Kazumichi Fujii

Vertical migration of radiocesium and clay mineral composition in five forest soils contaminated by the Fukushima nuclear accident

Abstract In forest soils contaminated by radiocesium (134Cs and 137Cs), deposition from the Fukushima nuclear accident, clay minerals might play important roles in long-term cesium (Cs) dynamics through sorption. To determine whether radiocesium can be retained within the organic layer and the upper mineral soil layers in the Fukushima region, we investigated the vertical distribution of 134Cs and 137Cs and the clay mineral composition in five soil profiles of varying radiocesium deposition levels and vegetation types. X-ray diffraction analyses and oxalate extraction suggested that hydroxy-interlayered vermiculites and short-range-ordered aluminum (Al) and iron (Fe) compounds (i.e, allophane and ferrihydrite) were major clay mineral species of the upper soil layers. The vertical soil distribution of 134Cs and 137Cs suggested that most of them were retained in the organic layer and upper mineral soil layer under different levels of deposition. Within 1.5 years after the accident, both 134Cs and 137Cs were leached from the organic layer, and most of these (59–73%) were accumulated in the upper soil layer (0–5 cm). The proportion of 137Cs (or 134Cs) leaching from the organic layer was greater at sites receiving greater amounts of precipitation. The substantial accumulation of 137Cs in the upper soil layer, irrespective of the 137Cs deposition level or clay mineral composition, suggests that sorption capacities of clays and organic matter are sufficiently high to retain 137Cs in the surface soil during at least the initial stage of contamination.

Biodegradation of low molecular weight organic compounds and their contribution to heterotrophic soil respiration in three Japanese forest soils

Low molecular weight (LMW) organic compounds in soil solution could be important substrates for heterotrophic soil respiration. The importance of LMW organic compound mineralization in heterotrophic soil respiration needs to be confirmed for different types of soils. The concentrations of LMW organic compounds in soil solution and mineralization kinetics of 14C-radiolabelled glucose, acetate, oxalate and citrate were studied in three Japanese forest soils (Andisol, Spodosol and Inceptisol) with varying adsorption capacities. Based on those results, the fluxes of LMW organic compound mineralization and their magnitude relative to heterotrophic soil respiration were quantified. Monosaccharides and organic acids comprised on average 5.9–11.2% and 0.9–1.4% of dissolved organic carbon in soil solution, respectively. Monosaccharide mineralization make up 49–74% of heterotrophic (basal) soil respiration at the soil-profile scale, while organic acid mineralization accounts for between 5% (Andisol) and 47–58% (Spodosol and Inceptisol) of heterotrophic soil respiration. The mineralization of LMW organic compounds is a substantial fraction of heterotrophic soil respiration regardless of soil type, owing to their rapid and continuous production and consumption. The specific contribution of organic acid mineralization to heterotrophic soil respiration varies depending on soil adsorption capacities, namely iron and aluminum oxides.

Soil acidification and adaptations of plants and microorganisms in Bornean tropical forests

In tropical forest ecosystems, a paradoxical relationship is commonly observed between massive biomass production and low soil fertility (low pH). The loss and deficiency of soil phosphorus (P) and bases generally constrain biomass production; however, high productivity on nutrient-deficient soils of Bornean tropical forests is hypothesized to be maintained by plant and microorganism adaptation to an acidic soil environment. Proton budgets in the plant–soil system indicated that plants and microorganisms promote acidification to acquire bases, even in highly acidic tropical soils. The nitric and organic acids they produce contribute to the mobilization of basic cations and their uptake by plants. In response to soil P deficiency and the recalcitrance of lignin-rich organic matter, specific trees and fungi can release organic acids and enzymes for nutrient acquisition. Organic acids exuded by roots and rhizosphere microorganisms can promote the solubilization of P bonded to aluminum and iron oxides and its uptake by plants from P-poor soils. Lignin degradation, a rate-limiting step in organic matter decomposition, is specifically enhanced in acidic organic layers by lignin peroxidase, produced by white-rot fungi, which may solubilize recalcitrant lignin and release soluble aromatic substances into the soil solution. This dissolved organic matter functions in the transport of nitrogen, P, and basic cations in acidic soils without increasing leaching loss. In Bornean tropical forests, soil acidification is promoted by plants and microorganisms as a nutrient acquisition strategy, while plant roots and fungi can develop rhizosphere and enzymatic processes that promote tolerance of low pH.

