article · Nature
Rising atmospheric carbon dioxide enhances the productivity of wild C4 grasses in arid environments, contradicting the traditional view that these plants do not respond to carbon dioxide fertilisation. Analysis of seventy experimental studies alongside thirty-two years of field observations from southern Africa reveals that elevated carbon dioxide reduces stomatal conductance in grasses. This physiological response curtails water loss and improves water use efficiency, driving significant increases in biomass. Over three decades of field monitoring, annual aboveground grass production grew by twenty-eight percent, equivalent to an increase of 0.37 tonnes of carbon per hectare each year. Ecological modelling suggests this enhanced productivity could persist under future climatic conditions. While interactions with fire, grazing herbivores, and woody plants make the ultimate fate of this stored carbon uncertain, the sustained growth of C4 savannas exerts a substantial influence on the global carbon cycle.
Tropical and subtropical savannas dominated by C4 grasses generate roughly thirty percent of global terrestrial plant production. Demonstrating that these grasslands actively capture more carbon as atmospheric carbon dioxide climbs reshapes understanding of global carbon sinks. This knowledge is essential for accurately forecasting future climate trajectories, tracking terrestrial carbon budgets, and assessing how dryland ecosystems adapt to ongoing atmospheric changes.
While the abstract focuses on foundational ecological observations and climate modelling rather than direct commercial products, the data could inform land management, rangeland yield forecasting, and carbon accounting frameworks. The research is at an early stage of scientific discovery, providing baseline empirical metrics on biomass expansion that agricultural and carbon market modellers may use to refine predictions of dryland carbon sequestration and grazing capacities.
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Abstract Rising atmospheric CO 2 concentrations are impacting the global terrestrial biosphere through indirect climate effects and direct effects on plant performance 1–3 . In tropical forests, long-term monitoring indicates a substantial CO 2 -driven carbon sink 4 . C 4 -grass-dominated tropical and subtropical savannas contribute approximately 30% of terrestrial net primary production 5 , and yet equivalent long-term analyses of CO 2 responses are lacking. Here we show a clear and consistent result across a meta-analysis of 70 CO 2 -addition experiments and 32 years of in situ field observations from southern Africa: CO 2 fertilization of wild C 4 grasses is widespread in dry conditions. In experiments, grasses reduced stomatal conductance under higher levels of CO 2 , limiting water loss while increasing carbon gain. In the field, improved water use efficiency translated into increased C 4 grass biomass production across three decades of observations. Finally, simulations via the Community Land Model 6 suggest that CO 2 fertilization of C 4 grass aboveground productivity may continue to increase under future conditions. Together, these results challenge the view that C 4 grasses are unresponsive to increasing levels of CO 2 , demonstrating instead that annual aboveground production of grasses in the field in southern Africa has increased by 28% over three decades (a CO 2 -driven increase of 75.1 g m −2 (95% confidence interval of 74.5–75.8 g m −2 ) or 0.37 tons C ha −1 of annual production). Although the fate of this carbon is uncertain (depending on feedbacks with fire, herbivory and woody vegetation), effects on the global carbon cycle may be profound.
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DOI: 10.1038/s41586-026-10935-4
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