Effect of temperature on germination and early growth of subterranean clover, capeweed and Wimmera ryegrass

Germination of annual pasture species was studied under controlled‐environment conditions in south‐western Australia at temperatures in the range from 4°C to 35°C. Subterranean clover (Trifolium subterraneum) and Wimmera ryegrass (Lolium rigidum) had a germination of 90% between 12°C and 29°C, whereas capeweed (Arctotheca calendula) had a high germination percentage in a much narrower temperature range with an optimum of 25°C. Growth of subterranean clover, capeweed and Wimmera ryegrass between 28 and 49 days after sowing (DAS) was also studied at two photon flux densities, 13 and 30 mol m^?2 d^?1, and at diel temperatures in the range from 15/10°C to 33/28°C. Pasture species grown at a density of 1000 plants m^?2 accumulated at least twice the amount of shoot dry matter when subjected to temperatures of 21/16°C and 27/22°C, compared with a lower temperature of 15/10°C and a higher temperature of 33/28°C. Except at the highest temperature and at high photon flux density, capeweed had lower green area indices (GAI) than the other two species at 28 DAS. Crop growth rates between 28 and 49 DAS were higher in Wimmera ryegrass than in the other two species, whereas subterranean clover had a lower relative growth rate than the other two species at all temperatures and both photon flux densities. Subterranean clover and capeweed intercepted a greater proportion of the incident radiation compared with Wimmera ryegrass. The values of radiation interception and GAI were used to estimate the number of DAS to reach 75% radiation interception [f_(0·75)]. The number of days to reach f_(0·75) decreased with increasing temperature from 15/10°C to reach a minimum at 27/22°C. The time taken to achieve f_(0·75) was always shorter by about 10 d when the photon flux density was 30 mol m^?2 d^?1 in the autumn compared with 13 mol m^?2 d^?1 in the winter. These results are discussed in relation to the early growth of annual pasture in the field.     

Root and shoot competition between established grass species and newly sown seedlings during spring growth

Competition between established Dactylis glomerata or Festuca pratensis / Taraxacum officinale swards and seedlings of Trifolium pratense was studied under field conditions in Norway. Root competition from the Festuca pratensis / Taraxacum officinale sward was significantly greater than that from a Dactylis glomerata sward. The balance in root and shoot competition varied between experimental years because of variation in environmental conditions. In the first experimental year, root competition had a greater effect on seedling dry weight than shoot competition, whereas the opposite was found in the second year. However, both root and shoot competition (full competition) in comparison with no competition gave proportionally the same effects in both years, indicating that an alleviation in root competition will be followed by intensified shoot competition. An increasing effect of shoot competition with time on plant dry weight was found. In a second experiment, seedlings of Lolium perenne and Trifolium pratense produced the highest plant dry weights in competition with an established Phleum pratense sward, followed by seedlings of Poa pratensis , Phleum pratense and Trifolium repens in decreasing order. However, no interactions between seedling species and competition treatments were found, indicating no differences in sensitivity between seedling species to competition from the established grass sward. The results are discussed in the context of renovating grassland by direct drilling.     

Pasture legumes differ in herbage production and quality throughout spring,impacting their potential role in fodder conservation and animal production

This study reports on the herbage production and quality of a range of pasture legume species during spring, at three sites with moderate to strongly acidic soils in southern NSW, Australia. These data have enabled prediction of livestock production when legumes are conserved as silage or hay. Total herbage production, its timing and quality differed significantly between species, which generally was not predicted by the traditional metric of time to flowering. Trifolium incarnatum L., T. michelianum L., Biserrula pelecinus L., Ornithopus sativus Brot. and Hedysarum coronarium L. all maintained growth rates exceeding 200 kg DM/ha/d for 4 weeks over spring, while T. vesiculosum Savi. maintained this for 6 weeks, with a peak growth rate of 561 kg DM/ha/d. Herbage quality of all species declined over time and was greatest in species with a rapid increase in stem‐to‐leaf ratio or with weak stems, resulting in lodging. The modelling inferred that maximizing potential livestock production via fodder conservation required earlier cutting. Only the indeterminate species B. pelecinus and Ornithopus spp. increased potential liveweight gain per hectare through delayed harvesting from (probable) silage to hay‐making time.     

