Japanese Forest Soils Research Articles

Effect of soil organic matter on the fate of 137Cs vertical distribution in forest soils

Understanding the fate of the vertical distribution of radiocesium (137Cs) in Japanese forest soils is key to assessing the radioecological consequences of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The 137Cs behavior in mineral soil is known to be primarily governed by interaction with clay minerals; however, some observations suggest the role of soil organic matter (SOM) in enhancing the mobility of 137Cs. Here we hypothesized that soil organic carbon (SOC) concentration profile determines the ultimate vertical pattern of 137Cs distribution in Japanese forest soils. In testing this hypothesis, we obtained soil samples that were collected before the FDNPP accident at four forest sites with varying SOC concentration profiles and quantified the detailed vertical profile of 137Cs inventory in the soils roughly half a century after global fallout in the early 1960 s. Results showed that the higher the SOC concentration in the soil profile, the deeper the 137Cs downward penetration. On the basis of the data for surface soils (0–10 cm), the 137Cs retention ratio for each of the 2-cm thick layers was evaluated as the ratio of 137Cs inventory in the target soil layer to the total 137Cs inventory in and below the soil layer. A negative correlation was found between the ratio and SOC concentration of the layer across all soils and depths. This indicates that the ultimate fate of 137Cs vertical distribution can be predicted as a function of SOC concentration for Japanese forest soils, and provides further evidence for SOM effects on the mobility and bioavailability of 137Cs in soils.

Introduction of web application on browsing Japanese forest soil map

Introduction of web application on browsing Japanese forest soil map

Priming effects induced by C and N additions in relation to microbial biomass turnover in Japanese forest soils

An understanding of the priming effect (PE), i.e. the effects of carbon (C) and nitrogen (N) inputs on the priming of pre-existing soil organic C mineralization, is fundamental to predicting future soil C cycling and climate feedback. Since the direction and magnitude of the PE depend on the turnover of microbial biomass C and N, we evaluated the PE in relation to pre-existing biomass C and N using dual labeling of glucose 13C and mineral 15N for Japanese moderately acidic (pH of 5.0) cedar and strongly acidic (pH of 4.1) cypress soils. The addition of C only to the cedar soil caused no PE with no change in biomass turnover relative to the control without C or N additions. The addition of N with C caused a positive PE, leading to a net loss of soil C stocks, and decreased pre-existing biomass N due to the higher turnover of biomass N relative to the control. The result for the cedar soil was in line with the stoichiometric decomposition theory but not with microbial N mining theory. By contrast, the addition of C only and both C and N to the cypress soil caused a negative PE. Our study revealed that increasing the pre-existing biomass N turnover can lead to a positive PE, accelerating net soil C loss, when the soil pH does not limit microbial activities.

Vertical distributions of radiocesium in Japanese forest soils following the Fukushima Daiichi Nuclear Power Plant accident: A meta-analysis

This study investigated the temporal change in vertical distributions of radiocesium inventories in Japanese forest soils during the early phase (from 2011 to 2017) following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, using three simple parameters. We calculated the fraction in the organic layer (Fl/t), the migration center (Xc) and the relaxation depth (α) using 99 soil inventory data sets. Fl/t decreased significantly from 2011 to 2017 (logistic analysis, p < 0.001). In addition, Fl/t in the FDNPP zone rapidly decreased compared to that in the Chernobyl Nuclear Power Plant (ChNPP) zone from the first year to the second year. Different migration rates from organic to mineral soil layers between previous studies in the ChNPP and this study have several possible causes such as organic litter features, climate and physico-chemical forms of initial deposition. In mineral soil layers in the FDNPP zone, only Xc increased significantly with time according to generalized mixed model analysis (p < 0.01). However, Xc and α in the ChNPP zone decreased from two to five years after the accident in 1986, which shows a high 137Cs retention in the organic layer even in the fifth year after the accident. The vertical migration of 137Cs in the mineral soil layer in the FDNPP zone appears to be due to low input of 137Cs from organic to surface mineral soil layer after the second year. These results indicate that 137Cs retention capacity of the organic layer can affect the apparent vertical migration of 137Cs in the underlying mineral soil layer.

Priming effect of Miscanthus sinensis derived biochar on brown forest soil

ABSTRACT 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.

