羊草种群种子生产的初步研究

 本文报道了国产优良牧草——羊草,在不同人为干扰的环境条件下,种群种子生产数量性状变化的若干规律。种群密度是成穗率的限制因素之一,在平均为604.7株／m2中等密度的数年割草场上,成穗率随密度增加呈幂函数y=dx-b形式下降,而在平均为1604.9株／m2高密度的长期连续割草场上,成穗率随密度增加呈直线y=a-bx形式下降。种子发芽率与千粒重呈显著正相关(r＝0.9768**)。放牧对成穗有不良影响,但对籽粒的干物质积累过程有一定的促进作用。长期连续割草对种群生殖生长的整个过程均不利,停刈后,自然恢复的速度缓慢。     

放牧影响下羊草种群生殖生态学的研究

在种群水平上系统研究了放牧对松嫩草原关草种群无性繁殖、有性生殖和生物量的生殖分配的影响。结果表明,放牧制约了羊草种群无性繁殖和有性生殖的更新途径,表现在随放牧强度增加,无性繁殖体营养技密度、根茎牙密度和有性生殖体种子生物量、结实数和生殖枝分化率等指标均显著下降,是生牧后下降迅速。随放牧强度增加,关草种群根茎生物量的分配比例显著增加,而同化器官、非同化器官和种子生物量分配比例都显著下降,极牧阶段几科     

Plastic responses of stem and leaf functional traits in Leymus chinensis to long-term grazing in a meadow steppe

植物对不同功能性状进行权衡, 通过表型可塑性达到对异质生境的适应是植物的一种生态对策。羊草(Leymus chinensis)是欧亚温带草原东缘的主要优势植物, 研究其对放牧的表型反应对揭示草原生态系统的放牧响应机制具有代表意义。该文以内蒙古呼伦贝尔草甸草原为例, 通过设置不同放牧压力与围封的长期试验, 研究了羊草茎叶功能性状对放牧的可塑性响应模式。结果表明: 1)与长期围封相比, 长期放牧导致羊草茎叶性状显著小型化, 其中, 株高和个体地上生物量分别降低76.82%和89.88%, 但3年短期围封对茎性状影响不显著, 说明羊草表型矮小化现象具有一定的保守性; 2)通过排序构建羊草性状可塑性变化谱, 发现茎质量、总质量、茎高、株高、叶面积等为对放牧响应的敏感性状, 而叶片数、茎粗、叶宽等较为稳定, 为惰性性状; 3)放牧干扰下, 羊草性状可塑性程度与其变异性之间符合y = y₀ + ae^bx拟合关系, 随着植物性状的响应强度增大, 其变异性增强; 4)偏最小二乘法分析发现茎长、株高、叶面积、叶长等性状的投影重要性指标大于1, 对地上生物量变化的解释率为68.6%, 是导致长期放牧下羊草个体生物量降低的主要因子。研究认为, 矮化型变是羊草的避牧适应对策, 在亚稳态下, 通过不同性状的权衡, 充分利用环境资源完成其生活史。     

草甸草原羊草茎叶功能性状对长期过度放牧的可塑性响应

植物对不同功能性状进行权衡, 通过表型可塑性达到对异质生境的适应是植物的一种生态对策。羊草(Leymus chinensis)是欧亚温带草原东缘的主要优势植物, 研究其对放牧的表型反应对揭示草原生态系统的放牧响应机制具有代表意义。该文以内蒙古呼伦贝尔草甸草原为例, 通过设置不同放牧压力与围封的长期试验, 研究了羊草茎叶功能性状对放牧的可塑性响应模式。结果表明: 1)与长期围封相比, 长期放牧导致羊草茎叶性状显著小型化, 其中, 株高和个体地上生物量分别降低76.82%和89.88%, 但3年短期围封对茎性状影响不显著, 说明羊草表型矮小化现象具有一定的保守性; 2)通过排序构建羊草性状可塑性变化谱, 发现茎质量、总质量、茎高、株高、叶面积等为对放牧响应的敏感性状, 而叶片数、茎粗、叶宽等较为稳定, 为惰性性状; 3)放牧干扰下, 羊草性状可塑性程度与其变异性之间符合y = y₀ + ae^bx拟合关系, 随着植物性状的响应强度增大, 其变异性增强; 4)偏最小二乘法分析发现茎长、株高、叶面积、叶长等性状的投影重要性指标大于1, 对地上生物量变化的解释率为68.6%, 是导致长期放牧下羊草个体生物量降低的主要因子。研究认为, 矮化型变是羊草的避牧适应对策, 在亚稳态下, 通过不同性状的权衡, 充分利用环境资源完成其生活史。     

