Influence of mist pH and acid anion on cation efflux from pinto bean foliage

The cation content of droplets collected from Phaseolus vulgaris (pinto bean) leaf surfaces during misting was more strongly influenced by mist pH (2.5, 4.0, or deionized water) than by source of acidity (HCI or H₂SO₄ + HNO₃). Concentrations of Ca²⁺, Mg²⁺, and K⁺ were highest in droplets from leaves treated with the pH 2.5 mists, but there were often no differences between the pH 4.0 and deionized water treatments. Cation content and pH of droplets from leaves treated with pH 2.5 mists increased across the three days of treatment, while those from leaves treated with less acidic mists decreased or did not change across the days of treatment. Source of acidity often affected foliar concentrations of Mg²⁺, K⁺, and Na⁺, but in inconsistent directions, and foliar concentrations of Mg²⁺ and K⁺ were unaffected by mist pH. Foliar Ca ²⁺ concentrations were often highest in leaves treated with pH 2.5 mists, in contrast to expectation, perhaps because of effects of acidic mist on foliar carbohydrate status. Despite the large efflux of cations from leaves treated with pH 2.5 mists, foliar cation concentrations in nonmisted foliage were sometimes lower than in misted foliage (Ca²⁺), but were higher in other cases (Na⁺) or indistinguishable in still others (K^?). While exposure of plants to highly acidic mists appeared to cause accelerated efflux of foliar cations, effects on foliar chemistry are probably dependent on soil nutrient status and on other aspects of plant vigor.     

Increasing pH releases colloidal lead in a highly contaminated forest soil

Colloids can play an important role in the leaching of lead (Pb) in soils, and liming to increase pH may produce conditions conducive to colloid release. We studied the effect of pH and the role of counterion valency on the mobilization of Pb in two topsoil horizons of a former shooting range. In batch experiments, the release of both dissolved and colloidal Pb was studied at a pH range between 3 and 7. The pH was adjusted with solutions of nitric acid (pH 3) and KOH and Ca(OH)₂ (pH 4–7) and the chemical composition, size and charge of the mobilized colloids were determined. In the presence of the monovalent K⁺‐ion concentrations of colloidal and dissolved Pb increased markedly with increasing pH. Colloids were stabilized not only by electrostatic but also by steric repulsion. Organic colloids seem to dominate at low pH of the KOH‐treatment; at pH > 4 mineral particles were also dispersed. Even though the presence of the Ca²⁺ ion reduced the concentrations of colloidal Pb more than did the K⁺ ion, our results of the Ca(OH)₂ treatment show that the relevance of both colloidal and dissolved Pb increases at a pH of about 5.8. Risk assessment on limed sites should therefore take into account both dissolved and colloidal Pb in judging the likelihood of Pb leaching.     

Lysimeter study with a cambic Arenosol exposed to artificial acid rain: I. Concentrations of ions in leachate

The effects of artificial acid rain on soil leachate composition were studied in a lysimeter experiment. Cambic Arenosol (Typic Udipsamment) in monolith lysimeters was treated for 6 1/2 yr with 125 mm yr^?1 artificial rain in addition to natural precipitation. Artificial acid rain was produced from groundwater with H₂SO₄ added. pH levels of 6.1, 4 and 3 were used. Increasing content of H₂SO₄ in the artificial rain increased the concentration of Ca²⁺ and Mg²⁺ in the leachate significantly. The pH of the leachate was slightly reduced only by the most acidic treatment (pH 3). The H^+? retention was not accompanied by a proportionate increase in the Al ion concentration. A slight increase in the Al ion concentration was only observed in the leachate from the pH 3-treated lysimeter. We conclud that cation exchange and/or weathering were the main buffer mechanisms in the soil. The study supports conclusions from other acidification studies, that acidic precipitation is likely to increase the leaching of Ca²⁺ and Mg²⁺ from soils.     

