Morphological defects in native Japanese fir trees around the Fukushima Daiichi Nuclear Power Plant

Abstract

After the accident at the Fukushima Daiichi Nuclear Power Plant (F1NPP) in March 2011, much attention has been paid to the biological consequences of the released radionuclides into the surrounding area. We investigated the morphological changes in Japanese fir, a Japanese endemic native conifer, at locations near the F1NPP. Japanese fir populations near the F1NPP showed a significantly increased number of morphological defects, involving deletions of leader shoots of the main axis, compared to a control population far from the F1NPP. The frequency of the defects corresponded to the radioactive contamination levels of the observation sites. A significant increase in deletions of the leader shoots became apparent in those that elongated after the spring of 2012, a year after the accident. These results suggest possibility that the contamination by radionuclides contributed to the morphological defects in Japanese fir trees in the area near the F1NPP.

Figure 1. Schematic diagram of Japanese fir tree in January 2015.

Figure 2. Map showing the observation sites.

A red star indicates the location of the Fukushima Daiichi Nuclear Power Plant. The base map was modified from the Digital Japan Portal Web Site (Geospatial Information Authority of Japan; GSI). Airborne monitoring results on 2013.11.19; the “Extension site of distribution map of radiation dose, etc.,/Digital Japan” was used as the source of the distribution of radiation dose.

Figure 3. Representative morphological defects in Japanese fir trees.

Arrowheads indicate the position of deleted leader shoot. (A) normal tree (S3), (B) defected tree (vertical forking, S1), (C) defected tree (horizontal forking, S2).

Figure 4. Relative frequency of main axis defects in Japanese fir trees from different sites.

The defects were counted by the observation of 5 annual whorls from the top of the trees. Trees with deleted or dead leader shoots in the lower whorls were excluded from observation; therefore the observed tree number for defects (n: indicated in the graph) were different from the total number of observed trees (Table 1). Bonferroni-corrected p-values are presented using Chi-square tests with df = 1.

Figure 5. Relative frequency of deleted leader shoot in the annual whorls of the main axis in Japanese fir trees from different sites.

The deletions were counted by the observation of 5 annual whorls from the top of the trees. Years indicate the time that the whorl branches sprouted out in the spring (Fig. 1). Trees with deleted or dead leader shoots by previous years were excluded from observation; therefore observed tree number (n: indicated in the graph) decreased in each year. Different letters indicate statistically significant differences compared to the whorls of 2010 in each site (**^{, ††, ‡‡}p < 0.01, *^{,†, ‡}p < 0.05, Bonferroni-corrected Fisher’s exact test). P < 0.0001 for each of 2012, 2013, and 2014 in S1; P < 0.0001 and P = 0.0032 for 2013 and 2014, respectively in S2; P = 0.0032 and 0.014 for 2012 and 2013, respectively in S3.

Figure 6. Number of lateral branches from the annual whorls of the main axis in Japanese fir trees from different sites.

The lateral branches were counted by the observation of 5 annual whorls from the top of the trees. The data are shown as mean ± SE. Years indicate the time that the whorl branches sprouted out in the spring. Trees with deleted or dead leader shoots by previous years were excluded from observation; therefore observed tree number (n) decreased in each year (n is indicated in the graph). Different letters indicate statistically significant differences compared to the whorls of 2010 in each site (**^{, ††, ‡‡}p < 0.01, *^{,†, ‡}p < 0.05, Bonferroni-corrected t test after one-way ANOVA). P < 0.0001 for 2013 in S2; P = 0.0012 for 2014 in S3; P = 0.00013 for 2012, and P < 0.0001 for each of 2013 and 2014 in S4.

Figure 7. Representative deleted leader shoot and apical bud of main stem in Japanese fir trees.

Arrowheads indicate the position of deleted leader shoot. (A) annual whorl of 2013 (S1), (B) winter buds of 2015 at the top of the main axis (S1).