Physiological and biochemical adjustments of the assimilatory system of advance regeneration of Norway spruce to cutting-induced changes in the environment

Various forestry practices (shelterwood systems, selective felling) promoted for the natural regeneration of Norway spruce can speed up the emergence of the advanced growth. Overstory removal can cause drastic environmental changes, resulting in the death of newly regenerated trees or blocking their growth. We studied changes in the content of photosynthetic pigments, parameters of chlorophyll a fluorescence, activity of antioxidant system enzymes in the needles of 20-year-old advance regeneration of Norway spruce and alteration of xylem radial growth rate in response to abrupt cutting-induced changes in the environment. Cutting led to inhibition of photochemical activity (the maximum photochemical efficiency of PSII (Fv/Fm), quantum yield of photosystem II (Y(II)) and relative electron transport rate (ETR) decreased), rearrangement of the pigment system (the content of chlorophyll a (Chl a) and chlorophyll b (Chl b) decreased, chlorophyll a/b (Chl a/b) ratio increased) and a sharp rise in non-photochemical quenching (NPQ). A year later, after clear-cutting, the needles had adapted to the new conditions. Low NPQ level was associated with increased Chl a content and Chl a/b ratio and upregulation of antioxidant enzymes. The activity of photochemical processes increased (Fv/Fm, Y(II), and ETR) and the radial xylem increment was promoted significantly. When using forestry practices involving overstory removal, it is necessary to consider that light intensity increase, associated reduction of air and soil humidity, as well as an increase in the air temperature, can have a negative effect on advance regeneration of Norway spruce growth after cutting down, effect that is reversed after one year.