Hydraulic strategy drives Amazon forest modelled response to drought

Plant hydraulics are crucial to understand impacts of droughts on single plants and whole forest ecosystems. The complex interplay of hydraulic mechanisms still poses challenges for vegetation modellers, regarding development and parameterization. Here, we apply a new hydraulic module developed for the dynamic global vegetation model LPJ-GUESS to the Amazon Basin. Special focus is given to the newly developed mortality process based on hydraulic-failure and to differences in hydraulic behaviour of plants.  The implemented hydraulic-failure process can explain observed mortality patterns at rainfall exclusion experiments in the Amazon. Modelled vegetation carbon is most sensitive to two of the hydraulic processes: The xylem vulnerability to water stress and the plant specific hydraulic behaviour, i.e. how plants regulate their water potential under drought stress. Applied to the whole Amazon Basin, our model shows a strong impact of the 2005 drought event across a wide margin of modelled species and parameters, which is in good agreement with empirical studies. We highlight the hydraulic behaviour of plants, for which little is known in the Amazon rainforest, and its relevance for ecosystem model development. Considering only one single plant functional type does not sufficiently capture the complex response of the Amazon rainforest to drought, hence future modelling studies should take the interaction and competition of different hydraulic strategies into account.