Sorption Behavior of Cesium in Two Greek Soils: Effects of Cs Initial Concentration,Clay Mineralogy,and Particle-size Fraction

The characteristics of Cs sorption behavior in two soils (soil 1 and soil 2) with nearly the same clay content and exhangeable K concentration, but with different clay mineralogy, were studied by the quantification of the distribution coefficient (k_d). It was observed that as the initial Cs concentration increased from 4 to 50 mg L^?1, the k_d values decreased in both soils, suggesting a progressive saturation of Cs available sorption sites. However, the presence of expansible 2:1 phyllosilicates minerals in the clay fraction of soil 2 maintained a high Cs sorption ability for this soil, even at high Cs concentrations. The experimental data were also fitted to the Freundlich isotherm and the results showed that parameters of the Freundlich equation could be used to estimate the degree of Cs sorption and the nature of the available sorption sites. For the studied soils, the k_f and the k_d values followed a similar trend and the n Freundlich constant values provided a reliable indicator for the soils’ clay mineralogy. The removal of the sand fraction enhanced Cs sorption in both soils and the absence of sorbed Cs ions on the quartz minerals, as observed by the SEM analysis, additionally supported the effect of particle-size fraction on Cs sorption.     

Adsorption Characteristics and the Effect of Dissolved Organic Matter on Mercury(II) Adsorption of Various Soils in China

To evaluate the adsorption characteristics and effects of dissolved organic matter (DOM) from wheat straw (DOM_W) and swine manure (DOM_S) on mercury [Hg(II)] adsorption by soils, a series of experiments was conducted on 26 soils with different soil properties.Results showed that the values of K_d (a solid–liquid partition coefficient) of soils varied within a range of 0.768–14.386 L g^?1. K_d values were mainly controlled by soil organic matter (SOM), cation exchange capacity (CEC), soil nitrogen (N), and soil sulfur (S). When DOM_W and DOM_S were added to the soil samples, the amount of Hg(II) adsorbed by the soils decreased significantly. Furthermore, based on the decreased percentage of adsorption of Hg(II) by soil upon adding DOM_W (P_DOMW) or DOM_S (P_DOMS), about 73.08% soils, the values of P_DOMS were smaller than those of P_DOMW. The P_DOMW values were related to SOM, pH, free Fe oxide content, and CEC, whereas P_DOMS values were related to soil free Fe/Al oxide contents. Therefore, we should pay more attention about mercury risk caused by the addition of exogenous organic matter in soils, especially for the soils with low or high pH, less SOM, low CEC, and less free Fe/Al oxide.     

Slow vapor‐phase desorption of toluene from several ion‐exchanged montmorillonites

The sorption and desorption of volatile compounds from soils and clays exhibit a wide range of kinetics. While much of the sorptive interaction is very rapid, a certain fraction of volatile compounds that enter soil and clays are only slowly desorbed. It is generally believed that the formation of this recalcitrant or slowly desorbing fraction of volatile organic compounds (VOCs) in soils is due to the diffusion of compounds to poorly accessible sorption sites. However, the exact nature of these sites is in doubt. In montmorillonite, there are two likely possibilities for formation of the recalcitrant fraction: sites between the clay lamella and sites within clay particle aggregates. Because montmorillonite may be an important fraction of many soils, we have explored the formation of slowly desorbing toluene on a montmorillonite clay that was ion exchanged with five different ions (K⁺, Na⁺, Ca²⁺, Mg²⁺, and Fe³⁺) to form mineralogically similar clays with varying interlamellar spacing. The recalcitrant fraction was quantified for varying sorption and desorption times. The type of ion exchanged into the clay appears to have an important influence on the formation of a recalcitrant fraction.     

Impacts of Soil Organic Matter and Temperature on Sorption of Acetazolamide on Four Soils

Batch sorptions of acetazolamide (AZ) were conducted using four soils from China. Sorption of AZ was found to be impacted by OC, clay content, and soil pH, with higher k_d values for soils with higher clay content. The k_d values of SOM-removed soils are much lower than those of bulk soils. Sorption data were well fitted with a Freundlich model (r² > 0.99). Chelating with the metal ions on the surfaces of soil particles was probably involved. With pH increase, the electrostatic attraction between anionic AZ and positively charged soil surface may increase. The sorption capacity decreased when the temperature increased from 20 to 40°C, and the calculated thermodynamics parameters of ΔG₀, ΔH₀, and ΔS₀ indicated that the sorption was a non-spontaneous, physisorption, and exothermic process. Sorption coefficients (k_d) for the compound in soil were low (ranging from 0.42 to 1.19 L·kg^?1) and indicated that low level sorption of AZ with appreciable risk of ground water contamination.     

