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Journal Articles

Sequential loss-on-ignition as a simple method for evaluating the stability of soil organic matter under actual environmental conditions

Sato, Yuhi*; Ishizuka, Shigehiro*; Hiradate, Shuntaro*; Atarashi-Andoh, Mariko; Nagano, Hirohiko*; Koarashi, Jun

Environmental Research, 239(Part 1), p.117224_1 - 117224_9, 2023/12

 Times Cited Count:0 Percentile:0.00(Environmental Sciences)

The stability of soil organic matter (SOM) is important for improving our understanding of the global carbon cycle and ongoing climate change. This study examined the applicability of loss-on-ignition of soil with a stepwise increase in temperature (SIT-LOI) to evaluate the stability of the SOM using soil samples from Japan having different organic matter (OM) and mineral contents and different mean residence times (MRTs), estimated from radiocarbon analysis, for SOM. As the result of this examination, SIT-LOI data was strongly correlated with MRTs. This clearly suggests that SIT-LOI can be an indicator evaluating the stability of SOM in actual environments.

Journal Articles

Effect of soil organic matter on the fate of $$^{137}$$Cs vertical distribution in forest soils

Koarashi, Jun; Atarashi-Andoh, Mariko; Nishimura, Shusaku

Ecotoxicology and Environmental Safety, 262, p.115177_1 - 115177_9, 2023/09

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

Predicting the fate of radiocesium ($$^{137}$$Cs) vertical distribution in Japanese forest soils is key to assessing the radioecological consequences of the Fukushima Daiichi Nuclear Power Plant accident. It is well documented that in mineral soil, the $$^{137}$$Cs behavior is mostly governed by interaction with clay minerals; however, observations have also been accumulated suggesting the role of soil organic matter (SOM) in enhancing the mobility of $$^{137}$$Cs. Here, we hypothesized that soil organic carbon (SOC) concentration profile determines the ultimate vertical distribution of $$^{137}$$Cs in Japanese forest soils. To test this hypothesis, we investigated the detailed vertical distributions of $$^{137}$$Cs in four Japanese forest soils with varying SOC concentration profiles roughly half a century after global fallout in the early 1960s. Results revealed that $$^{137}$$Cs retention ratios in each of 2-cm thick soil layers were negatively correlated with SOC concentrations of the layers, across all soils and depths. This demonstrates that the long-term fate of $$^{137}$$Cs vertical distribution is predictable as a function of SOC concentration for Japanese forest soils.

Journal Articles

Plastic-associated metal(loid)s in the urban river environments of Mongolia

Battulga, B.; Atarashi-Andoh, Mariko; Koarashi, Jun; Bolormaa, O.*; Kawahigashi, Masayuki*

Ecotoxicology and Environmental Safety, 261, p.115100_1 - 115100_10, 2023/08

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

The widespread distribution of plastic debris in the riverine environment is one of the major concerns of environmental pollution because of its potential impact on the aquatic ecosystem. In this study, we investigated accumulation of metal(loid)s on polystyrene foam (PSF) plastics collected from the Tuul River shore of Mongolia. Sorbed metal(loid)s on plastics have been extracted from collected PSF by sonication after peroxide oxidation. Size-dependent association of metal(loid)s indicated that PSFs act as vectors for the pollutants in the urban river environment. In addition, images from scanning electron microscopy (SEM) indicated not only the degraded surface of plastics showing fractures, holes, and pits, but also adhered mineral particles and microorganisms on PSFs. Interaction of metal(loid)s with plastics may be facilitated by altered surface physical and chemical properties of the plastics through photodegradation followed by an increase in surface area by size reduction and/or biofilm development in the aquatic environment. Enrichment ratio (ER) of metals on PSF samples suggested continuous accumulation of heavy metals on plastics. Our results demonstrate that the widespread plastic debris could be one of the carriers for hazardous chemicals in the environment. Since the influences of plastic debris on environmental health are major concerns to be solved, the fate and behavior of hetero-aggregates of plastics in aquatic environments should be continuously studied.

