Does ecophysiological behaviour explain habitat occupation of sympatric Clusia species in a Brazilian Atlantic rainforest?
MetadataShow full item record
Key message: Plasticity of ecophysiological acclimation determines habitat occupation of species ofClusiain an Atlantic rainforest of Brazil. Ecophysiological performance is not sufficient for explaining widespread versus locally restricted distribution of species among physiognomic sub-sites within the forest. Abstract: Four species of Clusia were studied that have distinct habitat distribution patterns within an Atlantic rainforest research reserve, in Espírito Santo state, southeast Brazil, throughout five sites: a riverine forest, a hill forest, two rock outcrops and an ecotone hill forest/rock outcrop. Clusiaaemygdioi Gomes da Silva & B. Weinberg and Clusia intermedia G. Mariz were locally widespread among the sites while Clusia marizii Gomes da Silva & B. Weinberg and Clusia spiritu-sanctensis G. Mariz & B.Weinberg were locally restricted. Clusia spiritu-sanctensis was the only obligate crassulacean acid metabolism (CAM) species, showing low 13C-discrimination (δ13C −16.5 to −19.2 ‰) and nocturnal acid accumulation. Data of 13C discrimination and photosynthetic performance show that C. marizii, C. intermedia and C. aemygdioi performed C3 photosynthesis. The latter may have some intrinsic capacity for CAM, which needs to be further studied. Because of local abundance Tibouchina heteromalla (D. Don) Cogn. (Melastomaceae) and Kielmeyeraocchioniana Saddi (Clusiaceae) were included for comparison with the Clusia species and for typical obligate C3-photosynthesis behaviour. We asked whether the habitat occupation patterns of the studied species could be explained by ecophysiological performance especially with respect to photosynthesis. The hill forest with a denser tree cover was the most shaded site, and the plants there had shade-plant characteristics, while at all the other sites the plants showed sun-plant features. Clusia intermedia consistently had an inferior performance. Nevertheless, it is equally abundant as C. aemygdioi in one of the sun-exposed, and probably most stressful rock outcrop sites. The obligate C3-species T. heteromalla performed remarkably well. The CAM in C. spiritu-sanctensis did not appear to be directly related to habitat occupation although it conferred plasticity by flexible expression of CAM phases. Flexibility of acclimation determined habitat occupation of the plants performing C3 photosynthesis. Ecophysiological performance of the four Clusia species was only slightly related to widespread versus restricted occurrence patterns. Thus, ecophysiological performance alone is not sufficient for explaining the local distribution and abundance of these species, and aspects related to reproductive output deserve future examination.