Vellozioid roots allow for habitat specialization among rock- and soil-dwelling Velloziaceae in campos rupestres

Plant growth on harsh substrates (habitat specialization) requires specific traits to cope with stressful conditions. We tested whether traits related to nutrient acquisition (root colonization by fungal symbionts, and plant morphological and physiological specializations), and nutrient use (leaf nitrogen (N) and phosphorus (P) concentrations and N- and P-remobilization efficiency), were related to habitat specialization for 27 species of Velloziaceae growing either in soil or on rocks in extremely P-impoverished campos rupestres habitats. If habitat specialization were to drive trait sorting, then we expect traits to differ between those substrates. Both soil and rock-dwelling species presented a very low proportion of root length colonized by arbuscular mycorrhizal and dark-septate fungi. However, rhizosheaths were only observed in soil-dwelling species, and vellozioid roots, a specialization that allows for mining P and dissolving quartzite rock, were mostly found in rock-dwelling species. We did not observe differences in nutrient-use traits between rock- and soil-dwelling species. Root specializations are strongly correlated with microhabitats, and the presence of vellozioid roots seems to mediate bare rock specialization. There is an overall P limitation of plant productivity both on rock and in soil of campos rupestres, which does not drive the sorting of traits related to above-ground nutrient use and symbiotic P acquisition. Therefore, nutrient impoverishment is indeed a very strong environmental filter in campos rupestres as a whole, but habitat specialization plays an important role in the spatial distribution of Velloziaceae between contrasting substrates.