宁南山区典型植物根际与非根际土壤微生物功能多样性

选择宁南山区9种典型植物的根际与非根际土壤为研究对象,采用Biolog方法对土壤微生物功能多样性进行了研究。结果表明:9种不同植物根际土壤与非根际土壤的微生物活性(AWCD)、微生物多样性指数和微生物均匀度指数均存在明显差异;除冰草外,其他各种植物的根际土壤的微生物活性AWCD、微生物多样性指数和微生物均匀度指数均比非根际土壤的高;9种典型植物根际土壤微生物主要碳源利用类型是羧酸类和氨基酸类,非根际土壤微生物主要碳源利用类型是羧酸类、胺类、氨基酸类;微生物活性、微生物多样性指数和微生物均匀度指数两两之间均达到了极显著相关,与土壤化学性质各指标之间均未达到显著相关水平。     

独山子区优势草本植物根际与非根际土壤微生物功能多样性

以独山子区3种优势草本植物的根际与非根际土壤为研究对象,采用Biolog-ECO微平板法对土壤微生物功能多样性进行了研究。结果表明:3种不同植物根际与非根际土壤微生物代谢活性(AWCD)、丰富度指数Shannon(H)和均匀度指数Mc Intosh(U)均存在不同差异,且博乐蒿根际土壤微生物功能多样性均优于非根际土壤及其他两种植物;根际土壤微生物对糖类、脂类、酸类和胺类碳源物质比较敏感,非根际土壤微生物敏感于酸类、氨基酸类以及糖类碳源,根际土壤微生物对碳源的利用能力更强,且不同植物根际环境微生物碳源利用特征不同;微生物活性、丰富度指数和微生物均匀度指数与土壤pH值、SOM、AP和NO-3-N存在显著正相关(P0.05);博乐蒿根际土壤养分含量与微生物活性均较高,对环境的适应性更强,在独山子区生态环境管理与建设中可对其进行关注。     

Presence and oxidation of amino acids in rhizosphere and non-rhizosphere soil

Manometric studies were carried out on the respiratory activity of different rhizosphere and non-rhizosphere soils to follow quantitatively the over-all microbial activity in the rhizosphere soil as affected by the species and growth phase of plant. Oxygen consumption was distinctly greater in rhizosphere soils as compared to that in non-rhizosphere soils. The difference between oxygen consumption by rhizosphere and non-rhizosphere soils changed with the course of plant growth and it was not the same in different plants. This difference in oxygen consumption might be a measure of the amount of available oxidizable substrate in the rhizosphere. A rhizosphere sample had greater diversity as well as higher concentration of free amino acids than a non-rhizosphere sample of the same soil. Bacterial counts pointed to preferential stimulation in the rhizosphere of bacteria requiring individual amino acids. amino acids, such as glycine, alanine, asparsic acid of tyrosine were oxidized more rapidly in rhizosphere than in non-rhizosphere soil, but the extsent of oxidation for each of the amino acids studied did not differ. The amount of oxygen consumed during oxidation of alanine, aspartic acid or tyrosine was about one-half of the total amount necessary for complete oxidation. With glycine a higher extent of oxidation (60%) was observed. These extents of oxidation of glycine and aspartic acid did not change on investigation at two different phases of plant growth.     

