Net and gross mineral N production rates at three levels of forest canopy retention: evidence that NH<Subscript>4</Subscript><Superscript>+</Superscript> and NO<Subscript>3</Subscript><Superscript>−</Superscript> dynamics are uncoupled

Alternative silvicultural systems were introduced in Coastal Western Hemlock forests of British Columbia, Canada, to reduce disturbance incurred by conventional clear-cutting and to maintain the forest influence on soil nutrient cycling. As we hypothesized, in situ pools and net mineralization of NH₄ ⁺ were lower under no and low disturbance (old-growth forest and shelterwood) compared to clear-cuts (high disturbance); in situ pools and net production of NO₃ ⁻ were very low across all treatments. Gross transformation rates of NH₄ ⁺ increased while those of NO₃ ⁻ decreased with increasing disturbance, suggesting that these processes were uncoupled. We conclude that shelterwood harvesting reduces the impact on forest floor NH₄ ⁺ cycling compared to clear-cutting, and that neither low nor high disturbance intensity results in substantial NO₃ ⁻ accumulation, as what occasionally occurs in other ecosystems. We hypothesize that the uncoupling of NH₄ ⁺ and NO₃ ⁻ dynamics may be due to the predominance of heterotrophic nitrification by lignin-degrading fungi that oxidize organic N rather than NH₄ ⁺–N, and whose activities are suppressed at high NH₄ ⁺ concentrations.     

Effect of CO<Subscript>2</Subscript> on nitrification and immobilization of NH<Subscript>4</Subscript><Superscript>+</Superscript>-N

A laboratory incubation experiment was conducted to demonstrate that reduced availability of CO₂ may be an important factor limiting nitrification. Soil samples amended with wheat straw (0%, 0.1% and 0.2%) and (¹⁵NH₄)₂SO₄ (200 mg N kg^–1 soil, 2.213 atom% ¹⁵N excess) were incubated at 30±2°C for 20 days with or without the arrangement for trapping CO₂ resulting from the decomposition of organic matter. Nitrification (as determined by the disappearance of NH₄⁺ and accumulation of NO₃^–) was found to be highly sensitive to available CO₂ decreasing significantly when CO₂ was trapped in alkali solution and increasing substantially when the amount of CO₂ in the soil atmosphere increased due to the decomposition of added wheat straw. The co-efficient of correlation between NH₄⁺-N and NO₃^–-N content of soil was highly significant (r =0.99). During incubation, 0.1–78% of the applied NH₄⁺ was recovered as NO₃^– at different incubation intervals. Amendment of soil with wheat straw significantly increased NH₄⁺ immobilization. From 1.6% to 4.5% of the applied N was unaccounted for and was due to N losses. The results of the study suggest that decreased availability of CO₂ will limit the process of nitrification during soil incubations involving trapping of CO₂ (in closed vessels) or its removal from the stream of air passing over the incubated soil (in open-ended systems).     

Effectiveness of Air,N<Subscript>2</Subscript> (gas), Fe<Superscript>+3</Superscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles on the Sonication of Less and More Hydrophobic Polycyclic Aromatic Hydrocarbons (PAHs) and Toxicity