松嫩平原异质生境羊草种群营养繁殖特征

多年生无性系禾草主要依靠营养繁殖实现种群的持续更新,而各类芽和由芽形成的苗为其种群进行营养繁殖的潜在种群。通过单位面积挖掘取样,利用营养繁殖世代数划分分株、根茎和各类型芽和苗的龄级,对松嫩平原封育草甸、长期割草草甸、封育积沙草甸和林间草地的羊草潜在种群组成和大小进行了比较研究。结果表明: 在生长季末期,羊草的潜在种群均由根茎芽和各龄级分蘖节向上生长的芽以及根茎苗和分蘖节苗组成。在4种生境条件下,羊草分株潜在种群由3～4个龄级组成,1～4龄级根茎均可形成潜在种群,其中,根茎潜在种群占整个羊草潜在种群数量比例为68.3%,占绝对优势。1龄分株和根茎产生的潜在种群占总体的60.2%,是潜在种群组成的主要部分,是种群更新的主要来源。分株潜在种群数量以长期割草草甸最高,根茎潜在种群数量以封育积沙草甸最高。营养繁殖力均以年轻龄级分株和根茎最高,根茎的营养繁殖力是分株的10.0倍,在羊草种群营养繁殖过程中始终占据优势。羊草的潜在种群构成在不同生境条件下变异较大,但体现出对生境差异的趋异适应。     

不同利用方式和载畜率对内蒙古典型草原群落初级生产力和植物补偿性生长的影响

基于2005年6月开始的放牧控制实验, 研究了不同草地利用方式和放牧强度对内蒙古典型羊草(Leymus chinensis)草原群落初级生产力和补偿性生长的影响。草地利用方式包括: 传统放牧、传统割草和放牧与割草轮换利用(混合利用)。结果表明: 传统放牧和混合利用方式下, 羊草群落地上生物量均随放牧强度增加逐渐降低。高载畜率下, 羊草群落地上净初级生产力表现为: 混合利用>传统割草>传统放牧, 说明混合利用方式优于传统放牧和传统割草利用方式; 而低载畜率则有利于草原的可持续利用和植物的补偿性生长。这一实验结果在一定程度上验证了放牧优化假说。在不同利用方式、地形因素的影响和采用不同的群落净生长量计算方法时, 随着放牧强度的变化, 等补偿、超补偿和欠补偿效应都可能出现。在低载畜率下, 群落大多表现出等补偿生长, 在高载畜率下, 群落大多表现出欠补偿生长。植物群落的补偿性生长与载畜率的关系可以用开口向下的二次函数或者斜率为负的线性函数模拟。说明随着载畜率的增加, 一些系统表现为欠补偿生长, 而另一些系统则表现为超补偿生长, 这可能与植物群落组成、地形部位(平地、坡地)和载畜率以及净生长量的计算方法有关。     

东北草原羊草种群种子生产与气候波动的关系

羊草（Leymus chinensis(Trin.)Tzvel.）是一种优良的多年生禾本科牧草。东北草原羊草种群种子生产有明显的丰欠年现象。通过对3个固定样地连续12－16年的调查和测定及其与不同生长发育阶段光照时间、积温、降水量的相关分析,发现气候变化是引起羊草种群种子生产丰欠年的重要因素之一。秋季低温、多雨,翌年将是种子生产的丰年,而高温、干旱则是欠年。相反,春季高温、干旱是种子生产的丰年,而低温、多雨则是欠年。气候因子对羊草种群种子生产有明显滞后的生态效应,其影响的生态时间差可长达10－12个月之久。用前一年8－10月不同阶段的降水可预报翌年羊草种群的抽穗数量和籽实产量,但由单项降水因子引起的诸数量变化为44％－61％。     

