Single and Combined Effects of Cadmium and Zinc on Carrots: Uptake and Bioaccumulation

ABSTRACT

The present study was conducted to evaluate the effects of different concentrations of cadmium (Cd) and zinc (Zn), singly and in combination, on uptake and bioaccumulation of Cd and Zn in Daucus carota L. (carrot) grown under natural field conditions. Carrot plants were treated with two Cd concentrations (10 and 100 μg mL^?1), two Zn concentrations (100 and 300 μg mL^?1), and two combined concentrations of Cd and Zn (10 + 100 and 100 + 300 μg mL^?1) 15 d after seed germination. Treatments were repeated at 10 d intervals up to 90 d of plant age. A control was also kept without a Cd or Zn treatment. Uptake, total accumulation rate (TAR), bioconcentration factor (BCF), primary transport index (PTI), secondary transport index (STI), and accumulation of Cd and Zn in root, stem, and leaf were quantified. The results show that uptake, TAR, and accumulation of Cd and Zn are concentration-dependent phenomena. Highest accumulation of Cd and Zn was found in the root, followed by the stem and then leaves. The results also showed that bioaccumulation of Cd in root, stem, and leaf was greater at the low metal-application rates of Cd and Zn in combination than at the higher rate. This study further showed that interactions of Zn and Cd are dependent on the concentrations of those metals in the soil.     

Interactive Effects of Cadmium and Zinc on Carrots: Growth and Biomass Accumulation

ABSTRACT

An experiment was carried out to assess the single and combined effects of cadmium (Cd) and zinc (Zn) on growth and component wise biomass accumulation in carrot (Daucus carota L.) plants, grown under natural field conditions. Carrot plants were raised in field and treated with 10 and 100 μ g mL^{? 1} of Cd, 100 and 300 μ g mL^{? 1} of Zn singly, and in combination through soil drench. A control was also kept without any treatments of Cd and Zn. The impacts of different treatments of Cd and Zn on carrots were evaluated in terms of number of leaves, leaf area, plant length, and component wise biomass accumulation at different plant ages. Growth indices were also calculated to assess the biomass allocation patterns in carrots. The results showed that the above parameters were significantly affected in carrots treated with Cd and Zn singly and in combination as compared to the control as well as plants treated with 100 μ g mL^{? 1} of Zn. The results also showed that treatments of Cd and Zn have significant effects on biomass allocation pattern. This study concludes that growth and biomass accumulation in carrots were significantly influenced by the concentration ratios of Cd and Zn in soil/root/stem/ leaves. It is clear from this study that combined treatments of Cd and Zn have more negative impacts on above parameters as compared to their individual treatments.     

Response of Wheat Plants to Zinc,Iron, and Manganese Applications and Uptake and Concentration of Zinc,Iron, and Manganese in Wheat Grains

This experiment was conducted at Zahak Agricultural Research Station in the Sistan region in southeast Iran. A factorial design with three replications was used to determine the effects of zinc (Zn), iron (Fe), and manganese (Mn) applications on wheat yield, Zn, Fe, and Mn uptakes and concentrations in grains. Four levels of Zn [soil applications of 0, 40, and 80 kg ha^?1 and foliar application of 0.5% zinc sulfate (ZnSO₄) solution], two levels of iron sulfate (FeSO₄; 0 and 1%) as foliar application, and two levels of Mn (0 and 0.5%) also as foliar application were used in this study. Results showed that the interactive effects of Zn and Mn were significant on the number of grains in each spike. The highest number of grains resulted from the application of 80 kg ZnSO₄ ha^?1 and foliar Mn. The interactive effects of Zn and Fe were significant on weight of 1000 grains. The highest weight of 1000 grains resulted from application of 80 kg Zn and foliar Fe. Application of 80 kg ZnSO₄ ha^?1 alone and 80 kg ZnSO₄ ha^?1 with foliar application of Mn significantly increased grain yield in 2003. The 2‐year results showed that foliar application of Zn increased Zn concentration and Fe concentration in grains 99% and 8%, respectively. Foliar application of Fe resulted in a 21% increase in Fe concentration and a 13% increase in Zn concentration in grains. The foliar application of Mn resulted in a 7% increased in Mn concentration in grains.     

