Abstract:
Over the last century an increase in mean soil surface temperature has been observed and it is predicted to increase further in the future. To evaluate the legacy effects of increased temperature on both nitrogen (N) transformation rates in the soil and nitrous oxide (N2O) emissions, an incubation experiment was conducted with soils taken from a long term in situ warming experiment on temperate permanent grassland. In this experiment the soil temperature was elevated by 0 (control), 1, 2 or 3°C (4 replicates per treatment) using IR-lamps over a period of 6 years. The soil was subsequently incubated under common conditions (20°C and 50% humidity) and labelled with NO315NH4 Gly, 15NO3NH4 Gly or NO3NH4 15N-Gly. Both inorganic N (NO3-+NH4+) and NO3- contents were higher in soil subjected to the +2 and +3°C temperature elevations. Analyses of N transformations using a 15N tracing model, showed that, following incubation, gross organic (and not inorganic) N transformation rates decreased in response to the prior soil warming treatment. This was also reflected in reduced N2O emissions associated with organic N oxidation and denitrification. A newly developed source partitioning model showed the importance of oxidation of organic N as a source of N2O. Concluding, long term soil warming can cause a legacy effect which diminishes organic N turn over and the release of N2O from organic N and denitrification.
