Ontogenetic changes of root and shoot respiration in trees

Abstract

Growth and adaptation of long-lived trees are supported by energy produced by whole-plant respiration. The energy is allocated to root and shoot for water and carbon acquisition, and the allocation changes during ontogeny according to body size. However, few empirical studies have investigated the respiration of root and shoot throughout ontogeny. We measured the respiration, fresh mass, and surface area of entire roots and shoots for 377 beech (Fagus crenata) trees, from germinating seeds to mature trees. On log-log coordinates, the root and shoot respiration rates versus whole-plant fresh mass were modeled by upward and downward convex trends, respectively. This was because root fraction in respiration increased during early growth stages and decreased in later stages. However, during early growth stage, increase of root fraction was more largely in surface area (max. 78.2%) than in respiration (max. 47.8%). These indicate that a rapid and low-cost increase of root surface area during early growth stage promotes shoot growth at later stages. In mature stage, declines of root growth toward an asymptote was followed by declines of shoot and whole-plant growth. Furthermore, the whole-plant respiration of beech were within the range of whole-plant respiration of seedlings to large trees of 51 species from Russia to Indonesia. This indicates that there is a general pattern in the scaling of whole-plant respiration that transcends phylogeny and environment. Here, we review the whole-plant level root-shoot relationships and explain the significance of whole-plant respiration, including roots, for understanding underlying mechanisms of tree growth.