Small GTPases SAR1A and SAR1B regulate the trafficking of the cardiac sodium channel Nav1.5

Background

The cardiac sodium channel Na_v1.5 is essential for the physiological function of the heart and causes cardiac arrhythmias and sudden death when mutated. Many disease-causing mutations in Na_v1.5 cause defects in protein trafficking, a cellular process critical to the targeting of Na_v1.5 to cell surface. However, the molecular mechanisms underlying the trafficking of Na_v1.5, in particular, the exit from the endoplasmic reticulum (ER) for cell surface trafficking, remain poorly understood.

鼎湖山针阔叶混交林凋落物CO2释放对模拟酸雨的响应

该研究2011年1月开始在鼎湖山针阔叶混交林(混交林)进行模拟酸雨实验,设置4个不同处理水平,即对照(CK)(pH为4.5左右的天然湖水)、T_1(pH=4.0)、T_2(pH=3.25)和T_3(pH=2.5)。2013年1—12月对不同酸雨强度处理下的森林凋落物CO_2释放速率进行为期1 a的连续观测,探讨酸雨对混交林凋落物C排放的影响。结果表明:凋落物CO2释放通量在对照样方为(1 507.41±155.19) g CO_2·m~(-2)·a~(-1),其中湿季和旱季分别占年通量的68.7%和31.3%。模拟酸雨抑制了森林凋落物CO_2释放,与CK相比,T_2和T_3处理下的CO_2释放通量分别显著降低15.4%和42.7%(P0.05);且这种抑制作用具有季节差异性,处理间的显著差异只出现在湿季。凋落物CO_2释放速率与土壤温度和土壤湿度分别呈显著指数相关和显著直线相关,同时,酸雨处理降低了凋落物CO_2释放的温度敏感性。混交林凋落物CO_2释放在模拟酸雨下的抑制效应与土壤累积酸化而导致的土壤微生物活性变化有关,表现为模拟酸雨作用下土壤pH值和微生物量碳显著下降。上述结果说明酸雨是影响混交林土壤碳循环的重要因子之一。     

Effect of sulfuric acid on sodium-hazard of irrigation water

Summary The sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP) and saturated hydraulic conductivity were measured under laboratory conditions in one neutral and four calcareous soils using simulated alkaline irrigation waters having salt concentrations ranging from 7 to 39 meq/l with the SAR from 3.8 to 8.4. Sulfuric acid was applied to the waters at sufficient rates to prevent calcium precipitation under an open system, ranging from 2.1 to 4.7 meq/l. At these acid rates, the pH of irrigation waters remained above neutral. This treatment reduced SAR and ESP in all cases tested, and increased the hydraulic conductivity of some soils when the SAR of the original irrigation waters was greater than approximately 7. The experimentally determined SAR was then compared with the values predicted based on some of the existing theories. The results indicated that the conventional method to estimate SAR with adjustment using the pH_C index of Langelier overestimates the effect of HCO₃ ^-, whereas the equation based on carbonate equibria gives a reasonable prediction of SAR in waters containing HCO₃ ^- as well as H₂SO₄. The SAR calculated by the latter method was also linearly related to the measured ESP with an equation, ESP=0.761 SAR, r²=0.986.Arizona Agr. Exp. Sta. J. No. 2449. Contribution from the Department of Soils, Water and Engineering. The University of Arizona, Tucson 85721. Supported in part by a grant from the Arizona Mining Association.Arizona Agr. Exp. Sta. J. No. 2449. Contribution from the Department of Soils, Water and Engineering. The University of Arizona, Tucson 85721. Supported in part by a grant from the Arizona Mining Association.     

