Interaction Effects of Arbuscular Mycorrhiza Fungi and Soil Applied Herbicides on Plant Growth

Interaction between mycorrhizal fungi and herbicide application and their effects on plant growth are issues around which there is little information. Therefore, to determine the effect of arbuscular mycorrhizal (AM) fungus in alleviating the effects of herbicide stress on growth of maize and barley, two pot experiments were conducted in Shahrood University of Technology in 2009 and 2010. Factorial experiments were arranged in completely randomized design with three replications. Experimental factors were a combination of two factors: (1) non-mycorrhiza (control) and Glommusmosseae, Glommusintraradices and Glommusfasciculatum as mycorrhizal inoculums; (2) herbicide treatments, which included three levels of metribuzin (0, 175 and 350 g a.i. ha^?1). In the second experiment, factors examined were inoculated soil with mycorrhiza fungi at two levels (with and without Glommusintraradices) and four rates of metribuzin (0, 175, 350 and 525 g a.i. ha^?1) and two levels of iron (0 (control) and 20 mg pot^?1). The results showed that soil inoculated with mycorrhiza had significantly increased dry weight, height and chlorophyll content of maize and barley in the low herbicide concentrations (175 g a.i. ha^?1) compared to non-inoculated treatments. Based on our results, mycorrhiza fungi can alleviate crop stress due to low doses of metribuzin injury through increase in plant growth.     

Response of corn to NPK fertilization grown in a Latosol in South Sulawesi,Indonesia

Abstract

Corn (Zea mays L.) is next to rice as an important food crop grown in South Sulawesi, Indonesia. However, yields obtained by farmers are rather low, around 0.6 to 1.0 ton/ha. Efforts to increase yield have been tried through the application of NPK fertilizers. A study was conducted to determine the effects of N, P and K application on corn yield and what soil constrains, in terms of nutrient elements in the corn plants, exist in the latsols found at Desa Tokka, Sinjai, and South Sulawesi. It was found that application of K significantly increased the growth and corn grain yields on the latosols at Sinjai. Without K, grain yield and the K content in the ear leaf were low. The correlation between grain yield and rate of K shows that an application of 72 kg K₂O/ha together with 90 kg N and 80 kg P₂O₅ per ha produce the best yield of 3.6 tons/ha. The K content in the ear leaf of 1.8% was related to this maximum yield.     

Container and Installation Time Effects on Soil Moisture,Temperature, and Inorganic Nitrogen Retention for an in situ Nitrogen Mineralization Method

Mineralization contributes significantly to agronomic nitrogen (N) budgets and is difficult to accurately predict. Models for predicting N‐mineralization contributions are needed, and development of these models will require field‐based data. In situ mineralization methods are intended to quantify N mineralization under ambient environmental conditions. This study was conducted to compare soil moisture and temperature in intact soil cores contained in cylinders to those in adjacent bulk soil, compare the effect of two resin‐bag techniques on water content of soil within cylinders, and assess the effect of installation duration on inorganic N retention by resins. The study was conducted at a dryland conventionally tilled corn (Zea mays L.) site and an irrigated no‐tillage corn site in eastern Nebraska. Soil in cylinders was slightly wetter (<0.05 g g^?1) and warmer (<1 °C) than adjacent soil. Soil water content was <80% water‐filled pore space (WFPS) at all sampling times and differed little between the two resin‐bag techniques. Greater soil water content and temperature conditions (though small) observed during most of the study period likely enhanced N mineralization within the cylinder compared to N mineralization in adjacent bulk soil, but the magnitude is likely much less than core‐to‐core variation normally observed in a field. Installing cylinders for more than 60 days resulted in loss of inorganic N from resins. Care is needed during installation to ensure that compaction of soil below the cylinder does not impede water movement through the intact soil core. The in situ method utilizing intact soil cores and resin bags replaced at 28‐ to 40‐day intervals is a viable method for measuring N mineralization.     

Does the Sulfur Assimilation Pathway Play a Role in the Response to Fe Deficiency in Maize (Zea mays L.) Plants?

