Carbon and water dynamics in contrasting East African drylands: implications for ecosystem function and resilience

Dryland ecosystems play a pivotal role in terrestrial biogeochemical cycles and are highly sensitive to climate variability and land-use change. In this study, we investigate coupled carbon (C) and water flux dynamics in two distinct East African dryland systems—a savanna rangeland supporting mixed livestock and wildlife grazing, and a rainfed cropland under minimal tillage—over 185 days encompassing variable moisture conditions.

Although cumulative C emissions were of similar magnitude in both systems, they exhibited markedly different temporal dynamics. The rangeland displayed highly pulsed C exchange patterns, with rapid shifts from net ecosystem C loss to uptake following rainfall events, underscoring the strong influence of precipitation pulses on dryland carbon cycling. In contrast, the cropland functioned as a net C sink during the peak growing season; however, inclusion of lateral C exports via chickpea harvest revealed an overall C source at the ecosystem scale over the observation period. These findings emphasize the need to account for non-vertical C fluxes when assessing land-use impacts in drylands.

We observed higher carbon use efficiency (CUE) in the cropland, linked to effective allocation of assimilated C to biomass facilitated by agronomic inputs and conservation tillage. Peak-season water use efficiency (WUE) was also elevated in the cropland, reflecting optimized management under sufficient soil moisture; yet when averaged across the full period, rangeland WUE exceeded that of the cropland, likely due to persistent vegetation cover and drought-adapted plant traits that promote conservative water use. Notably, the cropland exhibited a complex interplay between WUE and CUE, wherein gains in productivity were accompanied by increased respiration, illustrating nonlinear responses of dryland systems to management and environmental drivers.

Both ecosystems were co-limited by water and nitrogen, and plant physiological adaptations to dry spells—such as maintenance of photosynthesis under moisture stress—were key to sustaining CUE. Our results contribute to improved process-level understanding of carbon–water interactions, pulse-driven variability, and resilience in dryland biogeochemical cycles. They highlight the importance of integrating temporal variability, lateral fluxes, and land-use intensity into dryland carbon and water budget assessments under global change.