喷施茉莉酸对铝胁迫紫花苜蓿光合系统的影响

通过外源喷施不同浓度茉莉酸(5、25、50μmol/L),研究了茉莉酸对铝胁迫下紫花苜蓿幼苗生长和光合特性的影响。结果表明,100μmol/L AlCl_3处理使得紫花苜蓿生长受到抑制,其叶绿素含量下降,叶片的光合速率、气孔导度和蒸腾速率降低,光系统I (PSI)和光系统II (PSII)的相对电子传导速率、P700活性和环式电子传递量(CEF)也明显降低。外源喷施低浓度茉莉酸(～5μmol/L)对缓解苜蓿铝毒害的作用最为显著。外源喷施低浓度茉莉酸(5μmol/L)时,苜蓿根长、地上和地下生物量明显高于铝胁迫处理,同时叶绿素含量、光合速率、气孔导度和蒸腾速率明显升高;PSI和PSII的相对电子传导速率、P700活性和CEF值显著增加。而喷施过高浓度茉莉酸(～50μmol/L)对铝胁迫下紫花苜蓿的生长无明显缓解作用。研究结果表明低浓度茉莉酸对苜蓿铝毒害的缓解作用与茉莉酸改善铝胁迫苜蓿的光合作用和光化学系统电子传递能力密切相关。     

外源有机质存在下钙铝交互作用对茶园土壤铝的吸附能力与活性的影响

通过实验室模拟,研究不同含量外源有机质存在下（5%、10%和15%）,钙铝交互作用（钙/铝摩尔浓度比为1∶2、1∶1和2∶1）对茶园土壤铝的吸附能力和活性的影响。结果表明,钙铝交互作用显著增加了茶园土壤对铝的吸附量,外源有机质对钙铝交互作用下茶园土壤铝的吸附作用影响不明显;钙铝交互作用使茶园土壤水溶态铝含量增加,交换态铝含量下降,且随钙/铝比的增大交换态铝含量下降越显著;但外源有机质使钙铝交互作用下茶园土壤的水溶态铝含量下降,同时交换态铝含量显著增加。总的看,外源有机质使钙铝交互作用下茶园土壤活性铝含量增加,且随外源有机质含量的增加,活性铝含量增加的越显著。     

铝合金温室拱形ETFE膜屋面抗风性能分析

为分析铝合金结构拱形ETFE(乙烯-四氟乙烯热塑性聚合物)膜屋面的抗风性能,提高其设计的安全性,该文根据单轴拉伸试验数据,确定了ETFE薄膜材料的力学参数和应力应变关系;基于几何非线性有限元理论,推导了膜单元的基本方程;利用大型通用有限元软件ANSYS,采用支座提升法对骨架式拱形ETFE屋面进行了找形分析,建立了用于荷载分析的计算模型;对拱形ETFE屋面在风荷载工况下进行了算例分析,计算了膜面主应力分布和变形特征;分析了不同膜面预应力水平对承载性的影响。分析结果表明,风荷载主要影响ETFE膜屋面第一主应力的分布,适当增加膜面预应力可以显著提高其整体刚度和承载力。研究结论为铝合金温室拱形ETFE屋面的抗风计算分析和施工提供了参考。     

Effects of tillage systems on soil physical properties,root distribution and maize yield on a Colombian acid-savanna Oxisol

Abstract

Tillage systems may affect many soil properties, which in turn may alter the soil environment and consequently impact on root growth and distribution, and crop yield. In 1993, a long-term field experiment on sustainable crop rotation and ley farming systems was initiated on a Colombian acid-savanna oxisol to test the effects of grain legumes, green manures, intercrops and leys as possible components that could increase the stability of systems involving annual crops. In the present study, five agropastoral treatments (maize monoculture, maize-soybean rotation, maize-soybean green manure rotation, native savanna, maize-agropastoral rotation) under two tillage systems (no tillage and minimum tillage) were investigated. Lower bulk density and higher total porosity for all treatments and soil layers were found in no-tillage compared to the minimum tillage system. Between the two tillage systems, significantly higher maize grain yields (p<0.1) were obtained under no-tillage agropastoral treatments compared to the same treatments under minimum tillage. Maize yields on native savanna soils were markedly lower than in the rest of the treatments, indicating the need for improved soil conditions in subsoil layers for root growth of maize.     

