A New Modeling Application of Legacy Data on Ecosystem Stocks and Fluxes in Multiple Land Uses in the Eastern Amazon

Abstract:

Land-use change and its interaction with climate change remain significant threats to the integrity of Amazonian ecosystems. The responses and feedbacks of biogeochemical cycles to these changes play an important role in determining ecosystem responses to possible future trajectories for land stewardship through effects on rates of secondary forest regrowth, soil emissions of greenhouse gases, inputs of nutrients to groundwater and streamwater, and nutrient management in agroecosystems. The Terrestrial Ecology program at NASA supported numerous studies on these topics in the Amazon and Cerrado regions, both before and during the LBA-ECO project. Here we present analyses of data from this body of work on nutrient cycling in cattle pastures, secondary forests, and mature forests of the Paragominas area, where we are developing a stoichiometric model relating C-N-P interactions during land use change, constrained by multiple observations of ecosystem stocks and fluxes in each land use. Whereas P is conservatively cycled in all land uses, we demonstrate how pyrolyzation of N during pasture formation and management depletes available-N pools, consistent with observations of lower rates of N leaching and trace gas emission and consistent with secondary forest growth responses to experimental N amendments. Although the soils store large stocks of N and P, our parameterization of available forms of these nutrients for steady-state dynamics in the mature forest yield reasonable estimates of net N and P mineralization available for grasses and secondary forest species at rates consistent with observed biomass accumulation and productivity in these modified ecosystems. The multiple data constraints from measurements made by the type of integrated studies supported by the NASA TE program provide an important legacy that continues to support exploration of the functions, vulnerabilities, and resiliencies of these ecosystems.