A dependence of the photosynthesis rate on light is characterized by a number of parameters that are often used for comparison between plant species or for finding photosynthesis interconnections with other physiological processes. In order to properly assessed these parameters, we measured the maximum apparent photosynthesis rate (P max), dark respiration rate (R d), light compensation point (LCP), quantum yield corresponding to photosynthetic efficiency (QY), and the light saturation constant (K s), taking into consideration the leaf plastochron index during vegetation of one of the willow species (Salix dasyclados Wimn.). The P max value was the highest in the beginning of the growth season when the leaf reached 65% of its full area; after that P max slowly declined. The most important cardinal value for R d is its plateau reached by the end of leaf growth, i.e., later than the photosynthesis rate maximum. This plateau value also decreased during vegetation. The LCP value changed in the same way as R d but reached its plateau simultaneously with the photosynthesis rate maximum. QY also reached its maximum at the same time with the photosynthesis rate; during vegetation it changed more than twofold. The K s value also changed almost twofold during the season, reaching its maximum together or slightly later than the photosynthesis maximum and then remained constant. Thus, we have found significant changes in the parameters of the photosynthesis light curve during growth season. This shows that they can be used only after a thorough study of leaf development in each particular plant species. Usually performed measuring gas exchange parameters in fully developed leaves does not yield their maximum values and thus does not have any physiological sense.
Russian Journal of Plant Physiology – Springer Journals
Published: Jun 28, 2009
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