No abstract

In South America, the largest area of tropical savanna is the Brazilian Cerrado biome, which encompasses a considerable range of environmental variation, with different types of soil, geology, geomorphology and climate, as well as distinct types of vegetation. These savannas include two types of vegetation: one on hilly slopes, with relatively shallow interspersed with rocky soils (RS), known as Rocky Cerrado, and the other located on flat terrain with deep soils (DS), known as Typical Cerrado. Our objective was to evaluate the effects of the heterogeneity of the chemical and granulometric properties of the soils on the composition and diversity of the shrubby-arboreal strata of the RS and DS. We found that, despite the reduced abundance of woody plants in the RS, and the physical limitations on plant development imposed by the rocky outcrops found in this environment, the RS is characterized by similar species diversity to that found in the DS. We present evidence of greater heterogeneity in the species composition and edaphic proprieties of the RS in comparison with the DS. We conclude that the greater variation and heterogeneity in the substrates of the RS accounts for the similarity in the species diversity between the RS and DS, although we suspect that other drivers, not investigated here, may also be involved. The intense conversion of native vegetation within the study region interferes with the establishment of exclusive species in RS (e.g., Norantea guianensis Aubl.) and DS (e.g., Couepia grandiflora (Mart. & Zucc.) Benth.) and consequently threatens the community structure of both environments with fundamental implications for the conservation.

This study represents an important contribution to the structural, histochemical and biological understanding of ducts and cavities in leaves of four species of Calophyllaceae that occur in Amazonian savannas.• Samples of adult leaves were processed using light, scanning and transmission electron microscopy, as per usual methods for plant anatomy.• In paradermal sections, the lumina of ducts are elongated while those of cavities are short. Ducts occur exclusively in the central rib and are abundant in Kielmeyera rubriflora Cambess and Kielmeyera coriacea Mart. and Zucc and larger than in Calophyllum brasiliense Cambess and Caraipa densifolia Mart. In mesophyll, the type of secretory structure and distribution pattern of the ducts and cavities are distinct. In most species, the secreted metabolites are similar and consist of phenolic compounds, lipids, essential oils with oleoresins, mucilage, neutral polysaccharides, proteins and alkaloids, except in K. coriacea, which does not contain oleoresin. The secretion is probably synthesized by mitochondria, rough endoplasmic reticulum, ribosomes and dictyosomes and is externalized toward the lumen by granulocrine and eccrine processes.• In addition to being of diagnostic value for species identification, the attributes of the lumen shape, type of secretory structure, distribution pattern, identified metabolites and secretion mechanism are important for understanding the biological roles of ducts and cavities. The identified metabolites reveal a capacity for adaptation, resistance and protection from the action of herbivores and pathogens, and in water retention.