記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Forests  

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. The significance of aquatic lateral carbon (C) export in mangrove ecosystems highlights the extensive contribution of aquatic pathways to the net ecosystem carbon budget. However, few studies have investigated lateral fluxes of dissolved organic carbon (DOC) and inorganic carbon (DIC), partly due to methodological difficulty. Therefore, we evaluated area-based lateral C fluxes in a small mangrove estuary that only had one exit for water exchange to the coast. We sampled water from the mouth of the creek and integrated discharge and consecutive concentration of mangrove-derived C (∆C). Then, we estimated the area-normalized C fluxes based on the inundated mangrove area. DIC and DOC concentrations at the river mouth increased during ebb tide during both summer and winter. We quantified the ∆C in the estuary using a two-component conservative mixing model of freshwater and seawater. DIC and DOC proportions of ∆C concentrations at the river mouth during ebb tide was between 34% and 56% in the winter and 26% and 42% in the summer, respectively. DIC and DOC fluxes from the estuary were estimated to be 1.36 g C m−2 d−1 and 0.20 g C m−2 d−1 in the winter and 3.35 g C m−2 d−1 and 0.86 g C m−2 d−1 in the summer, respectively. Based on our method, daily fluxes are mangrove area-based DIC and DOC lateral exports that can be directly incorporated into the mangrove carbon budget.

DOI： 10.3390/f11101041

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Polar Science  

© 2020 Elsevier B.V. and NIPR Shrub encroachment and soil respiration (SR) are predicted to increase in the tundra ecosystem under climate warming, but little is known regarding potential causal relationships between shrubs and SR at a local scale. Multiple and complex belowground processes exist between the two phenomena, and consolidation is logistically difficult. Our study aimed to identify and integrate multiple belowground processes to elucidate the impact of shrub coverage on SR, using structural equation modeling (SEM). Results indicated that shrub coverage enhanced SR through root biomass, fungal community composition and soil temperature. SEM also revealed a potential indirect effect via interactions among those soil factors. Soil factors relating heterotrophic respiration affected on SR through more complex interaction among the factors. However, total effect sizes on SR were similar between factors relating autotrophic respiration and that relating heterotrophic respiration, suggesting that SR increases with shrub coverage would be unlikely to result from decreases in soil organic matter.

DOI： 10.1016/j.polar.2020.100562

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Soil Science and Plant Nutrition  

© 2020, © 2020 Japanese Society of Soil Science and Plant Nutrition. The stability of black soil carbon in the deep layers of Japanese volcanic ash soil (i.e., buried A horizons) is often explained by its unique chemical (molecular structure) and physical (associated with short-range-order minerals) recalcitrance. However, the stability of black soil C in buried A horizons may be changed by labile C supply for soil microbes. Here, we hypothesized that the mineralization of black soil C in buried A horizons of Japanese volcanic ash soil could be easily accelerated by a supply of labile C (i.e., a priming effect; PE). To test our hypothesis, we investigated the direction and magnitude of the PE with a buried A horizon in Japan using 13C-labeled glucose (2.188 atom %) in a short-term (21 days) incubation study. We also investigated the effect of mineral nitrogen (N), which could contribute to microbial activity in this incubation study. We found that a positive PE occurred by glucose supply with (182%) or without (181%) mineral N input over the 21-day incubation, and its values were very similar to the PE ratios previously reported in other deep soils. The estimated mean residence time (MRT) of black soil C considering PE was clearly accelerated by glucose supply, regardless of mineral N input, compared with the initial soil MRT. These results strongly support our hypothesis that the mineralization rate of black soil C in buried A horizons is easily accelerated by a labile C supply, and it also demonstrates important implications for the effects of global warming on buried A horizons (e.g., increased root exudation, fine root biomass supply, and N deposition) in Japanese volcanic ash soils.

