Plant growth carbon sink questioned

Climate change is likely to have a positive effect on plant growth in temperate latitudes, and one would expect this to result in increased carbon capture by soils – a negative feedback working against global warming. This biomass carbon sink is real enough, but it appears that the effect could be partially offset by a related increase in carbon dioxide emissions from leaf litter that stimulate carbon-belching soil microbes.

Writing in the journal Nature Climate Change, Emma Sayer and colleagues report on an experiment they conducted in Panama, in which leaf litter was added to soils and monitored for six years, with isotope measurements used to distinguish between the various carbon sources. The researchers found that the addition of leaf litter significantly raises carbon dioxide emission through a process known as ‘priming’, in which microbes are fuelled by rotting organic matter covering the soil.

A 30% increase in plant litter could release of more than half a tonne of carbon per hectare of lowland tropical forest soil each year, say the researchers. This is greater than estimates of climate-induced biomass increase over recent decades, in which case the effect may counterbalance expected gains in carbon storage from enhanced plant growth.

Further reading

Sayer et al., “Soil carbon release enhanced by increased tropical forest litterfall”, Nature Climate Change 1, 304 (2011)

Yakov Kuzyakov, “Ecology: Prime time for microbes”, Nature Climate Change 1, 295 (2011)