Increased carbon dioxide in the atmosphere has a positive effect on plant growth, and an increase in biomass leads to a greater carbon uptake by soils. This negative feedback could provide a mitigating factor in anthropogenic climate change, but its influence is likely to be less than previously understood.
Biologists Kees van Groenigen, Craig Osenberg and Bruce Hungate have revealed that rising levels of atmospheric carbon dioxide could lead to the increased production by soils of more potent greenhouse gases such as methane and nitrous oxide. Elevated CO2 reduces the evaporation of water from plant surfaces, increasing the water content of the surrounding soil, and thus promoting the growth of methane-producing anaerobic microorganisms. Nitrous oxide is produced in soils mainly by a process of denitrification.
From observations of wetlands and rice paddies, van Groenigen and his colleagues conclude that increased emissions of methane and nitrous oxide should negate nearly 17 percent of the climate change mitigation arising from the soil carbon sink. The implication is that the ability of terrestrial ecosystems to slow global warming has been overestimated.
van Groenigen et al., “Increased soil emissions of potent greenhouse gases under increased atmospheric CO2“, Nature 475, 214 (2011)
Alexander Knohl & Edzo Veldkamp, “Indirect feedbacks to rising CO2“, Nature 475, 177 (2011)