Afromontane Grassland Carbon Dynamics in a Changing World

Abstract

Mountain grasslands play a crucial role in supporting biodiversity, grazing livestock, and regional water supply, while storing large amounts of carbon in their soils and vegetation. Grassland functioning is tightly coupled with climate and management practices, making these ecosystems highly vulnerable to global changes. The Afromontane grasslands of the Maloti-Drakensberg Mountains are among southern Africa’s most important ecological and hydrological systems, providing essential provisioning services. Despite their importance, surprisingly little is known about the impacts of global change drivers on carbon dynamics in these ecosystems. Filling this knowledge gap would improve our understanding of the extent of the Afromontane grasslands carbon sink, and help predict future carbon dynamics.To address this gap, the NatuRA project has established a global change experiment in the Drakensberg Mountains focused on three global change drivers: warming, increased atmospheric nitrogen deposition, and changing grazing practices. The experiment spans an elevation gradient from 2000 to 3000 meters above sea level in a full factorial design made of a transplant treatment, nitrogen fertilization, and grazing manipulations. Measuring ecosystem carbon fluxes in this experimental design enables the assessment of how these drivers, individually and in interaction, affect key carbon-cycling processes.Ecosystem carbon fluxes were measured using a closed-loop chamber system connected to an infrared gas analyzer. We measured net ecosystem exchange and ecosystem respiration, from which gross primary productivity was calculated. Pairing these results with treatment-specific microclimate data allows us to assess the amount of carbon captured by the ecosystem and evaluate how the carbon cycle responds to warming, fertilization, and grazing intensity. By revealing how multiple global change drivers interact to shape carbon dynamics in the Drakensberg Mountains, this study can provide critical evidence for predicting the future role of these ecosystems and for informing sustainable land management in a rapidly changing climate.