Substrate-induced respiration responses to nitrogen and/or phosphorus additions in soils from different climatic and land use conditions

The fates of carbon (C) input to soils widely vary under different nutrient availability. In this study, both initial substrate-induced respiration (SIR) rates and substrate-induced growth responses to nitrogen (N) and/or phosphorus (P) additions were investigated together because the two approaches had been assessed separately in previous studies. A wide range of Japanese, Thai and Kazakh soils with different land uses were used, including acidic Japanese forest soils with low N availability, which has not been fully examined. We hypothesized that microbes in Japanese forest soils would mainly respond to N addition. The results showed that N addition decreased initial SIR rates to 75–87% for the acidic Japanese and Thai forest soils probably due to the increases in substrate C use efficiencies, but had no effect for other soils. P addition tended to increase initial SIR rates. In addition, P but not N addition resulted in the increases of specific microbial growth rates for all tested soils. In conclusion, soil microbes responded to P addition with enhanced their growth rates and initial SIR rates, whereas they responded to N addition with reduced initial SIR rates probably through efficient use of C only for the Japanese and Thai forest soils. Therefore, nitrogen availability will have a crucial role in microbial use of substrate C especially for acidic forest soils with low N availability.

Vertical distributions of global fallout 137Cs and 14C in a Japanese forest soil profile and their implications for the fate and migration processes of Fukushima-derived 137Cs

Vertical distributions of global fallout 137Cs and 14C were investigated in a Japanese forest soil in 2001. Even 38 years after the fallout, 137Cs was still observed mostly in the uppermost 5 cm. A preferential accumulation of 137Cs was found in a 1-cm-thick transition layer between organic-rich A and underlying B horizons. This unique observation indicated that 137Cs migrated through the A horizon at a rate of 0.20 % year−1 and the transition layer acted as a barrier for 137Cs migration to deeper layers. The vertical distributions of 137Cs and 14C were significantly correlated, suggesting a coupled downward migration of 137Cs and organic matter on a time scale of decades, along the same physical pathways.

Aluminum and acidity suppress microbial activity and biomass in acidic forest soils

To evaluate the effects of aluminum (Al) toxicity on microbial processes in acidic forest soils, we determined microbial biomass, soil enzyme activities associated with carbon (C), nitrogen, and phosphorus cycling (β-d-glucosidase and polyphenol oxidase, l-asparaginase, and acid phosphatase, respectively), exchangeable base cations, soluble and exchangeable Al (CaCl2–Al and KCl–Al), and organically bound (Alp and Fep) and both organically bound and noncrystalline forms (Alo and Feo) of Al and iron (Fe) in Japanese forest soils (25 Inceptisols, seven allophanic Andisols, and eight nonallophanic Andisols). The exchangeable calcium (Ca) and magnesium (Mg) concentrations decreased significantly with decreasing soil pH. In contrast, the KCl–Al and CaCl2–Al concentrations exponentially increased with decreasing pH, and the increase was steeper in Andisols than in Inceptisols. The Alp concentration also increased exponentially with decreasing soil pH in Andisols, and the Fep concentration increased in Andisols and Inceptisols, whereas the concentration of the noncrystalline Al pool (Alo − Alp) decreased with decreasing pH in Andisols. We showed that the β-d-glucosidase, polyphenol oxidase, and acid phosphatase activities were mainly suppressed by soluble and exchangeable Al, whereas l-asparaginase activity was depressed by soil pH. In Andisols, a negative effect of organically bound Al and Fe on the biomass C/organic C ratio was observed. These results suggest that Al toxicity and acidity repressed soil enzyme activities, leading to suppressed microbially mediated nutrient cycling, and that Al toxicity and a reduced availability of organic matter, as a result of Al and Fe binding, may protect a substantial pool of organic C from microbial degradation in acidic forest soils.

Factors contributing to soil nitrogen mineralization and nitrification rates of forest soils in the Japanese archipelago

