Transfer of 14C from the Atmosphere to Fruit Trees
Shogo IMADA, Takashi TANI, Ryuji ARAI, 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 radiation doseto 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 accumulation in them for an apple tree using stablecarbon isotope (13C). In FY 2015, we conducted two preliminary experiments (1) to reveal the effects of soil
temperature on potted young apple trees and (2) to clarify short-term retention of photo-assimilated 13C infruit-bearing shoot in fruit development stages by exposure to 13CO2. The former experiment was for checking
the requirement of soil temperature control in cultivating young apple trees in growth chambers.
To change the soil temperature in cultivated pots, the potted young trees (varieties of Fuji and Tsugaru)
were positioned on the ground surface or buried in the ground in three different climatic areas (Rokkasho,Kuroishi City and Morioka City). In addition, potted apple trees were preliminarily cultivated in the growthchambers with different temperature settings to check growth, leaf physiology and fruit maturity without
controlling soil temperature. We also exposed a fruit-bearing shoot of mature Fuji trees in Morioka City to13

CO2 on October 6 (before maturation stage), November 5 (maturation stage) and November 20 (harvest stage).

Inventories of 13C in leaves, branch and fruit 72 h after the exposures were measured in each fruit development
stage.
Soil temperature in the pots buried in the ground was lower in the daytime and higher in the nighttime incomparison with the pots positioned on the ground surface, while the daily average temperature did notapparently differ between the two. The differences of the soil temperature had hardly any effect on the growthof young apple trees in the field experiment. In the growth chambers with different temperature settings, thesoil temperature in the pots was similar to that of air temperature. The different temperature settings of thegrowth chambers did not largely affect the growth, leaf physiology and fruit maturity of the young apple trees.
Our preliminary short-term exposure to 13CO2 in the fruit-bearing shoots revealed that 13CO2 was assimilatedeven in the maturation and harvest stages, and that the transfer of assimilated 13C into the fruits decreased after
the maturation stage.

。

(a)

(b)

400.006
On the ground
Buried30

Rokkasho

0.004
200.002
10
Rokkasho00.006
RG R Dstem (mm mm -1 d -1)Soil tem perature (°C)

040302010040

Kuroishi City

0.004

0.002

0

Kuroishi City

0.006

Morioka City300.004
200.002100

Morioka City
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On
theBuried
据置
埋設groundふじ/M9Fuji/M.9

On
theBuried
据置
埋設groundつがる/M9Tsugaru/M.9

Seasonal changes in soil temperature (a) and the relative growth rate of stem diameter (RGRDstem)of young apple trees (b) in pots positioned on the ground and the buried pots in three different climate areas.
Error bars represent a standard deviation in six to seven replicates.
(a)(b)
10013C inventory (excess mg)(atom% excess)

13C concentration

10.10.01

葉○ Leaves△ Branch枝□ Fruit
果実

0.001
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0.1
0.01
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The 13C concentration (a) and inventories (b) in the leaves, branch and fruit of a fruit bearing shootof mature Fuji trees before maturation (October 6), maturation (November 5) and harvest (November 20)
stages. Error bars represent a standard deviation in three replicates.