Influence of Dissolved Organic Matter On the Bio-Availability and Toxicity of Metals in Soils and Aquatic Systems

Cations in soil are essential for the growth of plants and micro-organisms. Their availability is dependent on soil organic matter. Soil organic matter (SOM) is heterogeneous comprising amino, aliphatic and phenolic acids, but particularly humic substances. All these substances can complex cations selectively. Mechanisms of complexation with dissolved organic matter are discussed. Such complexation can lead to the apparently contradictory observations that dissolved organic matter (DOM) can either increase the concentration of some less soluble nutrients, making them more available for plant uptake, or make them less available and hence less toxic. the importance of DOM is discussed in relation to soil solution, particularly the rhizosphere, and also in relation to aquatic systems. the latter systems contain mainly dissolved humic substances whereas in the soil, non-humic substances assume a greater importance.

SOM in the rhizosphere is derived from plant, microbial and animal remains but much, especially the water-soluble compounds, are acquired through root exudation. Exudation has important consequences for enhanced nutrient availability as a result of the production of non-humic substances such as amino, aliphatic and phenolic acids. in future, the role of root exudation in relation to DOM and nutrient availability should be investigated more fully, particularly as predicted elevated CO₂ levels are likely to have a major impact on root exudation, nutrient availability, and possibly ecosystem community structure and functioning. It is likely that more information will become available on aquatic systems as more highly sensitive techniques and equipment capable of dealing with low concentrations of DOM in these systems become available.     

利巴韦林对4种作物种子发芽的影响

利巴韦林作为一种强效抗病毒药物在畜禽养殖业中应用广泛,有着较高的生态环境风险。采用室内培养箱培养的方法,研究了利巴韦林对4种作物(小麦、白菜、萝卜和番茄)的种子发芽、根伸长和芽伸长的影响。结果表明,利巴韦林对4种作物的种子发芽率影响不大,但其浓度与4种作物的根伸长及芽伸长抑制率显著相关(P<0.01或P<0.05),作物的根伸长比芽伸长对利巴韦林的胁迫更敏感。土壤中利巴韦林浓度与4种作物根伸长抑制率之间呈现正相关关系。根伸长的抑制率达到10%所对应的利巴韦林浓度(IC10)分别为:IC10(白菜)=4.25mg·kg-1,IC10(番茄)=29.7mg·kg-1,IC10(萝卜)=33.2mg·kg-1,IC10(小麦)=49.4mg·kg-1。可以看出,4种作物对土壤中利巴韦林胁迫的敏感性依次是:白菜>番茄>萝卜>小麦。从利巴韦林对4种作物的根伸长和芽伸长抑制率综合来看,小麦对利巴韦林的耐受性最强,而白菜对利巴韦林最敏感。     

环丙沙星对3种作物的毒性

为了研究环丙沙星对作物的毒性效应,为其可能对农业生产带来的风险提供评价依据,采用急性毒性实验方法,研究了环丙沙星对3种作物(玉米、萝卜和小白菜)种子发芽、根伸长及芽伸长的影响。结果表明,在环丙沙星作用下,3种作物的根伸长抑制率和芽伸长抑制率与药物浓度显著相关(P<0.05),发芽抑制率与药物浓度不相关(P>0.05);药物对根伸长及芽伸长的抑制高于对种子发芽的抑制;环丙沙星对玉米、萝卜和小白菜的根伸长和芽伸长的ID50(抑制率为50%时污染物浓度)分别为7.97、2.51、1.48mg·kg-1和11.23、2.90、1.95mg·kg-1,3种作物在环丙沙星的胁迫下,其敏感性顺序为:小白菜>萝卜>玉米。     

再生水湿地香蒲根内生细菌群落多样性及其水质特征分析

以北京白河人工湿地再生水补水河段香蒲根为研究对象,采用16S rDNA克隆文库技术对香蒲根内生细菌群落多样性进行分析,得出该克隆文库包括4大类群细菌,最优势类群为变形杆菌门Proteobacteria,其中包括Gammaproteobacteria、Betaproteobacteria、Epsilonproteobacteria、Alphaproteobacteria;其次为厚壁菌门Firmicutes、疣微菌门Verrucomicrobia、拟杆菌门Bacteroidetes;另外还包括部分非培养未确定种属的细菌.结合研究区再生水排放口与湿地下游水质数据,得出TN、TP、NO₃^-去除率达到了42.15%、47.34%、28.56%,表明湿地对再生水中的TN、TP、NO₃^-具有明显去除机制,说明香蒲根内生细菌克隆文库中菌株与湿地氮、磷等生物地球循环关系密切.     