DETERMINATION OF pH, LIME POTENTIAL, AND ALUMINIUM HYDROXIDE POTENTIAL OF ACID SOILS

pH values in CaCl₂ suspensions of some acid Scottish soils increase with time, in some cases by 0·4 units in 24 h. This is attributed to proton uptake by a complex ion displaced into solution, and to obtain unambiguous values, pH in CaCl₂ suspensions should be measured within an hour of making up the suspensions. In moderately to strongly acid soils, lime potential (LP) and aluminium hydroxide potential (AHP) vary with salt concentration and soil: solution ratio. Unique values for these ion-activity ratios can be obtained by equilibration with a single solution only when the reference cations, i.e. (Ca²⁺+Mg²⁺) for LP, and Al³⁺ for AHP, are the dominant exchangeable cations. Otherwise, equilibrium values should be obtained by interpolation from an exchange isotherm at the point where no exchange occurs, i.e. where Δ(Ca+Mg) = o for LP values and ΔA1 = o for AHP values.     

Soybean root growth in relation to ionic composition in magnesium-amended acid subsoils: Implications on root citrate ameliorating aluminum constraints

Abstract

Hydroponic studies with soybean (Glycine max [L.] Merr.) have shown that µmol L^?1 additions of Mg²⁺ were as effective in ameliorating Al rhizotoxicity as additions of Ca²⁺in the mmol L^?1 concentration range. The objectives of this study were to assess the ameliorative effects of Mg on soybean root growth in acidic subsoils and to relate the soil solution ionic compositions to soybean root growth. Roots of soybean cultivar Plant Introduction 416937 extending from a limed surface soil compartment grew for 28 days into a subsurface compartment containing acid subsoils from the Cecil (oxidic and kaolinitic), Creedmoor (montmorillonitic) and Norfolk (kaolinitic) series. The three Mg treatments consisted of native equilibrium soil solution concentrations in each soil (50 or 100 µmol L^?1) and MgCl₂ additions to achieve 150 and 300 µmol L^?1 Mg (Mg150 and Mg300, respectively) in the soil solutions. Root elongations into Mg-treated subsoils were compared with a CaCO₃ treatment limed to achieve a soil pH value of 6. Subsoil root growth responses to the Mg treatments were less than for the lime treatments. Root length relative to the limed treatments for all subsoils (RRL) was poorly related to the activity of the soil solution Al species (Al³⁺ and Al-hydroxyl species) and Mg²⁺. However, the RRL values were more closely related to the parameters associated with soil solution Ca activity, including (Ca²⁺), (Al³⁺)/(Ca²⁺) and (Al³⁺)/([Ca²⁺] + [Mg²⁺]), suggesting that Ca could be a primary factor ameliorating Al and H⁺ rhizotoxicity in these subsoils. Increased tolerance to Al rhizotoxicity of soybean by micromolar Mg additions to hydroponic solutions, inducing citrate secretion from roots to externally complex toxic Al, may be less important in acid subsoils with low native Ca levels.     

Sodium‐calcium interactions with growth,water, and photosynthetic parameters in salt‐treated beans

Calcium (Ca²⁺) amelioration of the plant's growth response to salinity depends on genetic factors. In this work, supplemental Ca²⁺ did not improve growth in Phaseolus vulgaris L. cv. Contender under high‐saline conditions and negatively affected several physiological parameters in nonsalinized plants. The response to supplemental Ca²⁺ was examined using plants grown in 25% modified Hoagland solution at different Na⁺ : Ca²⁺ ratios. In control plants (1 mM Ca²⁺; 1 mM Na⁺) surplus Ca²⁺ (4 or 10 mM) was associated with stomatal closure, decrease of hydraulic conductivity, sap flow, leaf specific dry weight, leaf K⁺ and leaf Mg²⁺ concentrations, and inhibition of CO₂ assimilation. Leaf water content was enhanced, while water‐use efficiency and dry matter were unaffected during the 15 d experimental period. The Ca²⁺ effect was not cation‐specific since similar results were found in plants supplied with high external Mg²⁺ or with a combination of Ca²⁺ and Mg²⁺. Relative to control plants, salinization (50 and 100 mM NaCl) caused a decrease in dry matter, hydraulic conductivity, sap flow, leaf Mg²⁺ activity, and inhibition of stomatal opening and CO₂ assimilation. However, NaCl (50 and 100 mM NaCl) enhanced leaf K⁺ concentration and water‐use efficiency. At 100 mM NaCl, leaf water content also significantly increased. Supplemental Ca²⁺ had no amelioration effect on the salt‐stress response of this bean cultivar. In contrast, the 50 mM–NaCl treatment improved stomatal conductance and CO₂‐assimilation rate in plants exposed to the highest Ca²⁺ concentration (10 mM). Phaseolus vulgaris is classified as a very NaCl‐sensitive species. The similarities in the effects caused by supplemental Ca²⁺, supplemental Mg²⁺, and NaCl salinity suggest that P. vulgaris cv. Contender has a high non‐ion‐specific salt sensitivity. On the other hand, the improvement in gas‐exchange parameters in Ca²⁺‐supplemented plants by high NaCl could be the result of specific Na⁺‐triggered responses, such as an increase in the concentration of K⁺ in the leaves.     

