Black leaf-clips increased minimum fluorescence emission in clipped leaves exposed to high solar radiation during dark adaptation

Under high solar radiation, the use of black leaf-clips for dark adaptation adopted by the continuous-excitation fluorometer Pocket PEA (Hansatech Instruments) is reportedly known to underestimate the maximum quantum yield of PSII photochemistry (Fv/Fm), because of a rising in minimum fluorescence emission (Fo), probably due to an increase of leaf temperature. In field-grown tomato or pepper, the temperature of the leaf portion covered by the black leaf-clip was monitored in clipped leaves exposed to solar radiation during dark adaptation (clipped-only leaves), and compared with clipped leaves protected from solar radiation by aluminium foil (clipped and shrouded leaves). Results confirmed the reportedly underestimation of Fv/Fm in clipped-only leaves mainly due to an increased Fo. In a tomato trial, leaf temperature raised from about 30 up to 44.5°C in clipped-only leaves, with a negligible increase in clipped and shrouded leaves. In two pepper trials, leaf temperature in clipped-only leaves increased from about 27 to 36.2°C or from about 33 to 40.9°C. A parameter for the clip-effect on fluorescence emission is proposed, which resulted to be 0.706, 0.241 and 0.358 for the three trials, respectively.