Application of fluctuating asymmetry indexes of silver birch leaves for diagnostics of plant communities under technogenic pollution

The prospects for applying the fluctuating asymmetry (FA) of silver birch (Betula pendula Roth) leaves for diagnosis of plant community conditions in technogenically polluted environments are considered with an example of the effect of heavy metals and chronic ionizing radiation. An increase in the minimum sample size to 150–180 leaves and measurements of morphometric traits with an improved accuracy of 0.06–0.07 mm made it possible to overcome the influence of sample size on FA parameters. The excess content of nickel (18.5 times with respect to the background level), lead (16.0 times), manganese (5.8 times), and copper (3.0 times) in birch leaves was accompanied by the increase in multivariate FA index by 20.0%. The chronic exposure to ionizing radiation (at absorbed dose rate on the soil surface of 4.74 µGy/h) elevated the multi-variate FA index of leaves by 29.8% and the content of chlorophylls a and b in leaves by 50.3 and 82.9%, respectively. It was found that the most informative morphometric trait for analysis of birch leaf FA is the distance between the bases of the first and second lateral veins; its FA index rose to 40.4% under the influence of heavy metals and to 53.6% under exposure to chronic ionizing radiation. Thus, FA can be regarded as a sensitive biomarker for detecting early negative responses of forest ecosystems to technogenic pollution.