Effects of sulfate on cadmium uptake by Swiss chard: I. Effects of complexation and calcium competition in nutrient solutions

The impacts of both sulfate (SO4) and calcium (Ca) concentrations in solution on plant uptake of cadmium (Cd) vary according to effects on both sorption of Cd by soil and on uptake by the plant root. This study investigated how complexation of Cd by SO4 affected plant Cd uptake in nutrient solution. Swiss chard (Beta vulgaris L. cv. Fordhook Giant) was grown in nutrient solution with SO4 concentrations varying between 8 mM and 58 m M, with ionic strength maintained constant across treatments using nitrate (NO3). In a separate experiment, solution Ca concentrations was also varied to compensate for SO4 complexation by Ca. Plant growth was unaffected by increasing SO4 concentrations in solution. Despite considerable reductions in free Cd2+ ion activities in solution by increasing SO4 concentrations, plant Cd concentrations were unaffected. Similarly, plant Cd concentrations were unaffected by increasing Ca concentrations in solution to compensate for SO4 complexation of Ca. These data suggest that the CdSO40 complex is taken up by plants with equal efficiency to the free Cd2+ ion.     

碱性土壤盐化过程中阴离子对土壤中镉有效态和植物吸收镉的影响

镉是土壤环境中对土壤质量有着极其重要影响的污染物之一,低含量下就能对人体和动物产生危害.镉在土壤中的有效态既决定了它的生物有效性及对环境的危害程度,又是人们对受污染土壤进行治理和修复的基础.作为盐化土壤中的典型组分,无机盐不可避免对镉的有效态及生物有效性等地球化学行为产生明显影响.研究了碱性土壤盐化过程中无机盐阴离子对土壤中镉有效态和植物吸收镉影响.研究方法为:以钠盐为例,实验研究了碱性土壤盐化过程中无机盐阴离子对土壤中镉有效态的影响;通过油菜种植试验,分析了无机盐阴离子对土壤中镉生物有效性的影响.研究结果表明,土壤盐化过程中,土壤溶液中Cl-浓度较低时,土壤中镉的有效态含量随Cl-浓度增加而增大,但当土壤中Cl-/Cd的比值大于100∶1时,土壤中镉的有效态含量达到最大值.土壤溶液中SO42-含量对土壤中镉有效态含量的影响不明显;随着土壤溶液中HCO3-含量的增加,土壤中镉的有效态含量明显减少.由于Cl-、SO42-是土壤溶液中的主要成分,随着盐度的增加,镉的有效态含量增加.油菜种植试验显示,当土壤中Cl-的含量增加时,土壤中镉的有效态含量增加,有利于植物对镉的吸收,因此油菜中镉的含量随土壤中Cl-的含量增加而增加,但当土壤有效态含量超过2 mg/kg后,油菜吸收镉已经达到最大.随着土壤溶液中SO42-浓度的增加,油菜中镉含量基本不变;土壤溶液中HCO3-的含量增加,植物中镉的含量随土壤中HCO3-含量增加而减少.这些特征与土壤镉有效态变化相吻合.通过各种措施控制土壤盐度和调节阴离子类型和含量,有利于降低土壤中镉的有效态含量,减轻镉的活化;农业生产中适当调整无机肥料的种类,可以减少农作物对镉的吸收.     