Abstract

The finding that the methionine is the sole precursor of the mugineic acid family phytosiderophores induced us to evaluate whether sulfur assimilation pathway has a role in plant response to Fe deficiency. Maize plants were grown for 10 days in nutrient solution (NS) containing 80 µM Fe in the presence (+S) or absence (?S) of sulfate. After removing the root extraplasmatic iron pool, half of the plants of each treatment (+S and ?S) were transferred to a new Fe deficient NS (0.1 µM final Fe concentration) (?Fe). The remaining plants of each pre‐culture condition (+S and ?S) were transferred to a new NS containing 80 µM Fe (+Fe). Leaves were collected 4 and 24 hours from the beginning of Fe deprivation period and used for chemical analysis and enzyme assays. Results showed that iron content in the leaves was lower in plants grown in S‐deficiency than in those grown in the presence of the macro‐nutrient. Iron deprivation produced an increase in the level of SH compounds in both nutritive conditions (+S and ?S). These observations are suggestive of some relationship between S nutrition and Fe uptake. For this reason, we next investigated the influence of Fe availability on S metabolism through the evaluation of changes in ATPs and OASs activity, the first and the last enzyme of S assimilation pathway respectively. Results showed that S‐starvation increased the activity of both enzymes, but this effect disappeared in plants upon Fe deficiency suggesting that S metabolism is sensitive to Fe availability. Taken together these evidences suggest that S metabolism is sensitive to soil Fe‐availability for plant nutrition and support the hypothesis of S involvement in plant response to Fe deprivation.     

Crop-specific differences in the concentrations of lipids in leachates from the root zone

Although lipids are involved in diverse soil processes and affect various soil properties, the contribution of rhizodeposits and the root zone to lipid concentrations and distributions in soils is unknown. For the first time, we determined the concentrations of alkanoic acids, n-alkanes and n-alkenes in root zone leachates and roots of maize and potato using gas chromatography/mass spectrometry (GC/MS). In total, the lipid concentrations of leachates were 100 μg g^?1 (maize) and 17 μg g^?1 (potato). The saturated n-alkanoic acids, ranging from n-C₁₄ to n-C₂₈ and having the maximum at n-C₂₂ (maize) and at n-C₁₆ (potato), were more abundant than the other compounds. Maize leachates had more alkanes (20 μg g^?1) than potato leachates (3.1 μg g^?1), but the members of the homologues were nearly the same. Comparison of these distributions with data for roots, microorganisms and soil indicated that the lipids in the leachates from the root zone mainly originated from abrasion of fine roots, rhizodeposits and rhizosphere microorganisms.     

Plant mineral contents of root tips from four sorghum cultivars after exposure to the anion channel blocker,sits

SITS (0, 0.01, 0.1, or 1.0 mM) influence on the absorption (1 hr) by 1‐cm root tips of Sorghum bicolor (L.) Moench cv GP‐10, SC 283, SC 574, or Funk G522DR seedlings of calcium (Ca), boron (B), phosphorus (P), zinc (Zn), manganese (Mn), iron (Fe), magnesium (Mg), and copper (Cu) from an Hoagland and Arnon complete mineral nutrient solution was evaluated by inductively coupled plasma emission spectrophotometry (ICP). Cultivar variation in response to SITS within each element was found. Multiple mechanisms of control for the absorption of each element among cultivars were evident.     

Effect of lead treatment on the distribution of essential elements in cucumber

Changes in the fresh and dry weight of leaf blades, petioles, internodes, and their ion concentrations as well as rates of root exudation were investigated in cucumber grown in hydroponic culture and treated with physiological concentrations of lead (Pb). The growth of flowering cucumber supplied with FeCl₃ shows a typical bell‐shaped curve derived from leaf dry weights, where the 4th, 5th, and 6th leaves are the largest ones. Lead inhibited growth up to 20% (except the youngest leaves which were stimulated), but did not cause morphological changes. Whereas root growth was also retarded by about 20%, exudation was inhibited to 50%, that is, the root resistance to water transport was increased by Pb. In spite of that the dry matter yield of internodes and petioles hardly reached 10 and 5% of that of leaf blades, respectively, their calcium (Ca), magnesium (Mg), and zinc (Zn) concentrations were almost the same. Similarly, the concentrations of these metals in the specific leaf blades are equal despite their different growth characteristics but the concentration of Mn is independent of the growth of the examined tissues. Lead was the only cation to accumulate in the largest leaves. The inhibitory effect of Pb on ion uptake was proportional to the growth inhibition of the tissues except manganese (Mn), the accumulation of which was stimulated by Pb in all the analyzed tissues and copper (Cu) which increased only in the internodes. We could not explain the extremely different ion distributions observed during the growth of cucumber. However, it is evident that the measurement of ion concentrations at whole shoot level is not enough to characterize ion interactions because only some ions accumulate at the same rate as tissues grow. These ions maintain stable concentration levels in shoot parts whereas others decrease or increase independently from growth.     