放牧影响下羊草草地主要植物种群生态位宽度与生态位重叠的研究

本文采用Shannon—Wiener和Pianka公式,在土壤水分、土壤含盐量和土壤有机质含量三维生态因子梯度上测定了松嫩草原碱化羊草草地放牧演替系列12种主要植物种群的生态位宽度和生态位重叠。结果表明,植物种群长期适应由放牧引起的群落和土壤环境因子梯度变化是种群生态位分化的主要原因。优势种羊草种群生态位宽度最大,三维上生态位宽度分别为0.910、0.869和0.930。五脉山黧豆和湿生植物生态位宽度均很窄。增加种表现出较强的适应环境能力,生态位宽度都较大。在放牧演替的先锋植物中,只有虎尾草生态位宽度较大(三维上平均0.707),角碱蓬和星星草种群生态位宽度均很窄。生态位宽度较大的物种与其它种群间生态位重叠较大。分布于相同或相邻放牧阶段及具有相同或相似环境要求的物种间生态位重叠较大。放牧条件下,羊草群落的演替过程也就是种群生态位分化的过程。     

羊草种群年龄结构及无性繁殖对策的分析

天然割草场羊草 ( Aneurolepidium chinense( Trin.) Kitag.)种群的生殖枝中有 87%为冬性植株。羊草分蘖节最老为 4龄 ,其生活时间可达 5个年度。在分蘖节成株的年龄结构中 ,1、2龄株占绝对优势 ,其所占比重达 92 .5 %。 1龄株生产力最高 ,至 3龄株生活力已明显衰弱。割草场羊草种群为增长型与稳定型混合的年龄结构类型。综合分析了羊草以根茎顶端成株调节种群年龄结构的无性繁殖对策 ,以及羊草草地自然持续更新的生物生态学机制     

松嫩平原羊草种群营养繁殖的季节动态及其生物量与密度关系的分析

本文根据野外定位定期观测,分析了羊草[Aneurolepidium chinense(Trin.)Kitag.]种群和羊草个体群营养繁殖的特点。结果表明,在整个生长季,羊草能不断地进行营养繁殖。在移植当年,羊草分蘖株个体群的营养繁殖潜力比实生苗个体群的更大,两个实验个体群的数量均符合于逻辑斯谛曲线增长。生殖生长对羊草的营养繁殖有较大的影响。天然割草场上的羊草种群在生物量达最高时期,种群植株的大小受密度的制约,平均单株重量与密度之间遵循-0.6699 幂的规律性变化。综合分析表明,在松嫩平原天然割草场上,羊草种群依靠营养繁殖更新延续、自我调节,但该种群尚未达到环境所能容纳的最大数量。     

Pyrenophora graminea on Winter Barley Seed: Effect on Disease Incidence and Yield Losses

Field experiments were carried out in 1982–83 and 1983–84 in Northern and Central Italy (3 locations) in order to investigate the effect of different levels of seed infection of Pyrenophora graminea on disease incidence and yield losses in ‘Perga’ winter barley. Six levels of natural seed infection, assessed by the deep-freezing blotter method have been compared in 8 row-plots, 7.5 m long, arranged in randomized blocks with 4 replications. The percentage of infected plants and tillers has been recorded in all locations and the yield in two of them. A highly significant correlation was found between seed infection, plant infection, tiller infection and yield reduction. Major ratios found were: infected seeds/infected seedlings 1: 0.4, infected tillers/yield loss 1: 0.9, infected seeds/yield loss 1: 0.3. The threshold of seed infection at which production was not significantly different from the healthy control was 14%. Therefore seed treatment is advisable, under the conditions of Northern and Central Italy, when the percentage of seed infection in commercial seed lots is above this level. A tolerance near zero is recommended in prebasic and basic seeds.     

Frost damage and winter nitrogen uptake by the grass Poa pratensis L.: consequences for vegetative versus reproductive growth

Frost damage can decrease nitrogen uptake by grasses over winter, and it can also decrease biomass production over the following growing season. However, it is not clear to what extent reduced nitrogen uptake over winter decreases grass production, or whether is it merely a symptom of root damage. We examined the growth response of the grass Poa pratensis L. (Kentucky bluegrass) to variation in the timing of freezing and nitrogen availability over winter in London, Ontario, Canada. All tillers were transplanted into untreated soil in early spring, and at peak seed maturation, root, shoot, and reproductive biomass were measured. There was an interaction between freezing and increased winter nitrogen availability, whereby nitrogen addition increased tiller biomass under ambient temperatures, but decreased tiller biomass in combination with a late winter freeze. The nitrogen response of ambient temperature tillers occurred primarily via increased seed production, whereas for frozen tillers seed production was generally absent. Our results support the hypothesis that nitrogen uptake over winter can increase growing season productivity in P. pratensis, but also demonstrate that increased nitrogen availability increases tiller vulnerability to frost. These results have important implications for grass responses to the alteration of soil freezing dynamics with climate change.     

