Warming affects soil metabolome: The case study of Icelandic grasslands

The effect of warming is stronger in arctic and sub-arctic latitudes than in temperate and tropical zones. We studied soil metabolomes along two soil-warming gradients (0 to +15 °C). One temperature gradient has been present for at least 50 years and possibly even centuries (long-term treatment), while the second gradient was created after a shallow crustal earthquake in 2008 (short-term treatment). Soil metabolomes at the two sites responded differently to warming. At the short-term warmed site, warming of ≤+3 °C already shifted soil metabolomic profiles relative to the controls, whereas at the long-term warmed site the soil metabolome only shifted at temperatures ≥+5 °C. Saccharides and amino acids, primary metabolites involved in protective mechanisms against heat, were the main compounds accumulated at the highest soil warming levels. Some secondary metabolites associated with a broad spectrum of stressors, like phenolic acids and terpenes, were also up-regulated. Across the IPCC scenario's, most climate models predict a substantial rise in mean annual temperature of up to 8 °C in the Arctic region by the end of the 21st century. Our results suggest that temperature increases of ≥+5 °C would permanently alter soil metabolomic profile, whereas smaller temperature increases of (≤+3 °C) would affect soil metabolome profile transiently, not permanently.