4种填闲作物对天津黄瓜温室土壤次生盐渍化改良作用的初步研究

通过夏季填闲的方式来解决设施农业次生盐渍化在20世纪初就已被提出,但相关研究在天津黄瓜温室土壤次生盐渍化改良方面还没有开展。通过盆栽试验研究了4种填闲作物（毛苕子、苏丹草、甜玉米和苋菜）对天津地区黄瓜温室土壤次生盐渍化的改良作用。结果显示,与对照土壤相比,4种填闲作物均能显著降低土壤可溶性盐分和Na^＋的含量（P〈0．05）,显著降低土壤养分和有机质的含量（P〈0．05）;毛苕子、甜玉米和苋菜能显著增大土壤K^＋／Na^＋的比值;高种植密度对次生盐渍化土壤的改良效果更为突出;4种填闲作物相比,毛苕子对黄瓜温室土壤次生盐渍化的改良效果最佳。既为改良天津黄瓜温室土壤次生盐渍化提供实践参考,也为延长设施土壤使用年限,促进天津设施蔬菜产业发展提供一种可行途径。     

Growth and phosphorus uptake of maize cultivated alone,in mixed culture with other crops or after incorporation of their residues

Intercropping or rotating of P‐efficient crop species which mobilize sparingly soluble P by their root exudates can have beneficial effects on growth and P uptake of P‐inefficient species. We aimed at studying the effect of intercropping or incorporating of crop residues of P‐efficient crops on the components of maize P‐uptake, i.e. the root‐system size and P influx (P‐uptake rate per unit root length). This was studied in 3 pot experiments in a low‐P sandy soil. In the first experiment, maize was intercropped with white lupine, sugar beet or oilseed rape, and with groundnut in the second experiment. In the third experiment, maize was grown after incorporating the crop residues of white lupine, sugar beet or oilseed rape. Maize growth and yield was strongly inhibited when intercropped with white lupine, sugar beet or oilseed rape, probably because of competition for nutrients. But with groundnut as the accompanying species, maize yield was increased by a factor of 3, mainly because of an enhanced P influx. Crop residues of oilseed rape and sugar beet increased the yield of maize by factors 2 and 1.6, respectively, because of a 3 and 2 times higher P uptake as compared to maize grown after maize without incorporation of crop residue. The reason for the higher maize P‐uptake after oilseed rape was an 11 times higher P influx as compared to maize without crop residues, and after sugar beet residues because of an enhanced root growth and a 4 times higher P influx. Lupine residues did not improve maize growth, mainly because of a low P influx, which was even less than that of maize grown without crop residues. The soil solution P concentration and calcium acetate lactate‐extractable P (CAL P) measured in this study did not reflect the P availability as indicated by the plants (P uptake, P influx). This indicates that other mechanisms such as P mobilization in the rhizosphere by root exudates or cell‐wall components were responsible for the increased P availability. These mechanisms need further investigation.     

不同耐密性玉米品种的根系生长及其对种植密度的响应

根系形态和分布对土壤中养分和水分的吸收有重要影响。增加耐密性是现代玉米（Zea may L.）育种的主要方向,而耐密性与根系的关系尚了解不多。本文以70年代主推的2个不耐密型品种（中单2号与丹玉13）和2个当代耐密型现代品种（先玉335和郑单958）为材料,将田间试验和室内水培试验相结合,在3个密度水平下,研究了不同耐密性玉米品种的根系差异及其对种植密度的响应。结果表明,目前推广的耐密型品种的根系要小于不耐密的老品种。不同耐密性品种之间的差异主要表现在040 cm。随着密度的增加,根显著变小、变细。密度主要降低020 cm土层中的根系生长,对深层根系影响较小。先玉335和中单2的根系长度对密度的反应较弱,郑单958和丹玉13较强。这说明先玉335主要依靠其小根系适应高密度,而郑单958既依靠较小的根系,同时依靠较高的根系反应性适应高密度。     

Impact of Fertilization and Irrigation on the Correlation between the Soil Plant Analysis Development Value and Yield of Maize

The degree of nitrogen (N) supply in maize under nonirrigated and irrigated conditions was measured using a Soil Plant Analysis Development (SPAD) 502 portable chlorophyll meter for 4 years. The lowest readings were obtained from a plot that has not been fertilized for 23 years. The highest SPAD value in the nonirrigated treatments was obtained in 2004, whereas the lowest was measured in the drought year of 2007. In the irrigated treatments, there was a closer correlation between fertilization and SPAD values during the examined 4 years. As the result of fertilization, the average increase of SPAD values in the irrigated plots was greater than in the nonirrigated plots. The result of irrigation on SPAD values was significant every year (P < 0.001), with the largest increase in the drought year of 2003. In the nonirrigated treatments, fertilization and grain yield had a weak correlation, whereas in the irrigated treatments the correlation between the two variables was strong.     

