The effects of CO ₂ and nutrient enrichment on photosynthesis and growth of Poa annua in two consecutive generations

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