Nitrogen (N) is the primary limiting nutrient for forest production. Therefore, understanding how environmental factors affect N transformation rates is essential for the provision of sustainable ecosystem services. Because these factors are interlinked, it is important to consider direct and indirect structural relationships to better understand the factors contributing to N transformations. In this study, we analyzed the structural cause–effect relationships surrounding N transformations by structural equation modeling using a database containing net and gross N transformation rates and related soil chemical properties from 38 sites across the Japanese archipelago. The average net N mineralization and nitrification rates in the Japanese forest soils were 0.62±0.68 and 0.59±0.65mgNkg−1d−1, respectively, and gross N mineralization and nitrification rates were 4.22±3.59 and 0.98±0.68mgNkg−1d−1, respectively. Compared with previous large scale studies, net and gross N transformation rates in Japanese forest soils were considerably diverse despite their relatively small land area and were representative of temperate forest ecosystems. Structural equation modeling analysis showed that net N transformations were directly affected by gross N transformations, which in turn were significantly and directly affected by soil organic matter contents. Soil organic matter was significantly affected by organic layer amount, tree species and soil group. The effect of soil group was the greatest among these factors, suggesting that soil organic matter contents in Japanese forest soils were mainly influenced by soil parent materials. This was especially evident for Andosols, which are derived from volcanic sediments and contain large amounts of soil organic matter leading to high N transformation rates in the Japanese forest soils. Among the factors related to organic layers and mineral soil layers, soil organic matter content and organic layer amount, which represent substrate availability, had significant effects on gross and net N transformation rates. However, by refining the scale of the dataset using soil groups/soil parent materials, the influence of substrate quality and soil chemical properties on N transformations was suggested. From the current dataset, it was indicated that soil parent materials were the most important factor controlling the pattern of N transformations in the soil of Japanese forest ecosystems. This conclusion should be repeatedly refined considering the spatial distribution of factors such as climatic conditions and forest types with additional site datasets obtained from future surveys.

Potential nitrogen immobilization as influenced by available carbon in Japanese arable and forest soils

Microbial nitrogen (N) immobilization following the addition of organic materials to soils regulates soil N availability, which affects plant growth and N leaching from soils. In this study, the potential for microbial N immobilization was evaluated by short-term incubation experiments following the addition of available carbon (C) under non-limiting conditions of N and phosphorus (P) to seven Japanese arable and forest soils. Glucose was added as a model substrate at concentrations close to microbial biomass C. The forest soils had lower pH and smaller increases in respiration rates after the glucose addition, and higher organic and biomass C compared to the arable soils. Microbial N immobilization, estimated by net decreases in extractable N, was significantly correlated with the concentrations of added glucose and was on average 43 mg N g−1 glucose C during 3- and 7-day incubation for all soils. Net increases in biomass N measured by the chloroform fumigation-extraction method using the common conversion factor of 0.54 at 3 and 7 days after the glucose addition were lower than the microbial N immobilization for all soils, and the biomass N accounted for a smaller portion of immobilized N in the arable soils than in the forest soils. Therefore, the present study suggests that microbial N immobilization would be dependent on the concentrations of available C in organic materials and higher than the increases in biomass N, especially for arable soils when organic materials are added to soils under non-limiting conditions of N and P.

Degree of Sulfate Saturation in Forest Soils Affected by Past Heavy Anthropogenic Deposition

The aims of this study were to assess sulfate adsorption in Japanese forest soils and to find and evaluate traces of past heavy anthropogenic sulfur deposition based on the degree of saturation as calculated based on the theoretical adsorption capacity determined by isotherm experiments and the amount of actual adsorbed sulfate. Investigations were conducted at two forest sites, a site in Yokkaichi that is exposed to serious air pollution containing sulfur compounds and a site in Inabu that is unpolluted. The distribution of phosphate-extractable sulfate concentration did not differ between the Yokkaichi site (1.11–13.2 mmol kg−1) and the Inabu site (0.40–11.0 mmol kg−1), and the values were higher than published data for North America and Europe. In contrast, the degree of sulfate saturation in soils of the Yokkaichi site was higher than that in soils of the Inabu site. These results indicate that the degree of sulfate saturation is valuable information for the evaluation of sulfur deposition history. The higher degree of saturation at Yokkaichi site may be due to enhanced sulfate adsorption by soils resulting from substantial past sulfur deposition.

Long-term changes in the chemical properties of Japanese cedar (Cryptomeria japonica) forest soils under high precipitation in southwest Japan

There is insufficient direct evidence of long-term changes in the chemical properties of forest soils to provide information for forestry management plans for sustainable site productivity. To understand changes in the chemical properties of forest soils in a specific high-precipitation climate in Japan, we re-investigated, in 1997, soil pits within a Japanese cedar (Cryptomeria japonica) forest in the Yanase region of Kochi Prefecture which had previously been surveyed in 1976. Comparison of the 1976 and 1997 results revealed significantly lower pH of surface and subsurface soils, and fewer exchangeable cations over time. In contrast, subsoil pH, concentrations of total carbon and nitrogen, and cation-exchange capacity (CEC) had not changed over the 21-year period. Estimation of proton and cation budgets in the forest ecosystem over 21 years, using data for the amounts in soil, biomass accumulation, and input through precipitation, revealed that biomass accumulation did not explain the cation depletion in soils. This suggests that cations were leached from the ecosystem. In contrast with previous reports, which showed Ca accumulation in Japanese cedar forest soils, our results indicated that high precipitation of more than 4,000 mm combined with acid deposition resulted in soil acidification and leaching of cations from soils, following the decrease in base saturation.

