The theory of complex networks has been recently used to explain ecological associations between nurses and seedlings in plant facilitation systems. The structure of these networks is potentially affected by morphological, ecological and evolutionary factors that can determine the facilitative interactions. In the present study, we evaluate the role of the projected crown area of the nurse plant, the dispersal syndrome, the abundance and the phylogeny relationships with seedlings as drivers of network structure in facilitation networks. To test these parameters, we used an ecotonal forest-grassland system in southern Brazil that experienced historical forest expansion over the grassland in the last few centuries. In two State Parks, Guartelá (GUA) and Vila Velha (VVL), we sampled tree species (nurses and seedlings) along four transects parallel to the forest edge, with five sampling stations along each transect. Tree seedlings (height >0.3 m) were sampled below the nurse's crown (i.e. isolated woody plants, height >1.5 m) and over the grassland area. A total of 160 nurses and 358 seedlings were sampled. Seedling abundance and richness were greater below a nurse's crown than on open grassland. Nurse abundance was the best predictor of the observed interaction matrix. Probabilistic matrices based on abundance, abundance and phylogeny, and dominance were able to predict the observed nestedness values, and they were also closest to the observed connectance, although all of the probabilistic matrices have underestimated this property. Specialization was predicted by abundance and phylogeny, abundance and projected crown area drivers for VVL, and the abundance based models were closest to the predicted specialization for GUA. The result of a similar pattern in predictability between sites indicates that the influences of morphology and evolutionary and ecological processes over the facilitation interactions are equivalent on a regional scale. Woody plant abundance was a key factor for the facilitation networks, driving forest expansion along the subtropical forest-grassland ecotone.

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Questions We analysed trait convergence and trait divergence assembly patterns across a metacommunity of grassland types (dry, wet and rocky) occurring along an edaphic gradient. We asked whether (1) floristics and phylogenetic structures vary among grassland types; (2) there is convergence and/or divergence in plant traits along the gradient; (3) the functional structure is influenced by phylogeny; and (4) abiotic or biotic filters generate the assembly patterns. Location Campos Gerais region, Paraná State, southern Brazil (ca. 25°15′02″ S, 49°59′59″ W). Methods We sampled plant functional traits and soil variables at 81.1‐m2 quadrats in three natural grassland vegetation types across three different sites. We analysed the relationship between species composition (abundance), phylogenetic relationships, functional traits and soil characteristics using matrix correlations, where soil characteristics were the predictors of functional and phylogenetic assembly patterns. Results A total of 168 plant species were sampled on the three vegetation types. Wet grassland quadrats were more similar to each other in species composition and phylogeny than with those on dry and rocky grasslands. We found trait convergence (not phylogenetically constrained) and trait divergence (phylogenetically constrained) assembly patterns in the three vegetation types along the edaphic gradient. Traits that generated convergence and divergence are related to strategies for survival in dry and low nutrient availability soils; nutritional soil gradient determined trait differences at small scales. Conclusion Species composition and phylogenetic structure of communities occurring in different grassland types are related to edaphic gradient. The occurrence of both trait convergence and trait divergence patterns suggests, respectively, that environmental filters and biotic filters (competition) are structuring the plant assemblages.

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In this work we assessed spatial and temporal variation of leaf pigment content of Clusia hilariana, a dominant CAM tree on the sandy coastal plains of SE Brazil. Chlorophyll a + b concentration, chlorophyll a/b ratio, and total carotenoid concentration were measured three times during the wet season. Chlorophyll a + b and total carotenoids decreased while the chlorophyll a/b ratio increased after a series of dry spells. We discuss our results in the context of Clusia literature, and argue that leaf-level pigmentation changes are an important source of phenotypic flexibility during acclimation to fluctuating light levels and groundwater availability.

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