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Amazonia; floodplain; growth strategy; leaflet size; specific leaf mass; varzea; waterlogging
Abstract:
Seasonal changes in specific leaf mass and leaf size were measured at monthly intervals along the annual cycle in six tree species with different growth strategies from Amazonian floodplains (Cecropia latiloba, Cecropiaceae; Crateva benthami, Capparidaceae; Nectandra amazonum, Lauraceae; Senna reticulata, Caesalpiniaceae; Tabebuia barbata, Bignoniaceae; Vitex cymosa, Verbenaceae). In their natural habitat, trees are exposed to extended periods of flooding, and the aim of the present study was to analyse whether there are seasonal changes in leaf specific weight and size, how these changes occur in trees with different growth strategies, and if the changes are related to the periodicity of flooding. Specific leaf mass was higher in waterlogged months in all species except Crateva benthami, average leaf age was higher in the aquatic than in the terrestrial period in all species, and mean leaf size was significantly lower in the aquatic period for three species (Crateva benthami, Senna reticulata and Tabebuia barbata). Reductions of leaf size were caused by leaf senescence and a subsequent loss of leaflets. Only for Senna reticulata leaf size reduction was a direct response to water stress: in waterlogged months, the newly produced leaves and leaflets were smaller than in the terrestrial period. Data in this study indicate a periodicity in several leaf traits which changes parallel to the flooding periodicity, but which is determined primarily by leaf age and senescence and only indirectly by flooding. The timing of the changes of specific leaf mass and leaf size was similar between species and was concentrated in the aquatic period, but the degree of changes differed among the species. Leaves of pioneer and non-pioneer species, and leaves of deciduous and evergreen species did not show a uniform trend, characteristic for certain growth strategies, as response to flooding. Apparently differences were closely linked to leaf age and can not be considered as adaptive to the changing hydric conditions.