Fluorescence spectra,fluorescence quantum yield and dissociation constant of sarafloxacin

In this study, the fluorescence spectra of sarafloxacin (SAR) under different pH conditions were investigated to determine the structural changes due to protonation that result from change in pH. At pH < 1.02, SAR exists in the H₃L²⁺ form for which the maximum fluorescence emission wavelength was about 455 nm. At pH 1.87–4.94, SAR exists in the H₂L⁺ form in which H₃L²⁺ loses one proton in the nitrogen molecule at the 1‐position in the quinoline ring. Fluorescence intensity was strong and steady and the maximum emission wavelength was 458 nm. At pH 7.14–9.30, the maximum emission wavelengths were gradually blue shifted to 430 nm with increase in pH, here SAR exists in the form of a bipolar ion HL in which H₂L⁺ loses a carboxyl group proton. At pH > 11.6, HL transforms into anionic L^? in which HL loses one proton from the piperazine ring, leading to a decrease in fluorescence intensity, and the maximum emission wavelength was red shifted to approximately 466 nm. The two‐step dissociation constant pKa for SAR was calculated, pK _a1 was 6.06 ± 0.37 and pK _a2 for SAR was 10.53 ± 0.19. In a pH 3.62 buffer solution with quinine sulfate as the reference, the fluorescence quantum yield of SAR at the maximum excitation wavelength of 276 nm was 0.09.     

Induction of some defense-related genes and oxidative burst is required for the establishment of systemic acquired resistance in <Emphasis Type="Italic">Capsicum annuum</Emphasis>

The inoculation of primary pepper leaves with an avirulent strain of Xanthomonas campestris pv. vesicatoria induced systemic acquired resistance (SAR) in the non-inoculated, secondary leaves. This SAR response was accompanied by the systemic expression of the defense-related genes, a systemic microoxidative burst generating H₂O₂, and the systemic induction of both ion-leakage and callose deposition in the non-inoculated, secondary leaves. Some defense-related genes including those encoding PR-1, chitinase, osmotin, peroxidase, PR10, thionin, and SAR8.2 were markedly induced in the systemic leaves. The conspicuous systemic accumulation of H₂O₂ and the strong increase in peroxidase activity in the pepper leaves was suggested to play a role in the cell death process in the systemic micro-hypersensitive responses (HR), leading to the induction of the SAR. Treatment of the primary leaves with diphenylene iodinium (DPI), an inhibitor of oxidative burst, substantially reduced the induction of some of the defense-related genes, and lowered the activation of the oxidative bursts in the systemic leaves distant from the site of the avirulent pathogen inoculation and subsequently SAR. Overall, these results suggest that the induction of some defense-related genes as well as a rapid increase in oxidative burst is essential for establishing SAR in pepper plants.     

Matrix association region/scaffold attachment region (MAR/SAR) sequence: its vital role in mediating chromosome breakages in nasopharyngeal epithelial cells via oxidative stress-induced apoptosis

Background

Oxidative stress is known to be involved in most of the aetiological factors of nasopharyngeal carcinoma (NPC). Cells that are under oxidative stress may undergo apoptosis. We have previously demonstrated that oxidative stress-induced apoptosis could be a potential mechanism mediating chromosome breakages in nasopharyngeal epithelial cells. Additionally, caspase-activated DNase (CAD) may be the vital player in mediating the chromosomal breakages during oxidative stress-induced apoptosis. Chromosomal breakage occurs during apoptosis and chromosome rearrangement. Chromosomal breakages tend to cluster in certain regions, such as matrix association region/scaffold attachment region (MAR/SAR). We hypothesised that oxidative stress-induced apoptosis may result in chromosome breaks preferentially at the MAR/SAR sites. The AF9 gene at 9p22 was targeted in this study because 9p22 is a deletion site commonly found in NPC.

Results

By using MAR/SAR recognition signature (MRS), potential MAR/SAR sites were predicted in the AF9 gene. The predicted MAR/SAR sites precisely match to the experimentally determined MAR/SARs. Hydrogen peroxide (H₂O₂) was used to induce apoptosis in normal nasopharyngeal epithelial cells (NP69) and NPC cells (HK1). Nested inverse polymerase chain reaction was employed to identify the AF9 gene cleavages. In the SAR region, the gene cleavage frequency of H₂O₂-treated cells was significantly higher than that of the non-treated cells. A few chromosomal breakages were detected within the AF9 region which was previously found to be involved in the mixed lineage leukaemia (MLL)-AF9 translocation in an acute lymphoblastic leukaemia patient. As for the non-SAR region, no significant difference in the gene cleavage frequency was found between the untreated control and H₂O₂-treated cells. Furthermore, H₂O₂-induced cleavages within the SAR region were reduced by caspase-3 inhibitor, which indirectly inhibits CAD.