Effect of surfactant on the estimation by solid phase microextraction of bioavailable pyrene in soil samples

This study was focused on the effect of the presence of surfactant on the bioremediation efficacy and sensitivity of solid phase microextraction (SPME) in the pyrene-contaminated soil. Soils with 1.3 and 7.6% soil organic matter (SOM) were tested for biodegradation by microorganisms and extracted by aqueous solutions of the matrix used for SPME. For the biodegradation test, the presence of Triton X-100 at 5× CMC (critical micelle concentration) significantly enhanced pyrene removal for soil with lower SOM content (1.3%). However, this removal was insignificant for soil with higher SOM content (7.6%). The results may suggest that 5× CMC was not sufficient to improve significantly pyrene desorption for soil with higher SOM content. For the bioavailability test, in the absence of Triton X-100, SPME estimation of bioavailability in soils with indigenous or seeded microorganisms had an error range within 15%. However, with addition of Triton X-100, SPME estimations showed a significant decline (41 and 77%), in relation to their predicted values, for soil samples with SOM of 1.3 and 7.6%, respectively. The main reason for this underestimation is that micelle formation from the application of surfactant impacted the concentration of dissolved pyrene, rather than competitive site occupation between pyrene and surfactant molecules for SPME fiber. Thus, if soil samples contain surfactant, SPME would significantly underestimate bioavailability and risk level of PAH-contaminated sites.     

Evaluation of Iodide and Iodate for Adsorption–Desorption Characteristics and Bioavailability in Three Types of Soil

Adsorption–desorption of iodine in two forms, viz., iodide (I⁻) and iodate (IO₃⁻), in three types of soil were investigated. The soils were: red soil developed on Quaternary red earths (REQ)— clayey, kaolintic thermic plinthite Aquult, Inceptisol soil (IS) and alluvial soil (AS)—Fluvio-marine yellow loamy soil. The isothermal curves of iodine adsorption on soils were described by Langmuir and Freundlich equation, and the maximum adsorption values (y _m) were obtained from the simple Langmuir model. As compared with the iodide, the iodate was adsorbed in higher amounts by the soils tested. Among three soils, the REQ soil adsorbed more iodine (I⁻ and IO₃⁻) than the IS and AS. The distribution coefficient (K _d) of iodine in the soils decreased exponentially with increasing iodine loading concentration. Desorption of iodine in soil was increased correspondingly with increasing adsorption values. The REQ soil had a greater affinity for iodine than the IS and AS at the same iodine loadings. In the pot experiment cultivated with pakchoi (Brassica chinensis L.) and added with two exogenous iodine sources, the iodide form was quickly taken up by pakchoi and caused more toxicity to the vegetable. The rate of iodine loss from soil was higher for iodide form as compared with the iodate. The iodine bioavailability was the highest but the persistence was the weakest in AS among the three soils tested, and the REQ soil showed just the opposite trend to that of the AS soil. This study is of theoretical importance to understand the relationship between iodine adsorption–desorption characteristics and their bioavailability in different soils and it also has practical implications for seeking effective alternatives of iodine biofortification to prevent iodine deficiency disorders.     

Linking microbial activity and soil organic matter transformations in forest soils under elevated CO2