Toxic Effect of Cadmium on Rice as Affected by Nitrogen Fertilizer Form

A nutrient solution experiment was conducted to determine the influence of N forms on growth, oxidative stress, and Cd and N uptake in rice plants. The treatments were consisted of two Cd levels (0 and 1 μmol) and three N forms (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results indicated that without Cd addition in the culture solution, the N forms had no significant effect on all measured parameters, including plant growth, photosynthetic traits, malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity, and Cd and N concentration, while Cd addition in the medium resulted in significant differences in measured parameters among the three forms of N fertilizers. The least inhibition of growth was noted in (NH₄)₂SO₄-fed plants, and the largest in Ca(NO₃)₂-fed plants, when plants were exposed to Cd stress. The highest photosynthetic rate and chlorophyll content was also recorded in (NH₄)₂SO₄-fed plants. Addition of Cd caused a remarkable increase in SOD activity and MDA content in plants, and the extent of increase varied with N form, with (NH₄)₂SO₄-fed plants being smallest. In comparison with the control plants, the N concentration in roots and shoots was not significantly affected in (NH₄)₂SO₄-fed plants, but significant decrease in root N concentration was found for the NH₄NO₃ and Ca(NO₃)₂-fed plants under Cd stress. Moreover, the significant differences were also noted among the three N forms in both root and shoot Cd concentrations, with (NH₄)₂SO₄-fed plants being the lowest. The results indicated that the toxic effect of Cd on rice varied with the form of N fertilizer.     

Correlations between nitrate and sulfate in the soil solution of disturbed forest ecosystems

Based on data from three German forest ecosystems severely disturbed by windthrow events, correlation patterns between NO₃ ⁻ and SO₄ ²⁻ dynamics in the soil solution are described. Each of the correlation types was related to site-specific SO₄ ²⁻ retention processes. The relative importance of SO₄ ²⁻ adsorption/desorption and precipitation/dissolution was found to be different for the studied soils depending on their contents of SO₄ ²⁻ -adsorbing sesquioxides and of A1 hydroxy sulfate minerals. Enhanced NO₃ ⁻ concentrations in the soil solution resulting from excess nitrification promoted either SO₄ ²⁻ adsorption or the dissolution of Al hydroxy sulfates. Both processes result in different ecological consequences: Whereas the former reaction reduces anion concentration peaks in the soil solution, the latter increases them. Thus, a prediction of cation export from soil ecosystems subjected to excess nitrification has to regard site-specific interrelationships between NO₃ ⁻ and SO₄ ²⁻. As a third type of conelation the independence of NO₃ ⁻ and SO₄ ²⁻ concentrations in the soil solution is presented. This type is suggested to be typical for soils with low SO₄ ²⁻. adsorption capacity and absence of A1 hydroxy sulfates.     

CHARACTERISTICS OF SALTS SECRETED BY TAMARIX APHYLLA

The composition and concentration of salts secreted by the salt glands of Tamarix aphylla L. grown under controlled nutrient conditions were determined. Eight ions, Na, K, Mg, Ca, Cl, NO₃, HCO₃, and SO₄, constituted 99 % + of the dry weight of salts secreted by plants grown on half-strength Hoagland's solution. The divalent cations Mg and Ca accounted for most of the cations; HCO₃ comprised about 60 % of the anions. The micronutrients B, Mn, Cu, Zn, and Mo were present in enriched concentrations in the secretion. The composition of the secretions was highly dependent on the composition of the root environment. The predominating cation in the saline culture solutions was also the predominant cation secreted. The accompanying anion in the culture solution influences the cation composition of the secreted salt. The concentration of the salt gland secretion averaged 0.5n , a 50-fold increase in concentration over the nutrient solution in which the plants were grown.     

Nutrient composition of Douglas-fir rhizosphere and bulk soil solutions

Rhizosphere soil solution is the direct source of nutrients for plant uptake. The nutrient composition of rhizosphere soil solution can be very different from that of bulk soil solution due to root exudation, nutrient uptake and rhizosphere microorganism activity. This study examined the nutrient composition of Douglas-fir rhizosphere soil solution in two soils belonging to the Nisqually and Pitcher soil series and compared rhizosphere solution with that of bulk soil solution. Fertilized and unfertilized Nisqually soils were also compared. Soil solutions were collected using centrifugation. Results indicated that nutrient concentrations in the rhizosphere solutions were typically higher than that of bulk soil solutions when no fertilizer was applied. Differences in the concentrations of nutrients between the rhizosphere and bulk soil solutions were masked by the addition of fertilizers. Rhizosphere solution pH also appeared to be affected by the concentration of NH₄ and NO₃ in the solution. With a higher concentration of NH₄ relative to NO₃ in the rhizosphere soil solution, the solution pH of the rhizosphere was lower than that of the bulk soil, but with a lower concentration of NH₄ relative to NO₃, the solution pH of the rhizosphere was higher than that of the bulk soil solution.     

