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 aninternal radiation 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, as a representative for fruit tree crops, using a stable carbon isotope (13C).
In FY 2018, 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 latter half of the fruit growing period. The sampletrees were then cultivated in artificial climate chambers. At the time of harvesting the fruits, sampling wasdone for fruits, leaves and current-year branches. 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, whichwere used in the experiment, is necessary for model construction, we measured the size of fruits, leaves, andcurrent-year branches of unexposed control sample trees at predetermined intervals. The C inventory in thesamples was nondestructively estimated by using allometric equations between the sample size and C
inventory, which was established by using destructively measured C biomass data for the trees.
The allometric equations to estimate C inventory in each plant part from the nondestructive
measurements were well established with R2 > 0.91 between estimated and observed values. The C inventory
data of the plant parts during the fruit development period were estimated by using the equation and themeasured size, followed by obtaining the growth curves of C inventory as logistic regression curves. The 13C
concentrations retained in the fruits at the harvest date increased with later exposure until 120 days afterflowering (DAF), followed by similar values after 120 DAF. In the leaves and current-year branches, theretained 13C concentrations consistently showed low values after 77 DAF. The retained 13C concentration
data in FY 2018 could be smoothly connected with those obtained in FY 2017 during the first half of the fruit
growing period except for a few data. All those data and the logistic regression curves of C inventory will beused for model construction in FY 2019.

a) Fruits

C inventory (mol C)

3y = 0.0028 x
R2 = 0.99
N = 3062b) Leaves

0.03

y = 0.030x
R2 = 0.96
N = 1291

0.020.1
1Vegetative shoots
y = 0.0091x
R2 = 0.91
N = 3630.01

0000250500

750

10000LAD1×LAD2×LOD (cm3)Fig. 1

0.2

0.4

0.6

00.8

5

LL×W (cm2) ×SLW (g cm–2)

101520

LB×BAD1×BAD2 (cm3)

The allometric equations between the size and C inventory of each sample of the fruits, leaves,and current-year branches of potted apple trees. LAD1 and LAD2 are lateral diameters of fruits
from perpendicular directions, and LOD is the longitudinal diameter. LL, W and SLW are thelength, width and specific leaf weight, respectively. LB is the length of current-year branches,and BAD1 and BAD2 are the basal diameters from the perpendicular directions.
*the broken lines indicate regression linesa) Fruits

12C inventory (mol C plant–1)c) Current-year branches
Bourse shoots
Spurs
y = 0.015x
y = 0.016x
R2 = 0.94
R2 = 0.95
N = 523
N = 6680.2b) Leaves5c) Current-year branches

1.5413620.5

1000501001502000050100150200050100150200

Measurement date (days after bud break: DAB)

Fig. 2The growth curves of C inventory for the fruits, leaves, and current-year branches of apple
trees obtained from allometric equations between sample size and C inventory.
*The data enclosed by the broken lines indicate C biomass obtained by the destructive
measurement at the harvest date. Solid lines indicate the growth curves obtained by the logistic
regression models.
a) Fruits

13C/(13C + 12C)

0.012b) Leaves

0.01350.01150.011

FY2018FY20170.0105

0.013

0.013

0.01250.0125

0.012

0.012

0.01150.0115

0.011

0.011

0.0105060120180c) Current-year branches

0.01350.0105060

120180060120180

Exposure date （days after flowering：DAF）

Fig. 3

13The C concentration in the fruits, leaves, and current-year branches at the harvest date (n = 5,mean ± S.D.). The data obtained in FY 2017 were shown together with those in FY 2018.