Cadmium,Lead, Copper,Zinc, and Nickel in Lettuce and Dry Beans as Related to Mehlich-3 Extraction in Three Brazilian Latossols

Lettuce (Lactuca sativa L.) and dry beans (Phaseolus vulgaris L.) were grown in three Brazilian Red-Yellow Latossols (Oxisols) in greenhouse conditions with cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), and nickel (Ni) applied to soils in treatments arranged as a randomized complete block design. Plant metals were analyzed in lettuce shoots and dry beans roots, stems, leaves, and seeds. After plant growth, soil samples from the pots were extracted with Mehlich-3 (M-3) for metal availability evaluation. The release of Ni in the M-3 extraction was dependent on the soil exchangeable aluminum (Al^{3 +}). Mehlich-3 was efficient for determination of availability of Cd, Pb, Cu, Zn, and Ni for dry beans and availability of Cd and Ni for lettuce. The dry bean leaves Cd, Pb, Cu, Zn, and Ni were highly correlated with their recovering from soils with M-3. The same was observed for Cd and Ni in lettuce shoots and the M-3 recovered metals from soils.     

Derivation of a Dynamic Model of the Kinetics of Nitrogen Uptake Throughout the Growth of Lettuce: Calibration and Validation

A kinetic model of nitrogen (N) uptake throughout growth was developed for lettuce cultivated in nutrient solution under varying natural light conditions. The model couples nitrogen uptake with dry matter accumulation using a two-compartment mechanistic approach, incorporating structural and non-structural pools. Maximum nitrogen uptake rates are assumed to decline with shoot dry weight, to allow for the effects of plant age. The model was parameterized using data from the literature, and calibrated for differences in light intensity using an optimization algorithm utilizing data from three experiments in different growing seasons. The calibrated model was validated against the data from two independent experiments conducted under different light conditions. Results showed that the model made good predictions of nitrogen uptake by plants from seedlings to maturity under fluctuating light levels in a glasshouse. Plants grown at a higher light intensity showed larger maximum nitrogen uptake rates, but the effect of light intensity declined towards plant maturity.     

Rhizosphere effects of maize hybrids and N forms on Cd bioavailability in a limed soil

Replacing new corn genotypes in agricultural practices requires adequate information on the reaction of the selected hybrids to Cd uptake in Cd-polluted soil and an understanding of interactions with N fertilizers. A 2 × 2 × 3 factorial pot experiment with limed soil (pH 8), two maize (Zea mays) hybrids (Pioneer cultivar yellow and Pioneer cultivar white), two N fertilization forms (NH₄ ⁺ and NO₃ ^?) and three Cd exposures (0, 2 and 5 mg kg^?1 soil) was conducted under greenhouse conditions. Shoot dry mass increased significantly with NH₄ ⁺ nutrition compared with NO₃ ^? nutrition in both maize hybrids, with greater negative influence of Cd application combined with NH₄ ⁺ nutrition. The yellow cultivar had significantly greater shoot dry mass and lower Cd uptake than the white cultivar. Both hybrids exhibited similar N uptake in shoots and roots, with the exception of yellow cultivar with NH₄ ⁺ nutrition without Cd application. NO₃ ^? nutrition always decreased Cd uptake in both cultivars compared with NH₄ ⁺ nutrition. The N balance (mean across cultivars and Cd supply) after harvest showed most N uptake with NH₄ ⁺ nutrition (63.4%) and N_min remains in the soil with NO₃ ^? nutrition (48.7%). Soil pH decreased more with NH₄ ⁺ (?0.95 pH units) than NO₃ ^? nutrition (?0.21).     

