Data and code for "Precipitation-driven carbon lability limits land carbon uptake by reducing fixation"

The land carbon sink predominantly reflects the balance between carbon fixed by plants and carbon released by respiration. The plant share of this balance is relatively well constrained by climate, but the carbon respired to the atmosphere by decomposers remains highly uncertain, constituting a major challenge for global carbon-cycle projections. Here we integrate carbon-flux measurements and decomposition-rate records from 262 sites worldwide to quantify ecosystem-scale carbon lability – the ratio of decomposer to plant carbon fluxes – and test whether it constrains the land carbon sink via stronger limitation on plants than decomposers. As expected, ecosystems with higher carbon lability exhibit significantly lower carbon fixation per unit standing biomass, while ecosystem respiration per unit biomass remains largely unaffected. Furthermore, precipitation emerges as the dominant driver of carbon lability globally, determining the sign of warming effects on the land carbon sink: rising temperatures increase carbon lability and weaken carbon sinks in wet regions, but have the opposite effects in dry regions. Notably, precipitation-driven carbon lability may outperform temperature in explaining variation in net ecosystem carbon uptake. These findings suggest that current models may overestimate the land carbon sink in regions where decomposer’s respiration is underestimated, such as the humid tropics.