Gas exchange and mass distribution of the cowpea (Vigna unguiculata [L.] Walp.) under water deficit

Drought tolerance is important for the survival and productivityof plants in environments where drought periods areincreasing as a result of climate variability attributable tonatural causes and climate change caused by human activities.The objective of this study was to evaluate the dynamicsof photosynthesis (A), stomatal conductance (gs) and intrinsicwater-use efficiency (WUE=A/gs) as a function of soil moisturecontent over a period of drought and the post-stress recoveryof 14 cowpea genotypes. The studied genotypes tolerated soilmoisture tensions close to -2 Mpa with no permanent wilting.Starting at a soil hydric potential of -0.7 MPa, decreases inphotosynthesis (A), stomatal conductance (gs) and transpiration(E) were evident, as well as an increase in A/gs, whichvaried by genotype. Estimating with regression models allowedfor the discrimination of the degrees of drought tolerancebetween the cultivars. At 4 days after resuming hydration, nosignificant differences were found between the means of A, gs,A/gs and E, suggesting drought tolerance in all genotypes. Thegenotypes: L-047 and L-034 conserved between 4 and 6 leaves,displaying the highest delayed leaf senescence during drought.Furthermore, they presented the highest biomass at 16 dayspost-stress recovery.