Long-term development of element budgets in a Norway spruce (Picea abies (L.) Karst.) forest of the German solling area

To evaluate ecosystem response to changing atmospheric deposition, element budgets were established over the period from 1973 to 1991 for a Norway Spruce (Picea abies (L.) Karst.) site. Budgets for Na⁺, Cl^?, Ca²⁺, Mg²⁺, N, S and H⁺ were based on total deposition and seepage water fluxes. The deposition of Ca²⁺, Mg²⁺, particularly, of S and H⁺ decreased with time, while calculated N deposition remained constant at a high level. The decrease in Ca²⁺ deposition led to a reduction of Ca²⁺ fluxes with seepage water. The decrease of Mg²⁺ deposition did not have an effect on the output fluxes of Mg²⁺. The reversibility of soil and seepage water acidification by reduced S deposition was delayed by the release of previously accumulated soil SO ₄ ^2? . The highest NO ₃ ^? fluxes were observed during the period of 1986 to 1988; NO ₃ ^? fluxes in general demonstrated a considerable annual and periodic variation. Total N accumulation in the ecosystem amounted to nearly 590 kg ha^?1 yr^?1 during the observation period. The major sink of N in the spruce site is the aggrading humus layer. The results emphasize the need for measurements over several years to make conclusions regarding the function of ecosystems in response to atmospheric deposition.     

An approach for the critical coagulation concentration estimation of polydisperse colloidal suspensions of soil and humus

Purpose

The critical coagulation concentration (CCC) is considered as one of the most important parameters to evaluate the particles aggregation and sedimentation behaviors in the environment. Even though there are a few methods for its measurement, each method has its limitations especially as those methods to be applied to polydisperse systems like soil. Thus, the purpose of this research is to establish a new and more reliable method for its determination.

Materials and methods

Two types of polydisperse colloidal materials were adopted: soil and humus in the experimental studies. The dynamic light scattering technique was employed to determine the effective hydrodynamic diameter of the particles or aggregates changing with time under different pH and electrolyte concentrations of CaCl₂ or KCl. In addition, the fractal dimension of aggregates was also detected with the static light scattering technique.

Results and discussion

A new aggregation rate total average aggregation rate (TAA rate) was defined firstly. We found the defined TAA rate increased linearly with the increase of electrolyte concentration at electrolyte concentrations lower than the CCC value, and the TAA rate stayed approximately constant at electrolyte concentrations higher than the CCC value; an intersection point of the two straight lines therefore could be observed, and the electrolyte concentration at the intersection point will theoretically be the CCC value. The experimental results for the two materials under different pH conditions indeed meet those theoretical predictions, which imply that the CCC value can be determined through the measurement of the TAA rate under different electrolyte concentrations. The comparison of the CCC values obtained between our new method and the widely applied stability ratio method showed that the new method was much better than the stability ratio method for the two polydisperse materials. In addition, the static light scattering measurements also showed that the variations of the fractal dimensions of the aggregates with electrolyte concentrations could be well explained by the CCC values obtained by the new method, which once again verified the applicability of the new method.

Conclusions

A new theory and a corresponding new method for the CCC estimation, which can be applied to polydisperse colloidal suspensions, were developed, and the new method has been demonstrated to be much better than the widely applied method for polydisperse materials in environment.     

Short-term effects of a simulated acid rain upon the growth and nutrient relations of Pinus strobus,L.

