茶树根际土壤性质及氮肥的影响

本文报导了对盆栽茶树根际土壤性质的研究结果。经外力抖落后仍粘在根系上的土壤作为根际土壤,其余土壤为非根际土壤。施氮显著降低土壤pH、交换性K、Ca、Mg含量和盐基饱和度,增加水溶性铝、有机交换态铝和吸附羟基态铝的含量。与非根际土壤相比,根际土壤pH、交换性Ca、Mg和盐基饱和度明显降低,而交换性K高于非根际土壤。根际土壤的水溶性铝、交换性铝、交换性铝饱和度和吸附羟基态铝的含量显著高于非根际土。上述结果说明茶树根际土壤明显酸化,增强了土壤铝有效度。铝在茶树根际微域环境中的这种变化,可能在茶树吸收铝的过程中起着重要作用。     

铝、镉胁迫下不同大麦品种根际的铝、镉形态分析

为明确铝(Al)、镉(Cd)单独及复合胁迫下作物根际毒害元素的化学形态及其生物有效性,采用盆栽试验,以耐铝性不同的两个大麦品种(铝敏感品种浙农大9号和耐铝品种Day ten)为试验材料,利用连续提取法和ICP-AES方法分析了拔节期大麦根际的Al、Cd化学形态及其含量.结果表明,所有处理中大麦植株根际溶出Al均主要以毒性较小的酸溶无机Al和腐殖酸Al存在,根际Cd则主要以残留态形式存在.Al、Cd单独胁迫下大麦根际土壤溶液中各形态Al、Cd的溶出量均显著增加,交换态含量占可提取Al、Cd总量的比例增加.其中浙农大9号根际活性Al、Cd含量的增幅均大于Dayton.与单独Al或Cd处理相比,复合胁迫下根际交换态Al和Cd含量增加,其他形态含量下降或变幅不大.     

铝胁迫下大豆根系分泌物对根际土壤的影响

以2个大豆品种（浙春2号和浙春3号）为材料，设置了4个铝浓度，分别在铝处理7d和14d时，测定大豆根系分泌物中的氨基酸、有机酸及可溶性糖，同时对大豆根际土壤的pH值、土壤酶和土壤呼吸速率进行分析。实验结果显示，虽然根系分泌物对根际土壤具有一定的酸化作用，但是随着铝浓度的升高，根系分泌物有使根际土壤酸碱度趋向平衡的效应。低铝浓度下，大豆根系分泌较多的可溶性糖和氨基酸，促使根际土壤酶活性的增强和土壤呼吸速率的提高，同时还可分泌较多的柠檬酸，与大豆的耐铝性相关。高铝浓度抑制主要根系分泌物的分泌，降低土壤酶活性和土壤呼吸速率；但高铝胁迫增加可溶性糖分泌量。实验结果表明，浙春2号大豆比浙春3号大豆耐铝；随着铝处理时间的延长，铝毒害作用明显。     

The effect of aluminum treatments on the root growth and cell ultrastructure of two soybean genotypes

Since aluminum (Al) toxicity often negatively affects the growth and production of crops in acidic soil, understanding the mechanisms of plant physiological response to Al toxicity would facilitate the development of more Al-tolerant crops. The objective of this research is, therefore, using transmission electron microscope and spectrophotometer to study the physiology and cell ultrastructure changes of two soybean cultivars of distinctly different sensitivities to Al toxicity, Zhechun 2 (Z.2, Al-resistant) and Zhechun 3 (Z.3, Al-sensitive) after Al treatments. Using these two cultivars, we conducted a 14-day nutrient solution experiment with Al concentrations set at 0, 10, 30, 60 and 90 mg L⁻¹. The results demonstrated that Al inhibited the growth of soybean root systems and severely damaged root cells. In contrast to the Al-resistant cultivar, the Al-sensitive cultivar Z.3 showed a larger plasma membrane permeability than Z.2 when treated with Al. In addition, the root elongation, activity, appearance of root tips and root hair zone were all altered by Al treatments. For example, after the 10 mg L⁻¹ Al treatment, the number of mitochondria had proliferated significantly in the root tip cells; plasmolysis was observed in the 30 mg L⁻¹ Al treatment; and the cell wall had ruptured and the cellular contents had disappeared in the high-level Al treatments. The results of our study showed in detail how soybean roots changed physiologically in response to Al stress.     

