Mechanisms of salt tolerance in seedlings of six woody native species of the Brazilian semi-arid

Abstract

The aim of this study was to evaluate the salt tolerance and physiological responses of six woody native species of the Caatinga ecosystem, on a soil salinity gradient in a greenhouse. The experimental design was of randomized blocks in a split-plot scheme; six plant species native of the Caatinga in the plots, and five levels of soil salinity in the sub-plots (1.2, 2.7, 4.7, 6.7 and 8.4 dS m-1), with five replications. The results demonstrate that species of the Caatinga ecosystem display a high capacity for adaptation in soils of low and moderate salinity. However, considering the reduction in total dry matter production at the highest salinity level, it was seen that only the species M. urundeuva was tolerant to salinity, and H. impetiginosus and E. velutina behaved as moderately tolerant. In the present study, it was also not possible to establish a clear relationship between the leaf gas exchange or the accumulation of organic solutes in the leaves with the degrees of salt tolerance. On the other hand, a strong relationship was seen between the Na+/K+ ratio and the degree of tolerance of the species under study, with the more tolerant species displaying less variation and lower values with the increases in soil salinity. These species, however, showed a low capacity for retaining Na+ in the stems, which may be a limiting factor on their use in revegetation projects of those areas degraded by secondary salinization.