We studied short- and long-term growth responses of Poa annua L. (Gramineae) at ambient and elevated (ambient +200 lmol mol 1) atmospheric CO2. In experiment 1 we compared plant growth during the early, vegetative and final, reproductive growth phases. Plant growth in elevated CO2 was significantly enhanced during the early phase, but this was reversed in the reproductive phase. Seed mass and percentage germination were significantly reduced in elevated CO2. Experiment 2 tested for the impact of transgenerational and nutrient effects on the response of Poa annua to elevated CO2. Plants were grown at ambient and elevated CO2 for one or two consecutive generations at three soil nutrient levels. Leaf photosynthesis was significantly higher at elevated CO2, but was also affected by both soil nutrient status and plant generation. Plants grown at elevated CO2 and under conditions of low nutrient availability showed photosynthetic acclimation after 12 weeks of growth but not after 6 weeks. Firstgeneration growth remained unaffected by elevated CO2, while second-generation plants produced significantly more tillers and flowers when grown in elevated CO2 compared to ambient conditions. This effect was strongest at low nutrient availability. Average above- and belowground biomass after 12 weeks of growth was enhanced in elevated CO2 during both generations, but more so during plant generation 2. This study demonstrates the importance of temporal/maternal effects in plant responses to elevated CO2.