茶园土壤铝动态及茶树铝吸收特性

本文报告了在茶园和根际土壤铝动态及茶树铝吸收特性方面的一些研究结果。1.对210个样品测定,茶园土壤交换性铝含量为2.5-988mg/kg,平均238 mg/kg。无定形和层间铝是茶园土壤铝的主要形态;植茶后茶园土壤的水溶性、交换性和有机结合态铝趋于增加。2.茶园土壤交换性铝含量随施氮量的提高而增加;供给茶树NH_4~+-N时,茶树根际土壤(距根表 1mm)的交换性铝显著增加。3.铝在一定范围(≤400 μmol/L)增加茶树侧根数量和长度。4.动力学研究表明茶树根系对铝的吸收表现为可饱和特性,初始时有一快速的吸收过程,并在约6h后转变为缓慢的吸收。     

Weed control and sesame (Sesamum indicum L.) response to preplant incorporated herbicides and method of incorporation

Field studies were conducted at two sesame-growing regions of Texas in 2004 and 2005 to determine weed control and sesame response to four dinitroaniline herbicides and their method of incorporation. Ethalfluralin, pendimethalin (formulated as Prowl EC), and trifluralin were applied at the X, 1X, and 2X of the suggested label dose for Gossypium hirsutum L. Pendimethalin (formulated as Prowl H₂O) was applied at the X, 1X, and 1X rate. Two methods of incorporation included rolling cultivator mixing wheels and spring tooth harrow. With rolling cultivator mixing wheels, all herbicides controlled Amaranthus tuberculatus (Moq.) J.D. Sauer at least 74% regardless of dose. The X dose of ethalfluralin and pendimethalin (formulated as Prowl EC), or the X and 1X dose of pendimethalin (formulated as Prowl H₂O) controlled Brachiaria platyphylla (Griseb.) Nash no better than 73% while all other doses of the herbicides controlled B. platyphylla at least 80%. The use of mixing wheels to incorporate the herbicides resulted in better sesame stands and less stunting than the use of the spring tooth harrow; however, sesame stands were reduced as herbicide rate increased when using mixing wheels. Ethalfluralin at the 1X dose, pendimethalin (formulated as Prowl H₂O) at the X dose, and trifluralin at the X dose produced the highest sesame yield while ethalfluralin at the 2X dose produced the lowest yield.     

Biological control of Macrophomina phaseolina by chemotactic fluorescent Pseudomonas aeruginosa PN1 and its plant growth promotory activity in chir-pine

Ten strains of Pseudomonas aeruginosa (PN1 ˜ PN10) isolated from rhizosphere of chir-pine were tested for their plant growth promontory properties and antagonistic activities against Macrophomina phaseolina in vitro and in vivo. P. aeruginosa PN1 produced siderophore, IAA, cyanogen and solubilized phosphorus, besides producing chitinase and β-1,3-glucanase. In dual culture, P. aeruginosa PN1 caused 69% colony growth inhibition. However, cell free culture filtrate also posed inhibitory effect but to a lesser extent. After 90 days, P. aeruginosa PN1 increased plant growth and biomass in pots trial containing M. phaseolina-infested soil. PN1 showed the strong chemotaxis toward root exudates resulting in effective root colonization. Moreover, increased population in rhizosphere of these bacteria was also recorded after 90 days of treatment. Thus, chemotactic fluorescent P. aeruginosa PN1 exhibited strong antagonistic property against M. phaseolina, suppressed the disease and improved plant growth of the seedlings of chir-pine proving potential biocontrol agent.     

