根修剪对黄土旱塬冬小麦(Triticum aestivum)根系分布、根系效率及产量形成的影响

通过田间试验研究了不同时期根修剪处理对冬小麦（Triticum aestivum）根系大小与分布、根系效率、水分利用效率及产量形成的影响。设置4个根修剪处理：越冬期小剪根（WS）、越冬期大剪根（WB）,返青期小剪根（GS）、返青期大剪根（GB）,未剪根小麦作为对照（CK）。结果表明,到花期时,各根修剪处理小麦的在0～120cm总根量均显著小于对照。与对照相比各根修剪处理主要是显著地减少了上层土壤中的根量。但WS和GS两小剪根处理和对照相比在中层土壤中有较大的根量;花后各处理小麦旗叶的气孔导度和蒸腾速率均显著大于对照。这说明根修剪处理减少了小麦表层的根量,从而削弱了表土干旱信号对作物与外界气体交换的抑制作用。花期时各根修剪小麦的净光合速率均显著高于对照,而单位面积上的根呼吸速率均显著小于对照,根修剪处理提高了小麦的根系效率,使更多的光合产物用于籽粒生产,从而提高了小麦的收获指数。根修剪还提高了小麦的水分利用效率,其中WS、WB、GS处理的水分利用效率显著高于对照。但是GB处理的水分利用效率却没有显著提高。因此,本研究进一步证明了由不同年代品种得到的推测,认为在旱地农业中,通过遗传育种或采用适当农艺措施优化根系分布,既可以减少生长前期作物对水分的过度消耗,又能够削弱花后表土过度干旱对作物生长抑制作用,同时降低根系对同化产物的消耗,对作物产量及水分利用效率的提高具有积极的作用。     

差巴嘎蒿灌丛土壤和根系含水量对降雨的响应

以科尔沁沙地半固定沙丘灌木差巴嘎蒿(Artemisia halodendron)为对象,用土钻取样法和壕沟法研究了2006年生长季降雨后差巴嘎蒿周围土壤和根系含水量的时空分布特征及其相互关系,并计算了该灌丛的水量平衡.结果表明:该灌丛在降雨后对水分有暂时存储作用;降雨结束后,灌丛主干的茎流作用使得灌丛中心位置的土壤含水量高于灌丛丛幅垂直投影1/4和3/4处的土壤含水量;雨后6 h灌丛根系含水量与灌丛中心位置的土壤含水量呈极显著的负相关(r=-0.89,P＜0.01);灌丛根系含水量在雨后126 h内出现胁迫脉冲间歇反应.水量平衡计算表明,灌丛边缘外1 m处土壤蒸散量高于灌丛覆盖区的蒸散量,灌丛覆盖可降低土壤水分蒸散速率.     

额济纳绿洲胡杨（Populus euphratica）酚类物质含量和分布及其与土壤水分的关系

采用分光光度法测定了额济纳绿洲胡杨(Populus euphratica)的披针形叶、卵圆形叶、嫩枝、枝(D《5 mm)、枝(5～10 mm)、主干树皮、根(D《2 mm)、根(2～5 mm)和根(5～10 mm)9类器官中的总酚、黄酮和缩合单宁含量.结果表明,总酚含量较高的器官为皮(27.93 mg/s),叶、根、枝中总酚含量分别为17.64 mg/g(两类叶均值)、16.72mg/g(三类根均值)、12.19 mg/g(三类枝均值);黄酮含量较高的器官为皮(51.30 mg/g),叶、根、枝中黄酮含量分别为28.45 mg/g(两类叶均值)、39.99 mg/g(三类根均值)、23.67 mg/g(三类枝均值);根中缩合单宁含量较高,三类根均值为22.10 mg/g,皮、叶、枝中缩合单宁含量分别为8.41 mg/g、4.03 mg/g(两类叶均值)、4.47 mg/g(三类枝均值).披针形叶和卵圆形叶中酚类物质含量没有显著性差异(P》0.05);随着枝不断成熟,嫩枝、枝(D《5mm)、枝(5～10mm)中酚类物质逐渐减少;随着根直径减少,根中缩合单宁逐渐增加,细根(D《2mm)中的缩合单宁含量最高(25.95 mg/g).分析胡杨各器官中酚类物质含量与土壤水分的关系,结果表明卵圆形叶中酚类物质含量与土壤水分含量成显著负相关关系(P《0.05,总酚:r=-0.949;黄酮:r=-0.923;缩合单宁:r=-0.944).研究揭示了极端干旱地区胡杨各器官中酚类物质的变化规律,及其与环境因子的相互作用关系.     