Conclusions

These results reaffirm our previous findings that oxidative stress-induced apoptosis could be one of the potential mechanisms underlying chromosome breakages in nasopharyngeal epithelial cells. MAR/SAR may play a vital role in defining the location of chromosomal breakages mediated by oxidative stress-induced apoptosis, where CAD is the major nuclease.

     

A paradox of leaf-trait convergence: why is leaf nitrogen concentration higher in species with higher photosynthetic capacity?

It is well known that leaf photosynthesis per unit dry mass (A_mass) is positively correlated with nitrogen concentration (N_mass) across naturally growing plants. In this article we show that this relationship is paradoxical because, if other traits are identical among species, plants with a higher A_mass should have a lower N_mass, because of dilution by the assimilated carbon. To find a factor to overcome the dilution effect, we analyze the N_mass–A_mass relationship using simple mathematical models and literature data. We propose two equations derived from plant-growth models. Model prediction is compared with the data set of leaf trait spectrum obtained on a global scale. The model predicts that plants with a higher A_mass should have a higher specific nitrogen absorption rate in roots (SAR), less biomass allocation to leaves, and/or greater nitrogen allocation to leaves. From the literature survey, SAR is suggested as the most likely factor. If SAR is the sole factor maintaining the positive relationship between N_mass and A_mass, the variation in SAR is predicted to be much greater than that in A_mass; given that A_mass varies 130-fold, SAR may vary more than 2000-fold. We predict that there is coordination between leaf and root activities among species on a global scale. Kouki Hikosaka is the recipient of the BSJ Award for Young Scientist, 2006.     

Identification and characterization of scaffold-associated region (SAR) of rRNA gene of silkwormAttacus ricini

identify the specific nuclear scaffold-bound DNA sequence in rRNA gene clusters of silkwormAttacus ricini, the detergent-like salt lithium 3′, 5′ diiodosalicylate (LIS) was used for the preparation of nuclear scaffold. Through Southern hybridization, using different DNA stretches of rRNA gene as the probe, a scaffold-associated region (SAR) in the 5-non transcribed spacer (NTS) of rRNA gene has been identified. Exonuclease III digestion was used to narrow down the sequence of matrix attachment fragment. It was defined as a specific attachment site within the SacII-EcoRI fragment. It is about 1 kb in length and AT-rich (> 70%). Computer analysis of the SAR sequencing data showed that there are topoisomerase II cleavage sites, ATATTT box, and yeast autonomously replication sequence (ARS). The d(AT)₁₈ specific DNA sequence of the SAR, which was determined previously, was an S1 nuclease hypersensitive site. It might be a cis-element of DNA-signal characteristic for SAR.     

Absorbed energy distribution from radiofrequency electromagnetic radiation in a mammalian cell model: Effect of membrane-bound water

