Growth responses of tropical forage plant species to vesicular-arbuscular mycorrhizae

Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.     

Influence of mefluidide on growth,development, and cell wall digestibility of sorghum

Application of mefluidide (N-[2,4-dimethyl-5-([(trifluoromethyl)sulfonyl]amino) phenyl]acetamide) inhibits plant development in perennial grasses. This study examined the effect of mefluidide on the morphological development and digestibility of sorghum. In the greenhouse, 5.9 × 10^–5 g active ingredient (a.i.) plant^–1 applied at the seedling, eight-leaf and boot stages reduced mean plant height 70%, 59%, and 2%, respectively. Heights were also reduced 14%, 15% and 35% by 5.9 × 10^–8, 5.9 × 10^–7 and 5.9 × 10^–6 gram a.i. plant^–1 applied at the eight-leaf stage. Field application of 0.26 or 0.52 kg ha^–1 mefluidide at either the eight-leaf or flagleaf stage reduced mean plant height of all cultivars. Basal tiller numbers increased 319% 28 d, and dry matter production was reduced 65% 42 d following mefluidide application at the eight-leaf stage. Treated stems were 34% higher and treated leaves were 7% higher in cellulase dry matter digestibility than control plants following mefluidide application at the eight-leaf stage. These results indicate that mefluidide application to vegetative stages in sorghum may enhance the forage value of the plants while it inhibits normal plant growth.     

Differential response of Trifolium species to 4-(2,4-dichlorophenoxy)butyric acid treatments

The differential response of white clover ( Trifolium repens L. cv. Regal Ladino) and berseem clover ( Trifolium alexandrinum L. cv. Mississippi ecotype) was investigated by treating greenhouse cultured plants with 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB). Berseem clover plants were significantly injured by a treatment concentration of 0.6 kg ha^-1 of 2,4-DB, whereas white clover plants were not injured by treatment levels below 2.4 kg ha^-1. The metabolism of 2,4-DB in cell suspension cultures of white clover and berseem clover was investigated using [ring-¹⁴C]-2,4-DB and non-labeled 2,4-DB. White clover cell cultures metabolized ca 4-fold more 2,4-DB than berseem cultures over a 44-h treatment period. The decrease in berseem cell population was 4-fold greater than the decrease in white clover cell population in response to the 8 μ M 2,4-DB treatment. The herbicide and its [ring-¹⁴C]-labeled metabolites were isolated from treated cells and medium after 44 h by partition and thin-layer chromatography. White clover cells metabolized 90% of the [¹⁴C]-2,4-DB and berseem clover cells metabolized 22% of the herbicide. The major portion of the radiolabel was in the glycoside fractions from extracts of both species. The differential response of Trifolium species to 2,4-DB is implied to be due to the differential rate of 2,4-DB metabolism to a glycoside by the clover plants.     

Effect of exogenous amino acids,glucose and citric acid on the patterns of short-term accumulation and loss of amino acids in the root-zone of sand-cultured forage rape (Brassica napus L.)

Amino acid loss from the roots of 25-day-old, sterile and non-sterile sand-grown forage rape plants, was determined over periods of up to 3.5 hours. Amino acid accumulation in the root-zone of sterile plants was concentration-dependent giving a convex accumulation profile. Amino acid levels in the root zone of non-sterile plants rapidly attained steady state values. Microbial assimilation of amino acids within the root zone appeared to lower amino acid concentrations, resulting in an underestimation of rates of amino acid loss from roots. The concentrations of most amino acids were higher after selected amino acids were supplied to the root zone. The response to exogenous acids was dependent on the concentration and composition of the acids added. Addition of a mixture containing ASN, GLN and GABA, each at 0.25 mM resulted in a greater increase in individual and total acid levels compared with a mixture containing ALA, SER, GLY and THR at the same concentration. Apparently, amino acids supplied exogenously competed with acids lost from the plant, by providing an alternative nutrient source for root zone micro-organisms. Addition of glucose and citric acid had a similar effect to addition of ALA, SER, GLY and THR, but were less effective than ASN, GLN and GABA at all concentrations tested. The nitrogen-rich amino acids ASN and GLN, and the -amino acid, GABA, appeared to compete more effectively with plant-derived acids than did ALA, SER, GLY and THR, the most abundent constituents of the plant-derived acids, which had the highest calculated rates of microbial consumption. Therefore, although bacterial consumption showed a dependence on amino acid concentration, a degree of selectivity for nitrogen-rich acids and gaba was also apparent.     

Patterns of short-term amino acid accumulation and loss in the root-zone of liquid-cultured forage rape (Brassica napus L.)