山药化感物质对山药和玉米种子萌发及幼苗生长的影响

本研究以山药零余子和玉米种子为受体材料,采用生物测试方法,以发芽率、发芽势、发芽指数、根长、茎长和干重为种子萌发和幼苗生长参数,研究山药植株腐解液、根系分泌物和根际土浸提液对受体材料的化感效应,旨在探明山药化感物质的释放途径,探索山药化感物质对不同受体材料的化感作用,为揭示山药连作障碍的机理奠定基础。结果表明：山药植株腐解液和根系分泌物对山药和玉米均有强烈的化感抑制作用,根际土浸提液的化感作用较微弱,化感作用强度为根系分泌物˃植株腐解液˃根际土浸提液,山药根系分泌物和植株腐解液含有丰富的化感物质,可能是山药自毒物质的主要来源之一,是山药化感物质研究的可靠基础材料;在试验设置的浓度范围内,山药化感物质对受体材料的抑制作用与其质量浓度呈正比,3种浸提液对受试材料的化感作用存在低促高抑的浓度效应,低于100 mg/mL时有微弱的促进作用,大于等于100 mg/mL就会产生强烈的抑制作用,随着浓度升高,化感抑制作用强度越大;山药的化感物质对玉米幼苗生长抑制强度大于种子萌发期,山药则相反;结合种子萌发和幼苗生长的综合化感效应指数,2种受试作物对山药化感作用的敏感程度为自毒作用强于他感作用。     

硫酸铝和硫酸酸化拟建茶园土壤的初步研究

用Ａｌ２（ＳＯ４）３和Ｈ２ＳＯ４作为酸化剂对拟植茶园的中偏碱性土壤进行土壤酸化试验，结果表明，两种酸化剂均能迅速酸化土壤，Ａｌ２（ＳＯ４）３的酸化效果高于Ｈ２ＳＯ４，前者能使土壤ｐＨ值明显下降，交换性酸总量显著上升。经淋洗后，交换性钙、镁含量明显下降，交换性钾、锰含量变化不大     

大豆生长及叶绿素荧光特性对铝胁迫的反应

采用溶液培养的方法，设置了不同的铝处理浓度和处理时间，对铝毒胁迫下的两个大豆品种（浙春2号、浙春3号）的根系生长和叶片的叶绿素荧光进行了研究。结果表明：铝抑制了大豆的根系干重、根系总长度、根系体积的增加。在高浓度的铝处理下，根系生长7 d后就受到了明显抑制。对茎叶干重的影响在14 d铝处理后才得到表现，茎叶部出现铝毒症状滞后于根部。根尖的根系活力在10 mg / L的铝浓度下有所增加，增强了根系吸收水分和矿质元素的能力。根系质膜透性随着铝处理浓度的增加而增大，在90 mg / L的铝处理下达到最大，植株受到严重伤害。低铝（10 mg / L）使大豆叶片的叶绿素含量少量增加，高铝（90 mg / L）胁迫叶绿素含量降低，且叶绿素a下降的幅度大于叶绿素b。荧光参数的研究表明，随着铝胁迫的增加，Fo下降，Fm、Fv / Fm增大，植株抵抗逆境的能力下降，光合电子传递减小，最终导致光合速率下降。两个大豆品种具有基因型差异，浙春2号比浙春3号更耐铝。     

Effect of rice-rice-rape rotation on physicochemical property and bacterial community of rhizosphere soil

Through collecting rhizosphere soil sample from a 30-year long-term fixed location test site that use “rice-rice-rape” crop rotation (RRR) and “rice-rice-fallow” continuous cropping systems (RRF), this paper investigated effects of long-term crop rotation on physicochemical property and bacterial community of rhizosphere soil. Results showed that total nitrogen (TN), total phosphorus (TP) and available potassium (AK) contents in rhizosphere soil under long-term RRR were decreased by 28.09%, 15.69% and 6.25% respectively. Alkali-hydrolyzable nitrogen (AN) and available phosphorus (AP) contents were 10.59% and 13.25% higher than those of soil in RRF respectively. Three soil samples collected during different periods also showed that RRR resulted in a lower rhizosphere soil pH than RRF. Clone library analysis revealed that significant difference in rhizosphere soil bacterial community was observed between RRR and RRF continuous cropping. Abundance of α-Proteobacteria, β-Proteobacteria and γ-Proteobacteria were higher in rhizosphere soil of RRR compared to RRF. pH of rhizosphere soil was significantly correlated with Acidobacteria level, while total organic carbon (TOC) content was significantly correlated with Proteobacteria level. Long-term RRR enhanced conversion of N and P in rhizosphere soil, increased bio-availability to crop, and promoted diversity of soil bacterial community. Bacterial diversity in RRR could be ecological significance in maintaining soil fertility and functionality.     

