Distribution of Manganese(Ⅱ) Chemical Forms on Soybean Roots and Manganese(Ⅱ) Toxicity

Distribution of chemical forms of manganese(Ⅱ)(Mn(Ⅱ))on plant roots may affect Mn(Ⅱ)absorption by plants and toxicity of Mn(Ⅱ)to plants at its high level.The chemical forms of Mn(Ⅱ)on soybean roots were investigated to determine the main factors that affect their distribution and relationship with Mn(Ⅱ)plant toxicity.Fresh soybean roots were reacted with Mn(Ⅱ)in solutions,and Mn(Ⅱ)adsorbed on the roots was differentiated into exchangeable,complexed,and precipitated forms through sequential extraction with KNO_3,EDTA,and HCl.The exchangeable Mn(Ⅱ)content on the roots was the highest,followed by the complexed and precipitated Mn(Ⅱ)contents.Mn(Ⅱ)toxicity to the roots was greater at pH 5.5 than at pH 4.2 due to the larger amount of exchangeable Mn(Ⅱ)at higher pH.The cations Al~(3+),La~(3+),Ca~(2+),Mg~(2+),and NH_4~+competed with Mn(Ⅱ)for cation exchange sites on the root surfaces and thus reduced exchangeable Mn(Ⅱ)on the roots,in the order Al~(3+),La~(3+)Ca~(2+),Mg~(2+)NH_4~+.Al~(3+) and La~(3+) at 100μmol L~(-1) decreased exchangeable Mn(Ⅱ)by 80%and 79%,respectively,and Ca~(2+) and Mg2+at 1 mmol L~(-1) decreased exchangeable Mn(Ⅱ)by 51%and 73%,respectively.Organic anions oxalate,citrate,and malate reduced free Mn(Ⅱ)concentration in solution through formation of complexes with Mn(Ⅱ),efficiently decreasing exchangeable Mn(Ⅱ)on the roots;the decreases in exchangeable Mn(Ⅱ)on the roots were 30.9%,19.7%,and 10.9%,respectively,which was consistent with the complexing ability of these organic anions with Mn(Ⅱ).Thus,exchangeable Mn(Ⅱ)was the dominant form of Mn(Ⅱ)on the roots and responsible for Mn(Ⅱ)toxicity to plants.The coexisting cations and organic anions reduced the exchangeable Mn(Ⅱ)content,and thus they could alleviate Mn(Ⅱ)toxicity to plants on acid soils.     

The effect of arbuscular mycorrhiza fungal propagules on the growth of subterranean clover (Trifolium subterraneum L.) under Mn toxicity in ex situ experiments

The role of intact extraradical mycelium (ERM) as the most effective fungal propagule in the formation of the tripartite symbiosis between indigenous arbuscular mycorrhizal fungi (AMF), rhizobia and subterranean clover was investigated under conditions of Mn toxicity. ERM was previously developed in 8 L pots under greenhouse conditions by growing plants, which exhibited various levels of mycotrophicity and were tolerant to the levels of Mn in the soil used in the experiment (Silene gallica L, Lolium rigidum L, Ornithopus compressus L. and Rumex bucephalophorus L). Contrasting conditions of the integrity of the ERM at the planting of subterranean clover were created by soil disturbance (ERM fragmented – soil disturbed; ERM intact – soil undisturbed). Where an intact ERM was present at the time of planting, growth of subterranean clover was 2.5 times greater after 21 days and 3.9 times after 42 days relative to other forms of AMF propagule. This enhanced growth was associated with a reduction in the Mn concentration of roots due to a greater AMF colonization at 21 days after planting. The protection granted by an enhanced AMF root colonization allowed a greater root nodule development, leading to more N acquisition and plant growth. The ERM can be developed in the soil by mycotrophic plants tolerant to the stressing agent and kept intact at the seeding of the crop to be protected by adopting appropriate tillage techniques.     

树干注射锰肥对新疆灰枣生长和品质的影响

锰是果树生长发育过程中不可缺少的一种重要微量元素。为了解锰在枣生长发育过程中所起的作用,本实验采用树干注射的方式在灰枣的萌芽期,花期和膨大期增施锰肥,并对树体的生长和品质指标进行了测定。结果显示:枣在不同生长期增施锰肥对枣树生长的影响都以2.0 g/tree 表现最好,其中干径增长量、基径增长量、枣吊增长量、单果重和产量分别比对照增长了26%、33%、19%、38%和19%。对营养品质的测定中,2.0 g/株的处理枣果铁、锰、锌和钙的含量分别是对照的47%、20%、22%和13%,糖酸比为57.36。各施肥处理对灰枣生长和品质的增加均有促进作用。综上所述,在灰枣的生长期配合施用锰肥,能有效促进枣树的生长和产量和枣果营养品质的提高。     

太湖流域农村生活污水污染物排放系数研究——以昆山为例

为估算农村生活污水污染物排放系数,于2007年8月至2008年7月在昆山锦溪镇周家浜村,通过每月收集不同收入家庭的排放污水,对生活污水排放量以及COD和氮磷排放情况进行了调查研究。结果表明,农村居民人均污水排放量、人均生活污水COD排放量和氮磷排放量的季节差异显著,且与家庭收入呈负相关趋势。农村生活污水COD、氨氮、总氮和总磷排放系数分别为58.3、3.6、6.2、0.4 kg.a-1.人-1,氮磷总排放系数达6.6 kg.a-1.人-1,明显高于以往文献中常用的3.3 kg.a-1.人-1,并对其原因进行了分析。该排放系数对太湖流域其他地区农村生活污水排放的估算具有一定参考价值。     

