Positive relationship between soil fertility, plant diversity, and gall richness

Abstract

The complexity of nutrient distribution patterns in soils is a determinant environmental component of the structure of plant communities. Numerous insect species that interact with plants are associated with these communities, and some of these interactions result in the formation of unusual structures called galls. In this study, we investigated the relationship of galls, soil fertility and plant communities in three vegetation types, herbaceous restinga (HR), shrub restinga (SR) and shrub-tree restinga (STR), in an area of restinga in southern Brazil. We identified 217 species belonging to 159 genera and 82 families. The plant diversity recorded in the STR was 42.8% higher than the diversity in the other vegetation types. Gall richness increased significantly with increased plant richness. The edaphic gradient was correlated with the floristic diversity in the vegetation types. Our data suggest that an increment in soil fertility (organic matter and litter thickness), associated with climatic conditions, should increase the number of plants that can potentially host galls and, consequently, the richness of galling insects. Gall richness may also be influenced by a higher occurrence of woody plants, due to an increase in leaf surface area available in the tree canopy, especially in STR.