Acidified precipitation may affect the productivity of forests by altering the availability of plant nutrients or by affecting the ability of trees to absorb and assimilate those nutrients. In this study, the short-term effects of simulated acid rain (pH range 5.6 to 2.3) upon the growth and nutrient relations of Eastern White Pine seedlings (Pinus strobus, L.) grown in a sandy loam soil were examined. Soil chemistry, soil leachate chemistry, seedling tissue chemistry, and seedling productivity were monitored. Inspite increased leaching of cations from the soil, resulting in near depletion of available K⁺¹, Mg⁺², and Ca⁺¹ at pH 2.3, seedling productivity increased with acidity through the 20-week experimental period. Foliar nitrogen concentrations indicate that fertilization with NO ₃ ^?1, added to the rain as HNO₃, may have caused the growth increase. Implications of cation losses and NO₃ ^?1 fertilization are discussed.     

Influence of alkaline particulates on the chemistry of fog water at Delhi,North India

Chemical analysis of fog water collected by impaction in a pre-cooled chamber in Delhi has shown high concentrations of major ions. The dominant ions measured were Na⁺, K⁺, Ca⁺², and Mg⁺². The concentrations of acidic ions, SO₄ ^?2 and NO₃ ^?, were low. The pH values in the fog water were highly alkaline and varied from 6.4 to 7.6. The high concentrations of soil-oriented components, especially Ca⁺², were more than sufficient to neutralize the small acidity in the fog water and were responsible for maintaining high alkaline pH. The pH values of fog water did not attain the low values in India (Delhi), as found in other polluted environments of Europe and the northeast United States.     

Activation of soil pyrophosphatase by metal ions

Inorganic pyrophosphatase activity in three soils decreased when exchangeable and soluble metals were removed by leaching with in NH₄OAc (pH 8). The effect of added metal ions at various concentrations in the leached soils showed that, at certain concentrations, Ba²⁺, Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ promoted, K⁺ and Na⁺ had no effect, and Fc²⁺ and Cu²⁺ decreased pyrophosphatase activity. At high concentrations (>50 mM). Co²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ inhibited pyrophosphatase activity in two soils. The concentration of metal ion needed for optimum activity of pyrophosphatase varied among the soils. The efficiency of the metal ions at optimum concentrations (average percentage increase for three soils in parentheses) in promoting pyrophosphatase was Ca²⁺ (47) > Mg²⁺ (42) > Ba²⁺ = Co²⁺ (29) > Ni²⁺ (27) > Zn²⁺ (20) > Mn²⁺(16). Pyrophosphatase activity in two leached soils adjusted to 50, 75, 100 or 150 mM PPi and Ca²⁺ or Mg²⁺ concentrations from 0 to 250 mM was at an optimum when the metal ion: PPi ratio was 1:1. Soil pyrophosphatase in the presence of 200 mM CaCl₂ or MgCl₂ was protected against inactivation by heat (90 C for up to 30 min).     

Microbial biomass and activity in alkalized magnesic soils under arid conditions

The effects of salinity and Mg²⁺ alkalinity on the size and activity of the soil microbial communities were investigated. The study was conducted along the border area of the alluvial fan of the Taolai River. Thirty soil samples were taken which had an electrical conductivity (EC) gradient of 0.93-29.60 mS cm⁻¹. Soil pH ranged from 8.60 to 9.33 and correlated positively with Mg²⁺/Ca²⁺ ratio, exchangeable Mg²⁺ percentage and HCO₃⁻+CO₃²⁻. Mg²⁺/Ca²⁺ varied considerably from 3.04 to 61.31, with an average of 23.03. Exchangeable Mg²⁺ percentage generally exceeded 60% and had a positive correlation with Mg²⁺/Ca²⁺. HCO₃⁻+CO₃²⁻ averaged 1.63 cmol kg⁻¹ and usually did not exceed 2.0 cmol kg⁻¹.Microbial biomass, indices of microbial activity and the activities of the hydrolases negatively correlated with Mg²⁺/Ca²⁺ or exchangeable Mg²⁺ percentage. Biomass C, biomass N, microbial quotient (the percentage of soil organic C present as biomass C), biomass N as a percentage of total N, potentially mineralizable N, FDA hydrolysis rate and arginine ammonification rate decreased exponentially with increasing EC. The biomass C/N tended to be lower in soils with higher salinity and Mg²⁺ alkalinity, probably reflecting the bacterial dominance in microbial biomass in alkalized magnesic soils. The metabolic quotient (qCO₂) positively correlated with salinity and Mg²⁺ alkalinity, and showed a quadratic relationship with EC, indicating that increasing salinity and Mg²⁺ alkalinity resulted in a progressively smaller, more stressed microbial communities which was less metabolically efficient. Consequently, our data suggest that salinity and Mg²⁺ alkalinity are stressful environments for soil microorganisms.     