Journal Articles

Tracking the behavior and characteristics of microplastics using a multi-analytical approach; A Case study in two contrasting coastal areas of Japan

Battulga, B.; Atarashi-Andoh, Mariko; Matsueda, Makoto; Koarashi, Jun

Environmental Science and Pollution Research, 30(31), p.77226 - 77237, 2023/05

 Times Cited Count:0 Percentile:0.00(Environmental Sciences)

The global survey for the presence of microplastics (MPs) in aquatic environments has attracted widespread scientific attention over the past decade. This study demonstrates a multidimensional analytical approach, including isotopic and thermogravimetric analyses to evaluate characteristics and behavior of MPs in the environment. The MP samples were collected in two contrasting coastal areas of Japan. The $$delta$$$$^{13}$$C values of field-collected polyethylene (PE), polypropylene (PP), and polystyrene (PS) MPs were ranged from -25.6 to -31.4, -23.4 to -30.9, and -27.3 to -28.6 per mil, respectively. The differences in $$delta$$$$^{13}$$C signature between MPs with the same polymer types (i.e., PE and PP) but different colors. Through thermal analysis, the single-step endothermic process was observed for environmental PE and PS-MPs. The results reveal that degradation may play a significant role in the behavior and characteristics of MP debris in the aquatic environment.

Journal Articles

Atmospheric ammonia deposition and its role in a cool-temperate fragmented deciduous broad-leaved forest

Katata, Genki*; Yamaguchi, Takashi*; Watanabe, Makoto*; Fukushima, Keitaro*; Nakayama, Masataka*; Nagano, Hirohiko*; Koarashi, Jun; Tateno, Ryunosuke*; Kubota, Tomohiro

Atmospheric Environment, 298, p.119640_1 - 119640_12, 2023/04

 Times Cited Count:1 Percentile:47.41(Environmental Sciences)

Journal Articles

Stable C and N isotope abundances in water-extractable organic matter from air-dried soils as potential indices of microbially utilized organic matter

Nagano, Hirohiko*; Atarashi-Andoh, Mariko; Tanaka, Sota*; Yomogida, Takumi; Kozai, Naofumi; Koarashi, Jun

Frontiers in Forests and Global Change (Internet), 6, p.1228053_1 - 1228053_9, 2023/00

 Times Cited Count:0 Percentile:0.01(Ecology)

Journal Articles

Development of a new model simulating contaminations of forest resources with radiocesium in Fukushima

Ota, Masakazu; Koarashi, Jun

Isotope News, (784), p.28 - 31, 2022/12

In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with $$^{137}$$Cs. However, $$^{137}$$Cs transfer processes determining the tree contamination (particularly for stem wood, a prominent commercial resource) remain insufficiently understood. We propose a model (SOLVEG-R) for simulating dynamic behavior of $$^{137}$$Cs in a forest tree-litter-soil system and applied it to contaminated forests of cedar plantation and natural oak stand in Fukushima to elucidate relative impact of distinct $$^{137}$$Cs transfer processes determining the tree contamination. The transfer of $$^{137}$$Cs to the trees occurred mostly ($$>$$99%) through surface uptake of $$^{137}$$Cs trapped by needles and bark during the fallout. Root uptake of soil $$^{137}$$Cs was several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, internal contamination of the trees proceeded through an enduring recycling (translocation) of $$^{137}$$Cs absorbed on the tree surface. A significant surface uptake of $$^{137}$$Cs through bark was suggested, contributing to 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining uptake occurred at needles) of the total uptake by the trees. It was suggested that the activity concentration of $$^{137}$$Cs in stem wood of the trees at these sites are currently (as of 2021) decreasing by 3% per year, mainly through radioactive decay of $$^{137}$$Cs and partly through dilution effect from tree growth.

Journal Articles

Ten years of warming increased plant-derived carbon accumulation in an East Asian monsoon forest

Zhang, J.*; Kuang, L.*; Mou, Z.*; Kondo, Toshiaki*; Koarashi, Jun; Atarashi-Andoh, Mariko; Li, Y.*; Tang, X.*; Wang, Y.-P.*; Pe$~n$uelas, J.*; et al.

