Spatial and temporal variation in nutrient availability under ambient and rainfall reduction conditions in the Brazilian Savanna

Abstract

Abstract Background and aims Climate models forecast decreases in rainfall for the Brazilian savanna (i.e. Cerrado), the most diverse tropical savanna worldwide. However, research on soil nutrients in the Cerrado and their response to climate change scenarios are still scarce. We sought to assess nitrogen (N) and phosphorus (P) availability in the three main Cerrado vegetation types (i.e. plant physiognomies; woodland, intermediate, and open savanna) under ambient (control plots) and rainfall reduction (treated plots) conditions. Methods Ion exchange membranes were incubated in the soil of each plot for 30-40 days at four climatic contrasting times (rainy, late-rainy, dry, and late-dry seasons) for two years. Results Nutrient availability varied among plant physiognomies, seasons, and years, with noteworthy interactions among some of these factors. The open savanna showed the lowest nutrient availability levels, but it strongly depended on the season and the year. In the dry season and under the rainfall reduction treatment, we observed a significant decrease in N availability but not in that of P. Conclusions Our result suggests a higher sensitivity of N than P availability to changes in soil moisture, and points towards a likely climate change-driven decoupling of the P and N cycles, at least in the short-term. Different plant physiognomies showed different sensitivities to the experimental rainfall reduction, with the woodland savanna consistently showing the strongest responses. These results highlight the need for an explicit consideration of the different Cerrado plant physiognomies when trying to fully understand the responses of this ecosystem to future climate change scenarios.