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91.
Seed mass is considered to be the least plastic component of reproductive yield. Yet, in invasive populations of garlic mustard, Alliaria petiolata, seed mass was highly variable (eightfold among populations, 2.5-7.5 fold within populations, two-threefold within individuals, and 1.4-1.8 fold within fruits). Variation in seed mass among populations explained nearly half of the total variance. Variation among seeds within fruits accounted for a further 25% of variance. Individual seed mass within a plant decreased with increased distance from the main stem, suggesting that access to parental resources limits seed size in a predictable manner. MANOVAs and Roy-Bargmann stepdown analyses revealed significant effects of seed mass, but not seed position (within a fruit or within an infructescence), on an array of subsequent seedling traits. Smaller seeds germinated significantly earlier, and seedlings from small seeds produced their first primary leaves significantly later and grew significantly taller. After accounting for seed mass as a covariate, only one seedling trait, date of first leaf emergence, was affected by seed position in a fruit. Differences in seed mass may therefore affect seedling recruitment via effects on early seedling growth in this weedy species. 相似文献
92.
The interaction between simulated cotyledon herbivory and interspecific competition was studied in a greenhouse experiment using two species of trees, Acer rubrum and Quercus palustris, which commonly invade abandoned agricultural fields. Herbivory treatments were applied as a gradient of cotyledon removal for A. rubrum with 0, 25, 50, 75, and 100% of cotyledon tissue removed. Cotyledons from Q. palustris were clipped and removed (control, early, and late removal) to create a gradient of seed reserve availability. The competition treatment consisted of plugs of old-field vegetation that filled the pots with perennial cover. Mortality of seedlings was higher with competition. There was a significant interaction between herbivory and competition with the highest mortality occurring with competition at the highest intensity of herbivory in both species. Herbivory reduced biomass for Q. palustris only, while competition reduced biomass in both species. Neither species showed an interaction between herbivory and competition for growth. There was a significant interaction between herbivory and competition on allocation patterns for both species, with greater allocation to roots with competition at the highest intensity of herbivory. This study demonstrates the potential for cotyledon herbivory and competition to interact, altering the invasion of tree seedlings into abandoned agricultural land. 相似文献
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94.
Field experiments were conducted in 2004 and 2005 to determine the effects of seed treatment with Rhizobium leguminosarum bv. viceae on damping‐off, seedling height, root nodule mass, root biomass, shoot biomass and seed yield of pea and lentil in a field naturally infested with Pythium spp. Compared with the untreated controls, treatment of pea seeds with R. leguminosarum bv. viceae strains R12, R20 or R21 significantly (P < 0.05) reduced incidence of damping‐off, promoted seedling growth and increased root nodule mass, root biomass and shoot biomass. Seed treatments with R12 or R21 also resulted in a significant (P < 0.05) increase in seed yield of pea. The strain R21 was most effective among the four strains of R. leguminosarum bv. viceae tested in peas. Although, the level of disease control by strain R21 was similar to seed treatment with the fungicide ThiramTM, R21 was more effective in enhancing root nodule production and promoting plant growth. For lentil, treatment of seeds with R. leguminosarum bv. viceae strains R12 or R21 significantly (P < 0.05) reduced incidence of damping‐off compared with the untreated control. All of the four strains of R. leguminosarum bv. viceae tested increased lentil seedling height, root nodule mass and shoot biomass, and all except R20 increased root biomass. Seed yield was higher for the treatments of R12 and R21. The strain R12 was most effective among the four strains of R. leguminosarum bv. viceae tested in lentil. Although, strain R12 was as effective as ThiramTM for control of damping‐off of lentil, it was more effective than ThiramTM for the production of root nodules and promotion of plant growth. The study concludes that seed treatment with R. leguminosarum bv. viceae is effective in control of Pythium damping‐off of pea and lentil and that the efficacy of control is strain specific, strain R21 for control of the disease on pea and strain R12 for control of the disease on lentil. 相似文献
95.
外源一氧化碳对干旱胁迫下水稻幼苗抗氧化系统的影响 总被引:4,自引:1,他引:3
以水稻(Oryza sativa L.) 品种‘D奇宝优1号'幼苗为材料,采用20%聚乙二醇(PEG-6000)模拟水分胁迫,研究外源一氧化碳(CO)对干旱胁迫下水稻幼苗抗氧化能力的影响,以探索CO提高水稻幼苗抗旱性的机制.结果显示,CO供体高铁血红素(Hematin,H)显著降低干旱胁迫下水稻幼苗叶片质膜相对透性和丙二醛(MDA)含量,提高脯氨酸和可溶性蛋白的含量,不同程度地促进叶片中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的活性,而CO清除剂血红蛋白(Hemoglobin,Hb)则逆转CO供体对干旱胁迫下水稻幼苗氧化损伤的缓解效应.由此表明,外源CO能通过调整保护酶活性和渗透调节物质含量来提高水稻幼苗的抗氧化能力,有效增强其抗旱性. 相似文献
96.
