Microbial responses to soil warming affect grass growth in Iceland
Grasslands in Iceland are expected to experience an average warming of approximately 5 °C in the near future. This warming affects plant growth and performance, while simultaneously influencing the soil biota with which plants interact. Under field conditions, it is difficult to disentangle the direct effects of warming on plant performance from indirect effects mediated by changes in microbial communities.
To address this challenge, Coline Le Noir de Carlan, together with her co-authors, conducted a greenhouse experiment in which typical Icelandic grasses were grown under controlled conditions in soils inoculated with microbiomes conditioned by ambient, medium-term (14 years; MTW), or long-term (>55 years; LTW) soil warming. This approach took advantage of natural soil warming caused by geothermal activity. Results were published in Plant Biology.
The research showed that root biomass of both plant species was reduced when grown with microbiomes conditioned by long-term warming. Moreover, the aboveground:belowground biomass ratio was positively correlated with warming intensity. The entire experiment was repeated to assess whether these effects were amplified under stress conditions; this was indeed the case for one of the two grass species. These plant responses coincided with shifts in the relative abundance of both known plant antagonists (such as plant pathogens) and mutualists (including mycorrhizal fungi).
Overall, the results demonstrate that long-term soil warming can indirectly reshape plant performance by altering soil microbial communities, with consequences that are further intensified under stressful conditions.
