How Do Coffee Trees Deal with Severe Natural Droughts? an Analysis of Hydraulic, Diffusive and Biochemical Components at the Leaf Level

We analysed field-grown coffee trees that faced the most severe drought event in the last 28 years in Brazil. Vulnerability curves indicated that water potentials were low enough to decrease leaf hydraulic conductance and carbohydrate content under drought. However, individual tree mortality was not observed indicating a great resilience of coffee to drought stress. Drought affects leaf photosynthesis by acting on hydraulic, diffusive and/or biochemical components. Here, we analysed two field-grown coffee (Coffea arabica L.) cultivars (Catuaí and Catimor) subjected to a severe natural drought (the most severe drought event in the last 28 years in Brazil) followed by a subsequent rehydration. We estimated leaf hydraulic vulnerability and found that the leaf water potential under drought reached values that were low enough to cause drastic decreases (up to 90%) in leaf hydraulic conductance (Kleaf) in both cultivars. Such Kleaf loss was associated with a reduced stomatal conductance (gs) under drought (c. 70%) and likely limited gas-exchange recovery upon rainfall as abscisic acid levels and gs were not correlated. Net photosynthesis rates (An) were largely limited by diffusive constraints, with gs explaining c. 90% of the variation in An. Rubisco carboxylation capacity and soluble protein content remained unaltered, in contrast to starch content which was drastically reduced by drought. Soluble sugars were less affected, with hexoses having an apparent role as osmolytes. Even though hydraulics, gas-exchange traits and non-structural carbohydrate pools were negatively affected, coffee trees did not present individual mortality, demonstrating a great resilience to drought events.