In this study, the effects of 1 h aeration, nitrogen gas N₂(g) sparging (15 and 30 min) and increasing ferric ions (Fe⁺³) as FeSO₄ (10, 20 and 50 mg L⁻¹) and Fe₃O₄ nanoparticles (1, 2 and 4 g L⁻¹) concentrations on three less hydrophobic and three more hydrophobic polycyclic aromatic hydrocarbons (PAHs) and toxicity removals from a petrochemical industry in Izmir (Turkey) were investigated in a sonicator with a power of 650 W and an ultrasound frequency of 35 kHz; 1 h aeration increased the yields in benzo[b]fluoranthene, benzo[k]fluoranthene and benzo[a]pyrene PAHs (less hydrophobic) from 62% to 67% to around 95–97% after 150 min sonication at 60°C. However, 1 h aeration did not contribute to the yields of more hydrophobic PAHs (indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene). The maximum yields were obtained at acidic and alkaline pH for more and less hydrophobic PAHs, respectively, after 60 and 120 min sonication at 30°C; 30 min N₂(g) sparging, 50 mg L⁻¹ Fe⁺³ increased the yields of less hydropobic PAHs after 150 min sonication at 60°C. Two milligrams per liter of Fe₃O₄ nanoparticles increased both less (87–88%) and more (96–98%) hydrophobic PAH yields. The Daphnia magna acute toxicity test showed that the toxicity decreased significantly with an hour aeration, 30 min N₂(g) sparging, 50 mg L⁻¹ Fe⁺³ and 2 g L⁻¹ Fe₃O₄ nanoparticles at 60°C after 120 and 150 min sonications. Vibrio fischeri was found to be more resistant to the sonicated samples than D. magna. Significant correlations were found between the physicochemical properties of sonicated PAHs and acute toxicities both organisms.     

Response of CH<Subscript>4</Subscript> oxidation and methanotrophic diversity to NH<Subscript>4</Subscript><Superscript>+</Superscript> and CH<Subscript>4</Subscript> mixing ratios

Methane oxidising activity and community structure of 11, specifically targeted, methanotrophic species have been examined in an arable soil. Soils were sampled from three different field plots, receiving no fertilisation (C), compost (G) and mineral fertiliser (M), respectively. Incubation experiments were carried out with and without pre-incubation at elevated CH₄ mixing ratios (100 ml CH₄ l⁻¹) and with and without ammonium (100 mg N kg⁻¹) pre-incubation. Four months after fertilisation, plots C, G and M did not show significant differences in physicochemical properties and CH₄ oxidising activity. The total number of methanotrophs (determined as the sum the 11 specifically targeted methanotrophs) in the fresh soils was 17.0×10⁶, 13.7×10⁶ and 15.5×10⁶ cells g⁻¹ for treatment C, G and M, respectively. This corresponded to 0.11 to 0.32% of the total bacterial number. The CH₄ oxidising activity increased 10⁵-fold (20–26 mg CH₄ g⁻¹ h⁻¹), the total number of methanotrophs doubled (28–76×10⁶ cells g⁻¹) and the methanotrophic diversity markedly increased in treatments with a pre-incubation at elevated CH₄ concentrations. In all soils and treatments, type II methanotrophs (62–91%) outnumbered type I methanotrophs (9–38%). Methylocystis and Methylosinus species were always most abundant. After pre-incubation with ammonium, CH₄ oxidation was completely inhibited; however, no change in the methanotrophic community structure could be detected.     

Studying the kinetics of <Superscript>137</Superscript>Cs selective sorption by the dynamic method with the measurement of radioactivity in the sorbent solid phase

The dynamic method was proposed for studying the kinetics of ¹³⁷Cs selective sorption by the measurement of the ¹³⁷Cs activity directly in the sorbent solid phase. A thin layer of the sorbent in a disposable syringe membrane filter (MF) was eluted with a ¹³⁷Cs solution containing K⁺ and Ca²⁺ ions with a gradual decrease in the solution flow rate from 6 to 0.2 cm³/min. The activity of the sorbed ¹³⁷Cs was determined periodically by placing the same MF in the detector well of a Wizard 1480 gamma counter. It was shown that the masses of the sorbent and water in the MF had no effect on the efficiency of the ¹³⁷Cs measurement. A linear relationship between the RIP(K) value and the square root of the time for the period between 4 and 30 days was revealed using this method. The relative increase in the RIP(K) with time changed by 6 times (from 0.034 to 0.208 days^−0.5) for the soils and by 20 times (from 0.008 to 0.153 days^−0.5) for the mineral sorbents. The RIP(K) values measured for the interaction of soddy-podzolic soils with ¹³⁷Cs during 24 hours using the standard limited volume method were lower than the values determined by the proposed dynamic method for the interaction period of 30 days by 50–100%.     