Seasonal and snowmelt-driven changes in the water-extractable organic carbon dynamics in a cool-temperate Japanese forest soil, estimated using the bomb-14C tracer

Water-extractable organic carbon (WEOC) in soil consists of a mobile and bioavailable portion of the dissolved organic carbon (DOC) pool. WEOC plays an important role in dynamics of soil organic carbon (SOC) and transport of radionuclides in forest soils. Although considerable research has been conducted on the importance of recent litter versus older soil organic matter as WEOC sources in forest soil, a more thorough evaluation of the temporal pattern of WEOC is necessary. We investigated the seasonal variation in WEOC in a Japanese cool-temperate beech forest soil by using the carbon isotopic composition (14C and 13C) of WEOC as a tracer for the carbon sources. Our observations demonstrated that fresh leaf litter DOC significantly contributed to WEOC in May (35–52%) when the spring snowmelt occurred because of the high water flux and low temperature. In the rainy season, increases in the concentration of WEOC and the proportion of hydrophobic compounds were caused by high microbial activity under wetter conditions. From summer to autumn, the WEOC in the mineral soil horizons was also dominated by microbial release from SOC (>90%). These results indicate that the origin and dynamics of WEOC are strongly controlled by seasonal events such as the spring snowmelt and the rainy season's intense rainfall.

Composition of inorganic elements and the leaching behavior of biomass combustion ashes discharged from wood pellet boilers in Japan

To evaluate the characteristics of wood ash as fertilizer, composition of inorganic elements and the leaching behavior were studied. The leaching behavior was evaluated by three leaching methods using different solvents (water, hydrochloric acid, and acetic acid: Japanese leaching test Nos. 18 and 19 and modified toxicity characteristic leaching procedure prescribed by the US Environmental Protection Agency). The ash composition varied according to raw materials for fuel and ash collection systems. Concentration of Na, Al, Si, and V became higher in bark ashes while that of K became higher in wood ashes. Pb, Cd, Se, and Zn were more volatile and enriched in fly ashes. Of the nutrient elements, K showed high water solubility and its phytoavailability also appeared high, although the amount of water-soluble K was low in bark ash. Ca and Mg had intermediate solubility while P was less soluble in both water and acetic acid. The amount of hazardous substances having leached was low for most, but not all the ashes, in terms of Pb, Cr and As. Nevertheless, the phytoavailability of these hazardous substances after their application to the forest appeared low, due to their amphoteric leaching behavior and the acidity of Japanese forest soils.

Regional modelling of carbon dynamics in Japanese forest soils

Regional modelling of carbon dynamics in Japanese forest soils

Continuous measurement of methane flux over a larch forest using a relaxed eddy accumulation method

We measured the methane flux of a forest canopy throughout a year using a relaxed eddy accumulation (REA) method. This sampling system was carefully validated against heat and CO2 fluxes measured by the eddy covariance method. Although the sampling system was robust, there were large uncertainties in the measured methane fluxes because of the limited precision of the methane gas analyzer. Based on the spectral characteristics of signals from the methane analyzer and the diurnal variations in the standard deviation of the vertical wind velocity, we found the daytime and nighttime precision of half-hourly methane flux measurements to be approximately 1.2 and 0.7 μg CH4 m−2 s−1, respectively. Additional uncertainties caused by the dilution effect were estimated to affect the accuracy by as much as 0.21 μg CH4 m−2 s−1 on a half-hourly basis. Diurnal and seasonal variations were observed in the measured fluxes. The biological emission from plant leaves was not observed in our studies, and thus could be negligible at the canopy-scale exchange. The annual methane sink was 835 ± 175 mg CH4 m−2 year−1 (8.35 kg CH4 ha−1 year−1), which was comparable to the flux range of 379–2,478 mg CH4 m−2 year−1 previously measured in other Japanese forest soils. This study indicated that the REA method could be a promising technique to measure canopy scale methane fluxes over forests, but further improvement of precision of the analyzer will be required.

