Sclerophylly in mangrove tree species from South Brazil

Abstract

Sclerophylly, a morphological trait that defines coriaceous and hard leaves, is presently accepted as a non-specific response to environments with acting multiple stresses. In mangroves, features such as flooded and unconsolidated soil, low availability of oxygen, and high salinity characterize this stressful environment. From 2 mangroves areas in the coast of Paraná state, leaves of 3 species (Rhizophora mangle, Laguncularia racemosa and Avicennia schaueriana) were collected and analyzed nutritionally and morphologically. Sclerophylly indices (Rizzini index and specific leaf area) indicated that all species are sclerophyllous. Considering nutritional and morphological traits, only some of them suggest sclerophylly, such as total leaf thickness in all species, the presence of a sub-epidermal layer in Rhizophora mangle and Avicennia schaueriana and sclereids in Rhizophora mangle. Comparatively, leaves presented different degrees of sclerophylly, in the following order: R. mangle > L. racemosa > A. schaueriana, considering all characteristics analyzed. This gradient of sclerophylly appears to be consequence of different strategies developed by each species in response to the stressful abiotic conditions of mangroves, especially the mechanisms for salinity tolerance.