Reducing residues of tetracycline and its resistance genes in soil-maize system and improving plant growth:Selecting the best remediation substance

Tetracycline(TC)and tetracycline resistance genes(TRGs)in plant edible tissues pose a potential risk to the environment and then to human health.This study used a pot experiment to investigate the effects of different remediation substances(worm castings,fungal chaff,microbial inoculum,and biochar)on the physiological characteristics of maize and the residues of TC and TRGs in the soil-maize system under TC stress.The results showed that TC significantly inhibited growth,disrupted the antioxidant defense system balance,and increased proline and malondialdehyde contents of maize plants.Tetracycline residue contents were significantly higher in root than in shoot,and followed the order root>stem-leaf>grain,which was consistent with the distribution of bioconcentration factors in the different organs of maize plants.The TC residue content in the soil under different treatments was 0.013–1.341 mg kg-1.The relative abundances of different antibiotic resistance genes in the soil-maize system varied greatly,and in maize plants followed the order intI1>tetW>tetG>tet B>tetM>tetX>tetO.In the soil,tetX had the highest relative abundance,followed by tetG and tetW.A redundancy analysis(RDA)showed that TC was positively correlated with TRGs.The addition of different remediation substances alleviated the toxicity of TC on maize physiological characteristics and reduced the TC and TRG residues in the soil-maize system,with biochar being the best remediation substance.These results provide new insights into the effect of biochar on the migration of TC and TRGs from soil to plants.     

丛枝菌根真菌对万寿菊生长、吸镉及生理特性的影响

A pot experiment was carried out to study the effects of three arbuscular mycorrhizal fungi (AMF), including Glomus intraradices, Glomus constrictum and Glomus mosseae, on the growth, root colonization and Cd accumulation of marigold (Tagetes erecta L.) at Cd addition levels of 0, 5 and 50 mg kg-1 in soil. The physiological characteristics, such as chlorophyll content, soluble sugar content, soluble protein content and antioxidant enzyme activity, of Tagetes erecta L. were also investigated. The symbiotic relationship between the marigold plant and arbuscular mycorrhizal fungi was well established under Cd stress. The symbiotic relationship was reffected by the better physiobiochemical parameters of the marigold plants inoculated with the three AMF isolates where the colonization rates in the roots were between 34.3% and 88.8%. Compared with the non-inoculated marigold plants, the shoot and root biomass of the inoculated marigold plants increased by 15.2%- 47.5% and 47.8%-130.1%, respectively, and the Cd concentration and accumulation decreased. The chlorophyll and soluble sugar contents in the mycorrhizal marigold plants increased with Cd addition, indicating that AMF inoculation helped the marigold plants to grow by resisting Cd stress. The antioxidant enzymes reacted differently with the three AMF under Cd stress. For plants inoculated with G. constrictum and G. mosseae, the activities of superoxide dismutase (SOD) and catalase (CAT) increased with increasing Cd addition, but peroxidase (POD) activity decreased with increasing Cd addition. For plants inoculated with G. intraradices, three of the antioxidant enzyme activities were significantly decreased at high levels of Cd addition. Overall, the activities of the three antioxidant enzymes in the plants inoculated with AMF were higher than those of the plants without AMF inoculation under Cd stress. Our results support the view that antioxidant enzymes have a great influence on the biomass of plants, and AMF can improve the capability of reactive oxygen species (ROS) scavenging and reduce Cd concentration in plants to alleviate Tagetes erecta L. from Cd stress.     

