Transfer of 14C from the Atmosphere to Fruit Trees
Shogo IMADA, Yasuhiro TAKO, Yuichi TAKAKU, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
Part of the14

C released from the nuclear fuel reprocessing plant in Rokkasho, Aomori, Japan in theform of CO2 is incorporated into the organic compounds of crop plants by photosynthesis and causes aradiation dose 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 foran apple tree using a stable carbon isotope (13C).
In FY 2017, we conducted a 13CO2 exposure experiment using three-year old potted ‘Fuji’ apple (Malusdomestica) trees (JM. 1) (hereafter, young apple trees) to obtain data for the model construction. The young
apple trees were exposed to 13CO2 (approximately 15 atom%) for 8 hours in an experimental chamber atdifferent fruit development stages, particularly during the first half of the fruit growing period. The sampletrees were then cultivated in artificial climate chambers, followed by sampling fruits, leaves and current-year
branches at the time of harvesting the fruits. The collected samples were analyzed for 13C concentration to
get 13C retention in the plant parts. Since the C inventory of plant parts during the growing season isnecessary for model construction, we measured the size of fruits, leaves, and current-year branches of
unexposed control sample trees. The C inventory in the samples was nondestructively estimated by using
allometric equations between the size and C concentration, which were established by destructively
measured C concentration data for the trees and other unexposed control sample trees.
The retained 13C concentrations in the fruits at the harvest date increased with later exposure during thefirst half of the fruit growing period, while those in the leaves and current-year branches had a peak with theexposure at around 45 days after buds broke and then decreased with later exposure. The allometricequations to estimate C inventory in the plant parts were well established, and the C inventory data during
the fruits developing period were obtained. All those data will be used for model construction together with13CO2 retention data during the latter half of the fruit growing period, which we plan to get in FY 2018.

54C mass (mol C)

0.05

Fruits0.04

y = 0.00301x
R2 = 0.993
N = 1073

30.4

Leavesy = 0.0293x
R2 = 0.891
N = 1280

0.03

Current-year branches

y = 0.00102x
R2 = 0.936
N = 938

0.3

0.2

20.02

10.01

00.1

00500
1000
LAD1×LAD2×LOD (cm3)

1500

000.40.8
LL×W (cm2) ×SLW

1.2

0100
200300
LB×BAD1 ×BAD2 (mm3)400Fig. 1 The allometric equations between the size and C mass of each of the fruits, leaves, andcurrent-year branches of potted apple trees. LAD1 and LAD2 are lateral diameters of fruits fromperpendicular directions, and LOD is the longitudinal diameter. LL, W and SLW are the length,
width and the time-dependent function of specific leaf area of leaves, respectively. LB is thelength of current-year branches, and BAD1 and BAD2 are the basal diameters fromperpendicular directions.

C mass (mol C plant–1)

155Fruits

2Leaves

410

Current-year branches

1.5

3125

0.5

100050

100

150

200

0050

100150

200

050

100

150

200

Days after bud break（DAB）

Fig. 2 The growth curves of C mass for the fruits, leaves, and current-year branches of apple trees (n =5, bars indicate standard deviation) obtained from allometric equations between size and Cinventory.

13C concentration (atom%)

1.28

1.38

Fruits1.38

Leaves

1.28

1.28

1.18

1.18

Current-year branches

1.18

1.08

1.08
050

100

150200

1.08
050

100

150

200

050

100

150

200

Days after bud break （DAB）

Fig. 3 The 13C concentration in the fruits, leaves, and current-year branches at the harvest date (n = 5,bars indicate standard deviation).
*Broken lines indicate the 13C concentration of control apple trees without 13CO2 exposure.