异裂菊属根际微生物群落结构及功能多样性

异裂菊属是广西喀斯特石山区典型的特有属,根际微生物是其能否有效吸收、有效利用土壤养分和适应石山恶劣土壤环境的最直接表征之一。该研究采用DGGE和Biolog两种方法对异裂菊属植物根际和非根际微生物多样性进行了研究。结果表明:(1)异裂菊属5个种根际pH、碱解氮等9个养分含量都高于非根际。(2)5个种的根际、非根际存在2个共有细菌类群,但在数量上存在差异,3个种的根际条带小于非根际;5个种的根际、非根际微生物群落较为相似,较易聚在一起。(3)绢叶异裂菊根际微生物对碳源利用能力最强,凹脉异裂菊非根际最弱,其他对碳源的利用能力较接近;异裂菊属种根际微生物利用碳源的能力都高于非根际,根际微生物多样性指数均高于非根际,优势度指数与非根际基本相同或略高于非根际,丰富度和均匀度指数与优势度指数规律相似;异裂菊属根际、非根际微生物利用的碳源主要是糖类、羧酸类和氨基酸类化合物,4个种根际微生物利用碳源的能力高于非根际。(4)阳离子交换量、黏粒含量百分率和碱解氮是影响异裂菊属根际微生物碳源利用模式的最重要因子。总体来说,土壤理化性质对异裂菊属植物根际微生物群落多样性具有重要影响,异裂菊属通过分泌羧酸、糖等多类化合物提高了根际微生物的活性,进而有效地提高了根际肥力水平。     

内蒙古草原典型植物对土壤微生物群落的影响

为了分析内蒙古草原不同植物物种对土壤微生物群落的影响, 采用实时荧光定量PCR (real-time PCR)以及末端限制性片段长度多态性分析(terminal restriction fragment length polymorphism, T-RFLP)等分子生物学技术, 测定了退化-恢复样地上几种典型植物的根际土壤和非根际土壤中细菌和真菌的数量及群落结构。结果表明, 不同植物物种对根际和非根际细菌及根际真菌数量均有显著影响。根际土壤中的细菌和真菌数量普遍高于非根际土壤, 尤其以真菌更为明显。对T-RFLP数据进行多响应置换过程(multi-response permutation procedures, MRPP)分析和主成分分析(principal component analysis, PCA), 结果表明, 大多数物种的根际细菌及真菌的群落结构与非根际有明显差异, 并且所有物种的真菌群落可以按根际和非根际明显分为两大类群。此外, 细菌和真菌群落结构在一定程度上存在按物种聚类的现象, 以细菌较为明显。这些结果揭示了不同植物对土壤微生物群落的影响特征, 对理解内蒙古草原地区退化及恢复过程中植被演替引起的土壤性质和功能的变化有一定的帮助。     

库布齐沙地两种植被恢复类型根际土壤微生物和土壤化学性质比较研究

油蒿(Artemisia ordosica)与中间锦鸡儿(Caragana intermedia)是库布齐沙地分布广泛的优良固沙植被类型,在植被恢复过程中受到关注。以库布齐沙地自然恢复的油蒿群落与人工种植的中间锦鸡儿群落为研究对象,以流动沙地为对照,采用野外调查、室内生化实验与统计分析相结合的方法,分析两种植被恢复类型根际与非根际土壤微生物、土壤化学性质的差异,研究土壤微生物与土壤化学性质间的相关关系,并运用综合指数法评价两种植被恢复类型对土壤生态系统的恢复效果,为库布齐沙地植被恢复与重建提供科学依据。主要结论如下:(1)与流沙对照相比,两种植被恢复类型根际、非根际土壤微生物数量、微生物生物量碳、氮含量均有不同程度的提高,其中,自然恢复的油蒿群落根际土壤微生物总数、细菌数量、微生物量碳和氮含量均显著高于中间锦鸡儿根际,真菌和放线菌数量分布表现为中间锦鸡儿油蒿;(2)两种植被恢复类型根际、非根际土壤有机质、全氮、全磷、速效氮、速效钾含量均比流动沙地有不同程度地提高,其中,油蒿根际、非根际土壤有机质、全氮、速效氮含量显著高于中间锦鸡儿;(3)影响油蒿和中间锦鸡儿群落土壤微生物数量、生物量碳和氮的土壤因子是有机质、p H值、全氮、速效氮、速效钾、速效磷,其中,对两种植被恢复类型土壤微生物数量和生物量有正向促进作用的主要因子是土壤有机质、速效钾和全氮含量;(4)运用综合指数法计算出基于14个土壤指标的土壤质量综合指数(SQI),SQI值排序为:油蒿根际中间锦鸡儿根际油蒿非根际中间锦鸡儿非根际流沙对照。自然恢复的油蒿群落对土壤质量的改良效果显著优于人工种植的中间锦鸡儿群落,是库布齐沙地生态恢复的适合途径之一。     