尼日利亚两个农业生态区施用氮肥和杂草干扰对热带玉米基因型的影响

Low soil nitrogen (N) and weed infestations are some of the major constraints to maize production in Nigeria.A split-split plot experiment in a randomized complete block design with three replicates was established at two sites with different agroecological zones,Ikenne (Typic Paleudalf) and Shika (Typic Tropaquept),in Nigeria in 2002 and 2003 rainy seasons to investigate the responses of four maize genotypes (Oba super II,Low N pool C2,TZB-SR,and ACR 8328 BN C7) to N fertilizer applied at four rates,0,30,60,and 90 kg N ha^-1,and three weed pressure treatments,no weed pressure (weekly weeding),low weed pressure (inter-row weekly weeding),and high weed pressure (no weeding throughout the growing season).Growth and yield parameters of maize and weeds were taken at flwering and harvest.The results indicated that there was a significant reduction in maize leaf area,leaf area index,and photosynthetically active radiation due to weed interference at both sites.The application of nitrogen at 90 kg N ha^-1 significantly increased maize leaf area.Reductions in maize growth and yield at flowering and harvest were significant due to weed interference at both Ikenne and Shika,thus showing that the reductions in maize growth and yield due to weed interference were not ecological zone specific even though weed species and their seed banks may differ.Ameliorative management options could thus be the same in the two agroecological zones.Application of 90 kg N ha^-1 led to a significant increase in maize grain yield at Shika while there was no fertilizer effect at Ikenne on grain yield.There was no significant difference between 60 and 90 kg N ha^-1,suggesting that 60 kg N ha^-1 could be a possible replacement for the higher fertilizer rate at least for the identified maize genotypes.Low weed pressure treatment led to 26% and 35% reductions in maize grain yield at Ikenne and Shika,respectively,while 22% and 51 % reductions,respectively,were observed due to high weed pressure.Generally,maize grain yield was higher at Ikenne than Shika.The maize genotypes Low N pool C2 and ACR 8328 BN C7 performed better than the other genotypes at Ikenne while the maize genotype Oba super II had the best performance at harvest at Shika.Application of nitrogen increased weed biomass at flowering at Ikenne.The maize grain yield was highest in the N-efficient genotypes,Oba super II and Low N pool C2;the susceptible genotype TZB-SR had the least yield at Shika.There existed a negative and significant correlation between maize grain yield and weed biomass at both sites.     

Effects of Exogenous Nitric Oxide and 24-Epibrassinolide on the Physiological Characteristics of Peanut Seedlings Under Cadmium Stress

Cadmium(Cd) is highly toxic to plants, animals, and humans. Limited information is available on the role of nitric oxide(NO)and/or 24-epibrassinolide(EBR) in response of plants to Cd stress. In this study, a hydroponic experiment was performed to investigate the effects of NO and/or EBR on peanut plants subjected to Cd stress(200 μmol L~(-1)) with sodium nitroprusside(SNP, an exogenous NO donor)(250 μmol L~(-1)) and/or EBR(0.1 μmol L~(-1)) addition. The results showed that Cd exposure inhibited plant growth, and this stress was alleviated by exogenous NO or EBR, and especially the combination of the two. Treatment with Cd inhibited the growth of peanut seedlings, decreased chlorophyll content, and significantly increased the Cd concentration in plants. Furthermore, the concentration of reactive oxygen species(ROS) markedly increased in peanut seedlings under Cd stress, resulting in the accumulation of malondialdehyde(MDA) and proline in leaves and roots. Under Cd stress, applications of SNP, EBR, and especially the two in combination significantly reduced the translocation of Cd from roots to leaves, increased the chlorophyll content, decreased the concentrations of ROS, MDA, and proline, and significantly enhanced the activities of superoxide dismutase(SOD), peroxidase(POD), and catalase(CAT) in peanut seedlings. Exogenous NO and/or EBR also stimulated the activities of nitrate reductase(NR)and nitric oxide synthase(NOS) and increased the contents of antioxidants, such as ascorbic acid(AsA) and reduced glutathione(GSH). Furthermore, exogenous NO and/or EBR enhanced Cd accumulation in the cell wall and thus decreased Cd distribution in the organelles in the roots. The concentrations of calcium(Ca), iron(Fe), magnesium(Mg), and zinc(Zn) were also regulated by exogenous NO or EBR, and especially by the two in combination. These results indicated that SNP and EBR, alone and particularly in combination, can mitigate the negative effects of Cd stress in peanut plants.     

