Recent field findings and modeling on non-structural carbohydrates (NSCs): How to synthesize?

With growing interest in tree decline and die-back events due to increased climate variability, ecophysiological roles and dynamics of non-structural carbohydrates (NSCs) have drawn wide attention recently. Accordingly, a lot of field data have been collected, but these achievements were not well incorporated in process-based vegetation models yet, where NSCs ecophysiology was implicitly applied or ignored. This review tried to fill the knowledge gap between recent developments of empirical and modeling studies on NSCs ecophysiology. We summarized the characteristics and dynamics of NSCs with their respective roles in tree physiology and tree mortality recently found in field studies; examined how these findings have been incorporated into vegetation models so far; then, provided alternative modeling approaches of NSCs dynamics and allocation strategies. As result, we addressed five key modeling issues in simulating spatial and temporal patterns of NSCs dynamics across different scales as follows: (1) interconversion between dual NSCs pools (i.e., rapid soluble sugar and slow starch pools), (2) incorporation of the sink-limited growth allocation strategy, (3) hydraulic limitation of NSCs transports between organs, (4) feedback mechanisms between tree NSCs and root symbionts, and (5) large-scale simulations of NSCs dynamics. This review emphasizes the limitation of traditional source-limited models to simulate die-back and recovery of various tree biomes. The development of process-based vegetation models considering NSCs ecophysiology explicitly will help to enhance our modeling capacity to understand vegetation responses to climate change.