Soil types select for plants with matching nutrient-acquisition and -use traits in hyperdiverse and severely nutrient-impoverished campos rupestres and cerrado in Central Brazil

Abstract

Understanding the mechanisms that underlie the generation of beta-diversity remains a challenge in ecology. Underground plant adaptations to environmental gradients have received relatively little attention. We studied plant nutrient-acquisition strategies and nutrient-use efficiency at three stages of pedogenesis in infertile soils from campos rupestres and on less infertile soil from cerrado sensu stricto in Brazil. All soils support very high plant diversity with high species turnover between soil types at small spatial scales (metres). We expected that differences in nutrient-acquisition and -use strategies would be associated with this high species turnover. With severely decreasing phosphorus (P) availability, we expected the effectiveness of arbuscular mycorrhizal (AM) symbioses for plant P acquisition to decrease, and reliance on nonmycorrhizal strategies (NM) to increase, while maintaining efficient nutrient use. Concentrations of total soil P and nitrogen (N) were greater in soils in cerrado than in those from campos rupestres, and the more weathered soils from campos rupestres were severely P and N impoverished. The proportion of the root length colonized by AM fungi was 71% in the soils from the cerrado and <1% in the most P-impoverished soil type from campos rupestres. Conversely, the proportion of species with nonmycorrhizal P-acquisition strategies such as rhizosheaths was greater in the most P-impoverished soils. Leaf [P] and [N] were very low and decreased with decreasing soil [P] and [N]. Leaf N:P ratios suggest P limitation of plant productivity in the campos rupestres but N-P colimitation in the cerrado. Photosynthetic rates decreased with increasing P impoverishment, but photosynthetic P-use efficiency was very high and photosynthetic N-use efficiency moderately high on all soils. Most species had very high P-remobilization efficiency during leaf senescence (>70%), but only moderate N-remobilization efficiency (~50%). Synthesis. We observed very high P-use efficiency and moderately high N-use efficiency in campos rupestres and cerrado species, consistent with plant productivity being more strongly limited by P than by N. Our findings demonstrate that different soil characteristics (nutrient availability and soil texture) select for species differing in nutrient-acquisition and -use strategies (especially below-ground traits) which is likely key for the very high species turnover at a very small scale between soil types (i.e., beta-diversity) in campos rupestres and cerrado.