Forest Ecosystem Research and Observation Station in Putuo Island, Tiantong National Station for Forest Ecosystem Research, and Shanghai Key Lab for Urban Ecological Processes and Eco-Restoration; School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200241, China.
Institute of Eco-Chongming (IEC), Shanghai, 200062, China.
Am J Bot. 2018 Jul;105(7):1165-1174. doi: 10.1002/ajb2.1132. Epub 2018 Aug 2.
The plant size-trait relationship is a fundamental dimension in the spectrum of plant form and function. However, it remains unclear whether the trait scaling relationship within species is modified by tree size. Investigating size-dependent trait covariations within species is crucial for understanding the ontogenetic constraints on the intraspecific economic spectrum and, more broadly, the structure and causes of intraspecific trait variations.
We measured eight morphological, stoichiometric, and hydraulic traits for 604 individual plants of a shade-tolerant evergreen tree species, Litsea elongata, in a subtropical evergreen forest of eastern China. Individual trait values were regressed against tree basal diameter to evaluate size-dependent trait variations. Standardized major axis regression was employed to examine trait scaling relationships and to test whether there was a common slope and elevation in the trait scaling relationship across size classes.
Small trees tended to have larger, thinner leaves and longer, slenderer stems than larger trees, which indicates an acquisitive economic strategy in juvenile trees. Leaf nitrogen concentrations increased with plant size, which was likely due to a high ratio of structural to photosynthetic nitrogen in the evergreen leaves of large trees. Bivariate trait scaling was minimally modified by tree size, although the elevation of some relationships differed between size classes.
Our results suggest that there are common economic and biophysical constraints on intraspecific trait covariation, independent of tree size. Small and large trees tend to be located at opposite ends of an intraspecific plant economic spectrum.
植物大小-性状关系是植物形态和功能谱中的一个基本维度。然而，目前尚不清楚物种内的性状缩放关系是否会受到树体大小的影响。研究物种内的大小依赖性状协变对于理解种内经济谱的个体发育限制以及更广泛的种内性状变异的结构和原因至关重要。
我们在中国东部的一个亚热带常绿森林中测量了 604 株耐荫常绿树种 Litsea elongata 的 8 种形态、化学计量和水力性状。个体性状值与树基直径回归，以评估大小依赖性状变化。采用标准化主轴回归检验性状缩放关系，并检验在不同大小类中是否存在共同斜率和高度的性状缩放关系。
小树的叶子比大树的叶子更大、更薄，茎更长、更细，这表明幼树具有获取性经济策略。叶片氮浓度随植物大小增加，这可能是由于大树常绿叶片中结构氮与光合氮的比例较高所致。尽管某些关系的高度在大小类之间存在差异，但双变量性状缩放受树体大小的影响最小。
我们的结果表明，种内性状协变存在共同的经济和生物物理限制，与树体大小无关。小树和大树往往处于种内植物经济谱的相对两端。