Corn yield variation as related to soil water fluctuation and nitrogen fertilizer. II. Soil water‐nitrogen‐yield relationships

Abstract

The aim of this study was to determine the relationships between soil water and nitrogen fertilizer and their effect on grain corn yield (Zea mays L.) in a zone where the limiting factor of yield and nitrogen efficiency is the water supply. The experiments were carried out for 10 years on a deep‐permeable well—drained chernozem in a temperate—continental dry climate with annual precipitation of about 500 mm.

Different nitrogen rates were applied and plant available soil water (PAW) was determined every year before and during the growing season. Multiple regressions were fitted for nitrogen rate, soil water and corn yield.

The results show that there is a significant interaction between soil water content, applied nitrogen and corn yield. The soil water explains the greatest part of yield variation, followed by the soil water‐added nitrogen interaction effect and the direct effect of added nitrogen. The PAH on July 1st gave a better correlation (R² = 0.88) than June 1st (R² = 0.85) or March 1st PAW (R² = 0.72). But the best correlation was obtained when both June and July PAW were taken together in the regression (R² = 0.914). July PAW was also more efficient in terms of yield per PAW. Thus, 1 mm of PAW on March, June and July 1st increased the control yield by 12.5, 14.6, and 18.3 kg grain/ha respectively, and by 18.0, 22.0 and 32.0 kg grain/ha for the fertilized yield (with 60 kg N/ha). At low soil moisture content, the applied N had no or even negative effect on water use efficiency and yield while at high PAW the water use efficiency was greatly increased by the applied N.     

Responses of photosynthesis,chlorophyll fluorescence,and grain yield of maize to controlled‐release urea and irrigation after anthesis

Controlled‐release urea (CRU) is a new type of urea, which may increase crop nitrogen (N)‐use efficiency compared with conventional urea (CU), but the conditions where it outperforms urea are not well defined. A field experiment assessing responses of plant growth and grain yield of maize to CRU and irrigation was conducted on a typical agricultural farm in Shandong, China. Five treatments of the two types of urea (75, 150 kg N ha^–1, 0 kg N ha^–1) were applied as basal fertilizer when sowing maize, and two water treatments (W₀ and W₁) were used 23 d after anthesis. Net photosynthetic rate (P_N) and chlorophyll concentration as well as leaf‐area index (LAI) increased significantly by both CRU and CU application, with the increases being larger in CRU‐treated plants than in CU‐treated plants at grain filling and maturing stages. CRU significantly enhanced the maximum photochemical efficiency (F_v / F_m), PSII coefficient of photochemical fluorescence quenching (q_P), and actual quantum yield of PSII electron transformation (Φ_PSII) but decreased the nonphotochemical quenching (NPQ). Cob‐leaf N concentration of CRU‐treated plants was significantly higher than that of CU‐treated plants under no irrigation, but not in the irrigation treatment 30 d after anthesis. Significant positive correlations were found between cob‐leaf N concentration and P_N both with and without irrigation. Grain yield of maize was significantly higher in the CRU treatment than in the CU treatment under both irrigation conditions. In conclusion, CRU as a basal application appeared to increase the N‐use efficiency for maize relative to CU especially by maintaining N supply after anthesis.     