Soil organic matter (SOM) dynamics ultimately govern the ability of soil to provide long‐term C sequestration and the nutrients required for ecosystem productivity. Predicting belowground responses to elevated CO₂ requires an integrated understanding of SOM transformations and the microbial activity that governs them. It remains unclear how the microorganisms upon which these transformations depend will function in an elevated CO₂ world. This study examines SOM transformations and microbial metabolism in soils from the Duke Free Air Carbon Enrichment site in North Carolina, USA. We assessed microbial respiration and net nitrogen (N) mineralization in soils with and without elevated CO₂ exposure during a 100‐day incubation. We also traced the depleted C isotopic signature of the supplemental CO₂ into SOM and the soils' phospholipid fatty acids (PLFA), which serve as biomarkers for living cells. Cumulative net N mineralization in elevated CO₂ soils was 50% that in control soils after a 100‐day incubation. Respiration was not altered with elevated CO₂. C : N ratios of bulk SOM did not change with elevated CO₂, but incubation data suggest that the C : N ratios of mineralized organic matter increased with elevated CO₂. Values of SOM δ¹³C were depleted with elevated CO₂ (?26.7±0.2 vs. ?30.2±0.3‰), reflecting the depleted signature of the supplemental CO₂. We compared δ¹³C of individual PLFA with the δ¹³C of SOM to discern incorporation of the depleted C isotopic signature into soil microbial groups in elevated CO₂ plots. PLFA i15:0, a15:0, and 10Met18:0 reflected significant incorporation of recently produced photosynthate, suggesting that the bacterial groups defined by these biomarkers are active metabolizers in elevated CO₂ soils. At least one of these groups (actinomycetes, 10Met18:0) specializes in metabolizing less labile substrates. Because control plots did not receive an equivalent ¹³C tracer, we cannot determine from these data whether this group of organisms was stimulated by elevated CO₂ compared with these organisms in control soils. Stimulation of this group, if it occurred in the elevated CO₂ plot, would be consistent with a decline in the availability of mineralizable organic matter with elevated CO₂, which incubation data suggest may be the case in these soils.     

Altered patterns of soil carbon substrate usage and heterotrophic respiration in a pine forest with elevated CO2 and N fertilization

To assess how heterotrophic microorganisms may alter their activities and thus their CO₂‐C return to the atmosphere with elevated CO₂ and changing N availability, we examined soil organic matter (SOM) dynamics at the Duke Free Air Carbon Enrichment (FACE) site, after N fertilizer was applied. We measured heterotrophic respiration during early and late stages of SOM mineralization in soil incubations to capture activity on relatively labile and refractory SOM pools. We also measured δ¹³C of respired CO₂‐C and phospholipid fatty acids (PLFAs) during early mineralization stages to track the microbial groups involved in substrate use. We calculated , a measure of δ¹³C_PLFA normalized by respired δ¹³CO₂, to assess microbial function with C substrates formed with elevated CO₂ and altered N availability, via the distinct δ¹³C of the supplemental CO₂. We also quantified extracellular enzyme activity (EEA) during labile and recalcitrant SOM mineralization. Early in the incubations, increased N availability reduced heterotrophic CO₂‐C release. By the later stages of SOM mineralization, elevated CO₂ soils with fertilization had respired 72% of the CO₂‐C respired by all other soils. values suggest that fungi in elevated CO₂ plots took up C substrates possessing the δ¹³C signature of recently formed SOM, and added N promoted the activity of Gram‐negative bacteria and reduced that of Gram‐positive bacteria, particularly actinomycetes. Consistent with this, the enzyme responsible for the degradation of peptidoglycan and chitin, compounds produced by Gram‐positive bacteria and fungi, respectively, experienced a decline in activity with N fertilization. If patterns observed in this study with N additions are reversed with progressive N limitation at this site, actinomycetes and other Gram‐positive bacteria responsible for mineralizing relatively recalcitrant substrates may experience increases in their activity. Such shifts in microbial functioning may result in increased turnover of, and C release from, relatively decay‐resistant material.     

Biotic and abiotic immobilization of ammonium, nitrite, and nitrate in soils developed under different tree species in the Catskill Mountains, New York, USA