热带砖红壤生长的小白菜吸收和累积PAHs的特征

为了了解和掌握热带土壤栽培的小白菜（Brassica rapa L. Chinensis Group.）对多环芳烃（PAHs）污染物的吸收和累积规律,为热带土壤的安全利用及农产品安全生产提供科学依据,于2013 年5-9 月在海南省农垦科学院海口试验站网室内进行了小白菜盆栽试验.各处理土壤分别施加3 种单体 PAHs 的质量分数梯度为0、0.4、0.8、1.6、3.2 mg·kg^-1,撒播小白菜种子出苗后,每盆留苗6 株,自然条件,常规管理,各处理小白菜培养30 d 后收获.小白菜和土壤样品,用超声水浴萃取,层析小柱净化后,利用气相色谱-质谱法测定样品中的3 种PAHs.结果表明,小白菜根和叶中3 种PAHs 累积量随土壤施加质量分数的升高而增加,根部和叶对Phe 最大累积量分别为86.25 ng·g^-1 和37.18 ng·g^-1,而对 BaP 的最大累积量分别为20.78 ng·g^-1 和3.56 ng·g^-1;小白菜根对Phe 与Fla 的生物富集系数较大,且二者无明显差异,但对 BaP 的生物富集系数较小,且差异显著（P=0.006）;3 种PAHs 单体在各种处理土壤中的残留在 84.49%-94.03%之间,各单体之间无明显差异,各处理之间也无明显差异.说明热带土壤生长的小白菜根和叶中3 种单体 PAHs 浓度显著低于其土壤中的浓度,且根部积累3 种单体PAHs 的浓度显著高于其叶中的浓度;小白菜叶对BaP 的吸收和累积量极少;小白菜根更易吸收和累积Phe 和Fla;小白菜生长30 d 后,绝大部分PAHs 仍残留在土壤中.     

酸铝胁迫下常绿杨根冠超微结构变化

中国的亚热带地区气候温暖湿润、雨量充沛,是中国速生丰产林基地,森林土壤多呈偏酸性和酸性,为富铝化酸性土壤,容易造成植物铝毒害。A-61/186（Populus×enramericana cv.）是澳大利亚 L．D．Pryor 博士选育的半常绿杨树无性系（semi-evergreen poplar clone）,母本为美国南方种的落叶型美洲黑杨（Populus deltoids Marsh）,父本为原产智利的常绿品种欧洲杨智利变种（Populus nigra cv.Chile）,是中国林科院郑世锴研究员于1987年从巴基斯坦引入中国的3个常绿杨品系之一,适合热带亚热带种植。以常绿杨A-61/186（Populus×euramericana cv.）根冠细胞为材料,采用水培酸铝胁迫实验,在胁迫30 d、60 d和90 d时在透射电子显微镜下进行根冠细胞超微结构的观察及拍片,研究在酸铝胁迫下浓度和作用时间对其超微结构的影响,探究铝毒条件下杨树根冠细胞的超微结构变化,并为根冠细胞铝毒亚显微水平评价提供资料。结果表明,随着铝浓度的升高,根冠细胞壁溶解断裂;细胞基质由凝胶态向分散碎块转变;淀粉粒数量有减少的趋向,淀粉质体数量有增加的趋向,而淀粉粒堆重心偏向由明显到不明显的趋向。随着铝作用时间的延长,根冠细胞在60 d浓度0.370 mmol·L^-1淀粉粒急剧减少;在90 d浓度0.666 mmol·L^-1淀粉粒质体急剧减少;淀粉粒堆或淀粉质体堆无重心偏向。     

标准化测试种子发芽和根伸长毒性试验的基质应用研究

种子发芽和根伸长毒性试验是研究和评价新化学物质对陆生生物危害性的重要手段之一。为探究在标准化测试中能否使用非推荐基质,以及使用推荐基质时能否用灭菌法替代酸洗法处理石英砂,选取8种植物种子在5种基质中进行试验。结果表明,不同基质对种子发芽率的影响较小,但基质较低的养分含量和特殊的物理结构易对部分种子根长形成胁迫,甚至直接制约根系发育。生菜、水稻在5种基质中的发芽率和根长无显著性差异;绿豆、甘蓝、西瓜在酸洗石英砂中的根长分别为25.1、24.5、29.0 mm,在其余4种基质中根长显著缩短;青瓜在吸水纸和发芽纸中发芽率偏低,仅为83.3%;玉米在酸洗石英砂和灭菌石英砂中的发芽率和根长无明显差异,为100%/45.7 mm和93.3%/44.8 mm,其他基质中显著偏低。标准化测试条件下,以推荐的酸洗石英砂上各种子的发芽率和根长为评判依据,生菜和水稻试验可使用本研究中任意基质,绿豆、甘蓝和西瓜试验仅可使用酸洗石英砂作为基质,青瓜和玉米试验可使用干热灭菌法替代酸洗法处理石英砂,并且青瓜试验还可使用滤纸基质。以上结果为测试机构在工作实践中优化试验条件提供理论依据。     

