Temporal decoupling between photosynthetic carbon assimilation and wood formation in a temperate forest: implications for source–sink dynamics

Quantifying temporal lags between photosynthesis and wood formation is essential for predicting forest carbon allocation under climate change, yet their magnitude and drivers remain poorly resolved across coexisting species. Here, we combined 4 yr of weekly microcore observations of wood formation with modeled daily photosynthetic production for 12 dominant tree species in a mixed broadleaf-Korean pine forest in Northeast China. Cross-correlation analysis was used to quantify the temporal lags between wood formation and photosynthesis at both species and stand levels. Wood formation lagged behind photosynthetic production by 6-30 d across species, with a stand-level average lag of 23 d. Linear mixed-effects models identified temperature, light, and water availability as the main environmental drivers of lag duration, with water-related conditions playing a particularly prominent role. Functional-trait analysis further showed that phenological sequence (growth-first vs leaf-first) significantly explained species-stand lag divergence, whereas specific leaf area, wood density, and leaf C : N, representing carbon acquisition, xylem construction cost, and photosynthetic nutrient investment, were not significant predictors. These findings indicate that temporal decoupling between photosynthetic production and wood formation is regulated by environmental conditions and species-specific phenological strategies. Incorporating time lags and functional diversity into ecosystem models may improve projections of forest carbon allocation under future climate scenarios.