Black leaf-clips of a commercial fluorometer increased leaf temperature during dark adaptation under high solar radiation

The use of black leaf-clips for dark adaptation under high solar radiation conditions is reported to underestimate the maximum quantum yield of PSII photochemistry (F-v/F-m) measured by the continuous-excitation fluorometer Pocket PEA. The decrease in F-v/F-m was due to a rise in minimum fluorescence emission (F-o), probably resulting from increased leaf temperature (T-l). In field-grown tomato and pepper, fluorescence parameters and T-l in the region covered by the black leaf clip were measured in clipped leaves exposed to solar radiation during dark adaptation (clipped-only leaves) and in clipped leaves protected from solar radiation by aluminium foil (shrouded clipped leaves). Results confirmed significant F-v/F-m underestimates in clipped-only leaves primarily due to increased F-o. In one tomato experiment, T-l increased from 30 to 44.5A degrees C in clipped-only leaves, with a negligible rise in shrouded clipped leaves. In two respective pepper experiments, T-l in clipped-only leaves increased from 27 to 36.2A degrees C and 33 to 40.9A degrees C. Based on the results of this study, a clip-effect parameter (P-CE) on fluorescence emission is proposed as the difference for F-v/F-m (or -F-o/F-m) between shrouded clipped leaves and clipped-only leaves, which resulted to be 0.706 for tomato, and 0.241 and 0.358 for the two pepper experiments.