Effects of elevated CO2 on flowering phenology and nectar production of nectar plants important for butterflies of calcareous grasslands

Efects of elevated CO2 on _Powering phenology and nectar production were investigated in Trifolium pratense, Lotus corniculatus, Scabiosa columbaria, Centaurea jacea and Betonica o.cinalis, which are all important nectar plants for butter_Pies. In glasshouse experiments, juvenile plants were exposed to ambient (350 ll l)1)and elevated (660 ll l)1)CO2 concentrations for 60_}80 days. Elevated CO2 signiRcantly enhanced the development of _Power buds in C. jacea. B. oficinalis _Powered earlier and L. corniculatus produced more _Powers under elevated CO2. In contrast, the number of _Powers decreased in T. pratense. The amount of nectar per _Power was not a_ected by elevated CO2 in the tested legumes (T. pratense and L. corniculatus), but was signiRcantly reduced (!)in the other forbs. Elevated CO2 did not signiRcantly afect nectar sugar concentra- tion and composition. However, S. columbaria and C. jacea produced signiRcantly less total sugar under elevated CO2. The nectar amino acid concentration re- mained una_ected in all investigated plant species, whereas the total of amino acids produced per _Power was reduced in all non-legumes. In addition, the amino acid composition changed signiRcantly in all investigated species except for C. jacea. The observed efects are unexpected and are a potential threat to _Power visitors such as most butter_Pies which have no alternative food resources to nectar. Changes in nectar production due to elevated CO2 could also have generally detri- mental e_ects on the interactions of _Powers and their pollinators.