Long-term biomass growth unimpeded by short-term photosynthetic decoupling

Plant carbon uptake depends on the balance between carbon sources (for example, photosynthesis) and sinks (for example, respiration, storage and growth), which together determine how much CO₂ uptake translates into lasting biomass gains^1-3. Eddy-covariance and tree-ring analyses have suggested a decoupling between photosynthetic carbon assimilation and growth on interannual timescales^4,5, often interpreted as evidence for widespread sink limitation⁵. Using long-term observations at flux towers and a global vegetation model ensemble, we show that such annual, or short-term, decoupling neither implies sink limitation nor constrains long-term growth. Across observations and more than half of the ensemble models, short-term correlations between photosynthesis and woody carbon biomass increment (r_ΔcWood,GPP) are weak, confirming previously reported decoupling. Despite the weak correlations, however, woody carbon biomass increased in proportion to photosynthesis between 1951 and 2020. Notably, there is no relationship between r_ΔcWood,GPP and the long-term sensitivity of biomass to photosynthesis across models. These results caution against inferring source-sink control from observational records and suggest that sink limitation is probably less prevalent than previously reported.