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Distribution ranges of plant species are related to physical variables of
ecosystems that limit plant growth. Therefore, each plant species response to
physical factors builds up the functional diversity of an ecosystem. The higher the
species richness of an ecosystem, the larger the probability of maintaining functions
and the higher the potential number of plant functional groups (FGs). Thus, the
richness potentially increases the number of functions of the highly diverse Atlantic
Rainforest domain in Brazil. Severe plant growth limitations caused by stress,
however, decrease species richness. In the Spodosols of the Mussununga, an
associated ecosystem of Atlantic Rainforest, the percentage of fine sand is directly
related to water retention. Moreover, the depth of the cementation layer in the
Mussununga’s sandy soil is a physical factor that can affect the plants’ stress
gradients. When a shallow cementation layer depth is combined with low water
retention in soils and with low fine sand percentage, the double stresses of flooding
in the rainy season and water scarcity in the dry season result. This study aimed to

identify FGs among Mussununga plant species responding to water stress gradients
of soil and to verify the effects of the gradients on plant species richness of the
Mussununga. A canonical correspondence analysis (CCA) of species abundance and
soil texture variables was performed on 18 plots in six physiognomies of the
Mussununga. Species richness rarefactions were calculated for each vegetation form
to compare diversity. The two main axes of the CCA showed two FGs responding to
soil texture and cementation layer depth: stress tolerator species and mesic species.
Physical variables affect plant diversity, with species richness rising as the fine sand
proportion also rises in the Mussununga. The effect of the cementation layer is not
significantly related to species richness variation.