Amino acid release from roots of sterile and non-sterile, solution-grown, 7-, 21- and 60-days-old forage rape plants (Brassica napus L.), was measured over periods of up to 6 hours. With sterile plants, release of amino acids into a fixed volume of collection medium (6, 12, 70 mL) was concentration-limited, giving rise to similar convex accumulation profiles for individual acids. In contrast, amino acid accumulation in continuously circulating collection medium was not concentration limited, giving a linear accumulation pattern. The compositions of accumulating amino acids, which were similar to those measured in root extracts, did not change significantly. However, the proportions of ALA, GABA, GLU and ILE in both root extracts and root-derived amino acids increased as plants aged. Older plants released more amino acids per plant, while younger plants released more amino acids g^-1 root DW. Using non-sterile plants, the patterns of change in amino acid concentration and composition in the collection medium were completely different from those determined with sterile plants. In general, with 7-days-old plants, and 60-days-old plants that had recently become non-sterile, an initial rise in the concentration of all acids was followed by a fall to low levels. The loss of amino acids was apparently due to microbial consumption. Individual amino acids attained maximum concentration at different times during the collection process. This is attributed mainly to concentration-dependent differential assimilation of amino acids, since those with the highest initial concentrations, the major components of the mixtures released from roots, declined the earliest. When calculated rates of amino acid release from roots (R_r) and microbial consumption of amino acids (R_c) were compared (for 7-days-old plants), the highest ratios of R_c/R_r were found for ASN, ARG, GLU, GLN, and LYS. This suggests a degree of selectivity for glutamate and nitrogen-rich acids on the part of the consuming micro-organisms. With 21-days old plants and 60-days old plants grown entirely under non-sterile conditions, fluctuations in amino acid concentration were similar for all acids.     

Effect of soil moisture stress on yield,nodulation and nitrogenase activity ofMacroptilium atropurpureum cv. Siratro andDesmodium intortum cv. Greenleaf

Summary The effect of soil moisture stress on growth, nodulation and nitrogenase activity of two tropical forage legumes,Macroptilium atropurpureum cv. Siratro andDesmodium intortum cv. Greenleaf was studied in a pot experiment. After ten weeks growth, the highest moisture stress (20 per cent water holding capacity) significantly reduced only the top weight of both plants. Moisture stress progressively retarded top growth in the two legumes. Similar trends were also observed in defoliated plants. Moisture stress had little or no effect on the nodulation or nitrogenase activity of the plants.     

The first optic ganglion of the bee

Summary The arrangement of first and second order neurons in an optic cartridge and the topographical relationships of the second order neurons within a cartridge and to groups of surrounding cartridges have been analyzed in the visual system of the bee, Apis mellifera, from light and electron microscope studies on Golgi preparations. At the level of the monopolar cell body layer, the nine retinula cell fibres of each ommatidium, the six short visual fibres arranged in a circle surrounding the three long visual fibres, become cartridges as a consequence of the appearance of the second order neurons (L-fibres) which join the R-fibre bundles. Two of the four different L-fibre types, L-1 and L-2, remain together in the centre of the cartridge throughout the lamina. The axons of the L-3 and L-4 fibres, however, have their position integrated into the circle formed by the endings of the short visual fibres. On the basis of further examination of light and especially electron microscopical Golgi material, the different L-fibres can be classified into four types which appear in each cartridge. The clear stratification in the first synaptic region (A, B and C) seems to be the best criterion for a morphological classification since such a classification necessarily also includes a functional basis. According to a naming system based on the position of the lateral processes, L-fibres with side branches in strata A, B and C are called L-1 fibres. Fibres with lateral processes in strata A and B are L-2 fibres; monopolar cell fibres with branches only in the second stratum B are L-fibres of type 3; and all monopolar cells with branches only in stratum C are called L-4 fibres. In addition to the branching pattern covering only the parent cartridge, two of the four fibre types (L-2 and L-4) have long collaterals reaching neighbouring cartridges: L-2 in stratum A and L-4 in stratum C. These collaterals presumably form a substrate for lateral interactions.     