锌、锰对棉花吸收氮、磷养分的影响及机理研究

较高或较低浓度的土壤锌、锰影响棉花对氮、磷养分的吸收、而合适的土壤锌、锰浓度能促进棉花根系和地上部对氮、磷的吸收和积累。提高植株及茎、叶、蕾、铃中氮、磷的含量,对棉花的生产发育,产量及产量构成因素都表现出明显的促进作用,通过水培试验研究发明,锌、锰在一定浓度条件下所表现的促进作用,主要是提高了棉花植株的根系活力,增加棉株叶片的叶绿素含量,调节棉株体内的酶活性,从而增加了棉花对营养物质的吸收、运输和代谢、提高了氮、磷的利用率、增加棉花的产量。     

锌锰钼配施技术在鸡脚草和百脉根混播草地中的应用

针对河南省土壤特点,锌锰钼肥的生理功能以及牧草生产利用中存在的问题,从2000年起对Zn、Mn和Mo肥3种微肥在鸡脚草(鸭茅)(DectylisglomerataL.)和百脉根(LotuscorniculatusL.)混播草地进行了应用性研究,详实地探讨三种微肥的应用范围和具体措施。研究证明:Zn肥对鸡脚草和百脉根混播草地的有效范围集中在200￣600mg/kg之间,最佳利用浓度为200￣400mg/kg,能够促进牧草光合作用和提高种子产量,对牧草生产没有影响。200mg/kg的Zn肥与500mg/kgMn肥和300mg/kg的Mo肥三者配施下,不但提高牧草的光合能力和种子产量,而且也显著地提高牧草产量(11.8%)。     

滇池主要入湖河流水质分析

 对滇池流域的4条入湖河流的总磷、总氮、COD污染进行了调查。结果表明，随着流域内旱雨季变化、河流流量变化、河流地段变化，总磷、总氮、COD含量存在明显差异。入湖口水样总磷、总氮、COD含量明显高于同一河流中、上游。雨季河流流量增加，总磷、总氮、COD含量仍明显增高，特别是雨季前期，由于旱季大量有机物在地面堆积，土壤有效P累积，雨后随地表径流进入河道，使COD、TP增加明显，持续降雨后又有下降趋势。     

家畜尿样COD测定中稀释倍数的探讨

综合相关研究资料,对利用CODCr法测定家畜尿样中COD值时样本的稀释倍数进行了探讨。通过计算确定适宜稀释倍数范围为30~50倍,并比较不同稀释倍数对家畜尿样中COD含量的影响,结果显示最佳稀释倍数为30倍。另外对测定过程中的不确定因素进行了分析。     

Aeration effects on CO2, N2O,and CH4 emission and leachate composition of a forest soil

The availability of O₂ is one of the most important factors controlling the chemical and biological reactions in soils. In this study, the effects of different aeration conditions on the dynamics of the emission of trace gases (CO₂, N₂O, CH₄) and the leachate composition (NO₃^‐, DOC, Mn, Fe) were determined. The experiment was conducted with naturally structured soil columns (silty clay, Vertisol) from a well aerated forest site. The soil monoliths were incubated in a microcosm system at different O₂ concentrations (0, 0.001, 0.005, 0.01, 0.05, and 0.205 m³ m^‐3 in the air flow through the headspace of the microcosms) for 85 days. Reduced O₂ availability resulted in a decreased CO₂ release but in increased N₂O emission rates. The greatest cumulative N₂O emissions (= 1.6 g N₂O‐N m^‐2) were observed at intermediate O₂ concentrations (0.005 and 0.01 m³ m^‐3) when both nitrification and denitrification occurred simultaneously in the soil. Cumulative N₂O emissions were smallest (= 0.05 g N₂O‐N m^‐2) for the aeration with ambient air (O₂ concentration: 0.205 m³ m^‐3), although nitrate availability was greatest in this treatment. The emission of CH₄ and leaching of Mn and Fe were restricted to the soil columns incubated under completely anoxic conditions. The sequence of the reduction processes under completely anoxic conditions complied with the thermodynamic theory: soil nitrate was reduced first, followed by the reduction of Mn(IV) and Fe(III) and finally CO₂ was reduced to CH₄. The re‐aeration of the soil columns after 85 days of anoxic incubation terminated the production of CH₄ and dissolved Fe and Mn in the soil but strongly increased the emission rates of CO₂ and N₂O and the leaching of NO₃^‐ probably because of the accumulation of DOC and NH₄⁺ during the previous anoxic period.     

Electron microscopic characterisation of iron and manganese oxide/hydroxide precipitates from agricultural field drains. 1

Scanning and transmission electron microscopic examination of drain precipitates revealed the presence of a slime/organic layer and fungi, bacteria (including filamentous and Fe bacteria), and possibly actinomycetes. Most of the filamentous structures were encrusted with Fe and Mn compounds. Treating the samples with acidified NH₂OH.HCl and leucoberbelin blue revealed some structures similar to Hyphomicrobium and Pedomicrobium spp., yeast cells, cocci, fungal spores, and relics of diatoms and amoebae. Both, scanning and transmission electron microscope-energy-dispersive analysis of X-rays showed a clear association of microbial structures with Fe and Mn oxides. It was suggested that Fe and Mn were being precipitated in the drains. However, the precipitates were not stable under natural conditions, and therefore we concluded that these precipitated oxides were also undergoing reductive dissolution. It thus appeared that precipitation of Fe and Mn, particularly Mn, had been mediated microbiologically in the drains.