6种固化剂对土壤Pb Cd Cu Zn的固化效果

通过在重金属污染土壤中分别施加沸石、石灰石、硅藻土、羟基磷灰石、膨润土和海泡石6种固化剂,研究了这6种固化剂对土壤中Pb、Cd、Cu、Zn的固化效果,筛选出几种效果较好的固化剂。实验结果表明：沸石、石灰石和羟基磷灰石均能够有效地降低土壤中交换态Pb、Cd的含量,并且明显减少了土壤中Pb、Cd的毒性浸出量,其中沸石最多降低土壤中交换态Pb、Cd含量分别达到48.7%和56.2%,减少土壤中Pb、Cd的毒性浸出量达到37.1%和30.1%;沸石、石灰石均能够有效降低土壤中交换态Cu的含量,降低量分别高达68.1%和85.2%,膨润土能有效减少土壤中Cu的毒性浸出量,减少量最高达到66.51%;石灰石对土壤中Zn有着良好的固化效果。     

Response of Cadmium Uptake in Different Barley Genotypes to Cadmium Level

A greenhouse hydroponic experiment was performed out to study the cadmium (Cd) uptake by four different barley cultivars at two Cd levels. The results showed that Cd concentrations in roots and shoots increased with Cd levels in the solution and Cd concentration in roots was much higher than that in shoots. The amount of Cd accumulated by plants increased continually with the duration of treatment, and the highest Cd concentration in roots and aboveground tissues was found approximately at the 100th and 70th day after Cd addition, respectively. Genotypes differed significantly in relation to Cd concentration in roots and aboveground tissues. Wumaoliuling showed a higher Cd concentration than the other three genotypes, while Mimai 114 had the lowest concentration. Cadmium uptake rate per plant increased slowly before the booting stage, then increased sharply during the 70–100 d period (approximately late elongation to booting stage), and after that Cd uptake rate tended to slow dramatically. However, the Cd uptake rate per unit of dry biomass showed a significant reduction after booting stage (70 d after Cd exposure), and the Cd uptake pattern varied by Cd levels in the medium. At the lower Cd level (0.1 μM), there were two peaks in Cd uptake rate, appearing at the seedling (20–30 d after Cd exposure) and stem elongation stages (50–70 d after Cd exposure), respectively, while there was only one peak at the stem elongation stage at the higher Cd level (1 μ M).     

苎麻根际抗Cd细菌筛选及对苎麻生长和吸收Cd能力的影响

本文报道从苎麻根际筛选出5株抗Cd细菌（cdr1、cdr2、cdr3、cdr6、cdr7）,通过16SrRNA基因序列分析结果显示,cdr1和cdr3属于金黄杆菌属（Chryseobacterium）,cdr2属于农杆菌属（Agrobacterium）,cdr6属于贪噬菌属（Variovorax）,cdr7属于黄杆菌属（Flavobacterium）。采用盒栽试验方法,研究了抗Cd细菌对苎麻生长和吸收Cd能力的影响。结果表明,在Cd添加量为10mg·kg^-1土壤中接种cdr6、cdr7能显著增加苎麻生物量和叶片叶绿素含量,降低植株地下部分丙二醛（MDA）含量,但对植株Cd含量没有影响。从平均值来看,接种cdr1和cdr3的苎麻株高低于对照,但只有接种cdr3的处理达到显著水平。接种cdr1和cdr3的苎麻地上和地下部分干重、叶片叶绿素含量均低于对照CK-1,但其差异均没有达到统计意义的显著水平。接种cdr1、cdr3的苎麻地上部分Cd含量显著高于对照CK-1。接种cdr2对苎麻植株生物量和Cd含量均没有显著影响。     

Soil Acidity Changes in Bulk Soil and Maize Rhizosphere in Response to Nitrogen Fertilization