高寒山区植物根抗氧化酶系统的季节变化与抗冷冻关系

在高寒山区（海拔2900m）和选取4种多年生草本植物,即无芒雀麦（Bromus inermis）、草地早熟禾（Poa sphyondylodes）、花誉麦（Bromus sinensis）和垂重申披碱草（Elymus nutans）,测定了秋末、冬初、冬季、春季气温变化过程中其根中丙二醛（MDA）含量和抗氧酶活力（过氧化氢酶（CAT）、过氧化物酶（POD）、超氧物歧化酶（SOD））和抗坏血酸氧化酶（APX）变化,分析了抗氧酶系统在根抗冷适应中的作用,结果表明,随秋末降温植物根中MDA含量增加,尔后下降,在冬季和翌年春季保持相对稳定。从9月初到10月下旬,4种植物根中SOD、CAT、POD活力平均增加170％、130％和56％。在冬季下降,但仍远高于9月,在春季气温上升过程中酶活力上升。根能在组织结冰状况下生存与其具备完善的保护酶系统,能及时清除氧自由基抑制膜脂过氧化维持膜完整性有关,据降温过程中MDA含量和抗氧酶活力变化,可将根冷适应分为两个阶段,即第1阶段平均气温在0℃以上,抗氧酶活力增强,MDA增加阶段,第2阶段平均气温降至0℃以下,最低气温降到－15℃以下,抗氧酶活力下降,MDA无明显变化阶段。     

3种滨藜属牧草苗期叶片解剖结构及生理特性对干旱的响应

通过盆栽控水试验,设置5个干旱胁迫水平,分别为最大田间持水量的80%(CK)、60%(轻度胁迫)、45%(中度胁迫)、30%(重度胁迫)、20%(极重度胁迫),并同步设计充足灌水后自然干旱实验,测定干旱胁迫对3种滨藜属牧草叶片形态解剖结构、叶片相对含水量、叶绿素含量、净光合速率、可溶性糖含量、质膜相对透性和丙二醛含量等生理生化指标的影响,以明确3种滨藜属牧草的抗旱特性,并探索其抗旱机理。结果表明:(1)3种滨藜属牧草均具有适应旱生环境的典型叶片结构特征,即在干旱胁迫条件下叶片组织结构形态表现为叶片栅栏组织逐渐变薄,而海绵组织在胁迫早期先变薄后增厚的现象,叶肉组织结构紧密度也出现了先降低后增高的规律。(2)随着干旱胁迫的加剧,叶片的可溶性糖含量增加,而其相对含水量减少,3种滨藜属牧草在土壤含水量很低的情况下叶片仍能保持高于52%的相对含水量。(3)在干旱胁迫下,3种滨藜属牧草叶片的叶绿素含量、净光合速率、气孔导度和蒸腾速率都发生显著变化,细胞膜受到的伤害程度有明显差异。(4)3种滨藜属牧草抗旱能力均较强,在干旱胁迫下其抗旱性综合表现为灰白滨藜变种1灰白滨藜变种2四翅滨藜。     

覆盖材料和沟垄比对土壤水分和紫花苜蓿干草产量的影响

为寻求半干旱黄土高原区种植紫花苜蓿的适宜覆盖材料和最佳沟垄比,采用完全随机设计布置大田试验,以传统平作为对照,研究不同垄覆盖材料(土壤结皮、生物可降解地膜和普通地膜)和不同沟垄比(沟宽:垄宽分别为60∶30、60∶45和60∶60,单位是cm)对土壤水分和紫花苜蓿干草产量等的影响。结果表明:通过对2012年和2013年紫花苜蓿生育期降雨量统计,2a平均值显示,无效降雨次数(53次)大于有效降雨次数(27次),无效降雨对总降雨量的贡献率(19%)小于有效降雨(81%)。就紫花苜蓿全生育期而言,与平作相比,SR_(30)、SR_(45)、SR_(60)、BMR_(30)、BMR_(45)、BMR_(60)、CMR_(30)、CMR_(45)和CMR_(60)(SR、BMR和CMR分别代表土垄、生物可降解膜垄和普通膜垄,下标分别表示垄宽为30、45cm和60cm)连续2a的平均根层(0—140 cm)土壤贮水量分别提高12.8、19.2、24.4、26.0、30.7、40.5、29.9、37.1 mm和47.7 mm。垄沟集雨种植第1年龄和第2年龄紫花苜蓿根层没有出现明显干层。与平作相比,SR_(30)、SR_(45)和SR_(60)的连续2a紫花苜蓿平均实际干草产量分别降低3%、8%和13%,WUE分别提高52%、58%和55%;BMR_(30)、BMR_(45)、BMR_(60)、CMR_(30)、CMR_(45)和CMR_(60)的连续2a紫花苜蓿平均实际干草产量分别提高14%、12%、7%、17%、19%和9%,WUE分别提高49%、62%、59%、51%、67%和56%。当紫花苜蓿生育期降雨量为380.7—427.6 mm和沟垄比为60 cm∶35—36 cm时,生物可降解膜垄和普通膜垄的紫花苜蓿实际干草产量达到最大值,为该地区垄沟集雨种植紫花苜蓿提供参考。