In situ mineral <Superscript>15</Superscript>N dynamics and fate of added <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript> in hoop pine plantation and adjacent native forest in subtropical Australia

Background, aim, and scope  Hoop pine (Araucaria cunninghamii) is a nitrogen (N) demanding indigenous Australia softwood species with plantations in Southeast Queensland, Australia. Soil fertility has declined with increasing rotations and comparison study of N cycling between hoop pine plantations, and adjacent native forest (NF) is required to develop effective forest management for enhancing sustainable forest production and promoting environmental benefits. Field in situ mineral ¹⁵N transformations in these two forest ecosystems have not been studied. Hence, the present study was to compare the differences in soil nutrients, N transformations, ¹⁵N fluxes, and fate between the hoop pine plantation and the adjacent native forest. Materials and methods  The study sites were in Yarraman State Forest (26°52′ S, 151°51′ E), Southeastern Queensland, Australia. The in situ core incubation method was used in the field experiments. Mineral N was determined using a LACHAT Quickchem Automated Ion Analyzer. ¹⁵N were performed using an isotope ratio mass spectrometer with a Eurovector elemental analyzer. All statistical tests were carried out by the SPSS 11.0 for Windows statistical software package. Results  Soil total C and N were significantly higher in the NF than in the 53-year-old hoop pine plantation. Concentrations of NO₃ ^– were significantly higher in the NF soil than in the plantation soil. The plantation soil had significantly higher ¹⁵N and ¹³C natural abundances than the NF soil. The NF soil had significantly lower C/N ratios than the plantation soil. NO₃ ^––N was dominated in mineral N pools in both NF and plantation soils, accounting for 91.6% and 70.3% of the total mineral N pools, respectively. Rates of net nitrification and net N mineralization were, respectively, four and three times higher in the NF soil than in the plantation soil. The ¹⁵NO₃ ^––N and mineral ¹⁵N were significantly higher in the NF soil than in the plantation soil. Significant difference in ¹⁵NH₄ ⁺–N was found in the NF soil before and after the incubation. Discussion  The NF soil had significantly higher NO₃ ^––N, mineral N, total N and C but lower δ¹⁵N, δ¹³C, and C/N ratios than the plantation soil. Moreover, the rates of soil net N mineralization and nitrification were significantly higher, but ammonification rate was lower in the NF than in the plantation. The NF soil had many more dynamic N transformations than the plantation soil due to the combination of multiple species and layers and, thus, stimulation of microbial activity and alteration of C and N pool sizes in favor of the N transformations by soil microbes. The net rate of N and ¹⁵N transformation demonstrated differences in N dynamic related to the variation in tree species between the two ecosystems. Conclusions  The change of land use and trees species had significant impacts on soil nutrients and N cycling processes. The plantation had larger losses of N than the NF. The NO₃ ^––N and ¹⁵NO₃ ^––N dominated in the mineral N and ¹⁵N pools in both forest ecosystems. Recommendations and perspectives  Native forest soil had strong N dynamic compared with the plantation soil. Composition of multiple tree species with different ecological niches in the plantation could promote the soil ecosystem sustainability. The ¹⁵N isotope dilution technique in the field can be quite useful for studying in situ mineral ¹⁵N transformations and fate to further understand actual N dynamics in natural forest soils.     

The role of mineralization of the organic matter of soddy-podzolic and peat bog soils in the accumulation of <Superscript>137</Superscript>Cs by plants

