Elevated carbon dioxide increases nectar production in Epilobium angustifolium L.

Effects of elevated CO2 and nutrient availability on nectar production and onset of flowering in five different seed families (genotypes) of Epilobium angustifolium were investigated in a greenhouse experiment. Elevated CO2 significantly increased nectar production per day (+51%, p < 0.01), total sugar per flower (+41%, p < 0.05), amino acid concentration (+65%, p < 0.05) and total amino acids per flower (+192%, p < 0.001). All other parameters tested, i.e., nectar sugar concentration, proportion of glucose/fructose and proportion of sucrose/(glucose + fructose), were not significantly affected by elevated CO2 and/or fertilization. However, elevated CO2 caused a marginally significant trend for earlier flowering in highly fertilized plants. No significant family x CO2 interaction was found in any of the tested parameters, but the response in nectar production varied considerably among seed families (+10 to +104%) and was significantly positive in two of the five seed families investigated. Our results are not consistent with earlier studies on effects of elevated CO2 on nectar production and flowering phenology in other plant species. It seems, on the other hand, that CO2 effects on nectar production are specific to species and genotype. Hence, no general conclusions about effects of elevated CO2 on these floral traits can be drawn at present, but it must be cautioned that elevated CO2 might not only increase floral rewards as in E. angustifolium, but might also lead to shifts or even disruptions in fine-tuned plant-pollinator interactions.