低湖田生态系统特点及开发利用研究

阐述了低湖田生态系统中的生物系统、土壤系统同水土体系的相互作用,分析了低湖田生态系统中的土壤特性及资源优势潜力。主要表现为：水温、泥温低,土壤通透性能差,结构不良;土壤处于强还原状态,有毒还原性物质含量高,不利于作物的正常生长;土壤微生物活动弱,微生物生物量显著低于正常土壤;土壤有机质矿化慢,土壤供氮能力弱,缺磷、缺锌严重。而水生经济植物莲藕的生物学特性决定其地下茎具有发达的通气组织,保证了植株在水中的正常呼吸和新陈代谢的需要,同时还能改善土壤通气性能和土壤氧化还原状态,增强土壤微生物活力,加快土壤有机质矿化状况。着重从低湖田生态系统所具备的优势入手,对低湖田的作物系统、土壤系统和水土体系进行了比较和分析,其作物生物量排序为：莲藕＞茭白＞菱＞水稻, 其作物产量排序为：莲藕＞茭白＞菱＞水稻;对作物系统的主体作物进行了优化,对土壤系统的关键营养元素进行了调控（N:P:K:16:16:16）,合理利用水土体系的特点构建生物共生的模式,提出了合理利用低湖田资源优势的措施和开发模式（鱼藕共生模式）,提高低湖田生态系统综合开发效益的整体水平。     

POTENTIAL,ACTUAL, AND EQUILIBRIUM EVAPOTRANSPIRATION IN A WHEAT FIELD 1

ABSTRACT: This paper examines the relationship between both potential (E*) and nonpotential evapotranspiration and equilibrium evapotranspiration (EQ) in an irrigated wheat field in southcentral Alberta, Canada. The control exercised by surface wetness and root reservoir moisture content in determining the value of the Priestley-Taylor constant a is explored. Also investigated is the relationship between a and the vapor flux fraction ET/(R-G) where ET is the actual evapotranspiration, R the net radiation, and G the soil heat flux. It is shown that evapotranspiration occurred at the potential rate (E*) when the available soil moisture (ASM) within the root zone was ≥3 percent. a varied from 0.84 for a dry soil to 1.49 for a saturated soil. The mean a for E* was 1.24. Surface wetness sustained evapotranspiration at the potential rate when such wetting exceeded 2mm d^?1 following a period of prolonged drawdown of soil moisture, α and ET/(R-G) were positively correlated and this correlation strengthened with increasing soil moisture for constant values of the energy partitioning factor s+γ/s where s is the slope of the saturation humidity-temperature curve and γ is the psychrometric constant. ET=EQ when ETI(R-G) lay within the range of 0.59 to 0.82 corresponding to Bowen ratio (β) values of 0.22 and 0.69, respectively.     

THE FLEXIBLE TOLERANCE METHOD FOR ESTIMATING HYDROLOGIC PARAMETERS IN THE ROOT ZONE1

In this study, a constrained minimization method, the flexible tolerance method, was used to solve the optimization problems for determining hydrologic parameters in the root zone: water uptake rate, spatial root distribution, infiltration rate, and evaporation. Synthetic soil moisture data were first generated using the Richards' equation and its associated initial and boundary conditions, and these data were then used for the inverse analyses. The results of inverse simulation indicate the following. If the soil moisture data contain no noise, the rate of estimated water uptake and spatial root distribution parameters are equal to the true values without using constraints. If there is noise in the observed data, constraints must be used to improve the quality of the estimate results. In the estimation of rainfall infiltration and surface evaporation, interpolation methods should be used to reduce the number of unknowns. A fewer number of variables can improve the quality of inversely estimated parameters. Simultaneous estimation of spatial root distribution and water uptake rate or estimation of evaporation and water uptake rate is possible. The method was used to estimate the water uptake rate, spatial root distribution, infiltration rate, and evaporation using long‐term soil moisture data collected from Nebraska's Sand Hills.