The role of mineralization of soil organic matter (SOM) in the mobilization of ¹³⁷Cs was estimated on the basis of data on the biokinetic fractionation of the organic matter of soddy-podzolic sandy-loam and peat bog soils and on the coefficients of the soil-to-plant transfer of radiocesium under field conditions. The peat bog soils were richer than the soddy-podzolic soils in the total organic carbon (by 7.9–23.8 times), the potentially mineralizable carbon (by 2.4–6.5 times), and the carbon of the microbial biomass (by 2.9–4.6 times). The agricultural use of the soddy-podzolic and peat bog soils led to a decrease in the SOM mineralization capacity by 1.1–1.8 and 1.4–2.0 times, respectively. Simultaneously, the portions of the easily, moderately, and difficultly mineralizable fraction of the SOM active pool changed. The coefficients of the ¹³⁷Cs transfer from the peat bog soils to plants were 3.3–17.6 times higher than those for the soddy-podzolic soils. The content of ¹³⁷Cs in plants grown on the peat bog soils was 2–65 times higher than that in the mobile (salt-extractable) soil pool by the beginning of the growing season. Strong positive linear correlations were found between the coefficients of the soil-to-plant transfer of ¹³⁷Cs and the total content of the SOM, the content of the microbial biomass, the content of the potentially mineralizable carbon, and the intensity of its mineralization. It was concluded that the decisive factors controlling the intensity of the ¹³⁷Cs transfer from mineral and organic soils into plants are the SOM content and its mineralization potential. The mineralization of the SOM is accompanied by the release of both ¹³⁷Cs and mineral nitrogen; the latter facilitates the transfer of radiocesium into plants.     

Short-term uptake of <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript> into soil microbes and seedlings of pine,spruce and birch in potted soils

Short-term competition between soil microbes and seedlings of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth) for N was assessed in a pot study using (¹⁵NH₄)₂SO₄ as a tracer. Seedlings were grown in organic and mineral soil, collected from a podsol soil; 3.18 mg (¹⁵NH₄)₂SO₄ per pot were injected into the soil, corresponding to 4 µg ¹⁵N g^-1 d.m. (dry matter) mineral soil and 17 µg ¹⁵N g^-1 d.m. organic soil. The amounts of N and ¹⁵N in the seedlings and in microbial biomass derived from fumigation-extraction were measured 48 h after addition of ¹⁵N. In the mineral soil, 19–30% of the added ¹⁵N was found in the plants and 14–20% in the microbial biomass. There were no statistically significant differences between the tree species. In the organic soil, 74% of the added ¹⁵N was recovered in the microbial biomass in birch soil, compared to 26% and 17% in pine and spruce soils, respectively. Correspondingly, about 70% of the ¹⁵N was recovered in pine and spruce seedlings, and only 23% in birch seedlings. In conclusion, plants generally competed more successfully for added ¹⁵NH₄ ⁺ than soil microbes did. An exception was birch growing in organic soil, where the greater amount of available C from birch root exudates perhaps enabled micro-organisms to utilise more N.     

<Superscript>15</Superscript>N uptake by mycorrhizal native and invasive plants from a N-eutrophied shrubland: a greenhouse experiment

In the coastal sage scrub (CSS) community of southern California, Artemisia californica and other native shrubs are gradually being replaced by invasive annual grasses, especially Bromus madritensis ssp. rubens. This decline may be attributed, in part, to local atmospheric N deposition, which causes elevated soil NO₃ ^–. Unaffected soils have low N with a relatively higher concentration of NH₄ ⁺ than NO₃ ^–. The objectives in this study were: (1) to compare the short-term uptake of ¹⁵NO₃ ^– and ¹⁵NH₄ ⁺ by B. madritensis and A. californica and (2) to discern whether ¹⁵NO₃ ^– or ¹⁵NH₄ ⁺ uptake is influenced by the mycorrhizal status of either plant species. Analysis of ¹⁵N concentrations indicated that both A. californica and B. madritensis took up more ¹⁵NO₃ ^– than ¹⁵NH₄ ⁺, but overall, B. madritensis took up 6–15 times more of both forms of ¹⁵N than A. californica. Mycorrhizal A. californica had an increased ¹⁵NH₄ ⁺ concentration in roots but not shoots. In B. madritensis, the only mycorrhizal response was a reallocation of ¹⁵NO₃ ^–, with mycorrhizal plants retaining a higher proportion of ¹⁵NO₃ ^– in roots. Overall, arbuscular mycorrhizae had a small effect on ¹⁵N uptake in this short-term study. However, the ability of B. madritensis to take up so much ¹⁵N may explain in part why it has been so successful in replacing A. californica in CSS.     

