Main content area

Nutrient and water dynamics of Amazonian canga vegetation differ among physiognomies and from those of other neotropical ecosystems

Mitre, Simone Kuster, Mardegan, Silvia Fernanda, Caldeira, Cecilio Frois, Ramos, Silvio Junio, Furtini Neto, Antonio Eduardo, Siqueira, Jose Oswaldo, Gastauer, Markus
Plant ecology 2018 v.219 no.11 pp. 1341-1353
Vellozia, carbon, carbon nitrogen ratio, drought, ecosystems, functional diversity, nitrogen, nutrient availability, nutrient content, savannas, shrublands, soil, species diversity, stable isotopes, tropical forests, water shortages, woodlands, Amazonia, Brazil
Ferriferous savannas, also known as cangas in Brazil, are nutrient-impoverished ecosystems adapted to seasonal droughts. These ecosystems support distinctive vegetation physiognomies and high plant diversity, although little is known about how nutrient and water availability shape these ecosystems. Our study was carried out in the cangas from Carajás, eastern Amazonia, Brazil. To investigate the N cycling and drought adaptations of different canga physiognomies and compare the findings with those from other ecosystems, we analyzed nutrient concentrations and isotope ratios (δ¹³C and δ¹⁵N) of plants, litter, and soils from 36 plots distributed in three physiognomies: typical scrubland (SB), Vellozia scrubland (VL), and woodland (WD). Foliar δ¹⁵N values in cangas were higher than those in savannas but lower than those in tropical forests, indicating more conservative N cycles in Amazonian cangas than in forests. The lower δ¹⁵N in savanna formations may be due to a higher importance of mycorrhizal species in savanna vegetation than in canga vegetation. Elevated δ¹³C values indicate higher water shortage in canga ecosystems than in forests. Foliar and litter nutrient concentrations vary among canga physiognomies, indicating differences in nutrient dynamics. Lower nutrient availability, higher C:N ratios, and lower δ¹⁵N values characterize VL, whereas WD is delineated by lower δ¹³C values and higher soil P. These results suggest lower water restriction and lower P limitation in WD, whereas VL shows more conserved N cycles due to lower nutrient availability. Differences in nutrient and water dynamics among physiognomies indicate different ecological processes; thus, the conservation of all physiognomies is required to ensure the maintenance of functional diversity in this unique ecosystem.