The growth and some physiological responses of rice to Cd toxicity as affected by nitrogen form

A hydroponic experiment was conducted to examine the effect of Cd stress on anti-oxidative enzyme activities at heading stage, yield components, root exudation and Cd and N uptake of rice plants grew in different N source i.e. (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results show that the effect of Cd stress on all measured parameters were N source dependent. Cd stress (1 μM) caused a remarkable reduction in grain yield and shoot biomass, an increase in root exudation, glutathione content, Cd concentration and catalase (CAT) and peroxidase (POD) activities of rice plants. In the plants under the control (without Cd addition) N source had no distinctive effect on the above measured parameters, but the differences among the three N forms in these parameters became significant when plants were exposed to Cd stress. Cd stress significantly increased POD and CAT activities, and gultathione content, with Ca(NO₃)₂-fed plants having the greatest POD and CAT activities and lowest glutathione content, and (NH₄)₂SO₄-fed plants being just opposite. Moreover, organic acid exudation varied also with N form for the Cd-stressed plants. In comparison with other two N forms, (NH₄)₂SO₄,-treated plants had higher grain yield, N concentration and lower Cd concentration in plants. The current results indicated that (NH₄)₂SO₄ is a better fertilizer for use in Cd contaminated soil.     

Effects of pH and nitrogen on cadmium uptake in potato

This study investigated the effects of pH and nitrogen form and concentration on cadmium (Cd) uptake by potato (Solanum tuberosum L.) grown in hydroponic culture. Potato plants grown in a pH-buffered nutrient solution for 10 d were exposed for 24 h to 25 nM CdCl₂ labelled with ¹⁰⁹Cd. Plants showed a significantly higher Cd uptake and accumulation at pH 6.5 than at pH 4.5 and 5.5. Nitrogen supplied as nitrate (NO₃ ^?) generally resulted in a higher Cd uptake and accumulation than N supplied as ammonium (NH₄ ⁺). This effect was most pronounced at pH 6.5. The N concentration increasing from 6.5 to 26 mM resulted in a decreased Cd influx when either NO₃ ^? or NH₄ ⁺ was used. Cd translocation to the shoot was increased when NO₃ ^? was used as the sole N source. In conclusion, pH had a strong influence on Cd uptake by roots and N form is especially important for Cd translocation within the potato plant.     

Nitrate accumulation and growth of Aster tripolium L. with a continuous and intermittent nitrogen supply*

Abstract The ‘tidal salt marsh’ ecotype of the halophyte Aster tripolium L. was grown in a nutrient solution with either a continuous or an intermittent NO₃^? supply with either Cl^? or SO₄^2? as the alternative anion. With increasing periods of NO₃^? supply per week the rate of the dry weight increment increased. When NO₃^? was supplied for longer than 48 h per week, the dry weight and the organic-N content in the shoots hardly increased, whereas the NO₃^? content in shoots and roots increased further. With alternated supply of a nutrient solution containing NO₃^? with one containing Cl^?, the internal NO₃^? content in the shoot was lower than in shoots grown in solutions in which NO₃^? alternated with SO₄^2?. It is concluded, that NO₃^? does not have a specific function in osmoregulation.     

