Resumo:
Hydraulic traits such as leaf hydraulic conductance (Kleaf ) define the xylem operational limits at the leaf level. Leaf hydraulic vulnerability was assessed in two field-grown coffee cultivars under a severe drought to test coffee susceptibility to hydraulic dysfunctions. Here we evaluated two field-grown coffee cultivars under severe (natural) drought and subsequent recovery with the following objectives: (1) to assess naturally occurring Ψ min and determine reliable hydraulic safety margins and (2) to test whether loss of conductivity is significant in leaves expanded in the drought season. The large negative Ψl experienced were sufficient to cause hydraulic failure and leaf loss. Leaf vulnerability curves followed a sigmoidal behaviour with Kleaf declining gradually as a function of Ψl. The Hybrid 12 displayed lower (more negative) P50 (26%) than Catuaí. We concluded that the coffee tree operates under narrow safety margins even under well-watered growth conditions and it is subjected to hydraulic failure upon severe drought events. Leaves that did not cross a given threshold for leaf abscission, likely to be the Ψl at P88, recovered from hydraulic loss presenting Kleaf similar to the new leaves that were developed over the rainy season
