Long term CO2 enrichment stimulates N-mineralisation and enzyme activities in calcareous grassland

Elevated concentration of atmospheric carbon dioxide will affect carbon cycling in terrestrial ecosystems. Possible effects include increased carbon input into the soil through the rhizosphere, altered nutrient concentrations of plant litter and altered soil moisture. Consequently, the ongoing rise in atmospheric carbon dioxide might indirectly influence soil biota, decomposition and nutrient transformations. N-mineralisation and activities of the enzymes invertase, xylanase, urease, protease, arylsulfatase, and alkaline phosphatase were investigated in spring and summer in calcareous grassland, which had been exposed to ambient and elevated CO2 concentrations (365 and 600 mul(-1)) for six growing seasons. In spring, N-mineralisation increased significantly by 30% at elevated CO2, while there was no significant difference between treatments in summer (+3%). The response of soil enzymes to CO2 enrichment was also more pronounced in spring, when alkaline phosphatase and urease activities were increased most strongly by 32 and 21%. In summer, differences of activities between CO2 treatments were greatest in the case of urease and protease (+21 and + 17% at elevated CO2). The stimulation of N-mineralisation and enzyme activities at elevated CO2 was probably caused by higher soil moisture and/or increased root biomass. We conclude that elevated CO2 Will enhance below-ground C- and N-cycling in grasslands. (C) 2003 Elsevier Science Ltd. All rights reserved.