DOI： 10.1080/00380768.2020.1753481

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Regional Studies in Marine Science  

© 2019 Elsevier B.V. There are insufficient data regarding forest productivity of mature mangroves near the northern limit of mangrove distribution in subtropical East Asia. We conducted the present study to determine the stand dynamics and net primary production (NPP) of a mature mangrove forest on Ishigaki Island in south-western Japan over three successive years, using a large permanent plot. The two mangrove species present were Bruguiera gymnorrhiza and Rhizophora stylosa. The aboveground biomass in the plot was high, despite the high latitude (24 ∘ 29 ′ N) of the site, gradually increasing from 158.4 Mg ha −1 to 164.6 Mg ha −1 over the three-year study period. This increase was attributable to an increase in the biomass of B. gymnorrhiza. The biomass of R. stylosa, however, decreased during the same period because of a threefold-higher mortality rate and a lower relative growth rate of this species compared with B. gymnorrhiza. The mangrove forest was in the late successional stage, following a pioneer R. stylosa forest that was widely distributed throughout the study plot as standing dead trees and logs. The aboveground NPP of the mangrove forest was 10.66 ± 1.46 Mg ha −1 y −1 , partitioned into 3.10 ± 0.51 Mg ha −1 y −1 as woody NPP (net increase in aboveground woody parts, SI), and 7.56 ± 0.99 Mg ha −1 y −1 as foliage NPP (litter production, including foliage and reproductive organs, L n ). The mature mangrove forest had a relatively low SI/L n ratio (0.41 ± 0.03), although litter fall production was within the range previously recorded for mangroves. The lower woody NPP in the mature mangroves was due to the exclusion of R. stylosa once the stand was in a late successional stage dominated by B. gymnorrhiza.

DOI： 10.1016/j.rsma.2019.100516

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Soil Science and Plant Nutrition  

© 2019, © 2019 Japanese Society of Soil Science and Plant Nutrition. Mangrove ecosystems play an important role in carbon (C) accumulation in tropical and subtropical regions. Below-ground deep anoxic soil is especially important for C accumulation. However, quantitative data on below-ground soil C stocks in mangrove ecosystems are lacking compared with data on above-ground biomass. In addition, soil C accumulation processes in mangrove ecosystems have not been sufficiently clarified. In this study, we quantified soil C stocks and focused on the mass of fallen litter and below-ground roots, which are produced by tree and that may directly influence soil C stocks in a mature subtropical mangrove in the estuary of Fukido River, Ishigaki Island, southwestern Japan. The principal species in this study site were Bruguiera gymnorhiza and Rhizophora stylosa, and total above-ground biomass at the site was 80.7 ± 1.3 (mean ± SD) Mg C ha−1 over the period from 2014 to 2016. Litter was collected in six litter traps from May 2013 to November 2016, it ranged from 7.8 to 11.5 Mg C ha−1, with the major proportion of litter being from foliage (leaves and stipules). The root C density at 90-cm depth was 27.1 ± 11.3 Mg C ha−1. The soil C stock in the mangrove forest at a depth of 90 cm at the study site was 251.0 ± 34.8 Mg C ha−1, and it seems to be lower value in the tropical region but it to be higher in subtropical East Asian mangrove sites. Dead roots, especially dead fine roots, but not fallen litter, were significantly positively correlated with soil C stocks. The δ13C values obtained from soils ranged from −29.3‰ to −27.0‰; these values are consistent with those for below-ground fine roots. These results strongly suggest that dead fine roots could be a main factor controlling soil C stocks at this study site.

DOI： 10.1080/00380768.2019.1660589

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Soil Science and Plant Nutrition  

© 2019, © 2019 Japanese Society of Soil Science and Plant Nutrition. The role of biochar in the mitigation of CO2 emissions has been extensively studied in agricultural soils but is not well understood in Japanese forest soils, especially in relation to CO2 emissions from applied biochar and native soil C (i.e., the priming effect; PE). We hypothesized that the type of biochar and/or the application method (mixed or sprinkled) affect the direction and magnitude of PE in forest soil, and in particular, negative PE can be achieved relatively easily if biochar produced under higher temperature conditions were sprinkled on the soil surface. To test our hypothesis, we measured CO2 emissions from biochar-amended brown forest soil in Japan and examined its PE by conducting a medium-term (~4 months) incubation study. As substrates, we used plain straw from the C4 grass Miscanthus sinensis (SU) and two qualities of biochar produced from it at either 300°C (BC300) or 800°C (BC800) and compared two application methods: mixed into or sprinkled onto the soil. BC800 had a greater C content and C:N ratio as well a lower volatile matter content and higher nonvolatile matter content than BC300. SU had the lowest C content and C:N ratio of all the substrates. We found that biochar quality (volatile and nonvolatile matter content) was clearly related to the decomposition rate when mixed into the soil, but we could not find this relationship when biochar was sprinkled onto the soil. The addition of biochar to the soil induced a positive PE in the early stages (except for BC800 sprinkled) but suppressed CO2 emissions from native soil organic matter (negative PE) in the later stages, whereas the PE with SU application was always positive regardless of application method. Our results suggest that when biochar is sprinkled onto soil it is more likely to suppress soil-derived CO2 emission than when mixed in soil; however, the trend based on biochar quality was unclear.

