Uso de atributos funcionais para elucidar causas e consequências da estrutura da comunidade vegetal e do funcionamento do ecossistema Restinga

Abstract

Plant form and function depend on internal stimuli (genetics and phenotypic plasticity) as well as external stimuli (environment) that act in the leaf, stem, and root. Water shortages and poor-nutritional sandy soils in the coastal region are cited as the main external stimuli to plants in the Restinga ecosystem. It has been proposed that coordination among plant organs tends to increase with environmental harshness due to a decrease in the viable niche space and an increase in the costs to adopt ecological strategies out of this viable niche space. The first thesis chapter aimed to test this hypothesis in the Restinga. Pairwise correlations of 21 functional traits of 21 species revealed that the stem had greater internal coordination than the leaf organ. In addition, a multivariate analysis showed high independence between stem and leaves, suggesting that stressful environments do not necessarily have plants with high coordination between organs. Functional coordination is directly linked to the success of plant occurrence and may interfere in the community organization. It is still not clear whether weak neutral effects can influence the distribution of functional traits, even though the community shows random patterns of compositional and phylogenetic structure. We addressed this question in the second thesis chapter. Functional variation in the community resulted from phenotypic responses of all species and individuals rather than particular sets of species or individuals, indicating environmental responses, but not strong patterns in the spatial distribution of traits. In this regard, we accept that the Restinga in the Northeastern South America is influenced by weak neutral effects. We concluded that occurrence and phylogenetic analyses may be insufficient for a complete understanding of the community and should be complemented with functional analyses. The manuscript was submitted to the Journal of Vegetation Science. A weak environmental response may result from low niche partitioning among species, which has been described as the main mechanism underlying the relationships between biodiversity and ecosystem processes. The third chapter assessed the extent to which facets of biodiversity and environmental aspects influence the annual litterfall production and wood biomass storage, as well as the role of rare- and common-species diversities on these components of primary productivity. We found that these components responded mainly to the abiotic environment and just secondarily to species richness and few functional traits, but not to other facets of biodiversity. We also found that rare-species diversity had less influence on litterfall than the diversity of common species, but the same influence on the biomass storage. In summary, I concluded that niche differences among species promote only modest effects on community structure and even lower effects on the ecosystem functioning of Restinga. These patterns deviate from that expected in the literature for stressful ecosystems, which highlights the relevance of its biodiversity.