EFFECTS OF ELEVATED CO2 ON FLOWERING PHENOLOGY AND NECTAR PRODUCTION

Effects of elevated CO2 on flowering phenology and nectar production w ere studied in five important nectar plants of calcareous grasslands, i.e. Lotus corniculatus, Trifolium pratense, Betonica officinalis, Sca biosa columbaria ia and Centaurea jacea. Glasshouse experiments showed that flowering probability was significantly enhanced in C. jacea. B. officinalis flowered earlier and L. corniculatus produced more flower s under elevated CO2. In contrast, the number of flowers decreased in T. pratense. The amount of nectar produced per flower was not affected in the investigated legumes (T. pratense, L. corniculatus), but was s ignificantly reduced in the other forbs. Elevated CO2 did not signific antly affect nectarsugar concentration and sugar composition. However, S. columbaria and C: jacea produced significantly less total sugar pe r flower under elevated CO2. The nectar amino acid concentration remai ned unaffected in all investigated plant species whereas the total of amino acids produced per flower was significantly reduced in all nan-l egumes. In addition, the amino acid composition changed significantly in all investigated species except for C. jacea. The observed effects are unexpected and are a potential threat to flower visitors such as m ost butterflies which have no alternative food resources except nectar . Changes in nectar production due to elevated CO2 could also generall y have detrimental effects on the interactions of flowers and their po llinators.