Plant and Soil, 481(1-2), p.349 - 365, 2022/12

 Times Cited Count:4 Percentile:60.99(Agronomy)

Journal Articles

A New approach to extracting biofilm from environmental plastics using ultrasound-assisted syringe treatment for isotopic analyses

Battulga, B.; Atarashi-Andoh, Mariko; Nakanishi, Takahiro; Koarashi, Jun

Science of the Total Environment, 849, p.157758_1 - 157758_11, 2022/11

 Times Cited Count:3 Percentile:38.08(Environmental Sciences)

Characterizing plastic-associated biofilms is key to the better understanding of organic material and mineral cycling in the "Plastisphere"-the thin layer of microbial life on plastics. In this study, we propose a new method to extract biofilms from environmental plastics, in order to evaluate the properties of biofilm-derived organic matter through stable carbon ($$delta$$$$^{13}$$C) and nitrogen ($$delta$$$$^{15}$$N) isotope signatures and their interactions with radionuclides especially radiocesium ($$^{137}$$Cs). After ultrasound-assisted separation from the plastics, biofilm samples were successfully collected via a sequence of syringe treatments. Biofilm-derived organic matter samples (14.5-65.4 mg) from four river mouths in Japan showed $$^{137}$$Cs activity concentrations of $$<$$75 to 820 Bq kg$$^{-1}$$ biofilm (dw), providing evidence that environmental plastics, mediated by developed biofilms, serve as a carrier for $$^{137}$$Cs in the coastal environment. Significant differences in the ($$delta$$$$^{13}$$C and $$delta$$$$^{15}$$N signatures were also obtained for the biofilms, indicating the different sources, pathways, and development processes of biofilms on plastics.

Journal Articles

Spatial variation in soil respiration rate is controlled by the content of particulate organic materials in the volcanic ash soil under a ${it Cryptomeria japonica}$ plantation

Abe, Yukiko*; Liang, N.*; Teramoto, Munemasa*; Koarashi, Jun; Atarashi-Andoh, Mariko; Hashimoto, Shoji*; Tange, Takeshi*

Geoderma Regional (Internet), 29, p.e00529_1 - e00529_11, 2022/06

 Times Cited Count:1 Percentile:13.31(Soil Science)

This study aimed to clarify the causes of spatial variation in soil respiration rate on volcanic ash soil. From January 2013 to August 2019, soil respiration rates were measured at 40 measuring points periodically at a 35-year-old ${it Cryptomeria japonica}$ plantation in Tokyo, Japan. In August 2019, the carbon content of the litter layer, total carbon content of soil organic matter (SOM), carbon content of the low-density fraction (LF-C) of SOM, fine root biomass, and bulk density of soil were measured at all measuring points. Results of the multiple regression analysis showed that the model with only the LF-C as an explanatory variable had the highest capability for predicting the respiration rate at a soil temperature of 20$$^{circ}$$C, indicating that LF-C, which is considered to be readily available to soil microorganisms, can be the main factor responsible for the spatial variation in soil respiration rate.

Journal Articles

Contamination processes of tree components in Japanese forest ecosystems affected by the Fukushima Daiichi Nuclear Power Plant accident $$^{137}$$Cs fallout

Ota, Masakazu; Koarashi, Jun

Science of the Total Environment, 816, p.151587_1 - 151587_21, 2022/04

 Times Cited Count:7 Percentile:69.58(Environmental Sciences)

In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with $$^{137}$$Cs. However, $$^{137}$$Cs transfer processes determining tree contamination (particularly for stem wood, which is a prominent commercial resource in Fukushima) remain insufficiently understood. This study proposes a model for simulating the dynamic behavior of $$^{137}$$Cs in a forest tree-litter-soil system and applied it to two contaminated forests (cedar plantation and natural oak stand) in Fukushima. The model-calculated results and inter-comparison of the results with measurements elucidated the relative impact of distinct $$^{137}$$Cs transfer processes determining tree contamination. The transfer of $$^{137}$$Cs to trees occurred mostly ($$>$$ 99%) through surface uptake of $$^{137}$$Cs directly trapped by leaves or needles and bark during the fallout. By contrast, root uptake of $$^{137}$$Cs from the soil was unsubstantial and several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, the internal contamination of the trees proceeded through an enduring recycling (translocation) of $$^{137}$$Cs absorbed on the tree surface at the time of the accident. A significant surface uptake of $$^{137}$$Cs at the bark was identified, contributing 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining surface uptake occurred at the needles) of the total $$^{137}$$Cs uptake by trees. It was suggested that the trees growing at the study sites are currently (as of 2021) in a decontamination phase; the activity concentration of $$^{137}$$Cs in the stem wood decreases by 3% per year, mainly through radioactive decay of $$^{137}$$Cs and partly through a dilution effect from tree growth.

