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

Drought tolerance is important for the survival and productivity

of plants in environments where drought periods are

increasing as a result of climate variability attributable to

natural causes and climate change caused by human activities.

The objective of this study was to evaluate the dynamics

of photosynthesis (A), stomatal conductance (gs) and intrinsic

water-use efficiency (WUE=A/gs) as a function of soil moisture

content over a period of drought and the post-stress recovery

of 14 cowpea genotypes. The studied genotypes tolerated soil

moisture tensions close to -2 Mpa with no permanent wilting.

Starting at a soil hydric potential of -0.7 MPa, decreases in

photosynthesis (A), stomatal conductance (gs) and transpiration

(E) were evident, as well as an increase in A/gs, which

varied by genotype. Estimating with regression models allowed

for the discrimination of the degrees of drought tolerance

between the cultivars. At 4 days after resuming hydration, no

significant differences were found between the means of A, gs,

A/gs and E, suggesting drought tolerance in all genotypes. The

genotypes: 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 days

post-stress recovery.