K高效和K低效基因型水稻Na和K的吸收和分布与水稻生长及体内K利用率之间的关系

A pot experiment with two rice (Oriza sativa L.) genotypes differing in internal potassium use efficiency (IKUE) was conducted under different sodium (Na) and potassium (K) levels. Adding NaCl at a proper level enhanced rice vegetative growth and increased grain yield and IKUE under low potassium. Addition of higher rate of NaCl had a negative effect on the growth of the K-efficient rice genotype, but did not for the K-inefficient genotype. Under low-K stress, higher NaCl decreased IKUE of the K-efficient rice genotype but increased IKUE for the K-inefficient genotype. At tillering stage and under low-K stress, adding NaCl increased K and Na contents and decreased the ratio of K/Na for both genotypes. At harvesting stage under low-K stress, adding NaCl increased K and Na contents and K/Na ratio for the K-efficient genotype but decreased the K/Na ratio for the K-inefficient genotype. The accumulated Na was mostly deposited in the roots and sheaths. At tillering stage, the K and Na contents and the K/Na ratios in different parts for both genotypes decreased in the following sequence: K⁺ in sheaths > K⁺ in blades > K⁺ in roots; Na⁺ in roots > Na⁺ in sheaths > Na⁺ in blades; and K/Na in sheaths >> K/Na in roots. The K-efficient genotype had a lower K/Na ratio in roots and sheaths than the K-inefficient genotype under low-K stress. At harvesting stage, K and Na contents in grains were not affected, whereas K/Na ratio in the rice straws was increased for the K-efficient genotype but decreased for the K-inefficient genotype by Na addition. However, this was not the case under K sufficient condition.     

深色有隔内生真菌柱孢顶囊壳对玉米幼苗生长、光合作用及耐铅能力的影响

Dark septate endophytic (DSE) fungi are ubiquitous and cosmopolitan,and occur widely in association with plants in heavy metal stress environment.However,little is known about the effect of inoculation with DSE fungi on the host plant under heavy metal stress.In this study,Gaeumannomyces cylindrosporus,which was isolated from Pb-Zn mine tailings in China and had been proven to have high Pb tolerance,was inoculated onto the roots of maize (Zea mays L.) seedlings to study the effect of DSE on plant growth,photosynthesis,and the translocation and accumulation of Pb in plant under stress of different Pb concentrations.The growth indicators (height,basal diameter,root length,and biomass) of maize were detected.Chlorophyll content,photosynthetic characteristics (net photosynthetic rate,transpiration rate,stomatal conductance,and intercellular CO2 concentration),and chlorophyll fluorescence parameters in leaves of the inoculated and non-inoculated maize were also determined.Inoculation with G.cylindrosporus significantly increased height,basal diameter,root length,and biomass of maize seedlings under Pb stress.Colonization of G.cylindrosporus improved the efficiency of photosynthesis and altered the translocation and accumulation of Pb in the plants.Although inoculation with G.cylindrosporus increased Pb accumulation in host plants in comparison to non-inoculated plants,the translocation factor of Pb in plant body was significantly decreased.The results indicated that Pb was accumulated mainly in the root system of maize and the phytotoxicity of Pb to the aerial part of the plant was alleviated.The improvement of efficiency of photosynthesis and the decrease of translocation factor of Pb,caused by DSE fungal colonization,were efficient strategies to improve Pb tolerance of host plants.     

污泥加石灰后作为肥料用于玉米生长中施肥研究

The use of sewage sludge on agricultural land provides an alternative for its disposal. Therefore, the aim of the present study was to evaluate the feasibility of using industrial sewage sludge produced in Pakistan, as an agricultural fertilizer. The agricultural soil amended with 250 g kg^-1 sewage sludge with or without lime treatment was used for the growth of the common local grain crop, maize （Zea maize）. The mobility of the trace and toxic metals in the sludge samples was assessed by applying a modified BCR sequential extraction procedure. The single extraction procedure was comprised of the application of a mild extractant （CaCl2） and water, for the estimation of the proportion of easily soluble metal fractions. To check the precision of the analytical results, the concentrations of trace and toxic metals in every step of the sequential extraction procedure were summed up and compared with total metal concentrations. The plant-available metal contents, as indicated by the deionized water and 0.01 mol L^-1 CaCl2 solution extraction fractions and the exchangeable fraction of the sequential extraction, decreased significantly （P 〈 0.05） with lime application because of the reduced metal availability at a higher pH, except in the cases of Cd and Cu, whose mobility was slightly increased. Sludge amendment enhanced the dry weight yield of maize and the increase was more obvious for the soil with lime treatment. Liming the sewage sludge reduced the trace and toxic metal contents in the grain tissues, except Cu and Cd, which were below the permissible limits of these metals. The present experiment demonstrates that liming was an important factor in facilitating the growth of maize in sludge-amended soil.     

