Effects of an Experimental Increase of Temperature and Drought on the Photosynthetic Performance of Two Ericaceous Shrub Species Along a North–South European Gradient

Plant ecophysiological changes in response to cli-matic change may be different in northern and southern European countries because different abi-otic factors constrain plant physiological activity. We studied the effects of experimental warming and drought on the photosynthetic performance of two ericaceous shrubs (Erica multiflora and Calluna vulgaris) along a European gradient of temperature and precipitation (UK, Denmark, The Netherlands, and Spain). At each site, a passive warming treat-ment was applied during the night throughout the whole year, whereas the drought treatment ex-cluded rain events over 6–10 weeks during the growing season. We measured leaf gas exchange