Effects of root exudates and pH on Plasmodiophora brassicae resting spore germination and infection of canola (Brassica napus L.) root hairs

Clubroot, caused by Plasmodiophora brassicae, is emerging as a serious threat to canola production on the Canadian Prairies. Germination of soil-borne resting spores (RSs) and their subsequent infection of canola root hairs are important requirements for the establishment of the clubroot pathogen in canola. Stimulation of RS germination by certain non-host plant species and elevation of soil pH by application of calcium-rich compost may provide some level of clubroot control in the field. Experiments were conducted under controlled conditions to determine the effects of (i) host and non-host root exudates (REs) and different pH values on the germination of RSs, and (ii) different pH values either alone or in conjunction with a Ca-containing nutrient solution (NS) on root hair infection of a susceptible canola cultivar. The percentage of RS germination was significantly enhanced when incubated with REs prepared in NS from three plant species compared to a NS alone or sterile dH₂O. Non-host REs from perennial ryegrass (Lolium perenne L.) produced higher spore germination than exudate preparations from canola (Brassica napus L.) and Chinese cabbage (Brassica rapa var. pekinensis, cv. Granaat) roots. The percentages of RS germination were higher at pH values ranging from 5.0 to <7.0, and lower at pH values >7.0 in both the presence and absence of REs. The effects of various pH values on the percent of root hair infection varied. Root hair infection was higher at relatively lower pH values (6.0–7.0) compared to either lower or higher pH values when a NS was added. It was however lower at pH values below 6.5 compared to those above 6.5 when the experiment was conducted in the absence of a NS. The possible impacts of REs, different pH values, and calcium levels in the soil on the severity of clubroot on canola are discussed.     

Root growth response of serradella species to aluminium in solution culture and soil

Serradella (Ornithopus) species are high‐quality pasture legumes that originate from the Mediterranean basin and have been increasingly used in southern Australian temperate grazing systems. They are generally regarded as tolerant of soils with low pH and, by inference, elemental toxicities such as aluminium (Al). No studies have examined the effect of high Al concentrations on the growth of French serradella (Ornithopus sativus Brot.) or newly developed cultivars of yellow serradella (O. compressus L.). Several cultivars/accessions of each species were grown in low ionic‐strength nutrient solutions at pH_Ca 4.5 containing a range of Al concentrations. Their susceptibility to root growth inhibition by Al was benchmarked against reference species ranging from Al‐sensitive to Al‐tolerant. Most serradella cultivars had moderate‐to‐high Al tolerance in solution culture but one yellow and two French serradella cultivars ranked alongside the Al‐sensitive reference species. A subset of cultivars and reference species were then grown in an Al‐toxic soil to test the validity of the solution culture results; these cultivars spanned the apparent range in Al sensitivity/tolerance indicated by the solution culture experiment. Variation in the relative root length achieved in Al‐toxic solution culture explained ~59% of the variation in the relative root length achieved in the acidic Al‐toxic soil. This result supports the conclusion that Al tolerance varies among serradella and that some cultivars may not thrive in soils with pH_Ca < 4.5 and elevated extractable Al concentrations.     

花生施钙对红壤旱土酸度及有害金属含量的影响

为探明花生施用钙肥对土壤酸度及有害金属元素铝、锰、镉、铅含量的影响，本研究选取大粒品种湘花2008、中粒品种湘花55、小粒品种蓝山小籽，以典型缺钙瘠薄酸性红壤旱土土柱试验，设置施钙与不施钙两个处理，测定根际土、0~20cm耕层土的pH值和有害金属元素含量。结果表明：各指标整体平均值受钙肥的影响，pH值增高4.93%，铝、镉、锰含量分别降低3.85%、2.13%、1.59%，铅含量升高0.66%。其中根际土，pH增幅远大于耕层土，湘花55＞湘花2008＞蓝山小籽；土壤铝含量降幅为根际土＞耕层土，湘花2008＞湘花55＞蓝山小籽；土壤锰含量降幅在耕层土湘花55＞湘花2008＞蓝山小籽，根际土大、中籽升高，小籽降低；土壤镉含量在耕层土、根际土降幅均以蓝山小籽最大，湘花2008小幅升高，湘花55有降有升；土壤铅含量大、中籽品种在根际土升幅大于耕层土，而蓝山小籽降低。