外源水杨酸对锰污染红壤中玉米的生长与抗氧化酶活性的调节作用

采用盆栽实验方法研究了外源水杨酸（SA）对锰污染红壤中玉米的生长、脂质过氧化程度、活性氧水平以及抗氧化酶活性的影响。结果表明,过量锰明显降低玉米植株干重,显著提高了茎叶和根中锰的含量。SA促进锰胁迫下玉米的生长,但对植株中锰的含量与分布无影响。过量锰处理下,玉米叶片超氧阴离子（O.2-）和过氧化氢积累显著增加,脂质过氧化、电解质渗透率和脯氨酸含量显著升高;而SA和过量锰复合处理下,这些指标则显著降低。过量锰诱导超氧化物歧化酶（SOD,EC1.15.1.1）、过氧化物酶（POD,EC1.11.1.7）活性升高,抑制过氧化氢酶（CAT,EC1.11.1.6）和抗坏血酸过氧化物酶（APX,1.11.1.11）活性;SA处理促进锰胁迫下SOD和POD活性进一步升高,减小CAT和APX活性下降的程度。这些结果提示,SA调节抗氧化酶活性,保护组织细胞免遭氧化损伤,是SA缓解过量锰对玉米毒害作用的重要生理原因。     

Corn yield variation as related to soil water fluctuation and nitrogen fertilizer. I. Soil water‐yield relationships

Abstract

The objective of this work was to study the effect of plant available soil water (PAW) in different soil layers before and during the growing season on corn yields (Zea mays L.) and to determine if the soil water may be a reliable index in forecasting the grain yield. The experiments were carried out for 10 years at the same site on a deep‐permeable well‐drained chernozem with good physico‐chemical and biological properties situated in a temperate‐continental dry climate with annual precipitation of about 500 mm and wide seasonal and annual fluctuation.

The results show that the maximum yields (MY) were highly correlated to water stored in the soil as well at the beginning as during the growing season. In most cases the yields were better correlated to PAW at the beginning of June (r = 0.96**) than at the beginning of March (r = 0.87**) or July (r = 0.91**). Nevertheless, the July PAW was more efficient in terms of yield per unit of PAW. Thus, 1 mm of PAW within 0–150 cm in March, June and July 1^st increases the MY by 16, 21 and 30 kg/ha of grain, respectively. The MY was more related to March and especially to June 1^st PAW (0–150 cm) than to June‐July precipitation.

The PAW from deeper soil layers was in almost all cases better correlated with MY and more efficient. Thus, for the PAW within 0–70 cm on March, June and July 1^st the simple correlation coefficients with yields were 0.69, 0.87** and 0.76* respectively while for the PAW within 0–150 cm the correlation coefficients were 0.87**, 0.96** and 0.91** respectively. Also, 1 mm of PAW within 0–100 cm on March, June and July 1st increases the yields by 23, 34 and 39 kg/ha while the PAW within 100–150 cm increases the yields by 40, 56 and 78 kg/ha respectively.

The results suggest that in this dry area the amount of yield is highly related to PAW at the beginning as well as during the growing season and that soil water may be a good index for forecasting yields as early as three month prior to harvest, except for years with weather accidents in late summer. They also show that PAW from deeper soil layers has a paramount effect on maximum corn yield.     

Critical Soil Zinc Deficiency Concentration and Tissue Iron: Zinc Ratio as a Diagnostic Tool for Prediction of Zinc Deficiency in Corn

ABSTRACT

Zinc (Zn) fertilizer application is most economic if based on soil test and plant analysis information. The aim of this study was to determine the soil test [diethylenetrinitrilopentaacetate (DTPA) and ethylenetriaminepentaacetic acid (EDTA) extractable] Zn-critical levels and tissue Fe/Zn ratio for corn (Zea mays L.). A greenhouse experiment with 12 soil series and two Zn fertilizer treatments (0 and 15 mg Zn kg^?1 as zinc sulfate) was conducted. Critical Zn deficiency levels were determined using the Cate-Nelson procedure. Relative corn yield varied from 0.59 to 1.64. Critical deficiency levels based on the Cate-Nelson method were 1.50 and 1.17 mg kg^?1 for DTPA and EDTA-extracted soil Zn, respectively. No accurate critical deficiency level could be established using the shoot Zn concentrations. The critical iron (Fe)/Zn ratio in the corn shoot was 3.9. Values greater than 3.9 indicate hidden Zn deficiency and probable response to applied Zn.     

Growth and Zinc Uptake and Use Efficiency in Food Crops

Zinc (Zn) deficiency in annual crops is very common in Brazilian Oxisols. Data are limited on Zn uptake and use efficiency during crop growth cycles. A field experiment was conducted during two consecutive years with the objective to determine shoot dry weight and Zn uptake and use efficiency in upland rice, dry bean, corn, and soybean during growth cycles. Shoot dry weight of four crops was significantly increased in an exponential quadratic fashion with increasing plant age. Rice and corn had higher shoot dry weights and grain yields than dry bean and soybean. Zinc concentration in rice and corn decreased in a quadratic fashion with increasing plant age. However, in dry bean and soybean, Zn concentration had a quadratic increase. Zinc uptake followed an exponential quadratic response in four crops, and it was higher in corn and upland rice than in dry bean and soybean. Zinc use efficiency in shoot dry‐weight production had significant quadratic responses in upland rice and soybean with increasing plant age. In corn, Zn use efficiency for shoot dry‐weight production was linear as a function of plant age. Zinc use efficiency for grain production was maximum for corn and minimum for soybean. Hence, cereals had higher Zn use efficiency than legumes.

