Morphological abnormalities in Japanese red pine (Pinus densiflora) at the territories contaminated as a result of the accident at Fukushima Dai-Ichi Nuclear Power Plant

Highlights

• Abnormalities in young Japanese red pine trees in Fukushima zone were studied.

• Typical abnormality was cancelling the apical dominance, i.e. branching of the trunk.

• Similar abnormalities were observed in Scots pine within the Chernobyl exclusion zone.

• The abnormality probability correlated with the dose rate received by the trees.

• Abnormalities occurred within 4 years after the beginning of exposure.

Abstract

Our research, carried out in 2014–2016 at eight sites in the radioactive contaminated territories of Fukushima Prefecture, showed that the young trees of Japanese red pine (Pinus densiflora) are sensitive to radiation. Irradiation induced cancellation of the apical dominance in this species. The effect is similar to that observed in young trees of Scots pine growing in the Chernobyl zone. At the same time, we did not observed any morphological abnormalities in mature trees of Japanese red pine. The probability of cancelling the apical dominance in Japanese red pine increased to 0.11 and 0.14 in the two less irradiated populations, and to 0.5 and 0.9 at sites were the absorbed dose rates were approximately 14 and 25 μGy h⁻¹, respectively. Most of the observed abnormalities appeared in the second whorl after the beginning of exposure. No new abnormalities were observed in the fifth whorl. This temporal pattern is similar to those reported for Scots pine in Chernobyl and for Japanese fir in Fukushima. Additional detailed studies are necessary for interpretation of the observed temporal pattern and, in general, for explanation of the mechanism of formation of the morphological abnormalities.

Introduction

The two largest nuclear accidents in history happened at the Chernobyl Nuclear Power Plant (ChNPP; in April 1986) and at the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP; in March 2011). Both accidents were rated Level 7 (IAEA, 2001, IAEA, 2011) according to the International Nuclear Event Scale (INES), and both accidents released large amounts of radionuclides into the environment, contaminating vast territories (UNSCEAR, 2008, UNSCEAR, 2014, Atomic Energy Society of Japan, 2015)). The highest INES Level 7 means that the event is classified as a major nuclear accident causing “widespread health and environmental effects” (IAEA, 2001, IAEA, 2013).

The consequences of the Chernobyl accident included not only severe radioactive contamination of ecosystems, but also radiation induced effects to non-human biota. In particular, a comprehensive study of radiation effects to the coniferous forest ecosystems reported that the coniferous forests near the ChNPP received extremely high doses of acute radiation and subsequently died (Kozubov and Taskaev, 2002). Further from the reactor, where dose rates were lower, the radiation effects included death of some trees and emergence of the numerous morphological abnormalities in survivors, such as shortening or elongation of leaves, shortening of twigs, absence of leaves at the young twigs and deformation of the tree trunks and branches, etc. (Kozubov and Taskaev, 2002). The broadleaved forests ecosystems survived, even those close to the ChNPP (Kozubov and Taskaev, 2002). During the first few years post-accident some abnormalities in broadleaved tree species were observed, such as changes in leaf shape and size; but in general damage to broadleaved forests were much than to Scots pine forests, which are widely present in the Chernobyl zone, or to the populations of Norway spruce. Similar morphological abnormalities as well as genetic defects in plant species in the Chernobyl zone were reported by other researchers (e.g., Kal’chenko et al., 1993a, Kal’chenko et al., 1993b, Rubanovich and Kal’chenko, 1994, Shevchenko and Grinikh, 1995, Geraskin et al., 2003a, Geraskin et al., 2003b and Geras’kin et al., 2013, Pozolotina, 2003).

Presently at Chernobyl, morphological abnormalities are observed mainly in Scots pine (Pinus sylvestris L.) and are almost exclusively presented by the cancelling of the apical dominance (Yoschenko and Bondar, 2009, Yoschenko et al., 2011, Kashparov et al., 2012). This abnormality is very easy to identify. Growth of the tree no longer occurs along a primary, single trunk, but occurs from two or more emerging branches that stem from the primary trunk. The abnormality significantly changes the shape of the tree's crown and, in most cases, leads to growth suppression. In previous studies (Yoschenko and Bondar, 2009, Yoschenko et al., 2011), we formulated the dose rate – effect dependency for this morphological abnormality. The effect sharply increased with chronic radiation dose rate and the frequency of the abnormality was high even at dose rates found in the most contaminated parts of the Fukushima zone (MEXT, 2012). We also found that the effect occurred in trees of 4–8 years of age, independent of dose rate (Yoschenko and Bondar, 2009, Yoschenko et al., 2011).

UNSCEAR (2014) inferred that estimated exposures to non-human biota in the Fukushima zone were too low to observe acute radiation effects. However, given the high radiosensitivity of the coniferous species widely spread in the Fukushima zone (as documented above), one might expect occurrence of the radiation induced effects in these species. Indeed, we observed an increased frequency of the morphological abnormalities in young trees of Japanese fir (Abies firma) growing in the Fukushima zone (Watanabe et al., 2015). Committee 5 (Protection of the Environment) of the International Commission on Radiological Protection emphasized that a careful evaluation is needed of the Fukushima data that suggest long-term environmental impacts (ICRP; Larsson, 2016). This implies a need for additional research in this field. In the present paper, we report results of our observations on morphological abnormalities in young populations of another conifer species, Japanese red pine (Pinus densiflora).