Plants of Distinct Successional Stages Have Different Strategies for Nutrient Acquisition in an Atlantic Rain Forest Ecosystem

Premise of research. Plant functional groups of different stages of tropical succession are adapted to distinct environments with different availabilities of such resources as light, water, and nutrients. The sites at early-successional stages commonly have low-fertility degraded soils and are colonized by fast-growing shade-intolerant plant species, while the sites at late-successional stages usually have soils with high contents of organic matter and nutrients and are colonized by slow-growing shade-tolerant plant species. In this study, we aimed to assess the strategies adopted by plants for nutrient acquisition over tropical succession.Methodology. Grassland, shrub vegetation, and secondary and mature forests of an Atlantic rain forest ecosystem in southern Brazil were studied. Fine roots were sampled to assess length density, specific root length (SRL), diameter, tissue density, root-hair length and incidence, and arbuscular mycorrhizal fungi (AMF) colonization. Rhizospheric and bulk soils were sampled to assess microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN); basal respiration; total and labile C; and concentrations of N, P, K, Ca, and Mg.Pivotal results. Fine roots with longer SRL, greater incidence of root hairs, longer root hairs, and greater AMF colonization were exhibited by plants in early-successional stages in contrast with plants in late-successional ones. Nutrient depletion zones were detected in the rhizospheres of plants in early-successional stages. Fine roots from the late-successional sites exhibited greater diameter and tissue density. High values for labile C, MBC, MBN, basal respiration, and the nutrient accumulation zone occurred in the rhizospheres of plants in late-successional stages in contrast with the rhizospheres of plants in early-successional ones.Conclusions. Our results suggest that early-successional plant species invest in fine roots with morphological features for a highly efficient nutrient uptake and in AMF (scavenging strategy), whereas late-successional plant species invest in other chemoheterotrophic microorganisms in the rhizosphere (mining strategy) for nutrient acquisition.