Exposure to warming and CO2 enrichment promotes greater above-ground biomass, nitrogen, phosphorus and arbuscular mycorrhizal colonization in newly established grasslands

In view of the projected increase in global air temperature and CO2 concentration, the effects of climatic changes on biomass production, CO2 fluxes and arbuscular mycorrhizal fungi (AMF) colonization in newly established grassland communities were investigated. We hypothesized that above- and below-ground biomass, gross primary productivity (GPP), AMF root colonization and nutrient acquisition would increase in response to the future climate conditions. Furthermore, we expected that increased below-ground C allocation would enhance soil respiration (R-soil). Grassland communities were grown either at ambient temperatures with 375 ppm CO2 (Amb) or at ambient temperatures +3A degrees C with 620 ppm CO2 (T+CO2). Total biomass production and GPP were stimulated under T+CO2. Above-ground biomass was increased under T+CO2 while belowground biomass was similar under both climates. The significant increase in root colonization intensity under T+CO2, and therefore the better contact between roots and AMF, probably determined the higher above-ground P and N content. R-soil was not significantly affected by the future climate conditions, only showing a tendency to increase under future climate at the end of the season. Newly established grasslands benefited from the exposure to elevated CO2 and temperature in terms of total biomass production; higher root AMF colonization may partly provide the nutrients required to sustain this growth response.