Continuous monitoring of fluorescence from a leaf of Ilex aquifolium, and of air temperature by the MONITORING-PAM revealed that Fm’ and F fluorescence levels dropped sharply during onset of a frost period on 07.01’09. Fluorescence levels recovered close to initial values only at beginning of April when day temperatures reached 20°C and night temperatures did not drop below 5°C.
Likely, the sustained fluorescence quenching during low temperatures reflects markedly increased dissipation of absorbed light energy. This energy dissipation can prevent damage by light under very low temperature conditions when light energy can not be used by biochemistry.