DOI： 10.1080/00380768.2019.1672101

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Soil Science and Plant Nutrition  

© 2019, © 2019 Japanese Society of Soil Science and Plant Nutrition. The response of soil organic matter (SOM) to global warming is a crucial subject. However, the temperature sensitivity of SOM turnover remains largely uncertain. Changes in the mineralization of native SOM, i.e., priming effect (PE) may strongly affect the temperature sensitivity of SOM turnover in the presence of global warming. We investigated the direction and magnitude of the PE in a Japanese volcanic ash soil at different temperatures (15°C, 25°C, and 35°C) using a natural 13C tracer (C4-plant, maize leaf) in a short-term (25 days) incubation study. In addition, we evaluated the temperature sensitivity expressed as Q10 value with and without the addition of maize to the soil and their relations to PE. We found that positive PE occurred at each temperature condition and tended to increase with decreased temperature, and these PE results were consistent with the microbial biomass at the end of the incubation period. CO2 emission from control soil (without maize) increased with increasing temperature (Q10 = 2.6), but CO2 emission from the soil with added maize did not significantly change with increasing temperature (Q10 = 1.0). This was caused by the suppression of CO2 emission from the soil with increasing temperature (Q10 = 0.9). On the other hand, soil-originated CO2 emission clearly increased with increasing temperature (Q10 = 3.4) when Q10 values were calculated on the assumption that the temperature and substrate supply increase at the same time (from 25°C). These results suggest that not only the temperature increase but also the labile carbon supply may be important for the temperature sensitivity of Japanese volcanic ash soil.

DOI： 10.1080/00380768.2019.1665969

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Aquatic Sciences  

© 2018, Springer International Publishing AG, part of Springer Nature. Humic substances (HS) are the primary constituents of dissolved organic matter (DOM) and play pivotal roles in aquatic systems. Optical indices of DOM, such as specific UV absorbance (SUVA254), the fluorescence index (FI) and biological index (BIX), have gained wide interest because of their ease of use. In this study, we explored the relationship between HS and the indices in the Trat River Basin (eastern Thailand) from headwaters to the river mouth through the distinct dry and rainy seasons to examine whether changes in index values reflect variability in the relative contribution of HS to DOM, or %HS. The results show that %HS and the indices did not exhibit significant linear relationships (FI and BIX, P > 0.05), or the relationships changed seasonally (SUVA254). However, analyzing the indices versus %HS did show clear DOM composition changes by season with more humic-like or terrestrial material in the rainy season. Relationships between DOM and dissolved iron (dFe) concentrations were also explored. Separating the relationships of DOM versus dFe into HS versus dFe and non-HS versus dFe provides us the opportunity to better understand which fraction contributes more to dFe mobilization. The results indicate stronger positive linear relationships between HS and dFe concentrations independent of river tributary. Overall, this study highlights the importance of quantifying HS for the study of DOM dynamics or compositional changes along a river transect as well as for DOM-induced iron mobilization.

DOI： 10.1007/s00027-018-0578-z

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Polar Science  

© 2018 Elsevier B.V. and NIPR Rapid glacial retreat in the High Arctic causes the expansion of new habitats, but the successional trajectories of soil microbial communities are not fully understood. We examined microbial succession along a chronosequence twice with a 10-year interval in a High Arctic glacier foreland. Soil samples were collected from five study sites with different ages and phospholipid fatty acids analysis was conducted to investigate the microbial biomass and community structure. Microbial biomass did not differ significantly between the two sampling times but tended to increase with the chronosequence and showed a significant correlation with soil carbon (C) and nitrogen (N) content. Microbial community structure clearly differed along the chronosequence and was correlated with C and N content. The largest shift in community structure over 10 years was observed in the newly exposed sites after deglaciation. The accumulation of soil organic matter was regarded as an important determinant both of microbial biomass and community structure over the successional period. In contrast, the initial microbial community on the newly exposed soil changed rapidly even in the High Arctic, suggesting that some key soil processes such as C and N cycling can also shift within the relatively short period after rapid glacial retreat.

