Temperate terrestrial ecosystems are currently exposed to climatic and air quality changes with increased atmospheric CO2, increased temperature and prolonged droughts. The responses of natural ecosystems to these changes are focus for research, due to the potential feedbacks to the climate. We here present results from a field experiment in which the effects of these three climate change factors are investigated solely and in all combinations at a temperate heath dominated by heather (Calluna vulgaris) and wavy hair-grass (Deschampsia flexuosa).

Climate induced increases in plant production may increase plant root exudation of dissolved organic compounds such as amino acids, and the release of amino acids during decomposition of organic matter. Such free amino acids in soil serve as substrates for soil microorganisms and are also acquired as nutrients directly by plants. We investigated the magnitude of the response to the potential climate change treatments on uptake of organic nitrogen in an in situ pulse labelling experiment with 15N13C2-labelled glycine (amino acid) injected into the soil.
In situ root nitrogen acquisition by grasses responded significantly to the climate change treatments, with larger 15N uptake in response to warming and elevated CO2 but not additively when the treatments were combined. Also, a larger grass leaf biomass in the combined T and CO2 treatment than in individual treatments suggest that responses to combined climate change factors cannot be predicted from the responses to single factors treatments.

The soil microbes were superior to plants in the short-term competition for the added glycine, as indicated by an 18 times larger 15N recovery in the microbial biomass compared to the plant biomass. The soil microbes acquired glycine largely as an intact compound (87%), with no effects of the multi factorial climate change treatment through one year.