大麦过氧化物体膜上的抗坏血酸过氧化物酶拟南芥的耐盐机制

Ascorbate peroxidases （APX）, localized in the cytosol, peroxisome, mitochondria, and chloroplasts of plant cells, catalyze the reduction of H2O2 to water by using ascorbic acid as the specific electron donor. To determine the role of peroxisomal type ascorbate peroxidase （pAPX）, an antioxidant enzyme, in protection against salt-induced oxidative stress, transgenic Arabidopsis thaliana plant carrying a pAPX gene （HvAPX1） from barley （Hordeum vulgate L.） was analyzed. The transgenic line pAPX3 was found to be more tolerant to salt stress than the wild type. Irrespective of salt stress, there were no significant differences in Na^＋, K^＋, Ca^2＋, and Mg^2＋ contents and the ratio of K^＋ to Na^＋ between pAPX3 and the wild type. Clearly, the salt tolerance in pAPX3 was not due to the maintenance and reestablishment of cellular ion homeostasis. However, the degree of H2O2 and lipid peroxidation （measured as the levels of malondialdehyde） accumulation under salt stress was higher in the wild type than in pAPX3. The mechanism of salt tolerance in transgenic pAPX3 can thus be explained by reduction of oxidative stress injury. Under all conditions tested, activities of superoxide, glutathione reductase, and catalase were not significantly different between pAPX3 and the wild type. In contrast, the activity of APX was significantly higher in the transgenic plant than in wild type under salt stress. These results suggested that in higher plants, HvAPX1 played an important role in salt tolerance and was a candidate gene for developing salttolerant crop plants.     

施用污泥后石灰性土壤中铜、锌、镉的植物有效性

The toxicity of trace elements (TEs), such as copper (Cu), zinc (Zn), and cadmium (Cd), often restrict land application of sewage sludge (SS) and there was little information about soil-plant transfer of TEs in SS from field experiments in China. In this study pot and field experiments were carried out for 2 years to investigate the phytoavailability of TEs in calcareous soils amended with SS. The results of the pot experiment showed that the phytoavailability of Zn and Cu in the SS was equal to 53.4%-80.9% and 54.8%-91.1% of corresponding water-soluble metal salts, respectively. The results from the field experiment showed that the contents of total Zn, Cu, and Cd in the soils increased linearly with SS application rates. With increasing SS application rates, the contents of Zn and Cu in the wheat grains initially increased and then reached a plateau, while there was no significant change of Cd content in the maize grains. The bioconcentration factors of the metals in the grains of wheat and maize were found to be in the order of Zn > Cu > Cd, but for the straw the order was Cd > Cu > Zn. It was also found that wheat grains could accumulate more metals compared with maize grains. The results will be helpful in developing the critical loads of sewage sludge applied to calcareous soils.     

Agronomic evaluation of Herbaspirillum seropedicae strain ZAE94 as an inoculant to improve maize yield in Brazil

Diazotrophic bacteria applied as a seed inoculant can improve the grain yield of several crops including maize. The current study aimed to test the agronomic efficiency and contribution of biological nitrogen fixation(BNF) of the endophytic diazotroph Herbaspirillum seropedicae strain ZAE94 to maize under field conditions. Eighteen field assays were conducted in four different locations during consecutive years on two hybrids and two varieties of maize in a random block design with four replicates using a peat-based inoculant. The inoculant containing the ZAE94 strain was applied without nitrogen(N)fertilization or with 40 kg N ha~(-1) and was compared to the application of 40 and 80 kg N ha~(-1) without inoculation. Crop productivity and N accumulation in the grain were evaluated in addition to ~(15)N natural abundance(δ~(15)N) to evaluate BNF in the treatments without N fertilization. Fertilization at 40 kg N ha~(-1) plus bacterial inoculation produced crop yields similar to the treatment with 80 kg N ha~(-1) and increased grain N content, especially in the off-season with 40 kg N ha~(-1). The inoculation treatments showed lower δ~(15)N values than the non-inoculated treatments, which was most evident in the off-season. The BNF contributed about 30% of N accumulated in plants inoculated with ZAE94. On average, 64% of the N fertilized plots showed an increase of the parameters evaluated in the inoculated treatments, compared with the control. Inoculation also increased root length, root volume, and leaf area, and these parameters were positively correlated with plant weight using a hydroponic assay. This study revealed that the application of H. seropedicae inoculant increased the amount of N in plants owing to BNF, and there is a better chance of yield response to inoculation under low N fertilizer application in the off-season.     