Zinc concentration in grain of dry bean and soybean was higher than in upland rice and corn, which is a desirable quality factor for human consumption so as to avoid Zn deficiency.     

海河流域合理生态用水比例的确定

Winter wheat-maize rotations are dominant cropping systems on the North China Plain, where recently the use of organic manure with grain crops has almost disappeared. This could reduce soil fertility and crop productivity in the long run. A 20-year field experiment was conducted to 1） assess the effect of inorganic and organic nutrient sources on yield and yield trends of both winter wheat and maize, 2） monitor the changes in soil organic matter content under continuous wheat-maize cropping with different soil fertility management schemes, and 3） identify reasons for yield trends observed in Xuzhou City, Jiangsu Province, over a 20-year period. There were eight treatments applied to both wheat and maize seasons： a control treatment （C）; three inorganic fertilizers, that is, nitrogen （N）, nitrogen and phosphorus （NP）, and nitrogen, phosphorus and potassium （NPK）; and addition of farmyard manure （FYM） to these four treatments, that is, M, MN, MNP, and MNPK. At the end of the experiment the MN, MNP, and MNPK treatments had the highest yields, about 7 t wheat ha^-1 and 7.5 t maize ha^-1, with each about 1 t ha^-1 more than the NPK treatments. Over 20 years with FYM soil organic matter increased by 80% compared to only 10% with NPK, which explained yield increases. However, from an environmental and agronomic perspective, manure application was not a superior strategy to NPK fertilizers. If manure was to be applied, though, it would be best applied to the wheat crop, which showed a better response than maize.     

Nutrient mobilization and nutrient contents of Zea mays in response to EDTA additions to heavy‐metal‐contaminated agricultural soil

Enhanced phytoextraction of heavy metals (HMs) using chelating agents and agricultural crops is widely tested as remediation technique for agricultural soils contaminated with less mobile HMs. Nutrients are complexed by chelating agents simultaneously to HMs. In this study, the effect of EDTA (ethylenediaminetetraacetic acid) application on nutrient mobility in the soil and nutrient contents of Zea mays was tested on the laboratory and on the field scale. EDTA effectively increased the mobility of total water‐soluble macronutrients (Ca, K, Mg, P) and micronutrients (Fe, Mn) in the soil solution. Thereby nutrient co‐mobilization did cause competition to target HMs during the phytoextraction process. Mobilization was caused by complexation of nutrient cations by negatively charged EDTA and by dissolution of oxides and hydroxides. Increased concentrations of negatively charged P indicate the dissolution of metal phosphates by EDTA. Higher total water‐soluble nutrient concentrations enhanced bioavailability and plant contents of all determined nutrients especially that of Fe. Mobilization of nutrients may result in leaching and loss of soil fertility.     

重金属铅镉对玉米生长及土壤微生物的影响

采用温室盆栽土培方法,研究了土壤中不同浓度重金属铅（Pb,0-800 mg.kg^-1）、镉（Cd,0-50 mg.kg^-1）单一及其复合处理对玉米（Zea mays L.）生长及土壤微生物（细菌、放线菌、真菌）数量的影响。结果表明,在重金属Pb、Cd单一及其复合处理下,玉米的株高、干重均低于对照,重金属Pb、Cd处理对玉米的生长存在负面影响。重金属Pb、Cd单一处理抑制细菌、真菌的生长,中低浓度Pb（≤300 mg.kg^-1）、Cd（≤10 mg.kg^-1）单一处理促进放线菌数量的增加,高浓度（Pb≥800 mg.kg^-1、Cd≥50 mg.kg^-1）则呈现抑制效应;Pb、Cd复合在高中低浓度下都抑制土壤微生物生长,减少微生物数量。玉米株高同土壤微生物之间相关性不显著;玉米干重同土壤细菌、真菌显著相关,同土壤放线菌之间相关性不显著。