Soil Properties Affecting Phosphorus Forms and Phosphatase Activities in Japanese Forest Soils

AbstractTo explore a possible phosphorus limitation of soil microbial processes, we fractionated phosphorus in Japanese forest soils (10 Inceptisols, three allophanic Andisols, seven nonallophanic Andisols, and one Spodosol) by sequential extraction into inorganic P (Pi) and organic P (Po) in H2O, 0

Potential carbon stock in Japanese forest soils – simulated impact of forest management and climate change using the CENTURY model

AbstractForest management and climate change may have a substantial impact on future soil organic carbon (SOC) stocks at the country scale. Potential SOC in Japanese forest soils was regionally estimated under nine forest managements and a climate change scenario using the CENTURY ecosystem model. Three rotations (30, 50, 100 yr) and three thinning regimes were tested: no‐thinning; 30% of the trees cut in the middle of the rotation (e.g. 15 year in a 30‐yr rotation) and thinned trees all left as litter or slash (ThinLef) and the trees from thinning removed from the forest (ThinRem). A climate change scenario was tested (ca. 3 °C increase in air temperature and 9% increase in precipitation). The model was run at 1 km resolution using climate, vegetation and soil databases. The estimated SOC stock ranged from 1600 to 1830 TgC (from 6800 to 7800 gC/m2), and the SOC stock was largest with the longest rotation and was largest under ThinLef with all three rotations. Despite an increase in net primary production, the SOC stock decreased by 5% under the climate change scenario.

Effects of carbon and nitrogen amendment on soil carbon and nitrogen mineralization in volcanic immature soil in southern Kyushu, Japan

Soil N mineralization is affected by microbial biomass and respiration, which are limited by available C and N. To examine the relationship between C and N for soil microbial dynamics and N dynamics, we conducted long-term laboratory incubation (150 days) after C and N amendment and measured changes in C and N mineralization, microbial biomass C, and dissolved C and N throughout the incubation period. The study soil was volcanic immature soil from the southern part of Japan, which contains lower C and N compared with other Japanese forest soils. Despite this, the area is covered by well-developed natural and plantation forests. Carbon amendment resulted in an increase in both microbial biomass and respiration, and net N mineralization decreased, probably due to increasing microbial immobilization. In contrast, N amendment resulted in a decrease in microbial respiration and an increase in net N mineralization, possibly due to decreased immobilization by microbes. Amendment of both C and N simultaneously did not affect microbial biomass and respiration, although net N mineralization was slightly increased. The results suggested that inhibitory effect on microbial respiration by N amendment should be reduced if carbon availability is higher. Thus, soil available C may limit microbial biomass and respiration in this volcanic immature soil. Even in immature soil where C and N substrate is low, soil C, such as plant root exudates and materials from above- and belowground dead organisms, might help to maintain microbial activity and N mineralization in this study site.

Gross nitrification rates in four Japanese forest soils: heterotrophic versus autotrophic and the regulation factors for the nitrification

Measurements of gross NH4+ and NO3− production in forest soils were conducted using the 15N pool dilution method. Mineral topsoils (0–10 cm depth) were collected from four forests from northern to southern Japan with a natural climate gradient to elucidate the mechanisms regulating gross nitrification rates in forest soils. Additionally, we attempted to evaluate the relative importance of heterotrophic nitrification in gross total nitrification using acetylene as a specific inhibitor of autotrophic nitrification. Distinct differences were found among sites in the gross rates of NH4+ production (3.1–11.4 mg N kg−1 day−1) and gross total nitrification (0.0–6.1 mg N kg−1 day−1). The rates of gross heterotrophic nitrification were low in this study, indicating that heterotrophic nitrification is of minor importance in most forest mineral topsoils in Japan. Significant relations were found between gross autotrophic nitrification and gross NH4+ production, soil N, and soil C concentrations, but none was found between gross autotrophic nitrification and soil pH. We determined the critical value of the gross NH4+ production rates for gross autotrophic nitrification under which no gross autotrophic nitrification occurred, as well as the critical soil C/N ratio above which gross autotrophic nitrification ceased. Results show that tight coupling of production and consumption of NH4+ prevents autotrophic nitrifiers from utilizing NH4+ as long as NH4+ availability is low.