In may and june 2011, the FORKAST working group "greenhouse gas exchange" carried out cross-project measurements of the gas exchange in grassland ecosystems. Measurements in the natural environment and in ecosystems under experimentally manipulated climatic conditions were performed in collaboration with the Coordination module. The measurement period began on the study area of TP5 (Prof. Foken / University of Bayreuth) in Voitsumra. Next, measurements followed at the study sites of the EVENT-experiment (TP8, Prof. Jentsch / University of Bayreuth) in the Botanical Garden Bayreuth. All measurements were carried out together with scientists from the sub-project 4 (Dr. Drösler) at the Technical University of Munich. The results should improve the relation of methods of eddy covariance studies, soil chamber, and soil respiration measurements. Furthermore, the drought impact on net CO2 exchange (NEE) of grassland ecosystems should be determined by means of experimental approaches. The findings provide insight into short-term ecosystem responses to extreme events (drought).