Carbon dioxide emission derived from soil organic matter decomposition and root respiration in Japanese forests under different ecological conditions

Abstract Soil chambers with 3 types of soil treatment were used to analyze the environmental factors controlling carbon dioxide (CO2) emission in forest soils of Japan and to separately determine CO2 emission from root respiration, microbial decomposition of organic matter in the O layer and in the mineral soil layers. Soil chambers were installed at the Kyoto, Miyazu-Oak, Miyazu-Cedar, Miyazu-Beech and Nobeyama sites; the sites differed from each other in soil temperature, vegetation and parent materials. The soil treatments applied at each of the 5 sites were as follows: (1) control plot, (2) O- plot with removal of the O layer, (3) root- plot with the suppression of root respiration by inserting the chambers to a depth of 20 cm and sealing the bottom. The CO2 emission levels at all sites were significantly correlated with soil temperature, but not with soil moisture levels. The annual rates of soil organic matter decomposition simulated based on the automatically recorded soil temperature were 5.1, 4.0, 5.2, 5.5 and 3.4 Mg C ha−1 at the Kyoto, Miyazu-Oak, Miyazu-Cedar, Miyazu-Beech and Nobeyama sites, respectively. These rates were influenced by soil temperature, litter fall rates and the carbon stocks. In contrast, the ratio of the annual rate of root respiration to the annual rate of soil respiration decreased as soil temperature decreased. Based on the carbon budget, the Miyazu-Cedar and Nobeyama sites appeared to have lost their soil carbon stock. For more accurate analysis, methods for the direct measurement of the input rate of root litter should be developed.

The incorporation of amino acids and nucleic acid bases into the seedling, reproductive stage and young ear portion of rice plants

SummaryThe incorporation of C14-amino acids (aspartic acid, glutamic acid, threonine and proline) and C14-nucleic acid bases (adenine, guanine, cytosine and uracil) into the seedling, reproductive stage and young ear portion of rice plant was investigated.It was found that C14-aspartic acid was incorporated into the rice seedling more rapidly than C14-threonine or C14-proline; on the other hand C14-proline was found to be more rapidly incorporated than C14-aspartic acid into reproductive stage plant and young ear portion.Similarly C14-adenine was incorporated into the rice seedling more rapidly than other C14-labelled bases. On the other hand C14-uracil was preferentially incorporated to C14-adenine or C14-guanine into the reproductive stage plant and young ear portion.It is suggested from the results obtained that proline is polymerized into polypeptide or protein in the rice plant more rapidly at the reproductive stage than at the seedling stage and that a higher proportion of pyrimidine bases might be involved into the metabolic process at the reproductive stage of rice plant.

Seasonal changes of photosynthetic bacteria and their products

Abstract In our preceding papers the distribution (1, 2), ecological problems (3,4), and the products of photosynthetic bacteria (5–8) have been studied. It was also reported that the growth and nitrogen fixation of photosynthetic bacteria were accelerated remarkably in the system of symbiosis with other heterotrophic microorganisms like Azotobacter (9) and Bacillus megaterium (10) ; moreover the products generated by photosynthetic bacteria were used by plants (11) and animals in water (2, 4), directly or indirectly. It is noteworthy that in paddy soil, this bacterial cells have a beneficial effect on the development of grains (11).

Rapid turnover of organic acids in a Dystric Brunisol under a spruce-lichen forest in northern Saskatchewan, Canada

Fujii, K., Morioka, K., Hangs, R., Funakawa, S., Kosaki, and Anderson, D. W. 2013. Rapid turnover of organic acids in a Dystric Brunisol under a spruce-lichen forest in northern Saskatchewan, Canada. Can. J. Soil Sci. 93: 295-304. Organic acids released by lichen play an important role in mineral weathering and podzolization in the Boreal-Tundra transition zone of Canada; however, importance of low-molecular-weight organic acids in the soil carbon (C) cycle in the black spruce-lichen forests remains unclear. We examined soil solution composition and mineralization kinetics of 14C-radiolabelled oxalate and citrate to quantify the C fluxes from organic acid mineralization in a Dystric Brunisol under a spruce-lichen forest in northern Saskatchewan. Oxalate concentration in soil solution was greatest in the lichen layer, while the high levels of citrate were observed in the lichen and organic (O) layers to the Ae horizon with the lowest sorption capacity. Oxalate and citrate were rapidly mineralized within the lichen and O layers and had short mean residence times (0.5 to 2.7 h). Substantial C fluxes due to citrate mineralization were observed both within the lichen and O layers, but oxalate mineralization led to C flux in the lichen layer only. The contribution of citrate and oxalate to microbial respiration was large (up to 57%) in the surface soil layers. Citrate was the dominant substrate for microbial respiration of the surface soil; however, it appears that oxalate could also be an important microbial substrate within the lichen layer, at least in summer months. We conclude that the exudation of low-molecular-weight organic acids by lichenous fungi, followed by their rapid mineralization, could play an important role in the C cycles of the sandy soils under spruce-lichen forest.