Cocksfoot (Dactylis glomerata) Grown for Production of Seed

In grasses grown for production of seed under field conditions,it has been found that only a small proportion of tillers produceinflorescences. For a period of 23 weeks from 4 February 1963a study was made of cocksfoot grown for production of seed inan attempt to discern whether the ability of tillers to becomereproductive was related to specific morphological features.Most tillers which initiated spikelets were rooted, and rootsquickly developed on unrooted tillers which had initiated spikelets.It appeared that larger tillers, judged on the basis of dry-weight,were more likely to become fertile than smaller tillers; importantfeatures of tiller size were the length of the stem and theweight of green leaf (lamina) borne by the tiller. The potentialnumber of inflorescences was reduced considerably by the death,in June, of tillers with completely differentiated apices.     

草地早熟禾种子产量构成因素的品种差异

对草地早熟禾 2 8个品种种子产量及性状进行了研究 .结果表明 ,2 8个品种间种子产量存在极显著差异 (P <0 .0 1) ,最高的品种为Balin和Monoply ,其产量达 6 4 3.4～ 6 5 0 .2kg·hm-2 ,为最低品种Elysee(90 .1kg·hm-2 )的 7.1倍 .生产性状相关分析表明 ,生殖枝数 /株、生殖枝高、花序长及小穗数 /生殖枝 4个性状为影响早熟禾种子产量的主要因素 .依据对种子产量及上述 4个性状测定值的聚类分析 ,可将 2 8个品种的种子生产性能分为极强、很强、强、中等、差和极差 6个类群 ,其中Monoply等 6品种为极强类群 ;Baronie、Balin和Sydsport、Entopper分别为很强和强类群 ;Nublue等 12品种为中等类群 ;Broadway等 4品种和Ram1、Elysee分别为差和极差类群     

Insights on the role of tillering in salt tolerance of spring wheat from detillering

Tillering is reduced by salinity, with the primary and secondary tillers being more affected than is the mainstem. To understand the importance of tillering in the salt tolerance of wheat plants, two contrasting genotypes of spring wheat (Triticum aestivum L.) were grown in a greenhouse under saline or non-saline conditions and were subjected to five progressive levels of detillering. Regardless of the genotype and salinity, shoot dry weight, seed yield and seed number per plant were all significantly decreased in the treatments where only one or two tillers per plant remained compared with the untouched treatment (more than three tillers), whereas these same variables per tiller tended to be increased on a per tiller (mainstem or substem tiller) basis. The increased seed yield per tiller observed with tiller reduction may be attributed to the enhanced seed number within the spikelet. Under saline conditions, the reductions in shoot dry weight, seed yield and seed number per plant for the salt-tolerant genotype Kharchia were of a greater magnitude in the treatments where only one or two tillers per plant were present compared with the untouched treatment, whereas the magnitude of this reduction in the salt-sensitive genotype Sakha 61 was decreased.     

Belowground bud production is linked to population establishment in Sorghastrum nutans (Poaceae)

Belowground bud production mediates many responses of tallgrass prairie grasses to temporal environmental variation, and clonal spread contributes to dominance in successional plant communities. However, we know little about the importance of these regenerative traits for vegetation establishment in grassland restoration and about their regional variability. Further, geographic seed or transplant sources affect plant performance. We investigated the effects of seed source on the number of belowground buds per tiller, clonal spread (total rhizome length adjusted for plant biomass), and population establishment in the native C₄ grass Sorghastrum nutans sown into tallgrass prairie restorations using reciprocal common gardens in three sites (in Nebraska, Kansas, and Oklahoma). We characterized buds per tiller and clonal spread at the plant level and related both traits to population establishment at the restoration plot level. Plant-level bud production significantly differed among seed sources and common garden sites, and was positively associated with plot-level establishment (density and canopy cover), but plant-level clonal spread did not differ among seed sources or common garden sites and was not associated with the plot-level establishment. Our results are among the first to link bud production, which varied among source populations, to differences in plant population establishment. These results suggest that we should more often consider differences among sources in traits closely tied to post-seeding population establishment. The use of sources that possess such traits may facilitate successful establishment in restoration settings.     