硒对铬胁迫下茄子生理特性及铬吸收的影响

为探讨硒对茄子中铬胁迫的缓解作用,采用土培盆栽方式,研究了不同铬胁迫水平下,施加不同浓度的硒对茄子生长、生理特性及铬吸收的影响。结果表明,随着铬浓度增加,单一铬处理植株生长明显受到抑制,铬毒害表现为株高、根长、根、茎、叶干重及叶绿素含量受抑制。随着铬浓度的增加,叶片中的叶绿素和可溶性蛋白呈下降趋势,丙二醛(MDA)含量呈上升趋势,超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性呈先上升后下降的趋势。铬硒混合处理结果表明硒有减轻茄子铬毒害的作用,不同浓度的铬胁迫下,施加不同浓度的硒缓解效果不同,10,20,40,80mg/kg的铬处理下,分别施用12,24,48,48mg/kg的硒缓解效果较好,茄子的株高、根长、生物量均有所增加,叶绿素含量、可溶性蛋白含量显著提高,丙二醛含量和植株体内铬的积累降低。     

Subcellular distribution and chemical forms of chromium in rice plants suffering from different levels of chromium toxicity

The subcellular distribution and chemical forms of different heavy metals in rice are correlated with their bio‐toxicity. An experiment was conducted to investigate the subcellular distribution and chemical forms of chromium (Cr) in two rice genotypes (Oryza sativa L. cv. Xiushui 113 and cv. Dan K5) differing in Cr accumulation, to understand the mechanisms of Cr toxicity and resistance in rice plants. The results show that Cr in the roots of rice plants exposed to Cr stress was mainly localized in cell walls, whereas Cr in leaves and stems was mainly present in both cell walls and vacuoles, suggesting that both compartments act as important protective barriers against Cr toxicity in rice plants. Although Cr ions in all plant tissues exist predominantly in the forms extracted by 80% ethanol and distilled water, the amount of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues was significantly increased under the highest Cr level (100 μM Cr) compared to the plants grown under lower Cr levels. These results indicate that excess Cr accumulated in rice plants under Cr stress is bound to undissolved or low‐bioavailable compounds, such as undissolved phosphate and oxalate, being beneficial for rice plants to alleviate Cr toxicity. In addition, under the highest Cr level (100 μM), Dan K5 had a higher percentage of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues compared to Xiushui 113 in both stems and leaves, indicating that more Cr ions in shoots of Dan K5 were bound to undissolved or low‐bioavailable compounds, in comparison with those of Xiushui 113. It is evident that the low bioavailability of Cr in the shoots of Dan K5 is related to a high Cr accumulation.     

外源24-表油菜素内酯对NaCl胁迫下桑树幼苗的缓解效应

为探究施加外源24-表油菜素内酯(EBR)对桑树耐盐性的影响,以桑品种桂桑优12为材料进行盆栽试验,在200 mmol·L^-1 NaCl胁迫下,研究外施不同浓度(0.01、0.10、1.00 μmol·L^-1)EBR对盐胁迫下桑树幼苗质量、根系特征、光合色素含量、活性氧(ROS)水平、丙二醛(MDA)含量、相对电导率、抗氧化酶活性和渗透调节物质含量等生理指标的影响。结果表明,与单一NaCl胁迫相比,外源添加0.10 μmol·L^-1EBR后,桑树幼苗地上鲜质量和干质量、主根长、总根长、根表面积、根平均直径、根总体积、叶绿素和类胡萝卜素含量均提高,叶片与根中产生羟基自由基(·OH)能力、产生超氧阴离子自由基($\text{O}_{2}^{\frac{{}}{\cdot }}$)活力、过氧化氢(H₂O₂)含量降低;叶片与根中的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性升高;脯氨酸、可溶性蛋白和可溶性糖含量增加;相对电导率和MDA含量降低。其中地下部鲜质量和根体积是盐胁迫下的1.56和1.57倍,叶片中CAT活性和可溶性糖含量达到盐胁迫下的1.57和1.68倍。本研究为揭示外施油菜素内酯增强桑树耐盐性的生理调控机制提供了参考依据。     

铬在芹菜中的累积、亚细胞分布及化学形态分析

采用盆栽试验,研究了Cr6+处理对美国西芹和日本西芹铬总累积量及器官中铬亚细胞分布和化学形态的影响。结果表明,对照处理（0mg·kg-1 Cr6+）芹菜根部和地上部铬在亚细胞中分布为：F3（可溶部分）＞F2（细胞器及膜部分）＞F1（细胞壁及残渣）;40mg·kg-1Cr6+处理为：F1＞F3＞F2,细胞壁(F1)是铬在芹菜细胞内的主要结合位点。芹菜根部和地上部铬化学形态以醋酸提取态占优势,NaCl和HCl提取态也占较大比例。60mg·kg-1Cr6+处理下2个品种芹菜地上部和根部铬含量均极显著增加（P＜001）;相同浓度铬处理下,铬含量和总积累量为：根＞叶＞茎,日本西芹各器官中铬含量和总累积量相对高于美国西芹。2个芹菜品种对铬的吸收均以根部为主要滞留器官,以细胞壁部位为主要的亚细胞分布区域,铬在芹菜体内以难溶性磷酸盐类、蛋白结合态类和草酸盐类为主要化学形态存在形式。     