Interactions of nitrogen fertilizers and forest humus—i fir and black pine

In incubation experiments in the laboratory interactions of urea or NH₄NO₃ with humus from stands of fir (Abies cephalonica, Loudon) growing on soils developed from flysch (shales) and limestone and with humus from stands of black pine (pinus nigra, Arn.) growing on soils developed from peridotites, limestone and schists were investigated.Fir humus from stands on flysch and limestone and black pine humus from limestone showed nitrification but it was absent from black pine humus from stands on peridotites and on schists. Humus from stands on schists showed appreciable ammonification. Increasing concentrations of urea did not initiate nitrification in the latter type of humus. No substantial N immobilization was detected in spite of relatively high P immobilization. Increases in concentration of Ca, Mg and K occurring on incubation of humus samples were related to the ability of a humus type to nitrify rather than to concentrations of added urea-N.Urea was hydrolyzed rapidly to NH⁺₄ during contact with various types of humus, resulting in an increase of pH. Production of NH⁺₄ from urea was only minimally affected by drying the humus samples at 70°C for 20 h before incubation but was reduced to 30% at 1–5°C.     

日光温室番茄缺镁与土壤盐分组成及离子活度的关系

研究了石灰性土壤日光温室不同栽培年限及番茄不同程度缺镁的土壤水溶盐分中离子组成、比例及Mg2+、Ca2+、K+离子活度等的变化及关系.结果表明:随着栽培年限的增加,温室土壤水溶盐分中Ca2+、K+、NO3-含量显著增加;水溶性盐分中阳离子以Ca2+为主,栽培5 a后NO3-成为阴离子主要成分;土壤中NO3-含量的增加是导致土壤盐分累积的主要因素.随番茄缺镁程度的加剧,土壤水溶性盐中Ca2+、K+、NO3-、全盐量及Ca2+/Mg2+、K+/Mg2+摩尔比均呈增加趋势,番茄出现缺镁的土壤含盐量达到盐渍化水平.随着土壤盐分含量增加,Ca2+、Mg2+活度均呈指数下降趋势,番茄缺镁的土壤溶液中Mg2+和Ca2+活度显著低于不缺镁土壤,(K+)/(Mg2+)、(Ca2+)/(Mg2+)活度比显著高于不缺镁土壤,(K+)/(Mg2+)活度比随缺镁程度加剧达显著差异,番茄缺镁的土壤溶液(K+)/(Mg2+)活度比大于1.盐分累积使Mg2+活度大幅降低以及K+富集对植物吸收Mg2+的拮抗作用是石灰性土壤上番茄缺镁的主要诱因.     

Leaching of nutrients and major ions from an arable field with an unfertilized fallow as infield buffer zone

