Effect of root exclusion on the soil microbial community response to warming

World temperature has been steadily increasing over the past century, resulting in alterations of most ecosystems. Particularly, high latitudes regions are expected to undergo severe climate changes. Soil microbes are key actors of the terrestrial system, fulfilling major functions such as nutrient cycling and therefore considerable efforts are made to understand their response to warming. Besides, they can be in tight interaction with roots, and the effect of such interactions are well documented, however, whether soil microbial community response to warming is mediated by plants through roots remains unclear.

Here, we took advantage of a geothermal temperature gradient (reaching a warming intensity of up to +6°C) located in two Subarctic grasslands to study the effect of middle (12 years) and long term (>60 years) warming on the root associated soil microbes. For this, we installed two differently mesh sized cores along the thermal gradient of both grasslands allowing us to compare portions of local soil either containing (1 mm mesh size) or excluding roots (30 µm mesh size).

We investigated the response of fungal and bacterial communities to warming under both root inclusion and exclusion over the seasons using a metabarcoding approach targeting the 16S rRNA gene and the ITS1 fungal region. We found that warming shifted both bacterial and fungal communities, and that this response was depending on the warming duration. However, root exclusion did not alter the overall microbial community. Surprisingly, we did not find an effect of season on the fungal community while it had a slight effect on bacteria. In addition, we found that Carbon and Nitrogen content were altered differently by warming when roots were excluded.

Overall, this study shows that, despite modifying soil conditions, root exclusion had low effect on the general soil fungal and bacterial communities response to warming.