Drought overrides CO2-driven carbon sink enhancement in Moroccan Atlas cedar forests

Increasing drought and extensive forest die-off may override the fertilization effect of rising atmospheric CO 2 (C a ), limiting the contribution of forests as carbon sinks. Tree-rings-based estimates of intrinsic water use efficiency (iWUE) have been recently improved, including the effects of diffusion through stomata and mesophyll, carboxylation and photorespiration. However, it remains unclear whether increasing iWUE is attributable to carbon gain or water shortage. We tested whether leaf g