Enhanced sorption and fixation of radiocaesium in soils amended with K-bentonites, submitted to wetting–drying cycles

The use of bentonites as soil amendment has met with little success in reducing plant uptake of radiocaesium. However, bentonites exchanged with K⁺ have pronounced Cs⁺ binding capacity when subjected to wetting–drying cycles. Fifty‐four different bentonites were collected and characterized for cation exchange capacity and chemical composition. The radiocaesium interception potential (RIP) increased up to 160‐fold (mean 25) when the bentonites were converted to the K‐form and subjected to wetting–drying cycles. This increase in radiocaesium sorption was ascribed to a collapse of the clay sheets into an illite‐like structure, and was most pronounced in bentonites with a high layer charge. The RIP values of K‐bentonites subjected to 25 wetting–drying cycles ranged from 0.22 to 44.3 mol kg^?1. The RIP yields, i.e. the RIP in soil–bentonite mixtures expressed per unit bentonite added, were even higher and ranged up to 99 mol kg^?1. This upper limit is about 10‐fold higher than the RIP value of illite (～ 10 mol kg^?1), the principal ¹³⁷Cs sorbent in soils of temperate climates. Wetting–drying also promoted fixation of radiocaesium in soils amended with K‐bentonites. About 30% of added ¹³⁷Cs could be desorbed with 1 m ammonium acetate (NH₄Ac) from an unamended soil after 25 wetting–drying cycles, while only between 8 and 21% of ¹³⁷Cs could be desorbed from a soil amended with bentonite and a K‐salt. These findings support the proposition that addition of K‐bentonite may be effective in reducing availability of ¹³⁷Cs in soils.     

Concentrations of Radionuclides (<Superscript>226</Superscript>Ra, <Superscript>232</Superscript>Th, <Superscript>40</Superscript>K,and <Superscript>137</Superscript>Cs) in Chernozems of Volgograd Oblast Sampled in Different Years

Data on the concentrations of natural (²²⁶Ra, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides and on the physicochemical properties of chernozems sampled in different years are presented. In 1952, upon the creation of the Penza-Kamensk state shelterbelt, three deep (up to 3 m) soil pits were examined within the former arable field under two-year-old plantations of ash and maple along the transect crossing the territory of the Beloprudskaya Experimental Station of the USSR Academy of Sciences in Volgograd oblast. The samples from these pits were included into the collection of dated soil samples of the Dokuchaev Central Soil Science Museum. Five pits were examined along the same transect in 2009: three pits under shelterbelts (analogues of the pits studied in 1952) and two pits on arable fields between the shelterbelts. In the past 57 years, certain changes took place in the soil structure, bulk density, and the content and composition of humus. The salt profile of soils changed significantly under the forests. The comparison of distribution patterns of natural soil radionuclides in 1952 and 2009 demonstrated their higher contents at the depth of 10–20 cm in 2009 (except for the western shelterbelt). Background concentrations of natural radionuclides in parent materials and relationships between their distributions and the salt profiles of soils have been determined; they are most clearly observed is the soils under shelterbelts. Insignificant contamination with ¹³⁷Cs (up to 34 Bq/kg) has been found in the samples of 2009 from the upper (0–20 cm) horizon. The activity of ¹³⁷Cs regularly decreases from the east to the west; the highest concentrations of this radionuclide are found in the topmost 10 cm. This allows us to suppose that ¹³⁷Cs was brought with aerial dust by eastern winds, and the shelterbelts served as barriers to the wind flow.     

Dynamics of Chernobyl <Superscript>137</Superscript>Cs contamination fields at long distances

Structural changes in the ¹³⁷Cs contamination fields in natural and agroecosystems of the northern forest steppe (the remote zone of the Chernobyl accident) were studied. It was shown that the lateral and vertical distribution of ¹³⁷Cs in soils of different biogeocenoses depends on the features of functioning biogeocenoses and the spatial variation of the initial fallout. The effect of biogeocenosis on the spatial variation of the contaminant distribution increases with time. At present, the variation of primary distribution in soils of agrocenoses is changing. The soils of forest biogeocenoses have retained the features of primary distribution, particularly in the upper 0-to 5-cm sublitter layer. The ¹³⁷Cs penetration depth is greatest in the soils of layland and functioning agrocenosis and least in the soils of forest biogeocenoses.     