Nitrogen retention in soil organic matter (SOM) is a key process influencing the accumulation and loss of N in forest ecosystems, but the rates and mechanisms of inorganic N retention in soils are not well understood. The primary objectives of this study were to compare ammonium (NH₄⁺), nitrite (NO₂^?), and nitrate (NO₃^?) immobilization among soils developed under different tree species in the Catskill Mountains of New York State, and to determine the relative roles of biotic or abiotic processes in soil N retention. A laboratory experiment was performed, where ¹⁵N was added as NH₄⁺, NO₂^?, or NO₃^? to live and mercury‐treated O horizon soils from three tree species (American beech, northern red oak, sugar maple), and ¹⁵N recoveries were determined in the SOM pool. Mercuric chloride was used to treat soils as this chemical inhibits microbial metabolism without significantly altering the chemistry of SOM. The recovery of ¹⁵N in SOM was almost always greater for NH₄⁺ (mean 20%) and NO₂^? (47%) than for NO₃^? (10%). Ammonium immobilization occurred primarily by biotic processes, with mean recoveries in live soils increasing from 9% at 15 min to 53% after 28 days of incubation. The incorporation of NO₂^? into SOM occurred rapidly (<15 min) via abiotic processes. Abiotic immobilization of NO₂^? (mean recovery 58%) was significantly greater than abiotic immobilization of NH₄⁺ (7%) or NO₃^? (7%). The incorporation of NO₂^? into SOM did not vary significantly among tree species, so this mechanism likely does not contribute to differences in soil NO₃^? dynamics among species. As over 30% of the ¹⁵NO₂^? label was recovered in SOM within 15 min in live soils, and the products of NO₂^? incorporation into SOM remained relatively stable throughout the 28‐day incubation, our results suggest that NO₂^? incorporation into SOM may be an important mechanism of N retention in forest soils. The importance of NO₂^? immobilization for N retention in field soils, however, will depend on the competition between incorporation into SOM and nitrification for transiently available NO₂^?. Further research is required to determine the importance of this process in field environments.     

Soil retention of 15N in a simulated N deposition study: effects of live plant and soil organic matter content

Background and aims

The impacts of atmospheric nitrogen (N) deposition on terrestrial ecosystem processes remain controversial, mostly because of the uncertainty regarding the fates of deposited N. We conducted a 16-week simulated deposition study to experimentally trace N in a greenhouse plant-soil system.

Methods

Using a two-way factorial design, we added (¹⁵NH₄)₂SO₄ solution twice a week to pots containing different soil organic matter (SOM) content and with or without a live plant (Salix dasyclados). The recoveries of ¹⁵N in soil, plant biomass, and leaching solution were quantified.

Results

We found most ¹⁵N was retained in soil (18.0–59.2%), with significantly more ¹⁵N recovered from high-SOM soils than from low-SOM soils. Plant presence significantly increased ¹⁵N retention in soil. Plant biomass accounted for 10–20% of the ¹⁵N input, with proportionally more ¹⁵N assimilated when plants were grown in low-SOM soils. Leaching loss of ¹⁵N was relatively low (10–17%).

Conclusion

Our study suggests that SOM content and plant presence significantly affect the fates of deposited N. Indeed, N would be preferentially retained in soils with high SOM content and live plant, while plants would assimilate more deposited N when grown in low SOM soils. Global biogeochemical models thus need to incorporate such soil-specific N retention and plant N assimilation.     

The Role of CEC and pH in Cd Retention from Soils of North of Iran

Cadmium (Cd) is a critical environmental chemical in which sorption reactions control its entry into soil solution. The aim of the present study was to evaluate Cd sorption characteristics of some soils of the northern part of Iran with a wide range of physicochemical properties. Duplicates of each sample were equilibrated with solutions containing 5 to 500 mg Cd L^?1 with 0.01 M CaCl₂ as background solution. The quantity of Cd retention was calculated as the difference between initial and equilibrated Cd concentration. Sorption isotherms including Freundlich, Langmuir, Temkin, Dubinin-Radushkevich, and Redlich-Peterson were used to evaluate the behavior of Cd sorption. Cadmium sorption data were well fitted to Langmuir, Freundlich, and Redlich-Peterson isotherms. The constant of Freundlich equation (k_F ) and adsorption maxima (b_L ) of Langmuir equation were related to pH and cation exchange capacity (CEC). The maximum buffering capacity (K_d ) was significantly correlated with pH (R² = 0.52, p ≤ 0.001) and calcium carbonate equivalent (CCE) (R² = 0.63, p ≤ 0.001). Redlich-Peterson constants (k_RP and a_RP ) were significantly correlated with pH (R² k_RP = 0.30, p ≤ 0.007) and (R² a_RP = 0.27, p ≤ 0.012). It seemed that pH, CEC, and CCE were the main soil properties regulating Cd retention behavior of the studied soils.     