Journal Articles

Dynamics of radiocaesium within forests in Fukushima; Results and analysis of a model inter-comparison

Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.

Journal of Environmental Radioactivity, 238-239, p.106721_1 - 106721_10, 2021/11

 Times Cited Count:11 Percentile:61.41(Environmental Sciences)

This study was aimed at analysing performance of models for radiocesium migration mainly in evergreen coniferous forest in Fukushima, by inter-comparison between models of several research teams. The exercise included two scenarios of countermeasures against the contamination, namely removal of soil surface litter and forest renewal, and a specific konara oak forest scenario in addition to the evergreen forest scenario. All the models reproduced trend of time evolution of radiocesium inventories and concentrations in each of the components in forest such as leaf and organic soil layer. However, the variations between models enlarged in long-term predictions over 50 years after the fallout, meaning continuous field monitoring and model verification/validation is necessary.

Journal Articles

Spatial variations in radiocesium deposition and litter-soil distribution in a mountainous forest catchment affected by the Fukushima nuclear accident

Atarashi-Andoh, Mariko; Koarashi, Jun; Tsuzuki, Katsunori; Takeuchi, Erina; Nishimura, Shusaku; Muto, Kotomi*; Matsunaga, Takeshi*

Journal of Environmental Radioactivity, 238-239, p.106725_1 - 106725_8, 2021/11

 Times Cited Count:1 Percentile:5.54(Environmental Sciences)

To understand the spatial variation in soil $$^{137}$$Cs inventory in complex mountainous topography, a whole-area investigation of $$^{137}$$Cs deposition in a broad-leaved forest catchment of a mountain stream was conducted using grid sampling. Across the catchment, organic and surface mineral soil layers were collected at 42 locations in 2013 and 6 locations in 2015. $$^{137}$$Cs deposition on the forest floor exhibited high spatial heterogeneity and altitude-dependent distribution over the catchment. The $$^{137}$$Cs retention ratio in the organic layer ranged from 6% to 82% in 2013. The $$^{137}$$Cs retention ratios had positive correlations with the material inventory in the organic layer and the elevation. The $$^{137}$$Cs retention ratios in the organic layer were less than 20% in 2015, even at the locations where the retention ratio was higher than 55% in 2013. Although there was spatial variation in the migration speed, $$^{137}$$Cs migration from the organic layer to mineral soil was almost completed within 4 y of the deposition.

Journal Articles

Soil microbial community responding to moderately elevated nitrogen deposition in a Japanese cool temperate forest surrounded by fertilized grasslands

Nagano, Hirohiko; Nakayama, Masataka*; Katata, Genki*; Fukushima, Keitaro*; Yamaguchi, Takashi*; Watanabe, Makoto*; Kondo, Toshiaki*; Atarashi-Andoh, Mariko; Kubota, Tomohiro*; Tateno, Ryunosuke*; et al.

Soil Science and Plant Nutrition, 67(5), p.606 - 616, 2021/10

 Times Cited Count:2 Percentile:18.14(Plant Sciences)

We analyzed the relationships between nitrogen deposition (deposition of nitrate and ammonium ions) and soil microbial properties in a cool temperate forest surrounded by normally fertilized pasture grasslands in northern Japan. The aim of the present study was to gain the primary information on soil microbial response to moderately elevated nitrogen deposition ($$<$$ 10 kg N ha$$^{-1}$$ y$$^{-1}$$). We established three experimental plots in the forest edge adjacent to grasslands and other three plots in the forest interior at least 700 m away from the grasslands. During May to November 2018, nitrogen deposition in each plot was measured. In August 2018, litter and soil (0-5 cm depth) samples were collected from all plots to measure net nitrogen mineralization and nitrification rates as indicators of microbial activity, and microbial biomass carbon and nitrogen and various gene abundances (i.e. bacterial 16S rRNA, fungal ITS, bacterial amoA, and archaeal amoA genes) as indicators of microbial abundance and structure. Nitrogen deposition in the forest edge was 1.4-fold greater than that in the forest interior, even while the maximum deposition was 3.7 kg N ha$$^{-1}$$. Nitrogen deposition was significantly correlated to the net nitrogen mineralization and nitrification rates and the 16S rRNA and bacterial amoA gene abundances. Microbial community structures were different between litter and soil samples but were similar between the forest edge and interior. Significant correlations of nitrogen deposition to the soil carbon to nitrogen ratio, and the nitrate and ammonium contents were also observed. Thus, our results show that moderately elevated nitrogen deposition in nitrogen-limited forest edges can stimulate microbial activities and abundances in soils.