三峡库区野生红三叶苗期抗旱性灰色关联分析

以三峡库区采集的9份野生红三叶和3份国内外品种为材料,在干旱胁迫下,测定其地上生物量、地下生物量和脯氨酸含量等10项指标,进行灰色关联度分析。结果表明,筛选出地下生物量、脯氨酸含量和叶绿素a含量3项可对红三叶抗旱性进行评价的指标;根据红三叶抗旱性评估模型综合评估值(φ_K)得出材料的抗旱性排序为:瑞德(Red)>CQ5>CQ9>多丽(Dory)>CQ2>CQ4>CQ7>CQ3>CQ1>巫溪>CQ8>CQ6。     

微囊藻毒素(MC-RR)对白三叶种子萌发及幼苗生理生化特性影响

以白三叶种子和幼苗为材料,研究了不同浓度MC-RR对白三叶种子萌发、抗氧化酶活性变化以及MC-RR在白三叶体内积累规律。结果表明,发芽率和发芽势随着处理浓度的增加而降低,在高浓度处理下,与对照相比显著降低;株高随着MC-RR处理浓度增加而显著降低,根长和鲜重在低浓度处理下显著增加,在高浓度处理下显著降低;抗氧化酶活性的变化不尽相同,SOD活性随着处理浓度的增加与对照相比呈先增加后降低而后又增加的趋势,POD活性随着处理浓度的增加呈先增加后降低的趋势,CAT活性的变化趋势不同于SOD和POD;单位鲜重白三叶MC-RR含量随着处理浓度的增加与0.05 mg/L处理下的MC-RR含量相比显著增加,而生物富集系数的变化趋势则与单位鲜重白三叶MC-RR含量相反,随着MC-RR处理浓度的增加而降低。说明随着MC-RR处理浓度的增加,白三叶受到的伤害增大。     

Nitrogen:sulphur ratio alters competition between Trifolium repens and Lolium perenne under cutting: Production and competitive abilities

Grasslands species, like others crops, no longer benefit from high atmospheric sulphur deposition. This may cause sulphur limitation and in turn may induce a shift in plant communities by altering species performance and competitive abilities. To test this hypothesis, a greenhouse pot experiment was designed to investigate the interacting effects of sulphur (S) and nitrogen (N) availability on production, morphology and competitive abilities of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). Plants were grown in monocultures and mixtures during 4 months. They were supplied with combinations of three levels of S and three levels of N and subjected to three defoliation events. Both S and N gradients altered plants performance and modulated competitive interactions. In L. perenne, above- and below-ground dry matter production, leaf and tiller number and contribution to mixture DM production were little affected by S, but highly by N. For T. repens, these traits were significantly increased by S, but only slightly by N. At establishment, T. repens was subjected to a significant interspecific competition at low N–low S and high N–high S. But at regrowth (cuts 2 and 3), T. repens was much more affected by intra- than interspecific competition. L. perenne was only sensitive to competition (intraspecific) when N supply was combined with no or moderate S supply. We conclude that N:S ratio of soil appears to drive species production, morphology and competitive abilities, which in turn affect leguminous–gramineous species ratio and grassland plant community structure. Since the growth of T. repens was significantly reduced in low S treatments, our results suggest that the drastic fall in atmospheric sulphur deposition could restrict leguminous species in high N soil conditions.     

马蹄金草坪的建植与养护技术

马蹄金属C3植物 ,具有相对较高的光饱和点 ,对光有较强的适应性 ,很适应云南气候环境 ,在云南广泛推广应用 ,为城市绿化增色不少。总结了 1990年至今对马蹄金草坪的建植与养护管理技术 ,为马蹄金草坪管理提供理论依据     

