Response of cowpea plants submitted to acid conditions: Aluminum and hydrogen stress

Aluminum (Al) is an important abiotic stress factor constricting the production of cowpea (Vigna unguiculata (L.) Walp.) in acid soil conditions. This study investigated the effect of Al and pH levels on the photosynthesis, proline accumulation, and nutritional status of two cowpea cultivars. Two pot experiments under greenhouse conditions were performed concurrently. Each experiment was carried out using a completely randomized design, in a factorial scheme 2 × 3 +1, in which each cultivar was exposed to two levels of Al (0.0 and 1.0 mmol L -1 ) and three levels of pH (3.3; 4.0, and 4.7), plus a control. There was an interaction effect of the factors Al and pH reducing significantly the internal CO 2 concentration (Ci) for BRS Caldeirão, and transpiration (E) and stomatal conductance (gs) for BRS Tracuateua, notably under growth conditions with Al (1 mmol L -1 ) and pH value of 4.7. For BRS Caldeirão, proline content was significantly reduced by the isolated effect of the factors Al and pH on shoot tissue. For BRS Tracuateua, proline content was significant only in roots, indicating a metabolic response to water stress damage. Under growth conditions with Al and pH value of 3.3, there was an improvement in nutrient uptake and accumulation according to nutritional status of both cultivars. In summary, cowpea response pointed that physiological, biochemical, and nutritional aspects of both cultivars improved at the lowest pH of 3.3 under Al-stress, and also that cv. BRS Tracuteua was less tolerant than BRS Caldeirão.