The spatial distributions of induced 27 or 2450 MHz radiofrequency (RF) electric fields (E-fields) and specific absorption rates (SARs) in a three-component spherical cell model (cytoplasm, membrane, extracellular space) were determined by Mie scattering theory. The results were compared to results for the same cell model but with 0.5 nm thick of bound water on the inner (cytoplasmic) and outer (extracellular) membrane surfaces (i.e., five-component cell model). The results provide insight regarding direct frequency-dependent RF radiation effects at the cellular level. Induced E-fields and SARs were calculated for two bound-water characteristic frequencies (400 or 1000 MHz) and ionic conductivities (1–1000 mS/m). In order to estimate the dependence of the results on bound water within the membrane per se, the model was revised to include bound water within the inner and outer membrane surfaces. The results were as follows: (1) On the x-axis, the y- and z-components of the induced E-field were of insignificant magnitude compared to the x-component for an incident E-field parallel to the x-axis; (2) the ratio of transmembrane E-fields induced by 2450 MHz vs. 27 MHz RF [i.e., E_x (2450 MHz)/E_x (27 MHz)] was 0.1; (3) for the three-component cell model, the corresponding SAR ratios [SAR (2450 MHz)/SAR (27 MHz)] in the cytoplasm and extracellular space were 1.66 and 5.0, respectively; (4) the SAR ratios [SAR (2450 MHz)/SAR (27 MHz)] for the cytoplasm and extracellular space for the five-component cell model were 1.66 and 5.0, respectively; (5) the ratio of the E-fields induced in the cytoplasmic and extracellular layers of bound water in the five-component cell model [E (2450 MHz)/E (27 MHz)] were 0.62 and 0.63, respectively; (6) the SAR ratios [SAR (2450 MHz)/SAR (27 MHz)] for the cytoplasmic and extracellular bound-water layers were 66 and 65.3, respectively; and (7) variation of bound-water characteristic frequency, ionic conductivity, or bound-water incorporation inside the membrane surfaces, per se, did not significantly affect the E-field or SAR ratios. These results indicate that frequency-dependent nonuniformities may occur in the distribution of induced RF E-fields and SARs at the cellular level. © 1995 Wiley-Liss, Inc.     

Spike activity in pulmonary slow-adapting receptors during forced breathing

Spike activity pattern of 34 slow-adapting pulmonary receptors (SAR) was investigated in anesthetized cats during relaxed respiration and forced inhalation of CO₂. It was found that approximately one half of the SAR investigated did not differ substantially from relaxed breathing and showed regular intensification in relation to lung stretch. The frequency-volume plot underwent a shift to the right (or else a steeper rise in frequency during inspiration) under these conditions in most of the other receptors. All test SAR showed a reduction in firing rate during exhalation. The pattern of frequency-volume relationship at lung volumes not exceeding respiratory volume was not disrupted. A reduction in firing rate occurred with respiration in all the SAR investigated. The summated spike train from SAR, characterized by averaged frequency of the latter's spike activity, showed a linear dependence on lung volume during both forced and relaxed respiration alike but frequency rose more sharply in the former. Reasons for the changed activity of test SAR during forced breathing are discussed together with possible consequences of these changes for reflex regulation of time phases during the respiratory cycle.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 629–636, September–October, 1989.     

SAR versus Sinc: What is the appropriate RF exposure metric in the range 1–10 GHz? Part I: Using planar body models

This is the first of two articles addressing the most appropriate crossover frequency at which incident power flux density (S_inc) replaces the spatial peak value of the specific energy absorption rate (SAR) averaged over 1 or 10 g (i.e., peak 1 or 10 g SAR) as the basic restriction for protecting against radiofrequency (RF) heating effects in the 1–10 GHz range. Our general approach has been to compare the degree of correlation between these basic restrictions and the peak induced tissue temperature rise (ΔT) for a representative range of population/exposure scenarios. In this article we particularly address the effect of human population diversity in the thickness of body tissue layers at eight different sites of the body. We used a Monte Carlo approach to specify 32000 models (400 models for each of 8 body sites for 10 frequencies) which were representative of tissue thicknesses for age (18–74 years) and sex at the eight body sites. Histogram distributions of S_inc and peak 1 and 10 g SAR corresponding to a peak 1 °C temperature rise were obtained from RF and thermal analyses of 1D multiplanar models exposed to a normally incident plane wave ranging from 1 to 10 GHz in thermo‐neutral environmental conditions. Examination of the distribution spread of the histograms indicated that peak SAR was a better predictor of peak tissue temperature rise across the entire 1–10 GHz frequency range than S_inc, as indicated by the smaller spread in its histogram distributions, and that peak 10 g SAR was a slightly better predictor than peak 1 g SAR. However, this result must be weighed against partly conflicting indications from complex body modeling in the second article of this series, which incorporates near‐field effects and the influence of complex body geometries. Bioelectromagnetics 31:454–466, 2010. © 2010 Wiley‐Liss, Inc.     