DOI： 10.1016/j.polar.2018.03.003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ecological Research  

© 2017, The Ecological Society of Japan. Dissolved organic carbon (DOC) plays an important role in C cycling in forest ecosystems. Here we measured the concentrations and fluxes of DOC in a cool-temperate broad-leaved deciduous forest (Takayama Forest) to quantify the contribution of DOC from different forest water flux conditions. Mean DOC concentration during the growing season increased in the sequence from bulk precipitation (2.98 ± 0.45 mg L−1), throughfall above dwarf bamboo (6.84 ± 0.45 mg L−1), throughfall below dwarf bamboo (7.08 ± 0.42 mg L−1), stemflow (15.05 ± 0.98 mg L−1), and litter leachate (21.33 ± 1.01 mg L−1). Litter leachate DOC concentration, being high in spring and autumn, which was fairly correlated with the amount of litterfall of bamboo and trees. In stemflow, the DOC concentration was high during early summer and gradually decreased, in addition, it also showed dramatic variation among different plant species. Litter leachate (72.5%) accounted for most of the DOC input to the soil during the growing season (311.5 kg C ha−1 7 months−1), while stemflow (1.6%) contributed the least. A great quantity of precipitation at the study site was associated with a subsequent high atmospheric contribution of DOC flux (8.6%), which was more than half of throughfall (16.5%). The high input of DOC to the soil and andisol soil characteristics at the Takayama Forest suggest that the DOC fluxes are vital to the soil carbon sequestration. Therefore, DOC fluxes should be taken into account when the carbon balance is assessed at forest ecosystems.

DOI： 10.1007/s11284-017-1488-6

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemosphere  

© 2017 Although mangrove forests are one of the most well-known soil organic carbon (SOC) sinks, the mechanism underlying SOC accumulation is relatively unknown. High net primary production (NPP) along with the typical bottom-heavy biomass allocation and low soil respiration (SR) have been considered to be responsible for SOC accumulation. However, an emerging paradigm postulates that SR is severely underestimated because of the leakage of dissolved inorganic carbon (DIC) in groundwater. Here we propose a simple yet unique mechanism for SOC accumulation in mangrove soils. We conducted sequential extraction of water extractable organic matter (WEOM) from mangrove soils using ultrapure water and artificial seawater, respectively. A sharp increase in humic substances (HS) concentration was observed only in the case of ultrapure water, along with a decline in salinity. Extracted WEOM was colloidal, and ≤70% of it re-precipitated by the addition of artificial seawater. These results strongly suggest that HS is selectively flocculated and maintained in the mangrove soils because of high salinity. Because sea salts are a characteristic of any mangrove forest, high salinity may be one of mechanisms underlying SOC accumulation in mangrove soils.

DOI： 10.1016/j.chemosphere.2017.02.074

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Forests  

© 2017 by the authors; licensee MDPI, Basel, Switzerland. The structural complexity, especially canopy and gap structure, of old-growth forests affects the spatial variation of soil respiration (Rs). Without considering this variation, the upscaling of Rs from field measurements to the forest site will be biased. The present study examined responses of Rs to soil temperature (Ts) and water content (W) in canopy and gap areas, developed the best fit model of Rs and used the unique spatial patterns of Rs and crown closure to upscale chamber measurements to the site scale in an old-growth beech-oak forest. Rs increased with an increase in Ts in both gap and canopy areas, but the effect of W on Rs was different between the two areas. The generalized linear model (GLM) analysis identified that an empirical model of Rs with the coupling of Ts and W was better than an exponential model of Rs with only Ts. Moreover, because of different responses of Rs to W between canopy and gap areas, it was necessary to estimate Rs in these areas separately. Consequently, combining the spatial patterns of Rs and the crown closure could allow upscaling of Rs from chamber-based measurements to the whole site in the present study.

DOI： 10.3390/f8020036

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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