The storage and utilization of carbohydrates in response to elevation mediated by tree organs in subtropical evergreen broad-leaved forests

Global climate change can affect tree growth and carbon sink function by influencing plant carbohydrate synthesis and utilization, while elevation can be used as an ideal setting under natural conditions to simulate climate change effects. The effect of elevation on tree growth may depend on organ type. However, the allocation patterns of nonstructural and structural carbohydrates (NSCs and SCs, respectively) in different tree organs and their response to elevation remain unclear. We selected four dominant tree species, Schima superba, Castanopsis eyrei, Castanopsis fargesii and Michelia maudiae, along an elevation gradient from 609 to 1,207 m in subtropical evergreen broad-leaved forests and analyzed leaf, trunk, and fine root NSCs, carbon (C), nitrogen (N) and phosphorus (P) concentrations and the relative abundance of SCs. Leaf NSCs increased initially and then decreased, and trunk NSCs increased with increasing elevation. However, root NSCs decreased with increasing elevation. The relative abundance of SCs in leaves and trunks decreased, while the relative abundance of root SCs increased with increasing elevation. No significant correlations between SCs and NSCs in leaves were detected, while there were negative correlations between SCs and NSCs in trunks, roots, and all organs. Hierarchical partitioning analysis indicated that plant C/N and C/P were the main predictors of changes in SCs and NSCs. Our results suggest that tree organs have divergent responses to elevation and that increasing elevation will inhibit the aboveground part growth and enhance the root growth of trees. A tradeoff between the C distribution used for growth and storage was confirmed along the elevation gradient, which is mainly manifested in the "sink" organs of NSCs. Our results provide insight into tree growth in the context of global climate change scenarios in subtropical forest ecosystems.