不同基因型玉米品种对Pb的富集特征

为了研究不同基因型玉米品种对Pb的富集特征,选用2个Pb低富集玉米品种(曲辰11号、曲辰3号)和2个Pb高富集玉米品种(靖丰8号、旭玉1446),开展Pb胁迫(2 000 mg·kg-1)下的大田试验,研究了玉米植株生物量的变化、各部位Pb含量、Pb总吸收量、富集与转运规律、土壤p H值及有效态Pb含量。结果表明:(1)与对照相比,Pb胁迫导致4个玉米品种根、茎、叶和籽粒生物量不同程度的下降,总生物量下降9.65%~20.46%,但低富集玉米品种生物量的下降程度小于高富集玉米品种;(2)玉米各部位的Pb含量分配规律为根叶茎籽粒,分别为95.39~121.02、25.56~43.21、14.06~25.41、2.52~5.38 mg·kg-1;低富集玉米品种根的Pb含量高于高富集玉米品种,而茎、叶和籽粒的Pb含量低于高富集玉米品种;玉米植株对Pb的总吸收量为4.46~7.94 mg·株-1,低富集玉米品种植株的Pb总吸收量显著低于高富集玉米品种;(3)不同基因型玉米品种对Pb的富集系数和转运系数均小于1,表现为低富集玉米品种低于高富集玉米品种;(4)不同基因型玉米品种土壤p H值为6.60~6.82,且低富集玉米品种显著高于高富集玉米品种,土壤有效态Pb含量范围为969.86~1 116.15 mg·kg-1。     

Uptake and apoplastic retention of EDTA‐ and phytosiderophore‐chelated chromium(III) in maize

Increasing the mobilization and root uptake of chromium (Cr) by synthetic and plant‐borne chelators might be relevant for the design of phytoremediation strategies on Cr‐contaminated sites. Short‐term uptake studies in maize roots supplied with ⁵¹CrCl₃ or ⁵¹Cr(III)‐EDTA led to higher apoplastic Cr contents in plant roots supplied with ⁵¹CrCl₃ and in Fe‐sufficient plants relative to Fe‐deficient plants, indicating that Fe stimulated co‐precipitation of Cr. Concentration‐dependent retention of Cr in a methanol:chloroform‐treated cell‐wall fraction was still saturable and in agreement with the predicted tendency of Cr(III) to precipitate as Cr(OH)₃. To investigate a possible stimulation of Cr(III) uptake by phytosiderophores, Fe‐deficient maize roots were exposed for 6 d to Cr(III)‐EDTA or Cr(III)‐DMA (2'‐deoxymugineic acid). Relative to plants without Cr supply, the supply of both chelated Cr species in a subtoxic concentration of 1 µM resulted in alleviation of Fe deficiency–induced chlorosis and higher Cr accumulation. Long‐term Cr accumulation from Cr(III)‐DMA was similar to that from Cr(III)‐EDTA, and Cr uptake from both chelates was not altered in the maize mutant ys1, which is defective in metal‐phytosiderophore uptake. We therefore conclude that phytosiderophores increase Cr solubility similar to synthetic chelators like EDTA, but do not additionally contribute to Cr(III) uptake from Cr‐contaminated sites.     

