The adhesions of radioactivity pollution to the surfaces of cherry (Prunus×yedoensis) tree bark were studied by measuring ¹³⁷Cs concentrations. Moreover, the effects of decontamination were estimated by ¹³⁷Cs concentrations, GM survey-meter and the autoradiography method in Northern Fukushima Prefecture. The ¹³⁷Cs concentration in the bark grain less than 1 mm of the cherry tree in Fukushima City in 2015 was 254±0.4 kBq/kg. The ¹³⁷Cs concentration in bark of the cherry tree bark-washed with a high pressure washer in 2011 was 22.2±0.2 kBq/kg as half of the measured value in unwashed tree for control in 2014. The spots of autoradiography in imaging plate were transfer from cherry tree bark to the latex gloves used for decontamination treatment. Radioactivity counting rate on the surface of decontaminated bark of cherry tree was 1,010±15 cpm to 95±2 cpm by removing it using a trowel and a metal brush.

Radioactive carbon (¹⁴C) is the dominant radioactive nuclide in transuranic (TRU) waste. However, only a few studies to date have taken into account ¹⁴C transition in its gaseous form (¹⁴CO₂). For an appropriate biosphere assessment of geological disposal, it is important to understand the degree of ¹⁴CO₂ mixing with ambient air by vegetation. To evaluate the impacts of the structure of the plant community, relative to the vertical and horizontal wind speed, we characterized the structure of two gramineous plant communities (community-1, community-2) and compared the wind at three heights (middle, top, and above) of each community. The comparison of the two plant communities revealed that the biomass was the same, but the plant height of community-1 was 78% of that of community-2, and its vegetation density was approximately twice as high. Wind speeds of middle of the community with a higher vegetation density were less affected by the winds outside the community. It was assumed that the winds in the plant communities became more restricted as the community density increased. It is therefore suggested that effects of vegetation density are an important factor for the retention and the transition of ¹⁴CO₂ to vegetation.

Remarkable progresses in food chain analyses by using natural abundances of nitrogen and carbon isotopes are reviewed in particular reference to two empirical equations concerning the occurrences of isotope effects of C and N isotopes during feeding processes. We discussed the possible cause for the variability of 3.4±1.1‰ (Δδ¹⁵N) for the trophic fractionation of nitrogen isotopes during feeding processes (Empirical equation 1). The trophic effect of nitrogen isotopes was discussed by taking recent progresses on the distribution and variation of nitrogen isotope among amino acids. The empirical equation 2 was expressed as follows: a food chain seems to have comprehensive constant value of Δδ¹⁵N/Δδ¹³C value irrespective of vertebrate and invertebrate along food chains judging from the results obtained from completely different aquatic and land ecosystems. Possible reason on this constant was discussed.

Recent developments of isotopic measurement with emphasis on N₂O as the final analyte instead of N₂, can provide great opportunities for scientists to measure δ¹⁵N and δ¹⁸O of nitrogen compounds. The unique characteristics of N₂O such as its low atmospheric concentration, can allow us to measure δ¹⁵N and δ¹⁸O with only 20 nmol-N for nitrate. Moreover, this method is not only for nitrate and can be applicable as long as the target nitrogen compound, such as ammonium, nitrite, and dissolved organic nitrogen can be converted into N₂O. In this review, I introduce the applications of this method to investigate the complex dynamics of nitrogen in the environments.

Dietary analysis based on stable isotope tracers have been developed as a technique analyzing for food consumption patterns of human and animals. The advantage of isotope analysis is not only useful to estimate consumption rate of food resources, but also be a scientific method to shed light on feeding process which composed of biological and sociological phenomenon including statistic researches. This article addresses a new direction of isotopic dietary studies from three complementary case studies.

During 1981–2000, my research focused on the precise determination of the natural abundances of the ¹³C/¹²C and ¹⁵N/¹⁴N ratios (δ¹³C, δ¹⁵N) in many samples of plant tissues and metabolites. That research benefited from the previous work performed by pioneers in this field. My studies during that period provided the followings; (1) the identification of significant differences in the δ¹³C values in plant tissues and phloem sap affected by biotic (N acquisition, plant species and cultivars) and abiotic (drought) factors, (2) the discrimination of ¹⁵N/¹⁴N during the uptake, metabolism, and translocation of nitrate, ammonium and biologically-fixed N, and (3) the application of δ¹³C and δ¹⁵N tracing techniques for the quantification of plant residue dynamics (i.e., accumulation and degradation) in soils, plant N uptake from different sources (soils, chemical fertilizers, organic manures) and field biological N₂ fixation by legumes including trees and non-legumes such as sugarcane and sweet potato, respectively. Here I review my publications and findings which gave insight for a precise understanding of whole plant C/N metabolisms.