Minor stable carbon isotope fractionation between respired carbon dioxide and bulk soil organic matter during laboratory incubation of topsoil

A common assumption in paleoenvironmental reconstructions using soils is that the carbon isotope composition of soil-respired CO₂ is equivalent to the carbon isotope composition of bulk soil organic matter (SOM). However, the occurrence of a non-zero per mil carbon isotope enrichment factor between CO₂ and SOM (\(\varepsilon_{{{\text{CO}}_{ 2} - {\text{SOM}}}}\)) during soil respiration is the most widely accepted explanation for the down-profile increase in SOM δ¹³C values commonly observed in well-drained soils. In order to shed light on this apparent discrepancy, we incubated soil samples collected from the top 2 cm of soils with pure C₃ vegetation and compared the δ¹³C values of soil-respired CO₂ to the δ¹³C values of bulk SOM. Our results show near-zero \(\varepsilon_{{{\text{CO}}_{ 2} - {\text{SOM}}}}\) values (?0.3 to 0.4 ‰), supporting the use of paleosol organic matter as a proxy for paleo soil-respired CO₂. Significantly more negative \(\varepsilon_{{{\text{CO}}_{ 2} - {\text{SOM}}}}\) values are required to explain the typical δ¹³C profiles of SOM in well-drained soils. Therefore our results also suggest that typical SOM δ¹³C profiles result from either (1) a process other than carbon isotope fractionation between CO₂ and SOM during soil respiration or (2) \(\varepsilon_{{{\text{CO}}_{ 2} - {\text{SOM}}}}\) values that become increasingly negative as SOM matures.     

Influence of rhizodeposition under elevated CO2 on plant nutrition and soil organic matter

Atmospheric CO₂ concentrations can influence ecosystem carbon storage through net primary production (NPP), soil carbon storage, or both. In assessing the potential for carbon storage in terrestrial ecosystems under elevated CO₂, both NPP and processing of soil organic matter (SOM), as well as the multiple links between them, must be examined. Within this context, both the quantity and quality of carbon flux from roots to soil are important, since roots produce specialized compounds that enhance nutrient acquisition (affecting NPP), and since the flux of organic compounds from roots to soil fuels soil microbial activity (affecting processing of SOM).From the perspective of root physiology, a technique is described which uses genetically engineered bacteria to detect the distribution and amount of flux of particular compounds from single roots to non-sterile soils. Other experiments from several labs are noted which explore effects of elevated CO₂ on root acid phosphatase, phosphomonoesterase, and citrate production, all associated with phosphorus nutrition. From a soil perspective, effects of elevated CO₂ on the processing of SOM developed under a C4 grassland but planted with C3 California grassland species were examined under low (unamended) and high (amended with 20 g m^–2 NPK) nutrients; measurements of soil atmosphere 13C combined with soil respiration rates show that during vegetative growth in February, elevated CO₂ decreased respiration of carbon from C4 SOM in high nutrient soils but not in unamended soils.This emphasis on the impacts of carbon loss from roots on both NPP and SOM processing will be essential to understanding terrestrial ecosystem carbon storage under changing atmospheric CO₂ concentrations.Abbreviations SOM soil organic matter - NPP net primary productivity - NEP net ecosystem productivity - PNPP p-nitrophenyl phosphate     

The Temperature Response of CO<Subscript>2</Subscript> Production from Bulk Soils and Soil Fractions is Related to Soil Organic Matter Quality

The projected increase in global mean temperature could accelerate the turnover of soil organic matter (SOM). Enhanced soil CO₂ emissions could feedback on the climate system, depending on the balance between the sensitivity to temperature of net carbon fixation by vegetation and SOM decomposition. Most of the SOM is stabilised by several physico-chemical mechanisms within the soil architecture, but the response of this quantitatively important fraction to increasing temperature is largely unknown. The aim of this study was to relate the temperature sensitivity of decomposition of physical and chemical soil fractions (size fractions, hydrolysis residues), and of bulk soil, to their quality and turnover time. Soil samples were taken from arable and grassland soils from the Swiss Central Plateau, and CO₂ production was measured under strictly controlled conditions at 5, 15, 25, and 35 °C by using sequential incubation. Physico-chemical properties of the samples were characterised by measuring elemental composition, surface area, ¹⁴C age, and by using DRIFT spectroscopy. CO₂ production rates per unit (g) organic carbon (OC) strongly varied between samples, in relation to the difference in the biochemical quality of the substrates. The temperature response of all samples was exponential up to 25 °C, with the largest variability at lower temperatures. Q₁₀ values were negatively related to CO₂ production over the whole temperature range, indicating higher temperature sensitivity of SOM of lower quality. In particular, hydrolysis residues, representing a more stabilised SOM pool containing older C, produced less CO₂ g⁻¹ OC than non-hydrolysed fractions or bulk samples at lower temperatures, but similar rates at ≥25 °C, leading to higher Q₁₀ values than in other samples. Based on these results and provided that they apply also to other soils it is suggested that because of the higher sensitivity of passive SOM the overall response of SOM to increasing temperatures might be higher than previously expected from SOM models. Finally, surface area measurements revealed that micro-aggregation rather than organo-mineral association mainly contributes to the longer turnover time of SOM isolated by acid hydrolysis.     