Abstract

Leaching of nutrients and major ions from a tile-drained arable field was evaluated over a 25-year period (1980–2005). The soil, classified as a Gleyic Cambisol, received moderate applications of fertilizers. During later years the soil was more frequently under ley, and since 2002, an area of ravine (29% of the total field) has been managed as a permanent fallow with annual cutting without removing the grass material. A decrease in the concentration of nitrate nitrogen (NO₃?N) in the drainwater was estimated in 1980–2005, based on non-parametric tests on concentrations flow-normalized with a robust fitting curve procedure. The average concentration of soluble reactive phosphorus after pre-filtration (RP_f) of 0.030 mg l^?l corresponded to a calculated degree of phosphorus saturation (DPS) of 6% in acid extract of ammonium lactate from the topsoil. Between 1995 and 2005, concentrations of suspended solids (SS), RP and total organic carbon (TOC) decreased significantly in the drainage water from the entire field. Throughout the entire period, there was a negative net accumulation of the major ions to the soil. The order of decrease in relative terms was calcium (Ca²⁺)>magnesium (Mg²⁺)>sulphate (SO₄ ^2?)>chloride (Cl^?)>potassium (K⁺). In addition, the soil phosphorus (P) balance was negative. A significant reduction in ion concentrations in the drainwater, including sodium (Na⁺) and hydrogen carbonate HCO₃ ^?, was estimated. The order of reduction in relative terms was: SO₄ ^2?>Mg²⁺>Ca²⁺>HCO₃ ^?>Cl^?>NO₃ ^?>Na⁺>HPO₄. Altogether these trends were equal to approximately 0.1 mmol_c l^?1. yr^?1 of positively and negatively charged ions. Based on measured concentrations, decreasing trends in SO₄ ^2? and Ca²⁺ were also observed in the shallow groundwater (3.6 m below the soil surface), while K⁺, Na⁺ and HCO₃ ^? tended to increase. Trends of cations in deeper groundwater (5.8 m below the soil surface) were in some cases the opposite of the trends in the drainwater.     

Effect of Exogenous Silicon on Ion Distribution of Tomato Plants Under Salt Stress

Seedlings of two tomato cultivars were exposed to 0, 50, or 100 mM sodium chlroide (NaCl) stress with or without silicon (Si) for 10 days, and leaf electrolyte leakage, root activity, plant growth, and ion sodium, potassium, calcium, and magnesium (Na⁺, K⁺, Ca²⁺, and Mg²⁺) contents were determined. No significant differences were observed in total biomass and the root/crown ratio of salt-stressed plants treated with exogenous Si, but leaf electrolyte leakage of both cultivars treated with 50 mM NaCl and Si was lower than that in the same salt treatment without Si. Root activities of both cultivars were significantly affected by treatment with NaCl and exogenous Si. Application of Si induced a significant decrease in Na⁺ content and increases in K⁺, Ca²⁺, and Mg²⁺ contents in leaves of plants treated with 50 mM NaCl, and consequently the K⁺/Na⁺ and Ca²⁺/Na⁺ ratios increased by at least two times. The effects of Si on the ion contents of the roots were not notable.     

Physicochemical simulation of the ion exchange between humus acids and cations of different valencies

An approximate calculation was made for the ion exchange of black humic acids and the related fulvic acids with the cations H⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn²⁺, Cu²⁺, Fe³⁺, and Al³⁺. The calculation was based on the method of physicochemical simulation, the concepts of the chemical potentials of the elements, the experimental study of the equilibriums, and the determination of the activity coefficients of the monoionic forms of humus acids. Because of the presence of different functional groups, humus acids are considered as two-phase systems with specific activity coefficients for the monoionic forms of these acids in each phase. Examples of experimental studies and practical calculations of ion-exchange equilibriums in wide ranges of humus and solution cationic compositions were compared. Although the proposed approaches require perfecting, they can be used for solving practical problems and controlling equilibriums at the experimental stage.     

Acid deposition and throughfall fluxes of elements as related to tree species in deciduous forests of South Sweden

The influence of tree species and soil properties on throughfall fluxes were studied for 5 tree species, growing on initially identical soil. In three mixed deciduous forests with different soil properties, throughfall fluxes of 11 elements were measured during 2 yr for 100 to 150 yr old individuals of Fagus sylvatica L., Quercus robur L., Carpinus betulus L., Tilia cordata Mill. and Acer platanoides L.. Throughfall : precipitation flux ratios were: PO₄ ^3? (11 to 37), K⁺ (7 to 22), Mn²⁺ (5 to 14), Mg²⁺ (3 to 9), Ca²⁺ (3 to 5), Cl^? (1.9 to 2.6), Na⁺ (1.1 to 2.2), NH₄ ⁺ (1.5 to 2), SO₄ ^2? (1.5 to 2.1), NO₃ ^? (0.7 to 1.3) and H⁺ (0.1 to 0.5). The annual input of S to the soil by throughfall was for Fagus 22 to 29, Quercus 25 to 37, Carpinus 20 to 25, Tilia 24 and Acer 29 kg ha^?1. The annual input of N to the soil by throughfall was for Fagus 20 to 29, Quercus 14 to 22, Carpinus 15 to 22, Tilia 22 and Acer 20 kg ha^?1. Throughfall fluxes of Na⁺ and Cl^? differed between species, depending on different canopy filtering capacity of sea aerosol, and were greatest for Fagus and Quercus. Throughfall of Ca²⁺, Mg²⁺ and K⁺ were characterized by increased flux from poor to rich sites, with the greatest soil effect on Carpinus, and by a high leaching part, which increased in the same manner. Manganese throughfall showed especially soil effects, characterized of decreased flux from poor to rich sites, but also species effects, of which Carpinus had the greatest flux. pH in throughfall showed a pronounced seasonal variation with pH 6 to 6.5 for Fagus in the foliated season and pH 4.0 to 4.3 in the defoliated season. Carpinus and especially Quercus had lower pH at the poor site, but the differences decreased at the richer sites. The calculated annual acid input to the trees was 4 to 12 times greater than the H⁺ flux measured as pH in throughfall. An inorganic anion deficit in throughfall, probably due to the presence of organic anions, was proportional to K⁺, Ca²⁺ and Mg²⁺.     

