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Global warming puts the heat on dryland bugs
  • Microorganisms emit more greenhouse gases (CO2 and N2O) as drylands heat up
  • Higher atmospheric greenhouse gases increase global warming
  • Over 60% of Africa is covered by drylands
  • Global warming drives desertification
  • Livelihoods of billions of people at risk

Even bugs hardened to hot and dry conditions are sweating it over global warming. To test just how badly microorganisms are affected by climate change, researchers at the Dedeben Research Centre at the Tswalu Kalahari Reserve, a partner entity of Oppenheimer Generations Research and Conservation, set up experiments mimicking varying conditions of heat, water, and water and heat combined. They found that as drylands become hotter and drier, emissions of greenhouse gases (CO2 and N2O) by soil microorganisms escalate, which affects the amount of carbon and nitrogen that is stored in the soil. Fewer nutrients in soil will, in turn, also affect plant growth and biomass, exacerbating desertification.

Drylands are essential terrestrial biomes that cover over a third of land surfaces. They are home to 3 billion people, and are important for global crop production and food security. These fragile environments (i.e., they have low moisture availability, high ultraviolet (UV) radiation, and extreme temperature fluctuations) are expanding because of climate change, which could affect the livelihood of billions of people, especially in Africa, where more than 60% of the continent is covered by drylands [1]. These are expected to become warmer, with some regions forecasted to receive more frequent and intense rainfall, while other regions may experience only subtle changes in rainfall [2]. Southern Africa, containing the Kalahari Desert, is predicted to become drier and hotter, affecting an already threatened ecosystem.

Microbial communities in dryland soils are often overlooked in many climate change studies, but they are essential in regulating the amount of nutrients and carbon in soil. Warming and extended drought change the activities of microorganisms in drylands so that they release more greenhouse gases (GHGs) like carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), and higher GHG levels further intensify climate change. This process causes the soil to store less carbon, ultimately damaging soil health and fertility and causing soil degradation. Most of our understanding of the impacts and risks of climate change on drylands and microbial processes comes from global studies, leaving a large knowledge gap in the African context.

A research team led by microbial ecologist Jean-Baptiste Ramond at the Pontificia Universidad Católica de Chile, Santiago, Chile, decided to fill this research gap. The team is interested in knowing how different climate change mimicking scenarios will affect microbial groups and their processes (specifically for GHGs) in arid lands in Southern Africa, like the Kalahari Desert. To test this, they set up three climate change-induced conditions (water, water & heat, and heat) and a control at two sites at the Dedeben Research Centre. The two sites differed slightly in that the one had more grass cover and some shading from trees and shrubs than the other site. For the watering experiments, a 20 mm rainfall event was mimicked, while for the heat experiments, the air temperature was passively increased with open-top chambers by 1.5-2°C. For each experiment, soil and emitted gas samples were collected at different time intervals and then analysed at the laboratory. These experiments were performed in November 2021 and 2022.

The team found some interesting results from these short-term experiments:

  1. At both sites, microbial communities tended to fix CO2 (i.e., the process where inorganic carbon is converted to organic compounds) after the soil was wetted (up to 24 hours after watering), but released CO2 via soil respiration at higher temperatures in the heat treatment. Soil respiration is the process where microorganisms break down the organic carbon in the soil and convert it to CO2.
  2. Methanotrophs (i.e., methane-utilising bacteria) used more CH4 for biological processes than producing and releasing it into the atmosphere when the soil was wet (watering experiment) and/or hotter (heat experiment).
  3. Denitrifying bacteria (i.e. bacteria that convert nitrates into atmospheric nitrogen) were highly active, and N2O was both used and released into the atmosphere for all the experiments, but more so at higher temperatures. It is very likely that the higher plant cover at the one site contained more denitrifying bacteria and promoted the denitrification rate, as shown for other vegetated dryland areas (e.g., under plant canopies/shrubs) [3,4].

These findings highlight that as drylands become hotter and drier, CO2 and N2O emissions by soil microorganisms escalate, which will affect the amount of carbon and nitrogen that is stored in the soil. Fewer nutrients in soil will also affect plant growth and biomass. The higher atmospheric CO2 and N2O levels will aggravate global warming, ultimately causing the desertification and degradation of drylands.

But changes in soil water content through rainfall can have substantial impacts on CO2 and N2O emissions, as the researchers saw in the watering experiments. The rainfall they mimicked was comparable to a “large” event, and they have not yet explored the impacts of frequent and smaller events combined with heating. Further investigation of these factors will provide a more comprehensive understanding of the microbial process and GHG dynamics within Southern African drylands.


[1]   IPCC. 2018. Impacts of 1.5°C of Global Warming on Natural and Human Systems. In: An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Cambridge University Press, Cambridge, UK.

[2]    Trisos CH, Adelekan IO, Totin E, Ayanlade A, Efitre J, Gemeda A, et al. 2022. Africa. Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.

Cambridge University Press, Cambridge, UK.

[3]    Schaeffer SM, Billings SA, Evans RD. 2003. Responses of soil nitrogen dynamics in a Mojave Desert ecosystem to manipulations in soil carbon and nitrogen availability. Oecologia 134:547–553.

[4]    Schaeffer SM, Billings SA, Evans RD. 2007. Laboratory incubations reveal potential responses of soil nitrogen cycling to changes in soil C and N availability in Mojave Desert soils exposed to elevated atmospheric CO2. Glob Change Biol 13:854–865

Karen Jordaan is based at the Centre for Microbial Ecology and Genomics, Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Hatfield, 0028, South Africa

Jean-Baptiste Ramond is based at the Extreme Ecosystem Microbiomics & Ecogenomics (E²ME) Lab., Facultad de Ciencias Biológicas, Pontificia


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