Changes in the leaf structure and pigment complex of Betula pendula under conditions of technogenic air pollution

Atmospheric pollution in an urban environment not only disrupts the balance of elements in phytocoenoses, but also leads to changes at different levels of organization of plant organisms, including those affecting their photosynthetic apparatus. The anatomical and morphological features as well as photosynthetic pigment content in the leaves of Betula pendula Roth, growing in the zone of influence of the industrial cluster in Chelyabinsk (Russia) with varying degrees of toxic load, were studied. Six sites were selected taking into account the wind rose near the Chelyabinsk Metallurgical Plant: five impact and one background (northwestern part of the Kashtaksky pine forest). Based on the content of heavy metals in the soil, the total toxic load index was calculated for each impact site, which averaged 3.6. It was noted that in the impact sites the thickness of the leaf blade significantly increased (on average by 23%), largely due to the palisade mesophyll and upper cuticle. Moreover, the number of stomata increased, as well as the leaf mass per area (by an average of 30%), which was accompanied by a decrease in its area (by an average of 65%). Under conditions of increased technogenic load, a decrease in the content of chlorophylls a and b was also noted (on average by 44%), but the ratio between them did not change significantly (1.75 on average). Carotenoids turned out to be more stable: their content in impact sites reduced to a lesser extent. The conclusion about the significance of compensatory rearrangements of B. pendula photosynthetic apparatus during adaptation to long-term stress has been made.