Weather data

The air temperature and the relative air humidity were determined 2 m above the ground and the global radiation was obtained at the meteorological station ‘Dahlem’ of the Free University of Berlin (Institut für Meteorologie der Freien Universität Berlin, Germany) 610 m east and 750 m southeast of the site. All parameters were recorded at one-minute intervals from the beginning of March to the time of the last harvest. For the figures, one-hour-mean values were calculated. Additionally, in the field, the quantum flux (quantum flux [μmol quanta m⁻² s⁻¹] = radiation [Wm⁻²]∙λ [nm]∙0.836∙10⁻²) was recorded with a MQ-200 quantum flux meter (Apogee Electronics, Santa Monica CA, U.S.A.) and the air temperature and humidity controlled with a Voltcraft DL-121TH data logger (Voltcraft, Switzerland) several times during the experiment for comparison.