Biochar mineralization and priming effect on SOM decomposition in two European short rotation coppices

As studies on biochar stability in field conditions are very scarce, the carbon sequestration potential of biochar application to agricultural soils remains uncertain. This study assessed the stability of biochar in field conditions, the effect of plant roots on biochar stability and the effect of biochar on original soil organic matter (SOM) decomposition in two (Italy and United Kingdom) short rotation coppice systems (SRCs), using continuous soil respiration monitoring and periodic isotopic (δ¹³CO₂) measurements. When root growth was excluded, only 7% and 3% of the biochar carbon added was decomposed after 245 and 164 days in Italy and United Kingdom sites respectively. In the presence of roots, this percentage was increased to 9% and 8%, suggesting a small positive priming effect of roots on biochar decomposition. A decreased decomposition rate of original SOM was observed at both sites after biochar incorporation, suggesting a protective effect of biochar on SOM. This study supports the carbon sequestration potential of biochar and highlights the role of root activity on biochar decomposition, questioning the applicability of laboratory incubation studies to assess biochar stability.     

An oxygen-mediated positive feedback between elevated carbon dioxide and soil organic matter decomposition in a simulated anaerobic wetland

We examined the effects of elevated atmospheric CO₂ on soil carbon decomposition in an experimental anaerobic wetland system. Pots containing either bare C₄‐derived soil or the C₃ sedge Scirpus olneyi planted in C₄‐derived soil were incubated in greenhouse chambers at either ambient or twice‐ambient atmospheric CO₂. We measured CO₂ flux from each pot, quantified soil organic matter (SOM) mineralization using δ¹³C, and determined root and shoot biomass. SOM mineralization increased in response to elevated CO₂ by 83–218% (P<0.0001). In addition, soil redox potential was significantly and positively correlated with root biomass (P= 0.003). Our results (1) show that there is a positive feedback between elevated atmospheric CO₂ concentrations and wetland SOM decomposition and (2) suggest that this process is mediated by the release of oxygen from the roots of wetland plants. Because this feedback may occur in any wetland system, including peatlands, these results suggest a limitation on the size of the carbon sink presented by anaerobic wetland soils in a future elevated‐CO₂ atmosphere.     

Effect of Mineral and Organic Soil Constituents on Microbial Mineralization of Organic Compounds in a Natural Soil

This research addressed the effect of mineral and organic soil constituents on the fate of organic compounds in soils. Specifically, it sought to determine how the associations between organic chemicals and different soil constituents affect their subsequent biodegradation in soil. Four ¹⁴C-labeled surfactants were aseptically adsorbed to montmorillonite, kaolinite, illite, sand, and humic acids. These complexes were mixed with a woodlot soil, and ¹⁴CO₂ production was measured over time. The mineralization data were fitted to various production models by nonlinear regression, and a mixed (3/2)-order model was found to most accurately describe the mineralization patterns. Different mineralization patterns were observed as a function of the chemical and soil constituents. Surfactants that had been preadsorbed to sand or kaolinite usually showed similar mineralization kinetics to the control treatments, in which the surfactants were added to the soil as an aqueous solution. Surfactants that had been bound to illite or montmorillonite were typically degraded to lesser extents than the other forms, while surfactant-humic acid complexes were degraded more slowly than the other forms. The desorption coefficients (K_d) of the soil constituent-bound surfactants were negatively correlated with the initial rates of degradation (k₁) and estimates of ¹⁴CO₂ yield (P_o) as well as actual total yields of ¹⁴CO₂. However, there was no relationship between K_d and second-stage zero-order rates of mineralization (k_o). Microbial community characteristics (biomass and activity) were not correlated with any of the mineralization kinetic parameters. Overall, this study showed that environmental form had a profound effect on the ultimate fate of biodegradable chemicals in soil. This form is defined by the physicochemical characteristics of the chemical, the composition and mineralogy of the soil, and the mode of entry of the chemical into the soil environment.     