For reasons of the problems of establishment of some Ugandan trees in certain environments, we investigated the influence of temperature and light on germination and seedling growth of two locally threatened medicinal trees, Hallea rubrostipulata and Sarcocephalus latifolius, to facilitate their establishment. Field and controlled laboratory experiments were carried out to investigate the species germination requirements and seedling growth. Both species needed light to germinate. Hallea rubrostipulata had a temperature optimum of 25°C with 79% germination, while for S. latifolius, the total germination after 28 days was close to 60% at temperatures from 20 to 35°C. Seedlings of S. latifolius survived well at 35°C, while those of H. rubrostipulata died at this high temperature. Conversely, seedling of S. latifolius died at the low temperature of 15°C. However, in field experiment S. latifolius failed to germinate in the available degraded environments, probably because of predation and because the soil is not able to retain water long enough to support seedling growth. We, therefore, conclude that in this part of Uganda, nursery assistance is needed to establish healthy populations of Sarcocephalus and many other endangered trees. 相似文献
97.
Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland
Many early attempts at tallgrass prairie reconstruction failed to achieve the high species diversity of remnant prairies, and instead consist primarily of C4 grasses. We hypothesized that frequent mowing of established prairie grasses could create sufficient gaps in the aboveground and belowground environment to allow for the establishment of native forbs from seed. We studied forb seedling establishment in a 25‐year‐old prairie planting in northern Iowa that was dominated by native warm‐season grasses. In winter 1999, 23 species of native forbs were broadcast into the recently burned sod at a rate of 350 viable seeds/m2. Treatment plots were mowed weekly for either one or two growing seasons, and control plots were unmowed. Mowed plots had greater light availability than controls, especially when warm‐season grasses began to flower. Overwinter seedling mortality was 3% in mowed treatments compared to 29% in the controls. Forbs in mowed plots had significantly greater root and shoot mass than those in control plots in the first and second growing seasons but were not significantly more abundant. By the fourth growing season, however, forbs were twice as abundant in the mowed treatments. No lasting negative impacts of frequent mowing on the grass population were observed. Mowing a second year influenced species composition but did not change total seedling establishment. Experimental evidence is consistent with the idea that mowing reduced competition for light from large established grasses, allowing forb seedlings the opportunity to reach sufficient size to establish, survive, and flower in the second and subsequent years. 相似文献
98.
99.
100.
茂兰喀斯特森林林隙幼苗出现的时空格局 总被引:1,自引:0,他引:1
通过4次对茂兰自然保护区喀斯特森林林隙内种子的天然萌发情况进行观测,分析了林隙内幼苗的萌发数量、存活率及幼苗出现的时空分布格局。结果发现:林隙中大多数萌发的幼苗存活率均较高,平均存活率达50%以上,林隙的形成,不但提高了喀斯特森林树种的萌发率,也提高了幼苗的存活率。林隙中心、近中心、林隙边缘各区域幼苗的密度存在显著的空间差异,山拐枣(Poliothyrsis sinensis)、多脉榆(Ulmus castaneifolia)等树种在林隙中心幼苗密度最大,圆果化香(Platycarya longipes)、翅荚香槐(Cladrastis platycarpa)、圆叶乌桕(Sapium rotundifolium)、掌叶木(Handeliodendron bodinieri)、黄连木(Pistacia chinen-sis)和云贵鹅耳枥(Carpinus pubescens)等树种在林隙近中心幼苗密度最大,而樟叶槭(Acercinnamomifolium)、球核荚蒾(Viburnumpropinquum)、小叶青冈(Cyclobalanopsis myrsinaefolia)、轮叶木姜子(Litsea verticillata)等则在林隙边缘光照较弱的地方生长良好。幼苗出现的时间分布特征明显,整个观察期幼苗都持续萌发,但大多数树种幼苗出现在第2观测期(3月),幼苗出现数目从第2次到后面的几次观察期显著下降。林隙3个区域幼苗出现不是同步的,林隙中心的幼苗出现最快,与其它两个部位相比,林隙边缘的幼苗出现有滞后现象。研究结果表明林隙中心的环境条件有利于种子萌发,但林隙近中心却更利于幼苗存活。 相似文献