Hormesis and Paradoxical Effects of Drooping Birch (Betula pendula Roth) Parameters Under Motor Traffic Pollution

Abstract

Various plant indexes are used or recommended for bioindication. However, the nonmonotonic dose–response dependences (hormesis and paradoxical effects) of these indexes are insufficiently explored upon exposure to pollution. We studied the dependences of these Betula pendula indexes on the intensity of motor traffic pollution. Regression analysis did not reveal any dependence of chlorophyll and carotenoid content on traffic intensity (in 2008 and 2010-2013). Lipid peroxidation rate had different versions of paradoxical effects in 2008 and 2010 to 2012 and increased in comparison with control under an increase in pollution level in 2013. In 2010 to 2012, all dose–response dependences for total protein and thiol group content were biphasic and multiphasic paradoxical effects. In 2013, an increase in traffic intensity induced a linear reduction in protein content and an increase in thiol group level in comparison with the control. In most cases, the studied phenological indexes and seed production decreased monotonically in comparison with the control following an increase in traffic intensity. Only in 2010 and 2013, share of fallen leaves had hormesis and paradoxical effect accordingly. Fluctuating asymmetry had a paradoxical effect and hormesis in 2008 and 2012, accordingly, and increased in comparison with the control under an increase in the level of pollution in 2010 to 2011.

Change of Leaf Trait Asymmetry Type in Tilia cordata Mill. and Betula pendula Roth under Air Pollution

“…It was observed that adverse weather conditions impacted the leaf bilateral asymmetry [17,18]. This fact was also considered in detail in our previous studies [34,56].…”

“…We previously demonstrated that traffic intensity had a high correlation with the content of the main pollutants (oxides of sulphur, nitrogen and carbon as well as benzine, kerosene, benzo[a]pyrene, and formaldehyde) in the air along roads in Nizhni Novgorod (r = 0.8-0.9; p < 0.05). We also revealed the dependences of different plant parameters such as seed production indices, phenological traits, photosynthetic pigment content, leaf FA in B. pendula [34] and lipid peroxidation rate in B. pendula and T. cordata leaf [52] on traffic intensity. These facts confirm that the traffic intensity is an objective indicator of air pollution levels.…”

“…During this period, most leaves reach the full size but do not yet start to senesce. Therefore, the influence of growth and senescence processes on studied leaf traits can be excluded [34].…”

“…We previously evaluated leaf FA in these species, over a number of years, which was reported in a publication for B. pendula [34]. At the same time, we did not analyse FA transition to other asymmetry types in T. cordata and B. pendula under different levels of traffic pollution.…”

Morphometric Analyses of (Hidden) Directional Asymmetry in Leaf Blades

“…The apparent simplicity of the methodology very often led to a distortion of the results because of difference in size and heterogeneity of variables caused by environmental factors [13,25]. Recent studies of fluctuating asymmetry in birch leaves indicated the presence of a paradoxical non-monotonic effect and hormesis in which a relatively small toxic dose increases the asymmetry value [28].…”