Plant disease in an Arctic tundra ecosystem can alter and even reverse the effects of a changing climate on the carbon balance by changing plant composition, reports a study published online this week in Nature Climate Change.

Climate change can affect plant growth directly, but also indirectly through its influence on predation and disease. Plant growth in turn affects carbon storage, but how much carbon will be released in response to future climate is still highly uncertain.

Johan Olofsson and colleagues undertook a seven-year study into the effects of increased snow cover on tundra plant communities in Sweden. Despite the fact that plant growth was favoured by the insulating effects of increased snow cover in experimental plots, plant biomass decreased over the seven-year study owing to an outbreak of a parasitic fungus, Arwidssonia empetri. The disease killed the majority of the shoots of the dominant plant species, Empetrum hermaphroditum, after six years of increased snow cover, and significantly reduced instantaneous carbon exchange immediately afterwards.