The capacity of nitrogen (N) fertilizers to acidify the soil is regulated principally by the rate and N source. Nitrogen fertilizers undergo hydrolysis and nitrification in soil, resulting in the release of free hydrogen (H⁺) ions. Simultaneously, ammonium (NH₄ ⁺) absorption by roots strongly acidifies the rhizosphere, whereas absorption of nitrate (NO₃ ^?) slightly alkalinizes it. The rhizosphere effects on soil acidity and plant growth in conjunction with N rate are not clearly known. To assess the impact of these multiple factors, changes in the acidity of a Typic Argiudol soil, fertilized with two N sources (urea and UAN) at two rates (equivalent to 100 and 200 kg N ha^?1), were studied in a greenhouse experiment using maize as the experimental plant. Soil pH (measured in a soil–water slurry), total acidity, exchangeable acidity, and exchangeable aluminum (Al) were measured in rhizospheric and bulk soil. Plant biomass and foliar area (FA) were also measured at the V₆ stage. Nitrogen fertilization significantly reduce the pH in the bulk soil by 0.3 and 0.5 units for low and high rates respectively. Changes in the rhizosphere (the “rhizospheric effect”) resulted in a significant increase in soil pH, from 5.9 to 6.2. The rhizospheric effect × N source interaction significantly increased exchangeable acidity in the rhizosphere relative to bulk soil, particularly when UAN was added at a low rate. Only total acidity was significantly increased by the fertilizer application rate. In spite of the bulk soil acidification, no significant differences in exchangeable aluminum were detected. Aerial biomass and FA were significantly increased by the higher N rate, but N source had no effect on them. Although changes in acidity were observed, root biomass was not significantly affected.     

丛枝菌根真菌对紫花苜蓿吸收土壤中镉和锌的影响

采用温室盆栽试验方法,研究了镉（Cd）、锌（Zn）污染土壤中,8种不同丛枝菌根真菌（AMF）Glomus lamellosum（G.la）、Acaulospora mellea（A.m）、Glomus mosseae（G.m）、Glomus intraradices（G.i）、Glomus etunicatum（G.e）、Glomus constrictum（G.c）、Diversispora spurcum（D.s）、Glomus aggregatum（G.a）对紫花苜蓿（Medicagosativa L.）吸收Cd、Zn的影响。结果表明,Cd、Zn污染下AMF仍然明显侵染紫花苜蓿,并促进紫花苜蓿对Cd、Zn的吸收积累,但不同AMF影响的效应和植株不同部位对重金属的吸收积累规律存在差异。AMF处理下紫花苜蓿根部Cd、Zn含量和积累量明显增加,但地上部Cd、Zn的含量则降低,地上部Zn的积累量也减小,这表明AMF处理减弱了Cd、Zn由根部向地上部的运移,减轻了植物地上部毒害。接种AMF条件下,植株尤其是根部生物量增加是Cd、Zn在其体内含量和积累量增加的重要因素,不同种类AMF促进植株生物量增加的幅度不同,导致植株对Cd、Zn的积累和抗性存在差异。     

Extractability and Transformation of Copper and Zinc Added to Tropical Savanna Soil under Long-Term Pasture

The extractability and slow reactions of copper (Cu) and zinc (Zn) in a weathered savanna soil under Brachiaria decumbens, Digitaria smutsii, and Stylosanthes guianensis pastures were determined in a laboratory incubation study using a sequential extraction to remove operationally defined fractions of the metals, consisting of exchangeable, organically bound, precipitate [occluded in aluminum (Al) and iron (Fe) oxides], and residual metal fractions. The soils from the pasture fields were spiked with 100 mg Cu kg^–1 soil and 200 mg Zn kg^–1 soil for 24 weeks. Copper and Zn extractable with 1 N potassium nitrate (KNO₃) solution decreased exponentially with time but reached a steady state after 2–3 weeks. The concentrations of Cu and Zn exchangeable with potassium (K) were greater in the Digitaria smutsii field soil than Brachiaria decumbens and Stylosanthes guianensis field soils. The exchangeability of added Cu and Zn (indexed Mⁿ⁺ _(exch)) with time was described by a simple exponential decay equation: Mⁿ⁺ _(exch) = αe^βt, where α is a constant, β is a coefficient that defines the rate of transformation of added Cu and Zn from the exchangeable to nonexchangeable pools, and t is time. The β values for Cu (0.040–0.076 mg kg^–1 d^–1) were almost 10 times greater than those of Zn (0.005–0.007 mg kg^–1 d^–1). Sequential extraction of added Cu and Zn indicated that between 26 and 30% of the total Cu and between 19 and 30% of the total Zn were associated with organic matter. Similarly, between 35 and 38% of total Cu and between 47 and 60% of total Zn were associated with Fe, Al, and manganese (Mn) oxides. The differential capacity of the pasture fields to transform added Cu and Zn from exchangeable and labile form to nonlabile and nonexchangeable form appears to be governed by organic matter (OM), pH, and active Fe ratio in the pasture field soils.     