白车轴草和紫花苜蓿根瘤的显微及超微结构

通过对白车轴草(Trifolium repens Linn.)和紫花苜蓿(Medicago sativa Linn.)根瘤的显微及超微结构进行观察,发现其根瘤显微结构都由4部分组成,由外向内依次为：保护层、皮层、鞘细胞层和中心组织(侵染组织)。在中心组织的侵染细胞中,分布有大量的线粒体、高尔基体、核糖体及内质网,白车轴草根瘤侵染细胞中的细菌圆形或椭圆形,有明显的周膜、细菌细胞壁和质膜,在细菌发育过程中,周膜活动旺盛,有时相邻细菌的周膜发生融合,在周膜附近常分布有大量的内质网、高尔基体以及高尔基体小泡,似与周膜融合有关。紫花苜蓿细菌椭圆形、长棒形,甚至有的细菌呈分枝状。二者细菌细胞质中分布着大量的核糖体和纤维状的核物质。在白车轴草中还有染色很深的多聚磷酸盐颗粒。     

铜对三叶草-土壤酶系统的影响

通过盆栽实验研究了重金属Cu污染对植物(三叶草)-土壤酶(脲酶、蔗糖酶、过氧化氢酶和多酚氧化酶)系统的影响.结果表明,随着Cu浓度增加,脲酶、蔗糖酶、过氧化氢酶和多酚氧化酶活性均逐渐减小,与Cu浓度有高度相关性,蔗糖酶>多酚氧化酶>脲酶>过氧化氢酶.在处理浓度不变情况下,酶活性随时间而变化,且呈现低Cu浓度(<00 mg·kg^-1)时4种酶活性均有所上升,而Cu浓度增高(00～3 000 mg·kg^-1)时各酶活性逐渐下降的趋势.统计分析表明,在每一梯度浓度上,4种酶在Ⅰ、Ⅱ、Ⅲ组内均存在显著差异性(P<0.01),与植物受重金属Cu污染时的生长情况一致.随着Cu浓度增加,土壤pH值逐渐下降,而电导率上升;同一Cu浓度下的pH值和电导率均随时间呈缓慢上升趋势,统计分析显示,二者在Ⅰ、Ⅱ、Ⅲ组内均存在显著差异性(P<0.01).土壤pH值和电导率与4种土壤酶活性有高度相关性,多酚氧化酶>蔗糖酶>过氧化氢酶>脲酶.这4种酶同时可作为检测土壤环境质量的指标.     

白三叶草生长期西花蓟马的空间分布型变化

利用聚集度指标检验和比较频次法对白三叶草Trifolium repens生长期间西花蓟马Frankliniella occidentalis的空间分布型变化进行研究,结果如下：聚集度指标检验分析表明西花蓟马在白三叶草上的空间分布为聚集分布;利用频次拟合分析表明白三叶草上大部分生长期内其分布型为负二项分布,其聚集程度与虫口密度有关系,其空间分布不会因为一些人为干扰而改变。     

三叶草根系分泌物对多环芳烃微生物降解及加氧酶的影响

为揭示根际效应对多环芳烃降解的影响机制,建立恰当的植物-微生物联合修复模式,本研究向含有微生物及多环芳烃(芘和苯并\[a\]芘)的微宇宙中加入三叶草根系分泌物,分析其对多环芳烃降解的影响,研究降解过程中微生物加氧酶和16S rDNA基因拷贝数的变化,并对具有多环芳烃降解能力的微生物进行鉴定.结果表明： 分枝杆菌M1具有降解多环芳烃的能力;三叶草根系分泌物总有机碳(TOC)浓度为35.5 mg·L^-1时,芘和苯并\[a\]芘降解率明显提高,分枝杆菌加氧酶基因所占比例增加,表明其促进了分枝杆菌对芘和苯并\[a\]芘的降解;在降解过程中,加氧酶基因拷贝数明显增加,而16S rDNA数量增加不明显,表明前者与多环芳烃降解过程有关,而后者和微生物数量有关.三叶草根系分泌物使分枝杆菌加氧酶基因拷贝数明显增加,从而促进了分枝杆菌对多环芳烃的降解.
     

放牧及土壤斑块质量对白三叶密度及分枝格局的影响

对白三叶长期禁牧草地及土壤斑块质量不同的春季休牧草地的研究结果显示,４月份,在中等放牧强度草地上,约有７６．５％￣８０．４％的白三叶植株为茎部出现断折的残株,放牧草地植株密度明显高于对照草地。放牧草地较好的土壤营养条件使白三叶单株构件数量明显上升,但使分枝强度略有下降。白三叶各构件密度之间存在显著正相关。不同样地上白三叶的分枝均以２、３级分枝为主。放牧草地的分枝角度大小顺序为：１级分枝角＞２级分枝     

Branch and root formation in Trifolium repens is influenced by the light environment of unfolded leaves