Incorporation of Plant Residues into Soil Organic Matter Fractions With Grassland Management Practices in the North American Midwest

Disturbed grassland soils are often cited as having the potential to store large amounts of carbon (C). Fertilization of grasslands can promote soil C storage, but little is known about the generation of recalcitrant pools of soil organic matter (SOM) with management treatments, which is critical for long-term soil C storage. We used a combination of soil incubations, size fractionation and acid hydrolysis of SOM, [C], [N], and stable isotopic analyses, and biomass quality indices to examine how fertilization and haying can impact SOM dynamics in Kansan grassland soils. Fertilized soils possessed 113% of the C possessed by soils subjected to other treatments, an increase predominantly harbored in the largest size fraction (212–2,000 μm). This fraction is frequently associated with more labile material. Haying and fertilization/haying, treatments that more accurately mimic true management techniques, did not induce any increase in soil C. The difference in ¹⁵N-enrichment between size fractions was consistent with a decoupling of SOM processing between pools with fertilization, congruent with gains of SOM in the largest size fraction promoted by fertilization not moving readily into smaller fractions that frequently harbor more recalcitrant material. Litterfall and root biomass C inputs increased 104% with fertilization over control plots, and this material possessed lower C:N ratios. Models of incubation mineralization kinetics indicate that fertilized soils have larger pools of labile organic C. Model estimates of turnover rates of the labile and recalcitrant C pools did not differ between treatments (65.5 ± 7.2 and 2.9 ± 0.3 μg C d⁻¹, respectively). Although fertilization may promote greater organic inputs into these soils, much of that material is transformed into relatively labile forms of soil C; these data highlight the challenges of managing grasslands for long-term soil C sequestration.     

Potential for phytoextraction of137 Cs from a contaminated soil

Potential for phytoremediation of a soil contaminated with radiocesium was investigated in three phases: (1) hydroponic screening for plant species capable of accumulating elevated levels of cesium in shoots, (2) investigation of several amendments for their potential to increase the bioavailability of ¹³⁷Cs in the contaminated soil, and (3) bioaccumulation of radiocesium in shoots of plants grown in¹³⁷ Cs-contaminated soil.The bioaccumulation ratio for Cs in shoots of hydroponically grown plants ranged between 38 and 165. From solution, dicot species accumulated 2- to 4-fold more cesium in shoots than grasses. In studies investigating the bioavailability of ¹³⁷Cs in aged contaminated soil, ammonium salts were found to be the most effective desorbing agents, releasing approximately 25% of the¹³⁷ Cs. The extent of ¹³⁷Cs desorption from the soil increased with ammonium concentration up to 0.2 M. In a pot study conducted in a greenhouse, there was significant species-dependent variability in the ability to accumulate ¹³⁷Cs in the shoot from contaminated soil. The ability to accumulate ¹³⁷Cs from the soil increased in the order: reed canarygrass (Phalaris arundinacea) < Indian mustard (Brassica juncea) < tepary bean (Phaseolus acutifolius)< cabbage (B. oleracea var. capitata). It was also found that addition of NH₄NO₃ solution to the soil elicited a two- to twelve-fold increase in ¹³⁷Cs accumulation in the shoot. The greatest amount of ¹³⁷Cs (40 Bq g^-1 dw) was removed in shoots of cabbage grown in contaminated soil amended with 80 mmols NH₄NO₃ kg^-1 soil. Bioaccumulation ratios of 2–3 were obtained with the best performing plant species. These values are significantly greater than those previously reported in the literature (usually <0.1) for plants grown on aged contaminated soil. These results indicate that careful species selection along with amendments that increase the bioavailability of¹³⁷ Cs in the soil could greatly enhance the prospects for the use of plants to remediate ¹³⁷Cs-contaminated soils.