Underestimate of PS2 efficiency in the field due to high leaf temperature resulting from leaf clipping and its amendment |
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Authors: | J. -H. Weng |
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Affiliation: | (1) Department of Life Sciences, National Chung-Hsing University, Taichung, Taiwan |
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Abstract: | Chlorophyll fluorescence parameter Fv/Fm, an indicator of the maximum efficiency of PS2, is routinely measured in the field with plant leaves darkened by leaf clips. I found that on a sunny day of subtropical summer, the Fv/Fm ratio was often underestimated because of a large F0 value resulted from a high leaf temperature caused by clipping the leaf under high irradiance, especially for long (e.g. 20 min) duration. This phenomenon may overestimate the down-regulation of PS2 efficiency under high irradiance. When leaf temperature was lower than 40 °C, the F0 level of rice leaves under clipping remained practically unchanged. However, F0 increased drastically with leaf temperature rising over 40 °C. In most measurements, no significant difference in Fm was found between rice leaves dark-adapted by leaf clips for 10 min and for 20 min. Therefore, shading leaf clips to prevent a drastic increase of leaf temperature, using F0 measured immediately after the leaf being darkened to calculate Fv/Fm, as well as shortening the duration of leaf clipping are useful means to avoid an underestimate of Fv/Fm. |
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Keywords: | chlorophyll fluorescence leaf clip leaf temperature irradiance Oryza photosystem 2 efficiency rice |
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