Soil colloids-bound plasmid DNA: Effect on transformation of E. coli and resistance to DNase I degradation

The adsorption and binding of plasmid p34S DNA on four different colloidal fractions from a Brown soil and clay minerals in the presence of various Ca²⁺ concentrations, the ability of bound DNA to transform competent cells of CaCl₂-treated Escherichia coli, and the resistance of bound DNA to degradation by DNase I were studied. DNA adsorption on soil colloids and clay minerals was promoted in the presence of Ca²⁺. Kaolinite exhibited the highest adsorption affinity for DNA among the examined soil colloids and clay minerals. In comparison with organo-mineral complexes (organic clays) and fine clays (<0.2 μm), DNA was tightly adsorbed by H₂O₂-treated clays (inorganic clays) and coarse clays (0.2-2 μm). The transformation efficiency of bound DNA increased with increasing concentrations of Ca²⁺ at which soil colloid or clay mineral-DNA complexes were formed. DNA bound by kaolinite showed the lowest transformation efficiency, and especially no transformants were observed with kaolinite-DNA complex prepared at 5-100 mM Ca²⁺. Compared to organic clays and fine clays, DNA bound on inorganic clays and coarse clays showed a lower capacity to transform E. coli at different Ca²⁺ concentrations. The presence of soil colloids and minerals provided protection to DNA against degradation by DNase I. Montmorillonite, organic clays and fine clays showed stronger protective effects for DNA than inorganic clays and coarse clays. The protection mechanisms as well as the differences in transforming efficiency of plasmid DNA molecules bound on various soil colloidal particles are discussed. The information obtained in this study is of fundamental significance for the understanding of the horizontal dissemination of recombinant DNA and the fate of extracellular DNA in soil environments.     

Chemical Composition of Precipitation in Beijing Area, Northern China

Variations of anions (SO₄ ^2-, NO₃ ^-,NO₂ ^-, Cl^- and F^-),cations (K⁺,Na⁺, Ca²⁺, Mg²⁺ and ⁺) and pH values in precipitation, througfall and stemflow samples collected overa four-year period (1995–1998) in Beijing (two sitesZhongguancun and Mangshan) are presented. The annualvolume-weighted range of pH values were 6.57–7.11 inprecipitation, 5.46–6.86 in thoughfall and 5.32–6.41 instemflow. The fominant anion was , while Ca⁺and NH₄ ⁺ were the main cations in precipitation,throughfall and stemflow. Most of ion concentrations with precipitation, throughfall and stemflow volume showed negative correlation, except for some ones. Significant correlationvalues were also found between ions (SO₄ ^2-,NO₃ ^-, Cl^-, F^-, Ca²⁺,Mg²⁺ andNa⁺) in precipitation, throughfall and stemflow indicatedthe common sources of these ions such as coal combustion,automobile emission and fertilizers application. Compared toprecipitation, there was an increased ion concentration inthroughfall or in stemflow. Changes of ion concentrations werein Quercus liatungensis Koiz. and Pinus tabulaefornisCarr. throughfall (or stemflow) because of different crown andbark qualities of tree species.