荒漠草原不同植物根际与非根际土壤养分及微生物量分布特征

通过对宁夏荒漠草原6种地带性优势物种长芒草、蒙古冰草、甘草、牛心朴子、黑沙蒿和苦豆子植物根际与非根际土壤养分和微生物量分布特征进行研究,探讨不同植物根际养分的富集的相关性和差异性。研究结果表明:6种植物根际土壤养分和微生物量均表现出明显的富集效应,根际富集率大小依次为菊科(黑沙蒿)豆科(苦豆子、甘草)禾本科(长芒草、蒙古冰草)萝藦科(牛心朴子);全磷(TP)在根际和非根际中无显著差异(P0.05),其它土壤养分及理化指标在根际中均表现出显著富集(P0.05),土壤养分中以有机碳(SOC)的富集作用最为明显;土壤有效态养分较全量养分对植物根际微小的变化响应更为灵敏;不同荒漠植物根际与非根际SOC与全氮(TN)呈极显著线性关系(P0.01),TN与碱解氮之间呈极显著线性关系(P0.01),TP与有效磷(AP)没有显著的相关性(P0.05)。荒漠植物土壤有效养分在根际存在一定的富集,灌木和豆科植物的根际效应的大于禾本科植物,它们通过降低根际pH值可以提高根际养分,有利于在脆弱环境下对土壤养分的有效利用。     

根际效应对大豆田土壤线虫群落组成及多样性的影响

根际作为重要的环境界面是植物与环境之间物质能量交换的场所,关于根际效应的研究已成为土壤生态学的新兴热点领域,然而有关大豆根际效应对土壤动物多样性影响的研究报道并不多见。在三江平原选择连续耕作15a的大豆田,对大豆根际区与非根际区土壤线虫群落结构组成进行了对比分析。结果表明:大豆根际区土壤线虫总数、辛普森多样性指数(Dom)显著高于非根际区,根际区的物种数(S)、物种丰富度指数(SR)显著低于非根际区。说明大豆根际效应增加土壤线虫的丰度,但降低了线虫群落结构的复杂性。大豆根际区植物寄生线虫(PP)、食真菌线虫(FF)和食细菌线虫(BF)数量显著高于非根际区,而PP类群的比例在根际区却显著低于非根际区。这一研究结果表明食微线虫(FF和BF)类群在大豆根际区的比例增加更显著。食真菌与食细菌线虫数量比值(F/B)指示大豆根际区细菌生物量相对高于真菌生物量。研究结果丰富了农田土壤线虫多样性的研究内容,并为我国东北大豆田线虫病害的防治及定制相应的农业管理措施提供参考。     

施硒对水稻土壤硒有效性的影响

硒在华南稻区酸性土壤中极易被固定使其有效性较低.本研究旨在通过盆栽试验,探明施用硒肥对水稻根际和非根际土壤硒有效性的影响.结果表明: 施硒能提高水稻产量,增加籽粒硒含量;水稻根际土壤中水溶态硒、交换态硒、铁锰氧化物结合态硒、有机物-硫化物结合态硒和残渣态硒含量均低于非根际土壤.各施硒处理之间,根际和非根际土壤中硒的迁移系数没有显著差异;施硒对根和叶片之间硒的迁移系数也没有显著影响,但是施硒提高了叶片和籽粒之间硒的迁移系数.施用0.5 mg·kg^-1硒增加了水稻根系有机酸的分泌,而施用1.0、5.0 mg·kg^-1硒则降低了有机酸的分泌.根系有机酸的分泌对根际土壤pH值影响不大,根际土壤pH值反而高于非根际土壤,但施硒显著降低了根际土壤pH值.随着施硒水平的提高,根际土壤黏土矿物(高岭石)的红外吸收光谱不断增强.施入土壤中的硒多转化为水稻难以吸收利用的形态,且不易向根际移动.根系分泌的有机酸也并不是通过影响土壤pH值来提高土壤硒的有效性.     