Journal Articles

Transfer of $$^{137}$$Cs to web-building spiders, ${it Nephila clavata}$, and its pathways; A Preliminary study using stable carbon and nitrogen isotope analyses

Tanaka, Sota; Kakinuma, Hotaru*; Adachi, Taro*; Atarashi-Andoh, Mariko; Koarashi, Jun

Journal of Nuclear Science and Technology, 58(4), p.507 - 514, 2021/04

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Understanding the pathways of $$^{137}$$Cs transfer to predatory spiders is useful to assess long-term behavior of $$^{137}$$Cs in the environment, because spiders obtain food resources from both the grazing and detritus food chains in terrestrial-aquatic linking forest ecosystems. In the present study, we collected spider samples at forest interior and riverside. The sample collection was approximately 6.5 years after the FDNPP accident. Moreover, a transfer factor value (T$$_{ag}$$) for $$^{137}$$Cs in spiders was quantified. Stable carbon and nitrogen isotope ratios ($$delta$$$$^{13}$$C and $$delta$$$$^{15}$$N) of the spiders were also investigated to estimate the transfer pathways of $$^{137}$$Cs to the spiders.

JAEA Reports

Practical guide on soil sampling, treatment, and carbon isotope analysis for carbon cycle studies

Koarashi, Jun; Atarashi-Andoh, Mariko; Nagano, Hirohiko*; Sugiharto, U.*; Saengkorakot, C.*; Suzuki, Takashi; Kokubu, Yoko; Fujita, Natsuko; Kinoshita, Naoki; Nagai, Haruyasu; et al.

JAEA-Technology 2020-012, 53 Pages, 2020/10


There is growing concern that recent rapid changes in climate and environment could have a significant influence on carbon cycling in terrestrial ecosystems (especially forest ecosystems) and could consequently lead to a positive feedback for global warming. The magnitude and timing of this feedback remain highly uncertain largely due to a lack of quantitative understanding of the dynamics of organic carbon stored in soils and its responses to changes in climate and environment. The tracing of radiocarbon (natural and bomb-derived $$^{14}$$C) and stable carbon ($$^{13}$$C) isotopes through terrestrial ecosystems can be a powerful tool for studying soil organic carbon (SOC) dynamics. The primary aim of this guide is to promote the use of isotope-based approaches to improve our understanding of the carbon cycling in soils, particularly in the Asian region. The guide covers practical methods of soil sampling; treatment and fractionation of soil samples; preparation of soil samples for $$^{13}$$C (and stable nitrogen isotope, $$^{15}$$N) and $$^{14}$$C analyses; and $$^{13}$$C, $$^{15}$$N, and $$^{14}$$C measurements by the use of isotope ratio mass spectrometry and accelerator mass spectrometry (AMS). The guide briefly introduces ways to report $$^{14}$$C data, which are frequently used for soil carbon cycling studies. The guide also reports results of a case study conducted in a Japanese forest ecosystem, as a practical application of the use of isotope-based approaches. This guide is mainly intended for researchers who are interested but are not experienced in this research field. The guide will hopefully encourage readers to participate in soil carbon cycling studies, including field works, laboratory experiments, isotope analyses, and discussions with great interest.

Journal Articles

Formation and mobility of soil organic carbon in a buried humic horizon of a volcanic ash soil

Wijesinghe, J. N.*; Koarashi, Jun; Atarashi-Andoh, Mariko; Kokubu, Yoko; Yamaguchi, Noriko*; Sase, Takashi*; Hosono, Mamoru*; Inoue, Yuzuru*; Mori, Yuki*; Hiradate, Shuntaro*

Geoderma, 374, p.114417_1 - 114417_10, 2020/09

 Times Cited Count:10 Percentile:49.80(Soil Science)

Journal Articles

Effectiveness of decontamination by litter removal in Japanese forest ecosystems affected by the Fukushima nuclear accident

Koarashi, Jun; Atarashi-Andoh, Mariko; Nishimura, Shusaku; Muto, Kotomi*

Scientific Reports (Internet), 10(1), p.6614_1 - 6614_11, 2020/04

 Times Cited Count:10 Percentile:45.36(Multidisciplinary Sciences)

