Influence of industrial felling on the structure of spruce undergrowth needles

Changes in the structure of spruce undergrowth needles (Picea obovata L.) after clearcutting were studied. The study was carried in the bilberry spruce forest and in a spruce forest clearing in the middle taiga of the European North-East of Russia. Annual vegetative shoots of spruce at the clearcut were statistically significantly superior to shoots under the forest canopy by 45–47% in length and by 44–53% in number of needles (p < 0.05). The loss of needles with age is more intensive under the forest canopy. The needle number of fifth year shoots is 1.5 times lower than that of shoots in the clearcut. The needles in the clearcut are 27, 13 and 15% larger in cross-sectional area, thickness and width, respectively (p < 0.001). It is associated with an increase in the number and/or size of cells of the needle tissues. The observed changes in the ultrastructure of mesophyll cells of annual needles during the growing season differed between plots. In the spruce forest the density of chloroplasts in cytoplasm increases from the beginning to the middle of the vegetation period, the number of mitochondria increases until fall. The maximum density of mesophyll cell organelles in the clearcut was observed in spring. The following are common for needles under the forest canopy and on the clearcut: gradual decrease of starch in green plastids from May to October, maximum number of granal thylakoids in chloroplasts in summer and accumulation of lipid droplets in the cytoplasm of mesophyll cells at the end of the vegetation period. Due to adaptation of the photosynthetic apparatus to increased insolation, chloroplasts in mesophyll cells at the clearcut are characterized by a greater proportion of twinned thylakoids throughout the growing season, compared to the spruce forest.