典型喀斯特峰丛洼地不同植被恢复对土壤养分含量和微生物多样性的影响

以桂西北典型喀斯特峰丛洼地植被恢复过程中草丛、灌丛、次生林、原生林4个植被恢复阶段为研究对象,通过测定优势种的根际与非根际的土壤p H、养分含量及微生物多样性,探讨不同恢复阶段根际土壤养分的富集效应及土壤微生物多样性的变化特征。研究结果表明:(1)4个恢复阶段的根际与非根际土壤养分均呈现显著差异;土壤有效态养分较全量养分对植物根际微小的变化响应更为灵敏;大多数养分表现出明显的富集效应,AP和AK在原生林的富集率明显高于其他恢复阶段;(2)4个恢复阶段细菌Shannon-Wiener指数(H)、丰富度指数(S)均高于真菌,根际土壤细菌与真菌Shannon-Wiener指数(H)、丰富度指数(S)与Pielou均匀度(EH)都高于非根际土壤;(3)4个恢复阶段土壤TN分别与p H、SOC、AN呈极显著正相关(P0.01),磷素、钾素与土壤微生物多样性呈显著相关(P0.05)。可研究结果为西南喀斯特脆弱区土壤生态功能恢复与植被恢复重建提供科学依据。     

高寒草甸黄帚橐吾种群根际/非根际土壤可培养微生物群落特征

黄帚橐吾（Ligularia virgaurea）是高寒草甸常见的毒杂草,被认为是指示一个地区草地植被退化的重要物种,研究其根际/非根际土壤微生物在不同海拔梯度上的群落特征具有重要意义。以甘南州高寒草甸不同海拔梯度黄帚橐吾根际/非根际土壤可培养微生物为研究对象,采用稀释涂布平板法和最大可能数法（MPN）测定了土壤微生物的数量及土壤理化因子的变化。结果表明：细菌在微生物总数中占比最大,根际微生物数量随海拔升高呈先增加后减小的变化,非根际则表现为递增的趋势,微生物功能群在根际和非根际土壤中均逐渐增加;根际土壤的微生物和功能群数量均高于非根际土壤。RDA分析发现,土壤温度、有机碳、电导率、pH、全氮、全磷、速效氮及脲酶对根际/非根际土壤微生物数量及功能群变化影响较大。通径分析可知：根际土壤中,细菌和真菌受速效氮和有机碳影响较大,放线菌主要受土壤温度和电导率的影响;根际土壤固氮菌和氨化细菌决策系数速效氮 > 有机碳 > 全氮;根际和非根际土壤中硝化细菌的影响因子各不相同,根际土壤决策系数最大和最小分别为全磷和全氮,非根际则是pH和脲酶。     

毛竹根际与非根际土壤重金属、理化性质及酶活性特征

于2014年2月至2015年1月在浙江省衢州市铅锌矿附近毛竹林地采集土样,对土壤重金属含量、pH以及土壤酶活性等的动态变化特征进行了研究。结果表明:根际土与非根际土的p H在1a中变化均不明显,且变化范围都处在4.50—4.85之间;非根际土的土壤含水率大于根际土,两者的变化幅度较大,最低值均出现在6月和10月;根际土中Zn和Cd的有效态含量远高于非根际土,而Pb的有效态含量则表现出非根际土大于根际土的特点;过氧化氢酶、磷酸酶、脲酶和脱氢酶在根际土中的活性明显高于非根际土;从土壤重金属有效态与土壤酶活性相关性来看,根际土中,除有效态Pb与过氧化氢酶呈显著负相关外,其余重金属元素有效态与土壤酶活性相关性均没有显著相关性,而在非根际土壤中,有效态Cd与过氧化氢酶呈极显著负相关,与脲酶呈显著负相关,Zn和Cd则与土壤酶活性之间没有显著相关性。综合研究结果表明,毛竹根际土壤质量总体上明显优于非根际土,这为毛竹今后作为植物修复的材料提供了一定的理论依据。     