Effects of biochar addition on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from two paddy soils

Impacts of biochar addition on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from paddy soils are not well documented. Here, we have hypothesized that N₂O emissions from paddy soils could be depressed by biochar incorporation during the upland crop season without any effect on CO₂ emissions. Therefore, we have carried out the 60-day aerobic incubation experiment to investigate the influences of rice husk biochar incorporation (50 t ha⁻¹) into two typical paddy soils with or without nitrogen (N) fertilizer on N₂O and CO₂ evolution from soil. Biochar addition significantly decreased N₂O emissions during the 60-day period by 73.1% as an average value while the inhibition ranged from 51.4% to 93.5% (P < 0.05–0.01) in terms of cumulative emissions. Significant interactions were observed between biochar, N fertilizer, and soil type indicating that the effect of biochar addition on N₂O emissions was influenced by soil type. Moreover, biochar addition did not increase CO₂ emissions from both paddy soils (P > 0.05) in terms of cumulative emissions. Therefore, biochar can be added to paddy fields during the upland crop growing season to mitigate N₂O evolution and thus global warming.     

Radioactive Contamination of Alluvial Soils in the Taiga Landscapes of Yakutia with <Superscript>137</Superscript>Cs, <Superscript>226</Superscript>Ra,and <Superscript>238</Superscript>U

The concentrations and distribution of ¹³⁷Cs in alluvial soils (Fluvisols) of the upper and middle reaches of the Markha River in the northwest of Yakutia and ²²⁶Ra and ²³⁸U in alluvial soils within the El’kon uranium ore deposit in the south of Yakutia have been studied. It is shown that the migration of radiocesium in the permafrost-affected soils of Yakutia owing to alluviation processes extends to more than 600 km from the source of the radioactive contamination. The migration of ¹³⁷Cs with water flows is accompanied by its deposition in the buried horizons of alluvial soils during extremely high floods caused by ice jams. In the technogenic landscapes of southern Yakutia, active water migration of ²³⁸U and ²²⁶Ra from radioactive dump rocks. The leaching of ²³⁸U with surface waters from the rocks is more intense than the leaching of ²²⁶Ra. The vertical distribution patterns of ²³⁸U and ²²⁶Ra in the profiles of alluvial soils are complex. Uranium tends to accumulate in the surface humus horizon and in the buried soil horizons, whereas radium does not display any definite regularities of its distribution in the soil profiles. At present, the migration of ²³⁸U and ²²⁶Ra with river water and their accumulation in the alluvial soils extend to about 30 km from the source.     

Agroecological optimums concerning saturation with calcium of soils contaminated by <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr

A close negative correlation between the biological availability of ⁹⁰Sr and ¹³⁷Cs for agricultural crops and the content of exchangeable calcium in soils has been revealed in a field experiment performed for soddy-podzolic loamy sandy soil. The efficiency of soil saturation with exchangeable calcium regarding ⁹⁰Sr discrimination is much higher in soils with a low supply of plants with this nutrient. For the bulk of the studied crops, the minimal biological availability of ⁹⁰Sr is registered at 1200–1400 mg/kg (6.0–7.0 mg-equiv./100 g) of the exchangeable calcium content in the soil and that of ¹³⁷Cs is registered at 1000–1100 mg/kg (5.0–5.5 mg-equiv./100 g). The crop productivity varies significantly depending on the exchangeable calcium content in the soil.     

