., , , # Scaling of leaf area with biomass in trees reconsidered: constant metabolically active sapwood volume per unit leaf area with height growth A brief summary of dataset contents, in the context of the methodology followed, is given below. * We tested leaf area-metabolically active sapwood volume relationship in *Ricinus communis* L.(Euphorbiaceae). We used the tetrazolium test to estimate volume of metabolically active sapwood volume. We cut each individual into segments 30 or 50 cm long (50 cm for plants above 2 m tall), and we measured the length, basal diameter, and apical diameter of each segment. 2 cm thick discs from each segment were placed into a solution of 2,3,5-triphenyl-2H- tetrazolium chloride (TTC), see Material and Methods for details of protocol. The TTC stain identifies the regions of metabolically active xylem and colours them red. * Estimating metabolically active sapwood area and volume - ImageJ 1.52a (Schneider et al., 2012) was used to calculate the total are...代谢速率与体重间的低异速生长（hypoallometric，斜率<1）缩放关系，通常被认为在各类生物中近乎普遍存在。然而，有充分理由对木本植物中的低异速生长缩放关系提出质疑——此类植物的代谢速率等同于叶面积，而该叶面积必须为代谢活性边材体积（metabolically active sapwood volume, VMASW）提供碳素。在同一物种种群内，随着植株长高，单位叶面积的VMASW升高的变异体（例如遵循2/3或3/4缩放关系），在长高过程中可用于生长和繁殖的碳素比例会相应降低。因此，自然选择应青睐那些随着植株长高，叶面积与枝条VMASW呈等速缩放（斜率=1）的个体。本研究采用四唑染色法（tetrazolium staining），对22株蓖麻（Ricinus communis）个体的总VMASW与总叶面积（total leaf area, LAtot）进行了测定，证实叶面积与VMASW呈等速缩放关系，且VMASW远小于总边材体积。鉴于LAtot-VMASW关系可能对诸多因子产生塑造作用…… # 重新审视树木叶面积与生物量的缩放关系：植株长高过程中单位叶面积的代谢活性边材体积恒定 下文结合所采用的研究方法，对数据集内容进行简要概述： * 本研究以大戟科蓖麻（*Ricinus communis* L.）为对象，验证了叶面积与代谢活性边材体积间的关联。采用四唑试验估算代谢活性边材体积：将每株植株切割为30或50 cm长的分段（株高超过2 m的植株采用50 cm分段），测量每段的长度、基径与顶径；截取每段的2 cm厚木片，浸泡于2,3,5-三苯基-2H-氯化四唑（2,3,5-triphenyl-2H-tetrazolium chloride, TTC）溶液中，具体实验流程详见材料与方法部分。TTC染色可识别代谢活性木质部区域并将其染为红色。 * 代谢活性边材面积与体积的估算——采用ImageJ 1.52a（Schneider等，2012）软件计算总面……