The rhizosphere microflora of wheat grown under controlled conditions II. Influence of the stage of growth of the plant,soil fertility and leaf treatment with urea on the rhizosphere soil microflora

Summary The rhizosphere effect of seminal roots of seedlings and of nodal roots of tillering plants of spring wheat ‘Kaspar’ was investigated under controlled conditions. The total number of micro-organisms recorded in the rhizosphere soil were significantly higher than for the non-rooted soil when investigated with the soil dilution plate method, but lower when fluorescence microscopy was used. Additions of inorganic fertilizer (NPK) decreased their numbers especially in rhizosphere soil of seminal roots and in non-rhizosphere soil, but did not change the ratio between bacteria and actinomycetes (B/A). In the rhizosphere soil the B/A ratio was higher than in the non-rhizosphere soil. An effect of urea leaf treatment was found with the dilution-plate method only in the rhizosphere soil of nodal roots, 3 to 7 days after the first treatment. Increased numbers of actinomycetes were found in this period in NPK fertilized soil, whereas increased numbers of bacteria were found at both fertility levels.     

赤杨对辽东落叶松人工林土壤氨基糖积累的影响

微生物残留物是土壤稳定性碳库的重要组成部分,然而其对固氮树种的响应还不清楚。以辽东山区日本落叶松(Larix kaempferi)人工纯林和落叶松-赤杨混交林为研究对象,以氨基糖作为微生物残留物的生物标识物,研究了赤杨对落叶松人工林根际和非根际土壤氨基糖积累的影响。结果表明,混交林中落叶松根际和非根际各氨基糖单体含量均显著高于纯林,说明赤杨引入有利于土壤微生物残留物的积累。其中,混交林落叶松根际及非根际土壤氨基糖葡萄糖含量分别比纯林高出99.5%(P0.01)和154%(P0.01);胞壁酸含量分别比纯林高出66.1%(P0.01)和132.3%(P0.01)。赤杨引入对氨基葡萄糖/胞壁酸比值的影响不显著,但显著增加氨基糖对土壤有机碳的贡献。冗余度分析表明全氮是驱动土壤中氨基糖发生变化的主要因子。表明赤杨引入显著提高微生物固持的土壤碳库和有机碳稳定性,这对落叶松人工林合理经营具有重要意义。     

秦岭典型林分夏秋两季根际与非根际土壤微生物群落结构

本试验主要以秦岭山脉锐齿栎(Quercus aliena var.acutidentata)、油松(Pinus tabuliformis)、华山松(Pinus armandii)、云杉(Picea asperata)4种典型林分为对象,利用BIOLOG微孔板法研究4种林分夏、秋两季根际与非根际土壤微生物群落代谢多样性。研究表明:(1)夏、秋季土壤根际与非根际的平均颜色变化率(AWCD)值截然不同,除秋季云杉外,其余处理均表现为非根际根际,且AWCD明显受到季节的影响。(2)夏秋两季4种林分根际与非根际土壤微生物功能多样性之间差异显著,其中锐齿栎林夏秋两季均表现为根际小于非根际,而其它3种针叶林则是夏季根际小于非根际,秋季根际大于非根际;锐齿栎林根际与非根际均为秋季低于夏季,其他3种针叶林则是非根际土秋季低于夏季,而根际土秋季高于夏季。(3)主成分分析显示各土壤微生物功能多样性具有显著差异,且4种林分夏秋两季根际与非根际主成分综合得分也有所不同,4种林分非根际土综合得分锐齿栎最高,其次是华山松和云杉,油松最低;根际土夏秋规律不同,夏季华山松和油松较高,云杉最低,秋季油松和云杉较高,锐齿栎最低,且综合得分与多样性指数达到显著或极显著的正相关。(4)冗余分析表明土壤理化性质的综合作用对土壤微生物群落功能多样性有显著影响。     

