Air temperature and drought stress during the experimental period from 2006 to 2009.

Ambient air temperature in relation to the long term mean (1981–2010), effect of warming on the daytime air temperature (8∶00–18∶00 h, UTC+1) and development of the drought stress from year-to-year.
1)difference to the norm ambient air temperatures (1981–2010) at the nearby WMO weather station Zürich/Fluntern, data provided by SwissMeteo.
2)in relation to control, see [27] for further details.
3)based on drought effects on soil water concentration [27], predawn leaf water potential [34] and foliage injury [17].