Anti-proliferative activity and structure-activity relationship of honokiol derivatives

As a known natural product with anti-tumor activity, honokiol has been widely researched and structural modified. Lots of honokiol derivatives have been found to possess good anti-proliferative activity and showed great potential in cancer therapy, but the SAR (structure-activity relationship) was still confused. Here in, the SAR were comprehensively researched by summary of reported derivatives and synthesis of novel derivatives. Amongst novel derivatives, the promising compounds A6 and A10 exhibited potent and selective anti-proliferative activities against K562 cell line with the IC₅₀ values of 5.04 and 7.08 μM respectively. The SAR was discussed around honokiol and 79 derivatives by the means of CoMFA and theoretical calculation, which provided useful suggestion for further structural optimization of honokiol derivatives.     

Identification and characterization of scaffold-associated region (SAR) of rRNA gene of silkworm Attacus ricini

identify the specific nuclear scaffold-bound DNA sequence in rRNA gene clusters of silkwormAttacus ricini, the detergent-like salt lithium 3′, 5′ diiodosalicylate (LIS) was used for the preparation of nuclear scaffold. Through Southern hybridization, using different DNA stretches of rRNA gene as the probe, a scaffold-associated region (SAR) in the 5-non transcribed spacer (NTS) of rRNA gene has been identified. Exonuclease III digestion was used to narrow down the sequence of matrix attachment fragment. It was defined as a specific attachment site within the SacII-EcoRI fragment. It is about 1 kb in length and AT-rich (> 70%). Computer analysis of the SAR sequencing data showed that there are topoisomerase II cleavage sites, ATATTT box, and yeast autonomously replication sequence (ARS). The d(AT)₁₈ specific DNA sequence of the SAR, which was determined previously, was an S1 nuclease hypersensitive site. It might be a cis-element of DNA-signal characteristic for SAR. Project supported by the National Natural Science Foundation of China (Grant No. 39570398).     

Spatial autocorrelation and the selection of simultaneous autoregressive models

Aim Spatial autocorrelation is a frequent phenomenon in ecological data and can affect estimates of model coefficients and inference from statistical models. Here, we test the performance of three different simultaneous autoregressive (SAR) model types (spatial error = SAR_err, lagged = SAR_lag and mixed = SAR_mix) and common ordinary least squares (OLS) regression when accounting for spatial autocorrelation in species distribution data using four artificial data sets with known (but different) spatial autocorrelation structures. Methods We evaluate the performance of SAR models by examining spatial patterns in model residuals (with correlograms and residual maps), by comparing model parameter estimates with true values, and by assessing their type I error control with calibration curves. We calculate a total of 3240 SAR models and illustrate how the best models [in terms of minimum residual spatial autocorrelation (minRSA), maximum model fit (R²), or Akaike information criterion (AIC)] can be identified using model selection procedures. Results Our study shows that the performance of SAR models depends on model specification (i.e. model type, neighbourhood distance, coding styles of spatial weights matrices) and on the kind of spatial autocorrelation present. SAR model parameter estimates might not be more precise than those from OLS regressions in all cases. SAR_err models were the most reliable SAR models and performed well in all cases (independent of the kind of spatial autocorrelation induced and whether models were selected by minRSA, R² or AIC), whereas OLS, SAR_lag and SAR_mix models showed weak type I error control and/or unpredictable biases in parameter estimates. Main conclusions SAR_err models are recommended for use when dealing with spatially autocorrelated species distribution data. SAR_lag and SAR_mix might not always give better estimates of model coefficients than OLS, and can thus generate bias. Other spatial modelling techniques should be assessed comprehensively to test their predictive performance and accuracy for biogeographical and macroecological research.     

