PNNL

Abstract

Non-structural carbohydrate (NSCs) stores buffer tree metabolism, osmotic regulation, and defense, thereby mediating tolerance and survival under climate extremes. Yet the functional and evolutionary determinants of interspecific variation in NSCs remain elusive, limiting forecasts of forest carbon allocation and mortality under global change. Here, we compiled a cross-species synthesis of NSCs concentrations across 281 woody species from 103 mixed forest communities worldwide, and quantified species-specific deviations from community means to disentangle intrinsic trait effects from environmental variation. We show that coniferous gymnosperms consistently maintained lower NSCs concentrations than coexisting angiosperms, whereas leaf habit, mycorrhizal type, and nitrogen acquisition strategy had negligible effects. Across species, stomatal sensitivity to water stress showed pervasive negative relationship with both soluble sugar and starch concentrations, suggesting anisohydric species have more NSCs, which linked stomatal regulation directly to carbon storage. Yet soluble sugars and starch displayed contrasting associations with gas exchange and structural traits, soluble sugars increased with photosynthetic capacity and declined with wood density, while starch showed the reverse pattern, revealing two coordinated but functionally distinct carbon storage axes. By integrating trait-based ecology with a community-centered framework, our study provides the first global, mechanistic evidence that stomatal regulation, carbon economics, and wood structure, rather than hydraulics, jointly, but differentially, govern interspecific carbohydrate reserves, offering a predictive foundation for modeling forest carbon allocation and resilience under climate change.