The effect of the osmotic potential and specific ion concentration of the nutrient solution on the uptake and reduction of nitrate by barley seedlings

Summary Short-term absorption experiments were conducted with intact barley (Hordeum vulgare L.) seedlings to observe the effects of the osmotic potential (Ψ^π) and salt species on nitrate uptake andin vivo nitrate reduction. The experiments consisted of growing barley seedlings for 5 days in complete nutrient solutions salinized to (Ψ^π) levels of −0.6, −1.8, −3.0, −4.2, and −5.4 bars with NaCl, CaCl₂ or Na₂SO₄. After the absorption period, the seedlings were separated into shoots and roots, weighed, then analyzed for NO₃. The nutrient solutions were sampled for NO₃ analysis each day immediately before renewing the solutions. The accumulative loss of NO₃ from the solutions was considered to be uptake whereas NO₃ reduction was the difference between uptake and seedling content. Lowering the (Ψ^π) of the nutrient solutions resulted in decreased concentrations of NO₃ in the plant, little or no effect (except at the lowest (Ψ^π) level) on uptake, and increased nitrate reductase activity. Increased rates of NO₃ reduction were in particular associated with the Cl concentration of the nutrient solution.     

Nitrogen nutrition of rice plants under salinity

Two rice (Oryza sativa L.) cultivars, Koshihikari and Pokkali, were grown in solution culture at three concentrations of NaCl or Na₂SO₄ [0 (S0), 50 (S1), and 100 (S2) mmol dm^–3] and three N contents [0.7 (N1), 7 (N2) and 14 (N3) mmol dm^–3]. Salinity significantly decreased dry matter of both cultivars. Pokkali had better growth than Koshihikari under both saline and non-saline conditions. Applications of N enhanced development of shoot dry mass under S0 and S1 treatments up to N2. Under S2, N application had no effect on shoot dry mass of both cultivars. Root dry mass of both cultivars decreased with increasing N application at S1 and S2. Shoot and root NO₃-N content in both rice cultivars increased with increasing N concentration in the nutrient solutions. The absorption of NO₃-N was less in Koshihikari than Pokkali plants, and also was much less in Cl^– than SO₄ ^2– salinity suggesting the antagonism between Cl^– and NO₃ ^–. In addition a significant negative correlation between concentrations of NO₃-N and Cl^– in the shoots or roots was observed in both cultivars     

Effect of Cl on Cd uptake by Swiss chard in nutrient solutions

Swiss chard (Beta vulgaris L., cv. Fordhook Giant) was grown in nutrient solution with Cl concentrations varying between 0.01 mM and 120 mM. Solution Na concentration and ionic strength were maintained in all treatments by compensating with NaNO₃. All solutions contained Cd (50 nM, spiked with ¹⁰⁹Cd). Three different Cd²⁺ buffering systems were used. In one experiment, Cd²⁺ activity was unbuffered; its activity decreased with increased Cl concentration as a result of the formation of CdCl_n ^2–n species. In the other experiments, Cd²⁺ activity was buffered by the chelator nitrilotriacetate (NTA, 50 M) and ethylene-bis-(oxyethylenenitrilo)-tetraacetate (EGTA, 50 M) at about 10^–9 M and 10^–11 M, respectively. Plant growth was generally unaffected by increasing Cl concentrations in the three experiments. In unbuffered solutions, Cd concentrations in plant tissue decreased significantly (p<0.01) (approximately 2.4-fold) as solution Cl concentration increased from 0.01 mM to 120 mM. However, this decrease was smaller in magnitude than the 4.7-fold decrease in Cd²⁺ activity as calculated by the GEOCHEM-PC program for the same range of Cl concentrations. In solutions where Cd²⁺ activity was buffered by NTA, Cd concentrations in plant tissue increased approximately 1.4-fold with increasing Cl concentration in solution, while the Cd²⁺ activity was calculated to decrease 1.3-fold. In solutions where Cd²⁺ activity was buffered by EGTA, Cd concentrations in the roots increased 1.3-fold with increasing Cl concentration in solution but there was no effect of Cl on shoot Cd concentrations. The data suggest that either CdCl_n ^2–nspecies can be taken up by plant roots or that Cl enhances uptake of Cd²⁺ through enhanced diffusion of the uncomplexed metal to uptake sites.Abbreviations DAS days after sowing - EGTA ethylene-bis-(oxyethylenenitrilo)-tetraacetate - HBED N,N-bis(2-hydroxybenzyl)-ethylenediamine-N,N-diacetate - NTA nitrilotriacetate     