The Cerrado of Brazil: A Success Story of Production on Acid Soils

The Brazilian Cerrado region which covers an area of 180 million ha is characterized by soils with favorable topography but very poor soil fertility, and due for that, it was considered until recently, unsuitable for agriculture. Liming for base saturation of 50%, in general, together with PKS and micronutrients correction allowed this region to become one of the most important “break baskets” of the world. In recent years the adoption of the notillage system is showing the relevant role of organic matter on soil fertility improvement. This region is now responsible for over 50% of the country soybean, corn, coffee and beef production.     

Distribution of Accumulated Aluminum and Changes in Cell Wall Polysaccharides in Eucalyptus camaldulensis and Melaleuca cajuputi under Aluminum Stress

Distribution of aluminum (Al) within plant components and Al-induced changes in cell wall polysaccharides in root tips of Eucalyptus camaldulensis Dehnh. seedlings were compared with those of Melaleuca cajuputi Powell. In E. camaldulensis, 0.5 mM Al (pH 4.2 for 40 d) reduced plant dry weight by 50%, increased callose concentration in the root tips and induced leaf necrosis. In comparison with M. cajuputi, Al concentrations were higher in roots and leaves of E. camaldulensis on both a fresh weight basis and in the cell sap, but were lower in the cell wall. Al increased pectin, hemicellulose and cellulose concentration in the cell walls of E. camaldulensis root tips. Al-induced leaf necrosis and growth reduction in E. camaldulensis is discussed in the context of potentially toxic concentrations of Al in plant tissue and changes in polysaccharide content which could reduce water and nutrient uptake and cell wall extensibility in roots.     

铝和镉胁迫对两个大麦品种矿质营养和根系分泌物的影响

A hydroponic experiment was carried out to study the effect of aluminum （Al） and cadmium （Cd） on Al and mineral nutrient contents in plants and Al-induced organic acid exudation in two barley varieties with different Al tolerance. Al- sensitive cv. Shang 70-119 had significantly higher Al content and accumulation in plants than Al-tolerant cv. Gebeina, especially in roots, when subjected to low pH （4.0） and Al treatments （100 μmol L^-1 Al and 100 μmol L^-1 Al ＋1.0 μmol L^-1 Cd）. Cd addition increased Al content in plants exposed to Al stress. Both low pH and Al treatments caused marked reduction in Ca and Mg contents in all plant parts, P and K contents in the shoots and leaves, Fe, Zn and Mo contents in the leaves, Zn and B contents in the shoots, and Mn contents both in the roots and leaves. Moreover, changes in nutrient concentrations were greater in the plants exposed to both Al and Cd than in those exposed only to Al treatment. A dramatic enhancement of malate, citrate, and succinate was found in the plants exposed to 100 μmol L^-1 Al relative to the control, and the Al-tolerant cultivar had a considerable higher exudation of these organic acids than the Al-sensitive one, indicating that Al-induced enhancement of these organic acids is very likely to be associated with Al tolerance.     

有机酸对森林土壤pH及铝形态变化的影响

采用连续提取法研究低分子量有机酸对南方酸性森林土壤pH及铝形态变化的影响.结果表明,在酸性土壤上,有机酸处理后土壤pH降低,土壤可溶性铝和有机络合态铝增加,交换态铝(Al3+)、单聚体羟基铝[Al(OH)2+、Al(OH)2+]和酸溶无机铝[Al(OH)3]减少,土壤中不同形态的铝都有向有机络合态铝转化的趋势,这种转化降低了土壤活性铝的含量,有利于减轻土壤铝对植物的危害,但不同的有机酸由于其性质和结构不同,对土壤铝形态转化的影响不同.土壤中各形态铝含量上层土壤大于下层土壤.     

腐植酸共聚物对赤红壤中活性铝的影响

研究了以合成腐植酸、丙烯酰胺、丙烯酸共聚物作为土壤结构改良剂改良赤红壤后，其土壤中活性铝的形态及含量变化．结果表明，该共聚物可抑制土壤中铝的活性，改良后的土壤活性铝的存在形态有所改变，活性铝的含量减少，土壤的pH提高．     

140份甜玉米自交系耐铝性鉴定

以华南农业大学选育的140份甜玉米自交系为材料,利用0.4 mmol·L-1的AlCl3溶液处理玉米幼苗,测定其相对根长、相对叶绿素含量、相对株高、相对鲜重和相对干重等值并汇总排序,进行耐铝性鉴定分析评价.结果表明,系统聚类分析将140份甜玉米自交系分为4个类群,类群Ⅲ中自交系平均耐铝水平较高.分析140个甜玉米自交系...