Morphometric Indices of Scots Pine Needle under Chronic Radiation Exposure

We have studied the morphometric indices of needles in Scots pine populations that grow in Bryansk oblast in sites with radioactive contamination long after the Chernobyl accident. The variability in needle weight and length, as well as the fluctuating asymmetry indices and occurrence of necroses and morphoses, were studied in four contaminated and two reference populations of Scots pine in 2011, 2013, and 2014. The exposure of needles in radioactively contaminated sites varied from 7 to 130 mGy/yr. We found brachyblasts with three needles in contaminated Scots pine populations; this morphosis was absent in the reference populations. A dependence of the occurrence of needles damaged by necrosis on the levels of radiation exposure in 2011 was found. However, it was statistically insignificant in other years. The length and weight of needles in contaminated populations differed from the control values; however, the dependence of these indices on the level of radiation exposure was not revealed in the studied range of doses. In 2011 and 2013, the index of fluctuating asymmetry in needle length exceeded the control levels in sites where the absorbed doses were 90 and 130 mGy; this index also tended to grow (statistically significantly in 2011) with an increase in the characteristics of radioactive contamination of the studied plots: the exposure dose rate and the specific activity of ⁹⁰Sr and ¹³⁷Cs in cones and of ¹³⁷Cs in the soil. Therefore, one can observe the consequences of chronic radiation exposure at the organismic level in populations of Scots pine (one of the most radiosensitive plant species) even 25 years after the accident. The data that we obtained in natural habitats confirm the international estimates, according to which the annual chronic radiation exposure of 100 mGy can be considered the limit of safe radiation exposure of natural populations according to morphological and ontogenetic parameters.