Phytoextraction of Cadmium and Zinc By Sedum plumbizincicola Using Different Nitrogen Fertilizers,a Nitrification Inhibitor and a Urease Inhibitor

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction by Sedum plumbizincicola using different nitrogen fertilizers, nitrification inhibitor (dicyandiamide, DCD) and urease inhibitor (N-(n-Butyl) thiophosphoric triamide, NBPT) were investigated in pot experiments where the soil was contaminated with 0.99 mg kg^?1 of Cd and 241 mg kg^?1 Zn. The soil solution pH varied between 7.30 and 8.25 during plant growth which was little affected by the type of N fertilizer. The (NH₄)₂SO₄+DCD treatment produced higher NH₄⁺?N concentrations in soil solution than the (NH₄)₂SO₄ and NaNO₃ treatment which indicated that DCD addition inhibited the nitrification process. Shoot Cd and Zn concentrations across all treatments showed ranges of 52.9–88.3 and 2691–4276 mg kg^?1, respectively. The (NH₄)₂SO₄+DCD treatment produced slightly higher but not significant Cd and Zn concentrations in the xylem sap than the NaNO₃ treatment. Plant shoots grown with NaNO₃ had higher Cd concentrations than (NH₄)₂SO₄+DCD treatment at 24.0 and 15.4 mg kg^?1, respectively. N fertilizer application had no significant effect on shoot dry biomass. Total Cd uptake in the urea+DCD treatment was higher than in the control, urea+NBPT, urea+NBPT+DCD, or urea treatments, by about 17.5, 23.3, 10.7, and 25.1%, respectively.     

The effect of an intermittent water-table gradient on soil and xylem nitrate in cotton

Summary Cotton (Gossypium hirsutum cv Deltapine 61) was grown in a sloping plot of soil in the field to examine the effect of a gradient of water-table depth on soil nitrate availability and plant uptake during two periods of the growing season. Before the water-table was imposed NO₃ was less concentrated at the lower end of the sloping plot. This was attributed to slow denitrification at microsites within the soil at the lower end which was wetter than further up the plot. At flooding NO₃ disappeared only slowly due to a carbon substrate limitation to denitrification in the soil. This loss occurred primarily in areas where the water-table was high and oxygen concentration in the soil solution was low. Plant NO₃ uptake, assessed by measuring the concentration in the xylem, parallelled the distribution of NO₃ in the soil solution. Under high water-tables xylem NO₃ levels fell but it was not possible to say whether this was due to impaired root function or to the reduced concentration of NO₃ observed in the soil solution. At intermediate water-table depths where soil NO₃ availability remained high xylem NO₃ concentration fell relative to the well drained control plants, suggesting that flooding had damaged the root system.Manufactured by Merck. Mention of commerical names does not imply endorsement by either CSIRO or USDA.     