The effect of acid rain on ultrastructure and functional parameters of photosynthetic apparatus in pea leaves

The ultrastructure and functional parameters of the photosynthetic apparatus in leaves of 14-day-old pea seedlings were studied in conditions of laboratory simulated acid rain (SAR). Pea seedlings were sprayed with an aqueous solution containing NaNO₃ (0.2 mM) and Na₂SO₄ (0.2 mM) (pH 5.6, a control variant), or with the same solution, which was acidified to pH 2.5 (acid variant). Functional characteristics were determined by chlorophyll fluorescence analysis. There was reduction in the efficiency of the photosynthetic electron transport by 25% accompanied by an increase in the quantum yield of thermal dissipation of excess light quanta by 85% without significant change in maximum quantum yield of PSII photochemistry (F_v/F_m). Ultrastructural changes in chloroplasts were revealed by transmission electron microscopy (TEM) 2 days after the SAR treatment of pea leaves. In this case, changes in the structure of the grana and heterogeneity of the thylakoids packing in the granum, namely, an increase in thylakoid intraspace widths and thickness of granal thylakoids compared to the control, were found. It was shown also that carbonic anhydrase activity was significantly inhibited in chloroplast preparations isolated from SAR-treated pea leaves. We hypothesize possible involvement of chloroplast carbonic anhydrase in thylakoid granal structure maintenance. The structural disturbances and the inhibition of photochemical activity of chloroplasts are possible consequences of the carbonic anhydrase inactivation by SAR treatment leading to violation of HCO₃ ^?–CO₂ equilibrium. The data obtained suggest that acid rains negatively affect the photosynthetic apparatus by disrupting the membrane system of the chloroplast.     

Arylsulfonamidopiperidone derivatives as a novel class of factor Xa inhibitors

The design, synthesis and SAR of a novel class of valerolactam-based arylsulfonamides as potent and selective FXa inhibitors is reported. The arylsulfonamide–valerolactam scaffold was derived based on the proposed bioisosterism to the arylcyanoguanidine-caprolactam core in known FXa inhibitors. The SAR study led to compound 46 as the most potent FXa inhibitor in this series, with an IC₅₀ of 7 nM and EC_2×PT of 1.7 μM. The X-ray structure of compound 40 bound to FXa shows that the sulfonamide–valerolactam scaffold anchors the aryl group in the S1 and the novel acylcytisine pharmacophore in the S4 pockets.     

Phosphonic and Phosphinic Acid Derivatives as Novel Tyrosinase Inhibitors: Kinetic Studies and Molecular Docking

A dozen of phosphonic and phosphinic acid derivatives containing pyridine moiety were synthesized and its inhibitory activity toward mushroom tyrosinase was investigated. Moreover, molecular docking of these compounds to the active site of the enzyme was performed. All the compounds ( 1 – 10 ) demonstrated the inhibitory effect with the IC₅₀ and inhibition constants ranging millimolar concentrations. The obtained results indicate that the compounds show different types of inhibition (competitive, noncompetitive, mixed), but all of them are reversible inhibitors. The obtained outcomes allowed to make the structure–activity relationship (SAR) analysis. Compound 4 ([(benzylamino)(pyridin‐2‐yl)methyl]phenylphosphinic acid) revealed the lowest IC₅₀ value of 0.3 mm and inhibitory constant of K_i 0.076 mm , with noncompetitive type and reversible mechanism of inhibition. According to SAR analysis, introducing bulky phenyl moieties to phosphonic and amino groups plays an important role in the inhibitory potency on activity of mushroom tyrosinase and could be useful in design and development of a new class of potent organophosphorus inhibitors of tyrosinase. Combined results of molecular docking and SAR analysis can be helpful in designing novel tyrosinase inhibitors of desired properties. They may have broad application in food industry and cosmetology.     

