Effects of elevated CO 2 on flowering phenology and nectar production

Abstract

Effects of elevated CO 2 on flowering phenology and nectar production were studied in five important nectar plants of calcareous grasslands, i.e. Lotus corniculatus, Trifolium pratense, Betonica officinalis, Scabiosa columbaria and Centaurea jacea. Glasshouse experiments showed that flowering probability was significantly enhanced in C. jacea. B. officinalis flowered carlier and L. corniculatus produced more flowers under elevated CO 2. 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 significantly reduced in the other forbs. Elevated CO 2 did not significantly affect nectar sugar concentration and sugar composition. However, S. columbaria and C. jacea produced significantly less total sugar per flower under elevated CO 2. The nectar amino acid concentration remained unaffected in all investigated plant species whereas the total of amino acids produced per flower was significantly reduced in all non-legumes. 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 most butterflies which have no alternative food resources except nectar. Changes in nectar production due to elevated CO 2 could also generally have detrimental effects on the interactions of flowers and their pollinators.