In plagiotropic plants, axillary buds on the stolon can be exposed to low red:far-red (R:FR) ratios, while the leaves may be positioned in the uppermost layer of the sward where they are exposed to a high R:FR ratio. We tested whether the light environment of unfolded leaves influences outgrowth of the axillary buds and the formation of nodal roots of Trifolium repens. Single plants were grown in a growth cabinet with high photosynthetic photon flux rate (PPFR) and a high R:FR ratio (F_HR_H, control), low PPFR and high R:FR (F_LR_H) or low PPFR and low R:FR (F_LR_L). In an additional treatment (SS), only stolons were shaded so that developing leaves grew into light conditions similar to the control treatment. Neutral shading (F_LR_H) had a minor effect on branching and did not influence root formation. A reduction in the R:FR ratio (F_LR_L) significantly delayed the outgrowth of axillary buds so that, compared to the control plants, the percentage of branched phytomers was reduced by 43% on the parent axis and by 75% on primary branches. Furthermore, the number of nodal roots per plant was reduced by about 30%. When only the stolons were shaded (SS), the percentage of branched and rooted phytomers was similar to that of the control plants. Extension of petioles and leaves was very variable, increasing the values in the F_LR_L treatment at least 2.5-fold compared with the control plants. It was concluded that the light environment of the unfolded leaves had a significant influence on the regulation of the outgrowth of axillary buds and that the high plasticity in petiole growth allows the positioning of the leaves in a light environment conducive to the stimulation of branch outgrowth. Received: 8 February 1997 / Accepted: 26 April 1997     

Effects of soil structural discontinuity on root and shoot growth and water use of maize

The role of roots penetrating various undisturbed soil horizons beneath loose layer in water use and shoot growth of maize was evaluated in greenhouse experiment. 18 undisturbed soil columns 20 cm in diameter and 20 cm in height were taken from the depths 30–50 cm and 50–70 cm from a Brown Lowland soil, a Pseudogley and a Brown Andosol (3 columns from each depth and soil). Initial resistance to penetration in undisturbed soil horizons varied from 2.5 to 8.9 MPa while that in the loose layer was 0.01 MPa. The undisturbed horizons had a major effect on vertical arrangement of roots. Root length density in loose layer varied from 96 to 126 km m^-3 while in adjacent stronger top layers of undisturbed horizons from 1.6 to 20.0 km m^-3 with higher values in upper horizons of each soil. For specific root length, the corresponding ranges were 79.4–107.7 m g^-1 (on dry basis) and 38.2–63.7 m g^-1, respectively. Ratios of root dry weight per unit volume of soil between loose and adjacent undisturbed layers were much lower than those of root length density indicating that roots in undisturbed horizons were produced with considerably higher partition of assimilates. Root size in undisturbed horizons relative to total roots was from 1.1 to 38.1% while water use from the horizons was from 54.1 to 74.0%. Total water use and shoot growth were positively correlated with root length in undisturbed soil horizons. There was no correlation between shoot growth and water use from the loose layers.     

Effects of VA mycorrhizal colonization on photosynthesis and biomass production of Trifolium repens L.

The influence of vesicular–arbuscular mycorrhizal (M) colonization on biomass production and photosynthesis of Trifolium repens L. was investigated in two experiments in which the foliar nitrogen and phosphorus contents of non-mycorrhizal (NM) plants were manipulated to be no lower than that of M plants. Throughout both experiments there was a stimulation in the rate of CO₂ assimilation of the youngest, fully expanded leaf of M compared with NM plants. In addition, M plants exhibited a higher specific leaf area compared with NM plants, a response that maximized the area available for CO₂ assimilation per unit of carbon (C) invested. Despite the increased rate of photosynthesis in M plants there was no evidence that the additional C gained was converted to biomass production of M plants. It is suggested that this additional C gained by colonized plants was allocated to the mycorrhizal fungus and that it is the fungus, by acting as a sink for assimilates, that facilitated the stimulation in the rate of photosynthesis of the plant partner.     

种间竞争梯度对白车轴草与其病原菌白车轴草单孢锈菌相互作用的影响（英文） 刘登义 Lars Ericson

 白车轴草(Trifolium repens)在与其病原菌白车轴草单孢锈菌(Uromyces trifolii-repentis)的长期相互作用中分化形成了抗病型(Resistance)无性系和易感型(Susceptibility)无性系。该研究工作旨在了解：1)在种间竞争不断增强的环境梯度中,抗病型无性系和易感型无性系的生长表现有何区别?2)在同样的实验条件下,分别对抗病型无性系和易感型无性系进行接种感染后,两者的生长表现又有何区别?在一严重感病的白车轴草自然种群中,分别标定17个抗病型无性系和14个易感     

豆链格孢菌对白车轴草生理代谢及活性氧清除系统酶的影响

通过盆栽实验,研究了接种豆链格孢菌对白车轴草叶组织细胞膜透性、色素含量、丙二醛(MDA)含量以及超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性的影响.结果表明,豆链格孢菌使白车轴草叶组织细胞膜透性上升,电导率显著升高,膜脂过氧化加强,MDA水平上升,色素含量下降.电导率和MDA含量均与感病时间呈显著正相关,而色素含量与感病时间呈显著负相关.豆链格孢菌刺激其寄主白车轴草叶片膜脂过氧化作用发生,积累大量的活性氧,使其超出防御酶的清除能力,致使活性氧清除系统遭到破坏,保护酶系统失衡,其中SOD和CAT活性显著下降,而POD活性明显上升.接种12d后,SOD和CAT分别降低了55.2%和37.8%,而POD比对照升高约1.6倍.