苜蓿花叶病毒粒子的统计学特征和分组

以一株来自于白车根草（Trifolium repens L.）上的苜蓿花叶病毒分离物AMV-SY为材料,在电镜下观察测量经醋酸铀负染的196个提纯病毒粒子,按其长度分成等距离的5个组,用统计分析方法确定组间的差异。所得各组粒子的平均大小依次是组Ⅰ：(20.4 ±2.5) nm×(18.7±2.3) nm,组Ⅱ：(28.0 ±2.4) nm×(18.1±2.1) nm,组Ⅲ：(36.0 ±2.4) nm×(17.2±2.0) nm,组Ⅳ：(44.8 ±2.7) nm×(16.9±2.0) nm,组Ⅴ：(52.0 ±3.0) nm×(17.4±1.0) nm。它们分别相当于前人根据X-射线衍射或核磁共振所测定的Ta-t,Ta-b,Tb, M和B型病毒粒子。方差分析表明,5组病毒粒子间长度差异极显著,即组Ⅰ<组Ⅱ<组Ⅲ<组Ⅳ<组Ⅴ;病毒粒子宽度差异也极显著,但仅组Ⅰ粒子的宽度明显大于组Ⅳ 和组Ⅲ,说明在没有病毒RNA参与的情况下,单由不含病毒RNA的外壳蛋白亚基所构成的粒子其横向结构较为松散。对AMV统计分析的结果与前人根据对病毒粒子结晶中典型的粒子进行X射线衍射分析或计算机模拟所获得的结果基本吻合,但组Ⅴ粒子,即最长一组AMV病毒粒子的统计长度明显小于结晶中X-射线衍射分析所测得最长的B型粒子。     

Genetic variation in a Norwegian germplasm collection of white clover (Trifolium repens L.)

Phenotypic (r_p), genotypic (r_g), genotype × location (r_gl) and error (r_e)correlations for important agronomic characters were estimated for eleven Norwegian populations of white clover (Trifolium repens L.), originating from between 58^°52′N and 69^°30′N latitude, and from altitudes of 10 to 450 m a.s.l. The populations were evaluated in monoculture clonal field plots for two years at two locations in Norway. All pairwise correlations between foliage height, leaflet length, dry matter yield (DMY) and general performance were positive and significant. Winter survival was positively correlated with general performance, spring growth and DMY, but negatively associated with internode length, while seed yield showed a small positive genotypic correlation with foliage height. Considerable differences were, however, revealed among populations with regard to sign and magnitude of the estimated correlations. Within-population estimates of r_g were consistently positive between DMY, general performance and most other characters; between foliage height on the one hand and leaflet length, winter survival and seed yield on the other hand, and between internode length and leaflet length, indicating pleiotropy. Correlations involving other character-combinations varied substantially among populations, and imply presence of linkage and/or coadaptation. Path coefficient analysis was used to partition the genotypic correlations between some of the characters into direct and indirect effects. Path coefficients revealed that foliage height had the highest positive direct effect on DMY, followed by winter survival and internode length. Leaflet length, which showed a positive, significant simple correlation with DMY, exhibited a negligible direct influence, counterbalanced nearly completely by the positive indirect effect on DMY via foliage height. Positive indirect effects on DMY via foliage height were also found for winter survival and internode length. The coastal populations from North and Middle Norway, and a southern highland population showed the largest expected responses to phenotypic selection for most of the characters. The results demonstrate that there is enough genetic variation in adapted local populations to develop new improved cultivars adapted to high-latitude environments that combine upright growth habit with sufficient winter-hardiness and persistency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrogen Fixation in Hybrids of White Clover (Trifolium repens L.) and Caucasian Clover (Trifolium ambiguum M. Bieb)

Hybrids between white clover (Trifolium repens L.) and Caucasian clover (or Kura clover, Trifolium ambiguum M. Bieb) are a potential route for the improvement of drought tolerance and persistence in white clover. However, to be agronomically viable they must show no significant reduction in their potential for nitrogen fixation relative to white clover. A comparative study of growth rate and nitrogen fixation was carried out in flowing solution culture without a supply of mineral nitrogen to the plants. The two parental species and two generations of backcross hybrids, with white clover as the recurrent parent, were assessed. The growth rate and N content of T. ambiguum were significantly lower than those of the other lines. However, dry matter production, nodule biomass per plant and rates of fixation were similar in second‐generation backcross plants and white clover. The results suggest that the agronomic potential of this novel germplasm is not compromised by limitations with respect to nitrogen fixation.