Transfer of 14C from the Atmosphere to Fruit Trees
Shogo IMADA, Yasuhiro TAKO, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
14Part of the C released from the nuclear fuel reprocessing plant in Rokkasho, Aomori, Japan in the formof CO2 is incorporated into the organic compounds of crop plants by photosynthesis and causes a radiationdose to people who consume the crops. The purpose of this study is to establish a dynamic compartment model
describing transfer of photo-assimilated 14C into fruits and its accumulation in them for an apple tree using astable carbon isotope (13C). In FY 2016, we conducted three preliminary experiments comparing two apple(Malus domestica) cultivars (‘Fuji’ and ‘Tsugaru’) (1) to determine the effects of temperature on potted young
apple trees in experimental growth chambers, (2) to clarify short-term retention of photo-assimilated 13C infruit-bearing shoots in different fruit development stages by exposure to 13CO2, and (3) to establish anestimation method for leaf, branch, and fruit biomass.
In the first experiment, we grew young ‘Fuji’ and ‘Tsugaru’ apple trees planted in pots in two experimental
growth chambers with different temperature settings and their growth was compared particularly during avigorous growth period. In both chambers, temperature was changed at 10 days intervals according to theaveraged day- and night-time temperatures of natural conditions, but the diurnal patterns were simulated for
only one chamber (Chamber A) and not for the other (Chamber B). Young ‘Fuji’ trees successfully bore fruit,
while ‘Tsugaru’ trees did not. The fruit diameter and its growth rate for ‘Fuji’ apples did not change withdifferent temperature settings. The shoot length and stem diameter and their growth rates did not vary between
the different temperature settings or between the cultivars.
We conducted the second experiment using the fruit-bearing shoots of mature ‘Fuji’ and ‘Tsugaru’ trees
in an orchard in Morioka, Iwate Prefecture. Three fruit-bearing shoots on trees were exposed to 13CO2 indifferent fruit development stages by using a newly developed exposure chamber system. Net assimilated 13C
during exposure and inventories of 13C in leaves, branch and fruit at 72 h after the exposures were measured
in each development stage. The 13C remaining ratio (13C inventory in each plant organ)/(net assimilated 13C
during exposure) of fruit increased from the early development stage to the development stage in both cultivars,
while the ratio in ‘Fuji’ apples decreased from the development stage to the late development stage, but not in‘Tsugaru’.
In the third experiment, we established an estimation method for the biomass of each plant organ bymeasuring the size of leaf, branch, and fruit of ‘Fuji’ and ‘Tsugaru’. Biomass of leaf, branch and fruit wasestimated by length, width, and the time function of specific leaf weight, by length and diameter, and by lateraland longitudinal diameters, respectively. High coefficients of determination were found between estimated andmeasured biomass in both cultivars (R2 > 0.93).

600.6a)

Growth rate of fruit diameter(mm day–1)

Fruit diameter (mm)Chamber A
Chamber B
40

20035

0.4

0.2

045
57
72
80
91
101
Days after the start of diapause termination (days)

Chamber AEFD

FDLFDFM1a) ‘Fuji’

10.8

LeavesBranchFruit

0.8

0.6
0.4
0.2

FM

0.4
0.2

6/1

7/1

8/1

9/1

10/1

11/1

5/1

6/1

7/1

8/1

9/1

10/1

11/1

The seasonal changes in the 13C remaining ratios (13C inventory in each plant organ)/(net assimilated
13C during exposure) in the leaves, branch, and fruit of the ‘Fuji’(a) and ‘Tsugaru’ (b) apple shoots
at 72 h after 13CO2 exposure in different fruit development stages. EFD, early fruit development
stage. FD, fruit development stage. LFD, late fruit development stage. FM, fruit maturation stage.
Number of samples for each point was three. Bars indicate standard deviation.

100100a) ‘Fuji’
y = 0.0809x
R² = 0.9891
n = 1260

8060

Fruit biomass (g‐dry)Fruit biomass (g‐dry)FD05/14020b) ‘Tsugaru’
y = 0.0719x
R² = 0.996
n = 1239

80
604020000200

400600

LAD1×LAD2×LOD (cm3)Fig. 3EFDb) ‘Tsugaru’

0.60Fig. 2Chamber B

Growth of fruit diameter (a) and its growth rate in three years old ‘Fuji’ trees (b) in two growthchambers (GCs) with different temperature settings（Chamber A, n = 8; Chamber B, n = 13; bars
indicate standard deviation）

13C remaining ratio

13C remaining ratio

Fig. 1b)

800

1000

0200400

600

800

1000

LAD1×LAD2×LOD (cm3)

The relationships between the product of lateral (bidirectional measurements; LAD1 and LAD2)
and longitudinal diameters (LOD) and their corresponding biomass in the fruit of ‘Fuji’ (a) and‘Tsugaru’ (b) apple trees