Arbuscular mycorrhizal colonisation increases copper binding capacity of root cell walls of Oryza sativa L. and reduces copper uptake

There is evidence that colonisation by mycorrhizal fungi can protect host plants from toxic concentrations of heavy metals. The mechanism by which protection is provided by the fungus for any particular metal is poorly understood. Rice (Oryza sativa L.) plants were inoculated with Glomus mosseae and grown for 4 weeks to ensure strong colonisation. The plants were then exposed to low to toxic concentrations of copper (Cu) and the uptake and distribution were examined. The effect of mycorrhizal colonisation on the cell wall composition and Cu binding capacity of roots was also investigated. Mycorrhizal plants showed moderate reductions in Cu concentrations in roots but large reductions in shoots. In roots, mycorrhizal plants accumulated more Cu in cell walls but much less in the symplasm compared to non-mycorrhizal plants. The differences in cell wall binding of Cu could be partly explained by changes in the composition of the cell wall. The mechanistic basis for the reduced Cu accumulation and the potential beneficial consequences of mycorrhizal associations on plant growth in Cu toxic soil are discussed.     

Study of the Transfer Coefficient of Cadmium and Lead in Ryegrass and Lettuce

Abstract

The aim of study was to find the correlation between the concentration of the total amount of heavy metals of soils and that of plants because it shows which elements can be accumulated by different plants. The transfer coefficient is the metal concentration in plant tissues aboveground divided by the total metal concentration of soil. Pot experiments were conducted under greenhouse conditions. The total lead (Pb) content (about 21 mg · kg^?1 soil) of soils was higher than the cadmium (Cd) content (about 0.21 mg · kg^?1 soil). The Cd concentration of lettuce (averaging 0.93 mg · kg^?1) was higher than that of ryegrass (averaging 0.20 mg · kg^?1). The transfer coefficient of Cd was lower in ryegrass (averaging 0.95) than in lettuce (4.47). In this experiment, the concentration of Cd was almost five times higher in the four‐leaf lettuce than the Cd content of soil. The transfer coefficient of Pb was generally 0.064 in both plants.     

Response of spring wheat (Triticum aestivum) to interactions between Pseudomonas species and Glomus clarum NT4

The effects of interactions between pseudomonads (Pseudomonas cepacia strains R55 and R85, P. aeruginosa strain R80, P. fluorescens strain R92, and P. putida strain R104) and the arbuscular mycorrhizal fungus Glomus clarum (Nicol. and Schenck) isolate NT4, on spring wheat (Triticum aestivum L. cv. Laura), grown under gnotobiotic and nonsterile conditions, were investigated. Although plant growth responses varied, positive responses to pseudomonad inoculants generally were obtained under gnotobiotic conditions. Shoot dry weight enhancement ranged from 16 to 48%, whereas root enhancement ranged from 82 to 137%. Shoot growth in nonsterile soil, however, was unaffected by pseudomonad inoculants, or reduced by as much as 24%. Shoot growth was unaffected or depressed by G. clarum NT4 whereas early root growth was enhanced by 38%. Significant interactions between the pseudomonad inoculants and G. clarum NT4 were detected. Typically, dual inoculation influenced the magnitude of response associated with any organism applied alone. The effect of these pseudomonads on G. clarum NT4 spore germination was investigated. Germination was inhibited when spores were incubated either on membranes placed directly on bacterial lawns of strains R85 and R104 (i.e., direct assay), or on agarose blocks separated from the bacteria by membranes (i.e., diffusion assay). When the agarose blocks were physically separated from the pseudomonad (i.e., volatile assay), there was no evidence of inhibition, suggesting that a nonvolatile, diffusible substance(s) produced by both strains R85 and R104 may inhibit G. clarum NT4 spore germination. Received: 11 December 1995     