Saltwater spray as an agent of natural selection: no evidence of local adaptation within a coastal population of Triplasis purpurea (Poaceae)

An ability to tolerate airborne saltwater spray is critical for plant populations in coastal environments. The opportunity for continued microevolution for improved salt tolerance can exist if there is variation in the response of genetic families to saltwater spray. Our objective was to determine whether or not there was differentiation among subpopulations near (15 m) and far (80 m) from shore and among families within subpopulations in relation to the effects of salt spray on life history traits in a population of the dunegrass Triplasis purpurea. In this annual, most seeds are matured in cleistogamous spikelets on axillary, leaf-sheath enclosed panicles and show poor dispersal capacity. Plants were reared in the greenhouse from seeds of 13 and 11 families from the near and far subpopulations, respectively. Fifty percent of plants in a family were subjected to 6 seawater sprays/wk, resulting in weekly salt deposition of 213 μg/cm(2); the others were sprayed with distilled water. Data were recorded on life span, tiller numbers, root and shoot dry mass, and seed production. There was no effect of subpopulation on any measured trait and, hence, no evidence for local adaptation to salt spray. Final tiller numbers, but not dry mass or seed production, were reduced by salt spray. However, for most traits there were significant family (within subpopulation) effects, indicating genetic substructuring. Life span and mean seed mass showed a significant family by treatment interaction, indicating genetic variation in phenotypic responses to salt spray. Life span and mean seed mass were reduced by salt spray in some, but not all, families. Path analysis revealed that an increase in life span or tiller number indirectly increased seed production via direct effects on vegetative mass. For this relatively salt-tolerant T. purpurea population on the south shore of Staten Island, New York, USA, salt sprays may not be a significant agent of natural selection. However, there are pronounced phenotypic differences among inbred family groups and opportunity for genetic substructuring within these subpopulations. Variable effects of salt spray among families could result in microevolutionary changes in life span and mean seed mass, both of which impact annual fitness in this dunegrass.     

The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration: 2. Grown as Young Plants from Seed

Young plants of two selection lines of Lolium perenne cv. S23with ‘fast’ and ‘slow’ rates of ‘maturetissue’ respiration were individually grown from seed,together with plants of S23, their common parent, in 9.2 cmpots in a controlled environment at 20/15 °C day/night temperatures. No significant differences were found between the genotypesin leaf extension and tiller production during this early stageof their growth. They did differ however, by an average of 26%,in the rate of dark respiration of fully expanded leaf laminae.The use of a simple model demonstrated that such a differencein respiration could alone account for the different rates ofdry matter production shown by the selection lines when grownas young crops from seed. Possible penalties of ‘slow’respiration are also considered. Lolium perenne L., ryegrass, respiration, maintenance respiration, stimulated swards, leaf growth, tiller production, carbon economy     

Host genotype overrides fungal endophyte infection in influencing tiller and spike production of Lolium perenne (Poaceae) in a common garden experiment

Leaves of many cool-season grasses are infected by endophytic fungi that can impact their populations. A common garden experiment with Lolium perenne was established in a lawn in New Jersey, USA, to investigate the impact of endophyte infection and host genotype on tiller and spike production over three years. Infected (E+) and uninfected (E-) plants of each genotype were monitored every 2-3 mo. Infection intensity within plants varied significantly among genotypes and years, but there was no evidence of directional change over time. Tiller production varied significantly among genotypes and was affected by endophytes: E+ plants of several genotypes produced more tillers than E- plants during the third year. E+ plants had greater aboveground biomass, but host genotype explained a far greater proportion of variation in tiller production, number, and biomass than infection. Plant survival, percentage flowering, flowering date, number of spikes, and mean tiller mass were unaffected by endophytes. However, the last three variables showed significant variation among host genotypes. Although studies have demonstrated a positive growth effect of endophytes on several grass hosts, in this experiment host genotype accounted for far more of the variation in tiller and spike production and in biomass of Lolium perenne than endophyte infection.     

不同放牧率对大针茅种群结构的影响

 采用连续放牧的方式研究了不同放牧率对大针茅(Stipa grandis)种群结构的影响。研究结果表明：在一定放牧率范围内,单丛分蘖密度随着放牧率的增加而增加,超过这个范围,单丛分蘖密度下降;单位面积生殖枝数、结实数和种子重随放牧率的增加而下降,种子千粒重在轻度和中度放牧率下最大;不同年龄株丛的分蘖密度存在很大差异,老龄株丛的分蘖密度最大,其次是成年株丛,幼龄株丛最小;轻度和中度放牧率能够刺激成年和老龄株丛分蘖,增加其单丛分蘖密度;老龄株丛在种群的有性生殖中占有重要地位,其生殖枝数目高于成年株丛。