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

Abstract

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 gains1–3. Eddy-covariance and tree-ring analyses have suggested a decoupling between photosynthetic carbon assimilation and growth on interannual timescales4,5, 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 (rΔcWood,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 rΔcWood,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. Using long-term observations and global vegetation models, Nguyen et al. show that the decoupling between photosynthesis and plant wood growth reported in recent studies neither implies sink limitation nor constrains long-term biomass growth.