We conducted a pilot-scale decontamination study in a deciduous broadleaved forest in Fukushima. The entire forest, other than two untreated areas, was decontaminated by removing the litter layer approximately 3.3 years after the accident. For three years after decontamination, we quantified $$^{137}$$Cs contamination levels in the litter and topsoil layers and in the tree leaves, in the untreated and decontaminated areas. The decreased inventories of litter-associated $$^{137}$$Cs in the decontaminated areas were observed only in the first year after decontamination. Generally, no decontamination effects were observed on the $$^{137}$$Cs transfer in tree leaves. The primary reason for this was the rapid shift in the main reservoir of $$^{137}$$Cs from litter layers to the underlying mineral soil, which differs from the observations in post-Chernobyl studies of European forest ecosystems. The results suggest that litter-removal decontamination can only be successful if it is implemented more quickly for Japanese forest ecosystems.

Journal Articles

Characterizing vertical migration of $$^{137}$$Cs in organic layer and mineral soil in Japanese forests; Four-year observation and model analysis

Muto, Kotomi; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Koarashi, Jun

Journal of Environmental Radioactivity, 208-209, p.106040_1 - 106040_10, 2019/11

 Times Cited Count:13 Percentile:48.08(Environmental Sciences)

Vertical distributions of $$^{137}$$Cs in the soil profile were observed at five forest sites with different vegetation types for 4.4 years after the Fukushima Dai-ichi Nuclear Power Plant accident, and $$^{137}$$Cs migration in the organic layer and mineral soil was analyzed based on a comparison of models and observations. Cesium-137 migration from the organic layer was faster than that observed in European forests, suggesting that the mobility and bioavailability of $$^{137}$$Cs could be suppressed rapidly in Japanese forests. The diffusion coefficients of $$^{137}$$Cs in the mineral soil were estimated to be 0.042-0.55 cm$$^2$$y$$^{-1}$$, which were roughly comparable with those of European forest soils affected by the Chernobyl Nuclear Power Plant accident. Model predictions indicated $$^{137}$$Cs mainly distributed in the surface mineral soil at 10 years after the accident. It suggest that the $$^{137}$$Cs deposited onto Japanese forest ecosystems will be retained in the surface layers of mineral soil for a long time.

Journal Articles

Effect of dry-wet cycles on carbon dioxide release from two different volcanic ash soils in a Japanese temperate forest

Nagano, Hirohiko; Atarashi-Andoh, Mariko; Koarashi, Jun

Soil Science and Plant Nutrition, 65(5), p.525 - 533, 2019/10

 Times Cited Count:3 Percentile:17.03(Plant Sciences)

In the present study, two volcanic ash soils (soil A and B) from a temperate broad-leaved forest in eastern Japan were incubated under repeated dry-wet cycles and continuously constant moisture conditions. The primary aims were to quantify the potential for enhancement of carbon dioxide (CO$$_{2}$$) release owing to increased water fluctuation and to examine differences in the responses of volcanic ash soils with different physicochemical properties. Soil B, rather than soil A, was a typical Andosol. During incubation at 20 $$^{circ}$$C for 120 days with five dry-wet cycles, the CO$$_{2}$$ release rate was measured periodically. Abundance of the stable carbon isotope in CO$$_{2}$$ ($$delta^{13}$$C-CO$$_{2}$$) was measured to capture changes in the origin of decomposed soil organic matter (SOM) owing to the dry-wet cycles. The CO$$_{2}$$ release rate under the dry-wet cycles was up to 49% higher than the values predicted from a parabolic relationship between CO$$_{2}$$ release and water content during incubation under the continuously constant moisture condition. The magnitude of CO$$_{2}$$ release enhancement was 2.7-fold higher in soil B relative to that in soil A. The $$delta^{13}$$C-CO$$_{2}$$ value in the dry-wet cycles was enriched by 0.3-2.3%$$_{0}$$ compared to that during incubation under the continuously constant moisture conditions, suggesting that the decomposition of old and/or well-metabolized SOM was enhanced by the dry-wet cycles. Thus, the present study suggests that Andosols, which have been believed to have a strong SOM stabilization ability, are vulnerable to dry-wet cycles. Then, increased water fluctuation in a future warmer world would have significant potential to stimulate CO$$_{2}$$ release from soils.

277 (Records 1-20 displayed on this page)