Factors Controlling the Spatial Variability of Copper in Topsoils of the Northeastern Region of the Iberian Peninsula, Spain

Aerosol samples were collected at Catania (Italy), from 16 March to 13 June 2005. The sampling was performed using a low pressure five-stage Berner cascade impactor. The samples were analysed for total aerosol mass, Water Soluble Organic Carbon (WSOC), Total Carbon (TC) and main inorganic ionic species. The Water-Insoluble Carbon (WINC) was derived by the difference: TC-WSOC. The samples share some common features: ammonium sulphate and carbon-containing species (both soluble and insoluble) are the largest contributors of fine particle mass, while coarse particles essentially consist of sea-salt, sodium nitrate and unaccounted PM (probably crustal material). The WINC/WSOC ratio decreases from the smallest size range to the large accumulation mode range (0.42–1.2 μm), while the ${\text{nssSO}}^{ = }_{4} $ and $ {\text{NH}}^{ + }_{4} $ contribution rises. The water-insoluble carbonaceous matter is the dominant component in the smallest particles (0.05–0.14 μm). We identified four different aerosol types, corresponding to different sources, contributing to the total particles load of the investigated urban environment: vehicular traffic, producing primary carbonaceous insoluble particles, secondary aerosols, dominating the composition of accumulation mode particles, and marine particles and mineral dust (both important components of the coarse aerosol fraction).     

生物炭和其他有机土壤改良剂对Ustoxic Quartzipsamment土壤上植物养分有效性的影响

A sandy soil, Nampong soil(classified as Ustoxic Quartzipsamment), was incubated under controlled condition i) to compare the mineralization of major plant nutrients derived from different types of biochars and other organic soil amendments; ii) to examine their effects on soil properties and plant nutrient availability; and iii) to evaluate the plant nutrient losses in leachate from the rooting zone of soil incorporated with the different amendments. The experiment was arranged in a completely randomized design with 3 replications.Five treatments of soil amendments used were cassava stem base biochar(CSB), rice husk biochar(RHB), chicken manure(CM),compost(CP), and no amendment application(control). The RHB treatment released the highest amounts of mineralized NO-3-N,available P and K(2.30–17.26, 5.50–42.90 and 43.00–187.63 mg kg-1, respectively) while the CM treatment releasing the highest NH+4-N in the range of 1.86–53.67 mg kg-1. The CSB and RHB treatments showed better continuity of mineralization of nutrients than the treatments of CM and CP, particularly in the case of the CSB treatment. In the soil column incubation experiment, the amounts of NH+4-N and NO-3-N in all treatments barely changed on Day 1 to Day 30 of incubation and then the amounts increased markedly on Day 60. On Day 60, the RHB treatment contained a very high amount of NO-3-N( 250 mg kg-1). This suggests that N would become more available 30 d after the incorporation. The CM treatment gave the highest amounts of organic matter and available P in the ranges of 4.64–8.94 g kg-1and 14.41–36.33 mg kg-1, respectively, during the 60-d column incubation. The CSB treatment tended to have higher available K throughout the measuring period. The NO-3-N was leached from the soil column quite quickly on Day 1 of incubation while the loss of NH+4-N decreased slightly from Day 1 until the end of the measurement. The amounts of P and K losses varied with the type of soil amendments, and the pattern of the loss was irregular.     

低氮胁迫对不同光皮桦基因型苗期生长及生理生化特征的影响

为探讨低氮胁迫对不同基因型光皮桦(Betula luminifera)生长及生理生化响应特性,本研究采用裂区设计,以光皮桦G49-3、G50-1和优3组培苗为材料,通过水培培养研究其在正常供氮(CK,15 mmol·L^-1 $NO_{3}^{-}$)和低氮胁迫(LN,0.03 mmol·L^-1 $NO_{3}^{-}$)条件下的苗期生长及生理生化响应。结果表明,低氮胁迫处理21 d后,3个光皮桦基因型的叶绿素含量、株高、地上部干重、地上氮含量和氮积累量均显著降低,其中G49-3降幅最大,G50-1降幅最小;3个光皮桦基因型根冠比、根系总根长、总表面积和平均直径均增加;叶片过氧化物酶(POD)、超氧化物岐化酶(SOD)和硝酸还原酶(NR)活性降低,G50-1降幅最低。实时荧光定量PCR(RT-qPCR)分析表明,相较于CK,低氮胁迫处理下3个光皮桦基因型叶和根中NRT1.1和NRT1.2均下调表达,而NRT2.1在根中上调表达,说明根中NRT2.1在低氮胁迫下的硝酸盐转运过程中发挥主要作用。综合隶属函数分析显示,G50-1平均隶属函数值(0.73)高于优3(0.44)和G49-3(0.34),表明G50-1耐低氮能力最强,而G49-3对低氮胁迫最敏感。本研究结果揭示了光皮桦响应低氮环境的生理机制,同时表明运用常规遗传改良手段筛选和培育耐低氮、氮高效利用的光皮桦良种是可行的。