1. IV. Alps-Adria Conference, 1st March, 2005 Portoroz, Slovenia CARBON BALANCE OF GRASSLANDS IN HUNGARY Nagy Z., Csintalan Zs., Balogh J, Czóbel Sz. Fóti Sz.&, Tuba Z., Department of Botany & Plant Physiology, Szent István University, Hungary - Carbon balance of grasslands in Hungary is measured continously at two sites at the present - Measurement techniques: eddy covariance and chamber methods - Cumulative values of net ecosystem exchange - Effects of extreme events, the 2003 drought

2. FLUXES eddies, carrying heat, momentum, water vapor and trace gases 3D sonic anemometer Open path IRGA 10-20Hz 1GB storage card ~ for one month data Covariances; products of deviations from the means

3. mol/m 3 * m/s

4. Bugac site, 46.69°N, 19.60°E, Hungarian Plains extensive semiarid sandy grassland used as pasture Measurements from July 2002

5. Gap filled cumulative NEE Sink activity, tolerance to drougth, but becoming source due to drough from the mid of the summer

6. Seasonal and diurnal dynamics of NEE Large variation between years in the length and productivity of the growing seasons

7. Mátra Mountains, Szurdokpüspöki, Hungary 300 m asl, 47.85°N, 19.73°E, brown forest soil of high clay content Measurements from June, 2003

8. Gap filled cumulative NEE Sink activity, less tolerant to drougth

9. The contrasting weather patterns between the two years determined the source-sink relation of this grassland. The potential role of extensively managed grasslands in the vegetation's carbon balance on a larger (i.e. regional) scale can be in their recovery potential. Seasonal and daily dynamics of NEE -Profound effect of drought -- Total respiration was less affected by drought than assimilation (months: August in 2003 an 2004). In this way there might be a positive feedback between drought and source activity from grasslands, triggered by heat and drought waves.