Distribution of Zinc Fractions in Some Major Soils of India and the Impact on Nutrition of Rice

Abstract

Speciation study of microelements in soils is useful to assess their retention and release by the soil to the plant. Laboratory and greenhouse investigations were conducted for five soils of different agro‐ecological zones (viz., Bhuna, Delhi, Cooch‐Behar, Gurgaon, and Pabra) with diverse physicochemical properties to study the distribution of zinc (Zn) among the soil fractions with respect to the availability of Zn species for uptake by rice plant. A sequential extraction procedure was used that fractionated total soil Zn into water‐soluble (WS), exchangeable (EX), specifically adsorbed (SA), acid‐soluble (AS), manganese (Mn)‐oxide‐occluded (Mn‐OX), organic‐matter‐occluded (OM), amorphous iron (Fe)‐oxide‐bound (AFe‐OX), crystalline Fe‐oxide‐bound (CFe‐OX), and residual (RES) forms. There was a wide variation in the magnitude of these fractions among the soils. The studies revealed that more than 90% of the total Zn content occurred in the relatively inactive clay lattice and other mineral‐bound form (RES) and that only a small fraction occurred in the forms of WS, EX, OM, AFe‐OX, and CFe‐OX. Rice (Oryza sativa L.) cultivars differ widely in their sensitivity to Zn deficiency. Results suggested that Zn in water‐soluble, organic complexes, exchange positions, and amorphous sesquioxides were the fractions (pools) that played a key role in the uptake of Zn by the rice varieties (viz., Pusa‐933‐87‐1‐11‐88‐1‐2‐1, Pusa‐44, Pusa‐834, Jaya, and Pusa‐677). Isotopic ally exchangeable Zn (labile Zn) was recorded higher in Typic Ustrochrept of Pabra soil, and uptake of Zn by rice cultivars was also higher in this soil. The kinetic parameters such as maximum influx at high concentrations (I_max) and nutrient concentration in solution where influx is one half of I_max (K_m) behaved differentially with respect to varieties. The highest I_max value recorded was 9.2×10^?7 µmol cm^?2 s^?1 at the 5 mg kg^?1 Zn rate for Pusa‐933‐87‐1‐11‐88‐1‐2‐1, and the same was lowest for Pusa‐44, being 4.6×10^?7 µmol cm^?2 s^?1 at the 5 mg kg^?1 Zn rate. The K_m value was highest for Pusa‐44 (2.1×10^?4µmol cm^?2 s^?1) and lowest for Pusa‐933‐87‐1‐11‐88‐1‐2‐1 (1.20×10^?4µmol cm^?2 s^?1). The availability of Zn to rice cultivars in Typic Ustrochrepts of Bhuna and Delhi soils, which are characterized by higher activation energy and entropy factor, was accompanied by breakage of bonds or by significant structural changes.     

Effect of vesicular-arbuscular mycorrhizae and zinc application on dry matter and zinc uptake of greengram (Vigna radiata L. Wilczek)

Summary In a greenhouse study we examined the effects of vesicular-arbuscular mycorrhizae (VAM) inoculation, using Glomus macrocarpum and of Zn application on dry matter production and Zn uptake by greengram in two mollisols. The VAM inoculation significantly increased the dry weight of different plant parts and the Zn uptake in both soils. Inoculated plants showed a greater response to the application of Zn at 2.5 and 5.0 mg kg^-1 soil in a Zn deficient clay loam soil. The inoculated plants also absorbed — more water than the uninoculated plants. Mass flow and diffusion were the principal processes by which Zn reached the plant roots; mass flow was particularly important in the absence of VAM in a sandy soil fertilized with higher Zn doses (5 and 10 mg kg^-1 soil). The greater supply of Zn to inoculated roots was attributed to an apparent diffusion process rather than to mass flow of Zn.     

