根系温度对番茄的影响(Ⅱ)—根系温度对番茄光合作用和水分代谢的影响

30℃根温时蕃茄光合速率最大,根温降低或升高时,光合速率均降低。不同根温影响光合作用的机制不同, 15℃根温影响了叶绿素含量及a/b比;40℃根温影响叶片水导、叶内CO₂分压并引起光合产物在叶片中的积累; 20-30℃根温时叶肉阻力等因素可能是光合作用的限制因子。30℃根温时蕃茄蒸腾速率最大,水分利用率最小,根温降低或升高,蒸腾速率均下降,水分利用率升高。低根温时,气孔部分关闭;高根温时,气孔关闭的同时根部阻力增大。     

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。     

黄土高原常用造林树种水分利用特征

在适宜土壤水分、中度干旱和严重干旱3种土壤水分条件下研究了黄土高原干旱、半干旱地区常用的人工造林树种84k杨树（Populus spp．）、刺槐（Robinia pseudoacacia）、沙棘（Hippophae rhamnoides）和油松（Pinus tabulaeformis）苗木生长及水分利用特征。结果显示,干旱胁迫使各树种成活率、生长速率、光合速率均显著下降;84k杨树和刺槐单叶水分利用率（WUE）在适宜水分下最高,沙棘的在中度干旱下最高;在中度干旱下,4个树种的总水分利用率最高。而严重干旱下最低。无论干旱与否,4个树种中沙棘生长速率最高。在中度干旱条件下,4个树种均可良好生长,而严重干旱下生长均受到显著抑制,其中84k杨树受影响最大;4个树种中沙棘和油松的耐旱性较强,同时油松在各种土壤水分下其生长速度和干物质生产均显著低于其它3个树种;刺槐和84k杨树的耗水量、生物量及水分利用率在3种土壤水分下均显著高于沙棘和油松,84k杨树和刺槐均属于高耗水树种;研究结果表明。84k杨树和刺槐不适宜大面积栽植在黄土高原缺水地区,仅适合栽植在阴坡、沟道等适宜水分条件下。沙棘和油松则适宜栽植在土壤水分较低的地区,如阳坡、峁顶等立地条件上。     

土壤大气湿度组合对玉米生长和WUE效应研究

采用人工气候生长箱盆栽试验,模拟土壤和大气湿度不同组合处理,发现土壤干旱和大气干旱显著抑制玉米生长。大气湿度提高,在一定程度能改善作物的水分状况,降低蒸腾,解除土壤干旱危害,产生生长和生理补偿效应,明显提高水分利用效率。     

The influence of ectomycorrhiza on nitrogen nutrition and growth of Pinus sylvestris seedlings

Ectomycorrhizal seedlings of Scots pine ( Pinus sylvestris L. cv.), inoculated with the fungus Suillus bovinus (L. ex Fr.) O. Kuntze, and non-mycorrhizal controls were grown in growth units with a circulating culture solution. Steady-state nutrition and constant relative growth rates were achieved by means of varied relative nutrient addition rates and free access of nutrients. Typical mycorrhizas always formed within a short period of time after inoculation. The nutrition/growth relationships were in principle similar to previous studies under steady-state conditions: there were close linear relationships between relative addition rate, relative growth rate and internal nitrogen concentration, i.e. an equilibrium established between nutrients added and taken up. This occurred when infected and uninfected seedlings were grown separately. When grown together in the same growth unit, there are indications that the fungus influenced the exudation pattern of the uninfected seedlings. More carbon was thus provided to the unspecified microflora in the cultivation system, and it was able to grow and withhold nitrogen from the seedlings. The mycorrhizal infection did not increase the specific uptake capacity of the roots, and the fungus constituted a sink for carbon. However, the nitrogen productivity (growth rate per unit of nitrogen per unit of time) was similar for mycorrhizal and non-mycorrhizal seedlings, so that there might be mechanisms which compensate for the carbon cost.     

Sensitivity of white clover to UV-B radiation depends on water availability, plant productivity and duration of stress

Abstract Nine populations of white clover ( Trifolium repens L.) were grown for 12 weeks with supplemental application of 13.3 kJ m⁻² d⁻¹ ultraviolet-B (UV-B) radiation under controlled environmental conditions. Drought was applied during the last four weeks of the experiment. Under well-watered conditions, UV-B decreased white clover growth on average by 20%. Cultivars bred for agricultural performance were sensitive to UV-B, while slow-growing ecotypes were UV-B-tolerant. After four weeks of water stress, there were no significant population differences in UV-B responsiveness. UV-B sensitivity decreased with increasing exposure to drought and with longer duration of UV-B irradiation, suggesting that the direction and extent of the UV-B 3× drought interaction depends on the duration of stress. The population comparisons indicate that low constitutive growth rate and adaptation to other forms of stress may be related to UV-B tolerance under well-watered conditions, but not during extended periods of drought.     

Phosphorus concentrations in the leaves of defoliated white clover affect abscisic acid formation and transpiration in drying soil

Increased leaf phosphorus (P) concentration improved the water-use efficiency (WUE) and drought tolerance of regularly defoliated white clover plants by decreasing the rate of daily transpiration per unit leaf area in dry soil. Night transpiration was around 17% of the total daily transpiration. The improved control of transpiration in the high-P plants was associated with an increased individual leaf area and WUE that apparently resulted from net photosynthetic assimilation rate being reduced less than the reductions in the transpiration (27% vs 58%). On the other hand, greater transpiration from low-P plants was associated with poor stomatal control of transpirational loss of water, less ABA in the leaves when exposed to dry soil, and thicker and smaller leaf size compared with high-P leaves. The leaf P concentration was positively related with leaf ABA, and negatively with transpiration rates, under dry conditions ( P < 0.001). However, leaf ABA was not closely related to the transpiration rate, suggesting that leaf P concentration has a greater influence than ABA on the transpiration rates.     

Effect of four acid soils on root growth of white clover seedlings using a soil-on-agar procedure

White clover (Trifolium repens L.) is widely distributed in the Appalachian region, except on highly acid soils. We used a procedure where a thin layer of soil is placed on top of solidified water agar to characterize effects of acid soil on seedling root growth. Our objectives were to evaluate the soil-on-agar technique by using four soils (non-limed and limed) with diverse chemical characteristics and to relate root emergence to the chemical properties of the soils. We used three white clover cultivars, Grasslands Huia, Grasslands Tahora and Sacramento. Daily counts of root emergence from soil into agar were made for 12 d. Liming hastened white clover root emergence in three of the four soils. Days to 40% emergence were closely related (P < 0.01) to soil pH and to species of soil solution Al that are associated with Al toxicity in dicotyledonous plants. The r2 values for the regression of days to 40% root emergence on were 0.95, 0.96, 0.94 and 0.96, respectively. Apparently, the primary factor responsible for delayed root emergence in the soil-on-agar procedure was Al toxicity. Because of the close relationship between root emergence and activity of toxic species of soil solution Al, we propose that the soil-on-agar technique should be useful for characterizing the response of many small-seeded species to Al.     

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。     

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