Asymmetric warming is one of the distinguishing features of global climate change, in which winter and night-time temperatures are predicted to increase more than summer and diurnal temperatures. Winter warming weakens vernalization and hence decreases the potential to flower for some perennial herbs, and night warming can reduce carbohydrate concentrations in storage organs. A new paper in Annals Of Botany examines whether asymmetric warming acts to reduce flower number and nectar production per flower in a perennial herb, Saussurea nigrescens, a key nectar plant for pollinators in Tibetan alpine meadows.
A long-term (6 years) warming experiment was conducted using open-top chambers placed in a natural meadow and manipulated to achieve asymmetric increases in temperature during the growing and non-growing seasons. Measurements were taken of nectar volume and concentration (sucrose content) and leaf non-structural carbohydrate content and plant morphology. Six years of experimental warming resulted in reductions in nectar volume per floret, floret number per capitulum and capitulum number per plant, whereas nectar concentration remained unchanged. Depletion of leaf non-structural carbohydrates was significantly higher in the warmed than in the ambient condition. Overall plant density was also reduced by warming, which, when combined with reductions in flower development and nectar volumes, led to a reduction of ∼90 % in nectar production per unit area.
The negative effect of asymmetric warming on nectar yields in S. nigrescens may be explained by a depletion of leaf non-structural carbohydrates. The results highlights a novel aspect of how climate change might affect plant–pollinator interactions and plant reproduction via induction of allocation shifts for plants growing in communities subject to asymmetric warming.
Mu, J., Peng, Y., Xi, X., Wu, X., Li, G., Niklas, K.J. and Sun,S. Artificial asymmetric warming reduces nectar yield in a Tibetan alpine species of Asteraceae. Annals of Botany 28 April 2015 doi: 10.1093/aob/mcv042