The Effect of Different Compost Compositions on Arbuscular Mycorrhizal Colonization and Nutrients Concentration of Leek (allium Porrum L.) Plant

ABSTRACT

Plant residue material produced compost is an organic fertilizer source and it is commonly used for soil amendments. Also in order to reduce the amount of chemical fertilizers need mycorrhizal inoculation can be used as an agricultural strategy. Thus, the aim of the research is to examine the effect of several residue materials produced compost and mycorrhizae fungi with two growth media on leek plant growth, nutrient uptake, and mycorrhizae spores’ production.

Eight different row organic materials and animal manures were used as compost production during 8 months. Leek (Allium porrum L.) plants were inoculated with Funneliformis mosseae and Claroideoglomus etunicatum with a level of 1000-spore per pot. The leek plant was analyzed for determination of nutrient concentration, root colonization, spore production, and shoot/root dry weight.

The composts were made from domestic waste, animal manure (bovine animal), animal manure (ovine animal), and different plant materials were determined to be the most suitable compost material for plant growth and mycorrhizal spore production compared to the rest of compost material. Mycorrhizal inoculation significantly increased leek plant growth and nutrient uptake especially phosphorus (P), potassium (K), copper (Cu) and zinc (Zn). Plants grown in 5:3:2 (volume/volume) growth media was responded better to the mycorrhizal inoculation than grown in 1:1:1 (v/v) growth media. Funneliformis mosseae inoculated plants have higher plant growth and nutrient uptake than that of Claroideoglomus etunicatum inoculation.     

Change of Zinc Forms in Rhizosphere and Nonrhizosphere Soils of Maize (Zea mays L.) Plants as Influenced by Soil Drought Condition

A rhizobox experiment was conducted to study the changes of various zinc (Zn) forms in rhizosphere and nonrhizosphere soils of maize (Zea mays L.) plants grown under well-watered and drought conditions. The tested soil was earth-cumulic orthic anthrosol sampled from the Shaanxi Province of China. The experiment was set at two levels of Zn, 0 and 5.0 mg Zn kg^?1 soil, and at two treatments of soil water content, 45%–50% (drought) and 70%–75% (well watered) of soil water-holding capacity. A completely randomized factorial design (2 Zn treatments × 2 water levels × 3 replicates) was set up. Adequate soil water supply enhanced growth and Zn accumulation of maize plants. Applying Zn increased plant biomass and Zn content more notably under well-watered conditions rather than drought conditions. Soil Zn was defined as water-soluble plus exchangeable (WSEXC) Zn, carbonate-bound Zn (CA), iron–manganese oxide–bound Zn (FeMnOX), organic matter–bound Zn (OM), and residual Zn (RES) forms using the sequential extraction procedure. Most of Zn was predominantly in the RES fraction. Zinc application increased the contents of WSEXC Zn, CA Zn, and FeMnOX Zn in soil. When Zn was added to the soil, the concentrations of CA Zn within 0–2 mm and 0–4 mm apart from the central root compartment (CC) were greater than other zones under the conditions of adequate and limited soil water supplies, respectively. Zinc application also resulted in an accumulation of FeMnOX fractions at a distance of 2 mm from CC. The FeMnOX Zn content in this compartment increased with soil drought. Under well-watered conditions, dry-matter weight and Zn concentration of shoots presented better correlations with CA Zn and FeMnOX Zn fractions in and near the rhizosphere as compared with drought conditions. It is suggested that in an earth-cumulic orthic anthrosol, soil moisture conditions affect the transformation of the added Zn into the CA and FeMnOX fractions near the rhizosphere and their bioavailability to maize plants.