In June, measurements were performed with a clear sky. Temperatures
during daytime were in the high twenties. An artificial lowering of the
temperature in the plant chamber to below 20°C on 8 June at about 16.00 h
caused an increase in net photosynthesis rate. Before this drop in
temperature, the maximum measured net photosynthesis rate was
approximately 19 kg CH20 ha -1 h -1 at about 13.00 h, but by lowering the
temperature to below 20°C the net photosynthesis rate increased to 22 kg
CH20 ha-~ h- ~. This increase in net photosynthesis rate was observed for
only a short time after the temperature shift. At constant temperature, net
photosynthesis rate was positively correlated with irradiance. After 16.00 h,
a drop in net photosynthesis rate was observed as a result of both a decrease