东北草地异质生境芦苇种群根茎芽年龄结构及输出规律

为明确异质生境条件下芦苇种群根茎芽年龄结构及输出规律,揭示芦苇种群的营养繁殖特性,采用单位土体挖掘取样,分别计数各龄级根茎芽的调查与统计方法,对东北草甸草原草甸土和盐碱土两个生境单优群落芦苇种群根茎芽动态进行比较分析。结果表明,两个生境芦苇种群根茎芽库主要均由6个龄级组成;草甸土生境在6—10月均为增长型年龄结构;盐碱土生境6—7月份为衰退型年龄结构,8月份为稳定型年龄结构,9—10月份为增长型年龄结构。根茎芽数量1—4a普遍以草甸土生境高于盐碱土生境,5—6a普遍以盐碱土生境高于草甸土生境,各龄级根茎芽数量与月份之间均符合y=a+bx直线关系(P0.05)。随着龄级的增加,休眠芽比率呈逐渐下降趋势,而萌发芽比率则呈逐渐上升趋势,5个生育期的休眠芽比率和萌发芽比率与龄级之间均符合y=a+bx直线关系(P0.01)。各龄级根茎的休眠芽具有一个相对稳定的萌发输出过程,草甸土生境根茎休眠芽按每年11%的比率萌发输出,而盐碱土生境根茎休眠芽按每年7%的比率萌发输出。虽然芦苇种群根茎芽年龄结构及年龄谱在异质生境中存在显著差异,但却有着相同的季节变化规律,均以不断形成新根茎的芽来维持着种群的营养繁殖更新。     

东北草地异质生境芦苇芽种群动态

典型无性系植物在适宜的环境中可以依靠芽持续更新,而芽库和芽流在异质生境中的变化是深入认识其营养繁殖特性的基础.采用单位土体挖掘取样,用当年形成的1龄级根茎芽作为输入,用各龄级根茎芽萌发作为输出,计数休眠芽与死亡芽,比较分析东北草甸草原草甸土和盐碱土2个生境单优势种芦苇种群的芽种群动态.结果表明:芦苇芽种群库存量、输入量、输出量、休眠量、死亡量和输入率均以草甸土生境显著大于盐碱土生境,输出率在草甸土生境和盐碱土生境间差异不显著,盐碱土生境休眠率显著大于草甸土生境,2个生境的死亡率均保持在<2%的较低水平.随着生长季的进程,2个生境芽库的输入量、输入率呈不断增加的趋势,输出量相对稳定,输出率呈先上升后下降的趋势,休眠量和休眠率呈不断降低的趋势.芽库和芽流与土壤含水量、土壤有机质、土壤速效氮含量呈显著正相关,与土壤p H值、土壤速效磷含量呈显著负相关.芽库和芽流有相同的季节变化规律,2个生境的芦苇种群均以不断形成新根茎的芽补充芽库和稳定输出维持其营养繁殖更新.     

松嫩平原旱地生境芦苇种群不同龄级根茎的干物质贮藏及水溶糖含量

通过对松嫩平原旱地生境单优种群落芦苇种群不同龄级根茎的调查测定,分析了一个生长季内3个生育期芦苇种群各龄级根茎干物质贮量和水溶糖含量的季节变化.结果表明:各生育期低龄级芦苇种群根茎中干物质贮量和水溶糖含量均较少,且与高龄级的差异较大;随着生长季的进程,低龄级根茎中干物质贮量和水溶糖含量迅速增加,且与高龄级的差异逐步缩小.在整个生长季,芦苇种群各龄级根茎均具有养分消耗和再贮藏乃至超补偿性贮藏的活性,其中,幼龄级根茎的活性更大.高龄级根茎的干物质贮量和水溶糖含量有一个逐年累积的增加过程.根茎干物质贮量在龄级间和龄级内的差异均达到了极显著水平(P<0.01),并且龄级间的差异大于龄级内.水溶糖含量仅在龄级间差异达到显著水平(P<0.05).随着龄级的增加,芦苇种群根茎的干物质贮量和水溶糖含量均呈二次曲线变化.     