闽江河口湿地土壤CH4产生与氧化速率对外源氮、硫添加的响应

通过室内培养实验,研究了外源氮、硫添加对闽江河口湿地土壤CH_4产生/氧化速率以及土壤理化性质的短期影响。NH_4Cl(N1)和NH_4NO_3(N3)处理在各培养阶段均显著促进土壤CH_4产生速率(P0.05),较对照分别提高136.70%和136.55%;NH_4Cl+K_2SO_4(NS1)和NH_4NO_3+K_2SO_4(NS3)处理在培养第3、6、12、15和18天均显著促进了CH_4产生速率(P0.05)。KNO_3(N2)、K_2SO_4(S)处理在不同培养时间对CH_4产生速率影响均不显著(P0.05);KNO_3+K_2SO_4(NS2)处理除在第21天外(P0.05),其他时间影响均不显著(P0.05)。N2、N3、NS2和NS3处理均显著促进了土壤CH_4氧化速率(P0.05),平均CH4氧化速率较CK分别提高了145.30%、142.93%、139.48%和112.68%。整体而言,不同添加处理并没有显著改变湿地土壤CH_4产生/氧化速率的时间变化规律,各处理均表现为随培养时间先增加而后逐渐降低。短期培养结束后,土壤可溶性有机碳(DOC)、电导率、p H值在不同处理间均不存在显著差异(P0.05);土壤NH+4-N含量在N1、N3、NS1和NS3处理下,NO_3~--N含量在N2、N3、NS2和NS3处理下,SO_4~(2-)含量在S、NS1、NS2和NS3处理下均显著高于对照处理(P0.05)。相关分析显示,DOC、铵态氮(NH+4-N)和硝态氮(NO_3~--N)是氮、硫添加处理下影响闽江河口湿地土壤CH_4产生/氧化速率短期变化的主要控制因素。     

镉胁迫下紫花苜蓿幼苗内源一氧化氮和活性氧的生成

以"甘农三号"紫花苜蓿幼苗为材料,在水培条件下,研究了不同浓度镉(Cd)胁迫下紫花苜蓿根、茎和叶内源一氧化氮(NO)和活性氧(ROS)的生成机制以及根系活力的变化.结果表明:在0~2.0 mmol·L-1范围内,随着Cd浓度的增加,幼苗内NO含量呈现先升高后降低的趋势,最后可维持在略高或持平于对照的水平.幼苗内一氧化氮合成酶(NOS)活性、硝酸还原酶(NR)活性、亚硝酸根离子(NO2-)含量和类胡萝卜素(Car)含量的变化与NO含量变化规律相似却又不全相同.NOS和NR是影响幼苗茎中NO含量的主要因素,NOS、NO2-和NR则是影响叶中NO含量的主要因素,而根中NO含量主要与NOS活性和NO2-含量有较大相关性.随着Cd浓度的增加,幼苗内过氧化氢(H2 O2)含量、丙二醛(MDA)含量、超氧阴离子(O-2·)含量和相对电导率(REC)呈现显著升高趋势,说明高浓度的Cd处理会使ROS大量积累,细胞膜遭破坏,细胞质外流,进而引发膜脂过氧化.随着Cd浓度的增加,紫花苜蓿根系活力的变化为先升高后降低,指示了低浓度Cd处理会促进植物代谢,增强其生命力;而高浓度Cd会致使植株代谢受抑制,细胞受损害.NO和ROS的相关性不大,说明二者虽同为自由基,但它们产生和变化方式大有差别.     

Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO₃)₂; +N and –N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO₃ ^– and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H⁺ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO₃ ^– but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO₃ ^–, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO₃ ^– is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO₃ ^– had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner     