New fin-line devices for radiofrequency exposure of small biological samples in vitro allowing whole-cell patch clamp recordings

The development and analysis of three waveguides for the exposure of small biological in vitro samples to mobile communication signals at 900 MHz (GSM, Global System for Mobile Communications), 1.8 GHz (GSM), and 2 GHz (UMTS, Universal Mobile Telecommunications System) is presented. The waveguides were based on a fin‐line concept and the chamber containing the samples bathed in extracellular solution was placed onto two fins with a slot in between, where the exposure field concentrates. Measures were taken to allow for patch clamp recordings during radiofrequency (RF) exposure. The necessary power for the achievement of the maximum desired specific absorption rate (SAR) of 20 W/kg (average over the mass of the solution) was approximately P_in = 50 mW, P_in = 19 mW, and P_in = 18 mW for the 900 MHz, 1800 MHz, and 2 GHz devices, respectively. At 20 W/kg, a slight RF‐induced temperature elevation in the solution of no more than 0.3 °C was detected, while no thermal offsets due to the electromagnetic exposure could be detected at the lower SAR settings (2, 0.2, and 0.02 W/kg). A deviation of 10% from the intended solution volume yielded a calculated SAR deviation of 8% from the desired value. A maximum ±10% variation in the local SAR could occur when the position of the patch clamp electrode was altered within the area where the cells to be investigated were located. Bioelectromagnetics 32:102–112, 2011. © 2010 Wiley‐Liss, Inc.     

Influence of acid rain and ozone on soil heavy metals under loblolly pine trees: A field study

A field growth chamber study was conducted to determine the effects of ozone and simulated acid rain (SAR) on soil heavy metals. Loblolly pine (Pinus taeda L.), grown in open-top chambers, was exposed to three concentrations of ozone (charcoal filtered air with 0.026 µL O₃ L^-1, and two non-filtered treatments in which ozone concentrations were 0.074 µL L^-1 and 0.147 µL L^-1, respectively) and two levels of SAR (pH 3.5 and 5.2). Ozone was applied for 12 h d^-1 for 9 months and acid rain deposition was 125 mm event^-1. After 9 months exposure, soil pH, organic matter and DTPA-extractable heavy metals (Cd, Pb, Zn, Mn, Fe, Cu) were determined on soil samples collected from exposed chambers at two depths (0–15 cm and 15–30 cm). Simulated acid rain decreased the original soil pH. The concentrations of Cd, Pb and Mn at SAR pH 3.5 were significantly higher than at SAR pH 5.2. Ozone did not affect Zn, Fe and Cu, but a significant interaction between pH and O₃ on Mn, Pb and Cd was observed. Due to the poor drainage capacity of this soil, leaching of heavy metals was not observed.     

Salt impacts on organic carbon and nitrogen leaching from senesced vegetation

Senesced vegetation is exposed to a wide range of salt concentrations in surface waters resulting from human activities which include deicing salts and irrigation water chemistry. Both dissolved organic carbon (DOC) and salt concentrations are rising in northern hemisphere watersheds, yet there has been little investigation of sodium as a potential mechanism for DOC increases. The objective of this study was to investigate the impact of solution sodicity and salinity on DOC and dissolved organic nitrogen (DON) leaching from five types of senesced and cut vegetation. Vegetation was soaked for 24 h in a series of sodium chloride (NaCl)–calcium chloride (CaCl₂) solutions with sodium adsorption ratios (SAR) of 2, 10, or 30 and electrical conductivities of 0.1 dS m^?1 through 3.0 dS m^?1. Vegetation was also soaked in a sodium bicarbonate (NaHCO₃) solution at SAR = 30 and stream water from local watersheds with a range of sodicity and salinity. The mass of both DOC and DON released increased as SAR increased in the NaCl solutions, but the total salinity had inconsistent effects on DOC and DON release. NaHCO₃ leached similar amounts of DOC and DON as NaCl. The SAR of the stream water solutions was able to explain 88 % of the variability in DOC leached from vegetation (p < 0.05). The results indicated that sodicity, quantified by SAR, had a significant impact on DOC and DON leaching from senesced vegetation and could be a potential mechanism to explain the observed increases in surface water DOC.