Photosynthetic insights into winter-green leaves in Quercus pubescens Willd. seedlings

Abstract

Quercus pubescens Willd. is a deciduous species that can retain leaves in the winter either as dead, standing leaves (marcescence), or as living, winter-green leaves. The retention of green leaves through winter is rare in continental areas. Winter-green leaves were observed on one-year-old seedlings of Q. pubescens in the winter of 2020 in the nursery of the Faculty of Forestry that lasted until the end of April 2021. The photosynthetic activity of photosystem II was measured using the rapid light curve method based on modulated pulse chlorophyll fluorescence. We assessed the potential photosynthetic activity of the leaves across the range of physiological stages: winter-green leaves retained from the previous growing season and on the leaves from the first, second, and third growth flush during the growing season. Photosystem II of winter-green leaves attained ~50-60% of the maximal photosynthetic activity obtained in spring and summer leaves, respectively. Climate data indicated that winter-green leaves exhibited frost resistance in the winter of 2020/2021, as their photosynthetic activity was preserved despite 33 days with sub-zero temperatures. The rapid light curve method also revealed the gradual acclimation of seedlings on a flush level, with leaves from the third flush best able to use available light under high temperatures and insolation efficiently. The results of rapid light use as an indicator of seedling acclimation are discussed. Some remarks on the possible practical significance of the winter-green leaves phenomenon (as in genetic selection) are highlighted.