Ontogenetic changes in root and shoot respiration, fresh mass, and surface area of Fagus crenata

Abstract

BACKGROUND AND AIMS: To date, studies on terrestrial plant ecology and evolution have primarily focused on the trade-off patterns in the allocation of metabolic production to roots and shoots in individual plants and the scaling of whole-plant respiration. However, few empirical studies have investigated the root:shoot ratio by considering scaling whole-plant respiration at various sizes throughout ontogeny. METHODS: Here, using a whole-plant chamber system, we measured the respiration rates, fresh mass, and surface area of entire roots and shoots from 377 Fagus crenata individuals, from germinating seeds to mature trees, collected from five different Japanese provenances. Nonlinear regression analysis was performed for scaling of root and shoot respiration, fresh mass, and surface area with body size. KEY RESULTS: Whole-plant respiration increased rapidly in germinating seeds. In the seedling to mature tree size range, the scaling of whole-plant respiration to whole-plant fresh mass was expressed as a linear trend on the log-log coordinates (exponent slightly larger than 0.75). In the same body size range, root and shoot respiration versus whole-plant fresh mass were modelled by upward convex (exponent decreased from 2.35 to 0.638) and downward convex trends (exponent increased from -0.918 to 0.864), respectively. The root fraction in the whole-plant respiration, fresh mass, and surface area continuously shifted throughout ontogeny, increasing in smaller seedlings during early growth stages and decreasing in larger trees. CONCLUSIONS: Our results suggest a gradual shift in allocation priorities of metabolic energy from root in seedlings to shoot in mature trees, providing insights into how roots contribute to shoot and whole-plant growth during ontogeny. The models of root:shoot ratio in relation to whole-plant physiology could be applied in tree growth modelling, and in linking the different levels of ecological phenomena, from individuals to ecosystems.