艾比湖湿地芦苇根际土壤氨氧化古菌的多样性和群落结构

【目的】旨在揭示耐盐植物芦苇根际与非根际土壤AOA群落结构间的差异,为深入研究盐生植物根际土壤微生物与耐盐性之间的关系提供理论基础。【方法】应用高通量测序技术以氨单加氧酶基因(amoA)为分子标记,对新疆艾比湖湿地荒漠生态系统不同季节(春、夏、秋)芦苇根际与非根际土壤氨氧化古菌(AOA)的多样性和群落结构进行研究。【结果】结果表明,不同季节芦苇根际土壤AOA多样性和丰富度存在差异,相比非根际土壤,夏季和秋季芦苇根际土壤AOA多样性较低丰富度较高,春季多样性较高丰富度较低。芦苇根际土壤中AOA的多样性为春季夏季秋季。AOA群落组成分析表明,土壤样品中AOA群落主要集中在泉古菌门(Crenarchaeota)和奇古菌门(Thaumarchaeota),其中泉古菌门为主要优势菌门。RDA分析表明,含水量(SM)、有机质(SOM)、总氮(TN)和pH是影响芦苇根际土壤AOA群落多样性和丰富度的主要环境因子。【结论】不同季节芦苇根际土壤AOA多样性及丰富度存在差异,相比非根际土壤,芦苇根际土壤AOA更丰富。     

Determination of low molecular weight dicarboxylic acids and organic functional groups in rhizosphere and bulk soils of Tsuga and Yushania in a temperate rain forest

Low molecular weight organic acids (LMWOAs) derived from root exudates, decomposing organic matter, and other sources are important ligands. The species of these LMWOAs in the Tsuga rhizosphere soil (TRS), and Yushania rhizosphere soil (YRS), and bulk soil (BS) from an alpine forest region were identified. LMWOA and organic functional groups were used to those fresh twigs and leaves, litters, and roots as comparison. The objectives of this study were to (i) develop a method that could be used to determine LMWOAs in soil solution by gas chromatography (GC), (ii) assess methods for processing LMWOAs in soil samples, and (iii) determine the relative proportions of organic carbon functional groups in the TRS, YRS and BS, and fresh plant materials with¹³C nuclear magnetic resonance (¹³C NMR) analysis. The proportion of organic acid contents followed the order of YRS > TRS > BS, and also showed significant differences (P < 0.05) from GC analysis. The amounts of malonic, fumaric and succinic acids in the YRS samples were greater than in the TRS and BS. Samples analyzed after 1 month of deep freeze storage (–24°C) showed no signs of decomposition. The proportion of organic functional groups in the rhizosphere and bulk soils quantified by ¹³C NMR analyses followed the general order: alkyl-C > O-alkyl-C > N-alkyl-C > acetal-C > aromatic-C > carboxylic-C > phenolic-C.     

持续干旱对樱桃根际土壤细菌数量及结构多样性影响

以1年生吉塞拉实生容器苗为试材,采用绿色荧光蛋白基因标记技术,研究了干旱胁迫(连续干旱0、7、14、21、28 d和35 d)对樱桃根际促生细菌YT3的标记菌YT3-gfp数量的影响,同时结合平板计数法和末端限制性片段长度多态性分析(terminal restriction fragment length polymorphism,T-RFLP)技术,研究了干旱对樱桃土壤中的微生物数量及细菌群落结构多样性影响。结果表明:樱桃根际土壤中的YT3-gfp数量是非根际土壤中的8.75—28.77倍,随着持续干旱强度的增加,YT3-gfp的数量先增加后减小。干旱对根际土壤中YT3-gfp数量的影响大于对非根际土壤的影响,分别在持续干旱至第21天和28天时,YT3-gfp的数量达到最大值。随着持续干旱强度的增加,根际土壤中细菌和放线菌数量先增加后减小,而真菌的数量一直减少。此外,持续干旱至第21天或28天时,樱桃根际土壤具有最高的丰富度指数、多样性指数和最低的优势度指数。基于T-RFLP的主成分分析结果显示持续干旱14—35 d时,其细菌群落结构成为一个相对独立的群,群落结构趋于多样性;而持续干旱7 d和42 d构成另外两个相对独立的群,群落结构趋于简单。以上分析可知,干旱对土壤微生物影响显著,一定强度的干旱可提高细菌和放线菌数量,提高细菌群落结构多样性,适当干旱对维持根际土壤细菌群落结构多样性是有益的。     

