SynopsisThe photon emission (ultraweak photon emission and delayed luminescence) of duckweeds (Spirodela polyrrhiza) and 1-2 year old tree seedlings (Picea abies, Abies alba and Fagus sihatica) was investigated by means of a single photon counting equipment. The decay kinetics of DL, the temperature dependence of UPE, and the anaerobic phase-induced kinetics of UPE were measured under/after treatment with ozone and UV-radiation. The results suggest that more consideration be given to photon emission as an indicator of stress-induced changes in plants.