Non-structural carbohydrates in fine roots and rhizomes in warmed subarctic grasslands

Abstract

Climate predictions for subarctic regions show a higher rise in surface temperature than the global average, which will subsequently raise the soil temperature (Ts) in those regions. In response to soil warming, an increase in photosynthetically active aboveground biomass is expected, which will modify the amount of carbon assimilated. This will impact the amount of carbon allocated to aboveground and belowground growth, to root exudations and surplus carbon that might be stored as non-structural carbohydrates (NSCs). We here ask the question if soil warming affects NSCs concentration and pools in fine roots and rhizomes in subarctic grasslands.We investigated the effects of soil warming duration (medium-term (11-yr) vs. long-term (>60-yr) warmed grassland) and magnitude from 0 to +8.4 °C on community-level soluble NSCs (glucose, fructose and saccharose) in short-living fine roots and long-living rhizomes. Additionally, we determined NSCs in fine roots and rhizomes of three dominating species- Anthoxanthum odoratum, Ranunculus acris and Equisetum spp. along the soil warming gradient.We saw a significant increase in community-level total NSCs in rhizomes driven by an increase in the amount of saccharose under medium-term warming. The community-level saccharose concentration in rhizomes was positively related to the abundance of grasses in both grasslands. Both changes in concentration of NSCs and biomass of fine roots and rhizomes at the community level contributed to a significant change in NSCs pool in belowground plant organs along the soil warming gradient. At the species level, the amount of NSCs was significantly higher in Ranunculus acris; the significant difference in fine roots and rhizomes in their NSCs was observed in Equisetum spp. and the significant effect of soil warming on NSCs in fine roots and rhizomes was observed in Anthoxanthum odoratum.We highlight the species-specific differences in NSCs concentrations and analyze the effects of soil warming duration and magnitude on the community-level change in NSCs reserves in belowground plant organs.