Biodegradation kinetics of monosaccharides and their contribution to basal respiration in tropical forest soils

Low molecular weight (LMW) organic compounds in soil solution are easily biodegradable and could fuel respiration by soil microorganisms. Our main aim was to study the mineralization kinetics of monosaccharides using 14C-radiolabelled glucose. Based on these data and the soil solution concentrations of monosaccharides, we evaluated the contribution of monosaccharides to basal respiration for a variety of tropical forest soils. Further, the factors controlling the mineralization kinetics of monosaccharides were examined by comparing tropical and temperate forest soils. Monosaccharides comprised on average 5.2 to 47.7% of dissolved organic carbon in soil solution. Their kinetic parameters (V max and KM ), which were described by a single Michaelis-Menten equation, varied widely from 11 to 152 nmol g−1 h−1 and 198 to 1294 µmol L−1 for tropical soils, and from 182 to 400 nmol g−1 h−1 and 1277 to 3150 µmol L−1 for temperate soils, respectively. The values of V max increased with increasing microbial biomass-C in tropical and temperate soils, while the KM values had no correlations with soil biological or physicochemical properties. The positive correlation between V max values and microbial biomass-C indicates that microbial biomass-C is an essential factor to regulate the V max values in tropical and temperate forest soils. The biodegradation kinetics of monosaccharides indicate that the microbial capacity of monosaccharide mineralization far exceeds its rate at soil solution concentration. Monosaccharides in soil solution are rapidly mineralized, and their mean residence times in this study were very short (0.4–1.9 h) in tropical forests. The rates of monosaccharide mineralization at actual soil solution concentrations made up 22–118% of basal respiration. Probably because of the rapid and continuous production and consumption of monosaccharides, monosaccharide mineralization is shown to be a dominant fraction of basal respiration in tropical forest soils, as well as in temperate and boreal forest soils.

Fluxes of dissolved organic carbon and nitrogen throughout Andisol, Spodosol and Inceptisol profiles under forest in Japan

Leaching of dissolved organic matter (DOM) is an important process in the translocation and stabilization of organic carbon (C) and in influencing nitrogen (N) availability in forest soils. The roles of DOM in soil carbon and nitrogen cycles were evaluated by quantifying the fluxes of dissolved organic carbon (DOC) and nitrogen (DON) entering and leaving the organic (O), A and B horizons. In Spodosol and Inceptisol soils, DOC fluxes were highest in the O horizon (149 to 344 kg C ha−1 yr−1), decreasing in the A and B horizons. In Andisol soils, DOC fluxes were low throughout the profile because of low DOC production in the O horizon (53 kg C ha−1 yr−1) and the high adsorption capacity of amorphous aluminum (Al) and iron (Fe) (hydr)oxides in the mineral horizons. In Spodosol soil, DOC from the O horizon represented a large proportion of C input into the mineral soil, whereas this contribution appeared to be small in Andisol soil. The DOM was enriched in nitrogen during decomposition and humification of the foliar litter, but DON was a small proportion (5–31%) of total dissolved nitrogen (TDN) in surface soil solutions. The narrow DOC/DON and DON/TDN ratios were attributable to the low C/N ratios of the foliar litter (33–40). It was quantitatively shown that the importance of DOM in C and N cycles in forest soils varied depending on soil types and litter C/N ratio.

In situ short-term dynamics of CO2 flux and microbial biomass after simulated rainfall in dry croplands in four tropical and continental ecosystems

Abstract The wet–dry cycles of soil primarily drive carbon (C) dynamics in dry croplands that mainly experience sporadic rainfall events. We evaluated the in situ short-term (hourly) dynamics of soil carbon dioxide (CO2) efflux and microbial biomass, to compare the significance of a single rainfall event with/without C substrate to reveal the effects of a single rainfall on the soil C dynamics in clayey dry croplands in four different climates and ecosystems. The experiments were conducted on four clayey dry croplands as follows: Thailand (TH) and Tanzania (TZ) in tropical climates, and Kazakhstan (KZ) and Hungary (HG) in continental climates. Hourly measurements of soil CO2 efflux, in situ microbial biomass (MB) and in situ microbial activity (qCO2) were conducted after the application of simulated rainfall (W plots) and rainfall/glucose (WG plots) treatments. We also evaluated the easily mineralizable carbon (EMC) by incubation. The rainfall treatment caused an increase in the qCO2 but not in MB, causing a clear but short C flush in all W plots (10–37 h), while the WG treatment caused an increase both of qCO2 and MB, resulting in substantially longer and larger C flush in the WG plots (ca. 100 h). The ratio of the cumulative soil CO2 flux caused by rainfall treatment to EMC was larger in TH-W and TZ-W plots (8.2 and 4.9%, respectively) than in the KZ-W and HG-W plots (2.9 and 1.1%, respectively). In addition, applied glucose was more heavily mineralized in the TH-WG and TZ-WG plots (15.0 and 9.7%, respectively) than in the KZ-WG and HG-WG plots (6.4 and 3.4%, respectively), because of the different MB increment patterns for the first 24 h, i.e., immediate and large MB increments in TH and TZ, but not in KZ and HG. These results reveal a possible mechanism that causes the rapid decomposition of soil organic carbon and applied organic matter in the dry tropical cropland.