Abstracts of Platform Presentations from the Phytoremediation Session at the 14th Annual West Coast Conference on Contaminated Soils,Sediments, and Water (March 15–18, San Diego,CA)

Previous field studies indicate that zucchini (Cucurbita pepo) has a unique ability to phytoextract persistent organic pollutants from soil. It is unlikely that C. pepo evolved a unique mechanism favoring POP extraction and uptake, but all plants have evolved means to facilitate nutrient acquisition from soil. We have hypothesized that the exudation of organic acids as a means to acquire phosphorus could facilitate the uptake of persistent organic pollutants by increasing contaminant bioavailability to the plants. In one study, we assessed DDE uptake and organic acid exudation by zucchini (an uptaker of POPs) and cucumber (a non-uptaker of POPs) under various cultivation and nutrient conditions. Under dense planting (5 plants in a 5-kg pot of DDE-contaminated soil), zucchini accumulated significant and expected amounts of DDE but surprisingly, under these stressed conditions, cucumber phytoextracted greater amounts of DDE. The cucumber rhizosphere concentrations of organic acids were significantly higher than that of zucchini, suggesting that the increased organic acid exudation promoted DDE uptake by cucumber. Conversely, under non-stressed conditions zucchini phytoextracted significantly greater quantities of pollutant than cucumber but no differences in organic acid content of the rhizosphere of the two species were observed. Separately, zucchini and other species were grown under field conditions and weekly amendments of different nutrients were made (nitrogen, phosphorus, nitrogen/phosphorus, aluminum sulfate to bind phosphorus in the soil). The uptake and translocation of the weathered pollutant and inorganic elements was found to vary with nutrient amendments. Lastly, data will be presented from rhizotron units constructed to facilitate not only the direct in situ isolation of exuded organic acids but also the isolation of xylem sap and rhizosphere soil pore water from individual plants. The role of cultivation conditions and nutrient availability in controlling root morphology, organic acid exudation, and contaminant uptake will be discussed.     

Studies on soil rhizosphere: speciation and availability of Cd

ABSTRACT

The rhizosphere soils of two durum wheat (Triticum turgidum var. durum L.) cultivars Kyle and Areola grown in two selected soils of southern Saskatchewan were collected both at 2-week and 7-week plant growth stages. The cadmium availability index (CAI), determined as M NH₄CI-extractable Cd, pH and the distribution of the particulate- bound Cd species of the soils were carried out and the data were discussed in comparison with those of the corresponding bulk soil. At the 2-week growth stage, the pH of the rhizosphere soil was less than that of the corresponding bulk soil and the CAI values were higher in the rhizosphere soil, indicating that more Cd was complexed with the low-molecular-weight organic acids (LMWOAs) at the soil-root interface and was extractable by M NH₄CI. Compared with the bulk soils, the CAI values were 2–9 times higher in the soil rhizosphere of the plots fertilized with Idaho monoammonium phosphate fertilizer at 2-week growth stage, which is attributed to the combined effects of the Cd introduced into the soil rhizosphere from the fertilizer (Cd content of the fertilizer was 144 mg kg^?1) and complexation reactions of phosphate and LMWOAs with soil Cd. At 7-week plant growth stage, such differences were not observed. The increased amounts of carbonate-bound and metal-organic complex-bound Cd species of the rhizosphere soils are due to the increased amounts of carbonate, a product of plant respiration, and the LMWOAs at the soil-root interface, respectively. Simple correlation analysis of the data showed that the CAI of the rhizosphere soils of the control plots correlated at least two orders of magnitude better with the metal-organic complex-bound Cd whereas the CAI of the rhizosphere soils treated with Idaho phosphate correlated better with carbonate-bound Cd species in comparison to other species.