In situ experimental exposure of fruit-bearing shoots of apple trees to 13CO2 and construction of a dynamic transfer model of carbon

Seasonal accumulation of photoassimilated carbon relates to growth rate and use for new aboveground organs of young apple trees in following spring

Deciduous trees accumulate carbon (C) in woody parts during the growth season which is subsequently used for the initial development and growth of newly formed organs in the following season; however, it is unclear which period during the growth season contributes to C accumulation. Three-year-old potted Malus domestica (apple) trees were grown in controlled growth chambers during the growth season and exposed to 13CO2 in an exposure chamber at seven different periods of the growth season, including vegetative and reproductive growth periods. Approximately half of the trees were harvested in late autumn, and the remaining trees were grown in a field in the following year. The 13C accumulation in the different organs in late autumn, and its concentration in the new aboveground growth during the following growth season, was determined. The concentration of the photoassimilated 13C in woody parts (shoots, trunk, rootstock and coarse roots) in the late autumn was higher in the trees labeled during the period of vigorous vegetative growth than in those labeled during other periods of growth. Furthermore, 13C concentration in the leaves, annual shoots, flower buds and flowers in the following early spring was also high in the trees labeled during this period. The concentration of 13C in the flower buds and flowers was positively correlated with that in the woody parts in the late autumn and old shoots in the following spring. Hence, the seasonal accumulation of photoassimilated C in woody parts in late autumn is related to growth rates during the growth season and its use for the initial development of newly formed organs in the following spring. These results suggest that under non-stressed conditions, C accumulated during the period of vigorous vegetative growth largely contributes to the C reserves that are used for the development of new organs in the following year.

RETENTION OF ORGANICALLY BOUND DEUTERIUM IN GRASS PLANTS EXPOSED TO HEAVY WATER VAPOUR AT DIFFERENT GROWTH STAGES

Potted timothy grass plants were exposed to heavy water (HDO) vapour at seven different periods during the third growth of harvestable shoots (the part 5-cm above the ground surface), and the concentration of non-exchangeable organically bound deuterium (NE-OBD) was measured in harvestable shoots, stubbles and roots at the third harvest. The excess concentration of NE-OBD was obtained as an increase in the concentration of NE-OBD against the background level. On average, this value was 1.8- to 2.6-fold higher in the harvestable shoots than in the stubble for plants exposed to HDO vapour during the period when the harvestable shoots grew faster than the stubble. Our results suggest that the separation of harvestable shoots and stubble, both of which are generally combined as one part in studies on the metabolism of organically bound tritium (OBT) in grass, could contribute to a realistic evaluation of OBT transfer from timothy to livestock.

DIRECT ASSIMILATION OF ATMOSPHERIC CARBON BY IMMATURE APPLE FRUITS

Although fruit development primarily depends on photoassimilation by leaves, immature green fruits can also directly assimilate atmospheric CO2. To elucidate the process of C accumulation due to direct assimilation by fruit, we conducted a 13CO2 exposure experiment in an orchard in late June with immature 'Fuji' apples (Malus domestica). Four fruits from three trees were enclosed in transparent plastic bags and exposed to 13CO2 using an in-situ exposure system. Fruits were collected prior to and immediately following exposure in early July, late September and mid-November, and 13C concentrations in the peduncle, skin, flesh and core (including seeds) were measured. The higher assimilated 13C concentrations measured following exposure indicated that the fruits directly assimilated atmospheric 13C. The 13C concentration in fruit skin was higher immediately after exposure and in early July compared with that prior to exposure. In late September and mid-November, 13C concentrations were close to natural levels.

EXPERIMENTAL EVALUATION OF DISTRIBUTION OF 14C PHOTOASSIMILATED INTO CARBOHYDRATES IN DIFFERENT GROWTH STAGES OF FRUIT-BEARING APPLE SHOOTS USING A 13CO2 IN-SITU EXPOSURE SYSTEM

In this study, we aimed to investigate the photoassimilation process of 14CO2 into agricultural plants through determining the photoassimilated carbohydrate-13C in each part (leaves, current branch and fruit) of the fruit-bearing apple shoots exposed to 13CO2 in different growth stages (early and late fruit development stages). The carbohydrate content was assessed as soluble (ethanol-extracted fraction) and other (HCl-extracted and residual fractions) components. The total (i.e. sum of the three fractions) bulk carbohydrate concentrations in all parts of the shoots were statistically similar between different growth stages. The changes in the concentration of 13C-labeled soluble carbohydrate (i.e. ethanol-extracted fraction) to the total content between different growth stages were statistically unclear among all parts of the shoot. These results suggest that the distribution ratio of photoassimilated 13C in soluble and other components in the apple shoot was thereabout constantly independent of the growth stages.

RESEARCH ON THE ENVIRONMENTAL EFFECTS OF RADIONUCLIDES AT IES - AN OVERVIEW

This paper summarises the research works of the Institute for Environmental Sciences on the environmental behaviour of radionuclides related to the first commercial-spent nuclear fuel reprocessing plant at Rokkasho Village, Aomori Prefecture, Japan. The distribution and fluctuation in natural radiation in Aomori Prefecture were estimated as basic data. Radionuclides possibly released from the plant operation have been continuously measured using a variety of samples from different locations in Aomori Prefecture. During the test of cutting and chemical treatment of the spent fuel rods from 2006 to 2008, the concentration of 85Kr, 14C, 3H and 129I in the air increased, whereas that of 3H and 129I increased in several environmental samples. A numerical simulation model consisting of several sub-models was constructed for predicting the behaviour of released radionuclides in the environment and for evaluating the realistic radiation dose of residents around the facility.

Investigation of ratio of carbon to hydrogen (C/H ratio) in agricultural plants for further estimation of their productivity of organically bound tritium

The carbon to hydrogen ratio (C/H ratio, w/w) in plants is a key factor in estimating the amount of hydrogen in the photosynthetic product. The amount of hydrogen calculated from photosynthetic model estimation associated with the C/H ratio is an essential parameter of the estimation model of productivity of organically bound tritium (OBT) by plants. To propose a sophisticated estimation model of OBT by agricultural plants, temporal changes in the C/H ratio of six plant species (Japanese radish, cabbage, orchard grass, paddy field rice, apple, and radish) during their cultivation were investigated for each plant part. The C/H ratio in the plants cultivated in the field and growth chamber generally exceeded 6, which is the value for the primary photosynthetic monosaccharides, such as glucose and fructose (both chemical formulae, C₆H₁₂O₆). In the vegetative parts (e.g. Japanese radish leaves, cabbage leaves and roots, rice leaves and roots, and radish leaves and fine roots) the C/H ratio fluctuated irregularly or remained constant within an approximate range of 6.6-7.3 during cultivation. The C/H ratio in enlarged organs (e.g. Japanese radish root, rice ear, apple fruit, and radish main root) decreased continuously, approaching 6. These results suggest that the C/H ratio can be generally set as approximately 6.9 except for enlarged organs, in which the ratio may change over time during cultivation, within an approximate range of 6-7.