胡敏酸对铵钾在粘土矿物上交互作用的影响

Interaction of ammonium (NH+4) and potassium (K+) is typical in field soils. However, the effects of organic matter on interaction of NH+4 and K+have not been thoroughly investigated. In this study, we examined the changes in major physicochemical properties of three clay minerals (kaolinite, illite, and montmorillonite) after humic acid (HA) coating and evaluated the influences of these changes on the interaction of NH+4 and K+on clay minerals using batch experiments. After HA coating, the cation exchange capacity (CEC) and specific surface area (SSA) of montmorillonite decreased significantly, while little decrease in CEC and SSA occurred in illite and only a slight increase in CEC was found in kaolinite. Humic acid coating significantly increased cation adsorption and preference for NH+4, and this effect was more obvious on clay minerals with a lower CEC. Results of Fourier transform infrared spectrometry analysis showed that HA coating promoted the formation of H-bonds between the adsorbed NH+4 and the organo-mineral complexes. HA coating increased cation fixation capacity on montmorillonite and kaolinite, but the opposite occurred on illite. In addition, HA coating increased the competitiveness of NH+4 on fixation sites. These results showed that HA coating affected both the nature of clay mineral surfaces and the reactions of NH+4 and K+with clay minerals, which might influence the availability of nutrient cations to plants in field soils amended with organic matter.     

Role of plants in the spatial differentiation of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr statuses on the aggregate level

The increased concentration of an element in plant biomass compared to the soil mass is an essential condition for the differentiated spatial distribution and status of the element on the aggregate level. Two forms of this differentiation have been revealed for ¹³⁷Cs and ⁹⁰Sr. Transfer of ¹³⁷Cs from plant roots and concentration on the surface of soil aggregates have been established experimentally. Indirect data also point to the potential localization of ¹³⁷Cs on the surface of intraaggregate pores. The effect of radionuclide concentrating on the outer and inner surfaces of aggregates is due to the rapid and strong fixation of cesium microamounts by mineral soil components. ¹³⁷Cs from the surface of aggregates is more available for the repeated uptake by plant roots than from the intraped mass. The distortion of this spatial differentiation mainly occurs during the reaggregation of soil mass, which in turn decreases the availability of the radionuclide to plants. For ⁹⁰Sr, its elevated concentration in the form of organic residues has been revealed in the inter- and intraaggregate pore space. However, due to the high diffusion rate, ⁹⁰Sr is relatively rapidly (during several months under pot experimental conditions) redistributed throughout the entire volume of soil aggregates and its major part gradually passes into the phase of humic compounds, to which the radionuclide is bound by exchange sorption. The high level of the next root uptake (higher than for ¹³⁷Cs by one to two orders of magnitude) favors the permanent renewal of loci with increased ⁹⁰Sr concentrations in the inter- and intraaggregate pore space in the form of plant residues.     

Effects of cow manure and sewage sludge on the activity and kinetics of <Emphasis Type="SmallCaps">l</Emphasis>-glutaminase in soil

A study was conducted to investigate the effects of cow manure and sewage sludge application on the activity and kinetics of soil l-glutaminase. Soil samples were collected from a farm experiment in which 0, 25, and 100 Mg ha⁻¹ of either cow manure or sewage sludge had been applied annually for 4 consecutive years to a clay loam soil (Typic Haplargid). A chemical fertilizer treatment had also been applied. Results indicated that the effects of chemical fertilizer and the solid waste application on pH in the 18 surface soil (0–15 cm) samples were not significant. The organic C content, however, was affected significantly by the different treatments, being the greatest in soils treated with 100 Mg ha⁻¹ cow manure, and the least in the control treatment. l-Glutaminase activity was generally greater in solid-waste applied soils and was significantly correlated (r = 0.939, P < 0.001) with organic C content of soils. The values of l-glutaminase maximum velocity (Vmax) ranged from 331 to 1,389 mg NH₄ ⁺–N kg⁻¹ 2 h⁻¹. Values of the Michaelis constant (K _m) ranged from 35.1 to 71.7 mM. Organic C content of the soils were significantly correlated with V _max (r = 0.919, P < 0.001) and K _m (r = 0.763, P < 0.001) values. These results demonstrate the considerable influence that solid waste application has on this enzymatic reaction involved in N mineralization in soil.