氮添加对亚热带常绿阔叶林土壤溶液化学特性的影响

土壤溶液被称作"土壤的血液",是土壤中各种生物化学反应的中介物质,在外界环境发生变化时,土壤溶液化学成分能在其他土壤指标尚无变化之前对环境变化做出迅速响应。为了探索持续增加的大气氮（N）沉降对森林生态系统的影响,以华西雨屏区亚热带常绿阔叶林为对象,设置对照（CK,0 g m^-2 a^-1）,低N（LN,5 g m^-2 a^-1）,高N（HN,15 g m^-2 a^-1）三种N处理,通过人工施加硝酸铵（2017年9月起改施硝酸钠及氯化铵）的方法模拟N沉降增加情景,N处理42个月后,使用负压土壤溶液采样器定位收集A层（37-45 cm）及B层（52-60 cm）土壤溶液,并进行分析（每月1次,为期1 a）。结果表明：对照处理中A、B两层土壤溶液NO₃^-浓度达（3.94±0.77）mg/L、（4.27±1.13）mg/L,N添加显著提高两层土壤溶液NO₃^-浓度和B层NH₄⁺浓度;N添加显著降低土壤溶液pH,且显著增加Al³⁺浓度,Ca²⁺和Mg²⁺含量有增加趋势,但影响不显著;N处理使A层土壤溶液可溶性有机碳（DOC）浓度显著降低,对两层土壤溶液芳香化指数（AI）无显著影响;两层土壤溶液电导率（EC）及氧化还原电位（Eh）显著增加;此外,两层土壤溶液中许多化学成分均呈现极显著相关,特别是NO₃^-与EC相关系数达到了0.855。本研究中,对照处理极高的NO₃^-含量以及B层土壤溶液硝酸盐浓度高于A层,表明该亚热带常绿阔叶林N的有效性超过植物和微生物的总营养需求而发生淋溶,该生态系统已达到氮饱和状态,此外N添加会显著促进土壤酸化和铝离子活化,表层土壤溶液DOC的降低一定程度反映了凋落物分解受N添加的抑制作用,显著升高的氧化还原电位可能导致土壤中某些金属元素的迁移率降低。     

Combination Effect of NaCl Salinity and Nitrogen Form on Mineral Composition of Sunflower Plants

The effect of two N-forms (NH₄ ⁺ and NO₃ ^–) and NaCl on pattern of accumulation of some essential inorganic nutrients was examined in sunflower (Helianthus annuus L.) cv. Hisun 33. Eight-day-old plants of were subjected for 21 d to Hoagland's nutrient solution containing 8 mM N as NH₄ ⁺ or NO₃ ^·, and salinized with and addition of NaCl to the growth medium had no significant effect on total leaf N. However, root N of NH₄-supplied plants decreased significantly with increase in NaCl concentration, whereas that of NO₃-supplied plants remained unaffected. There was no significant effect of NaCl on leaf or root P, but the NO₃-supplied plants had significa concentration of leaf P than that of NH₄-supplied plants at varying salt treatments. Salinity of the rooting med did not show any significant effect on Na⁺ concentrations of leaves or roots of plants subjected to two differen N. NH₄-treated plants generally had greater concentrations of Cl^– in leaves and roots and lower K⁺ content in leaves than NO₃-supplied plants. Ca²⁺ concentrations of leaves and roots and Mg²⁺ concentrations of leaves decreased in NH₄-supplied plants due to NaCl, but they remained unaffected in NO₃-treated plants.     

Variation in nutrient availability and plant species diversity across forb and graminoid zones of a Northern New England high salt marsh

Plant zonation patterns across New England salt marshes have been investigated for years, but how nutrient availability differs between zones has received little attention. We investigated how N availability, P availability, and plant N status varied across Juncus gerardii, Spartina patens, and mixed forb zones of a Northern New England high salt marsh. We also investigated relationships between several edaphic factors and community production and diversity across the high marsh. P availability, soil salinity, and soil moisture were higher in the mixed forb zone than in the two graminoid zones. NH⁺ ₄-N availability was highest in the J. gerardii zone, but NO^– ₃-N availability and mid season net N mineralization rates did not vary among zones. Plant tissue N concentrations were highest in the mixed forb zone and lowest in the S. patens zone, reflecting plant physiologies more so than soil N availability. Community production was highest in the J. gerardii zone and was positively correlated with N availability and negatively correlated with soil moisture. Plant species diversity was highest in the mixed forb zone and was positively correlated with P availability and soil salinity. Thus, nutrient availability, plant N status, and plant species diversity varied across zones of this high marsh. Further investigation is needed to ascertain if soil nutrient availability influences or is a result of the production and diversity differences that exist between vegetation zones of New England high salt marshes.