Resposta do feijão caupi a condições ácidas: interações alumínio x hidrogênio e manganês x hidrogênio

Abstract

Cowpea is a food of great nutritional importance, and has socioeconomic relevance as a source of income for small farmers in the north and northeast regions of Brazil. The goals of this work were to investigate the effect of the interaction of Al x H and Mn x H on growth, photosynthesis, nutritional status and proline accumulation in two cowpea cultivars (BRS Caldeirão and BRS Tracuateua). It was used washed sand as substrate, and nutrient solution as a source of nutrients for plant growth. In the study 1, young plants of cowpea cv. BRS Caldeirão and BRS Tracuateua were exposed to a factorial combination of two levels of Al (0.0 and 1.0 mM) and three levels of pH (3.3, 4.0 and 4.7), plus a control treatment. In the study 2: young plants of cowpea (BRS Caldeirão and BRS Tracuateua) were exposed to a factorial combination of two levels of Mn (0.0 and 72 µM) and three levels of pH (3.7, 5.0 and 6.3), plus a control treatment. In both studies, control treatment was composed of ¼ Hogland´s solution, without Al in the study 1 and without Mn in the study 2. For BRS Caldeirão and BRS Tracuateua, the results showed that growth parameters were not affected by the Al and pH interaction. However, physiologic parameters like rate of photosynthesis (A), internal carbon content (Ci) and index of total performance (PItotal) were significantly reduced for BRS Caldeirão, caused inhibitory injuries to the photosynthetic apparatus, specially under pH conditions of 4.7. Proline accumulation was lower in shoot with nutrient solution containing Al 1 mM for BRS Caldeirão, while for BRS Tracuateua the lower proline accumulation in root lead to water stress. The nutrient composition in shoots showed that Al reduced the content of Ca and Mg for BRS Caldeirão, reducing also the contents of P and S by the interaction effect with pH 4.7, while for BRS Tracuateua the contents of P, Ca and Fe were significantly reduced in shoot. In the study 2, for BRS Caldeirão the growth parameters like shoot and total dry matter were higher in plants treated with excess of Mn (72 µM), while for BRS Tracuateua, Mn stress reduced the leaf biomass production. The BRS Caldeirão presented tolerance to toxic levels of Al, Mn e H in nutrient solution, while the BRS Tracuateua was less tolerant.