松嫩平原杂类草草甸和榆树疏林草原大油芒种群的年龄结构

对松嫩平原杂类草草甸和榆树疏林草原上大油芒种群的年龄结构及各龄级构件的物质生产力和营养繁殖力进行了研究.结果表明:在2003和2006年中,2个生境的大油芒种群分蘖株均由2～3个龄级组成,根茎由4个龄级组成,分蘖株和根茎均以1a和2a所占比例最大,年龄结构呈增长型或稳定型;分蘖节芽以1a或2a者占优势,根茎顶端芽在芽库中所占比例为29.4%～45.0%,对翌年种群的更新具有重要作用;分蘖株、根茎的物质生产力和营养繁殖力均以1a或2a构件最大,根茎比分蘖节具有更旺盛的营养繁殖力.     

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。     

扎龙自然保护区不同生境条件下羊草种群构件的年龄结构

对黑龙江国家级自然保护区扎龙湿地不同生境条件下羊草种群构件的年龄结构进行了研究。结果表明,在7月末羊草种群的腊熟期,3种生境种群分蘖株均由3个龄级组成,林间风沙土生境为1 080株.m-2,沙土生境为1 290株.m-2,草甸土生境为1 011株.m-2,均以1龄和2龄级分蘖株占绝对优势,3龄级分蘖株所占比例甚小,呈增长型年龄结构。根茎均由4个龄级组成,以沙土生境最多,累积长度为8 000 cm.m-2,草甸土生境最少,为6 948 cm.m-2,均呈增长型年龄结构。各生境根茎物质的储量随着龄级的升高而降低。芽均由4个龄级组成,其数量以草甸土生境最大,为2 279个.m-2,沙土生境次之为2 113个.m-2,林间风沙土生境最少为1 410个.m-2,均呈增长型年龄结构。     

松嫩平原水淹恢复演替过程中羊草无性系种群构件的年龄结构

对松嫩平原羊草草甸水淹恢复演替过程中不同大小羊草无性系斑块的种群构件年龄结构进行了研究。结果表明 ,羊草种群分蘖株在斑块中心由 4个龄级组成 ;最外圈层由 3个龄级组成。根茎在斑块中心和中间圈层均由 2～ 4个龄级组成 ,最外层由1～ 2个龄级组成。潜在种群冬性苗和分蘖节芽总量各圈层均由 4个龄级组成。斑块中心的分蘖株种群为稳定型年龄结构 ,向外发展至增长型年龄结构。根茎长度和潜在种群在各圈层均呈增长型年龄结构。在水淹羊草草甸的恢复过程中 ,不同大小羊草无性系斑块均呈不断扩展的趋势。在生存空间充足时 ,羊草的分蘖节在一个生长季里可以繁殖多个世代。通过羊草根茎的年龄结构可预测演替的进程     

松嫩平原野古草种群构件结构动态

野古草是根茎型无性系禾草,在松嫩平原草甸经常形成单优种群落。采用单位面积挖掘取样、分株按营养繁殖世代划分龄级、根茎按实际生活年限划分龄级的方法,对松嫩平原单优群落和混生群落的野古草种群构件结构进行了调查与分析。结果表明,在生长季初期两群落野古草种群均以春性分株和根茎芽占优势,且分株及芽构件结构相对稳定,芽库的输出率单优群落为80.4%,混生群落为62.5%;整个生长季分株由2—3个龄级组成,1a分株数量是2a的2.9—10.2倍,其生物量各月份所占比例平均为93%,随着龄级的增加依次明显减少,呈增长型年龄结构;根茎由3—4个龄级组成,根茎累积长度及生物量均以2a占绝对优势,为稳定型年龄结构;分株生产力1a明显高于2a,对种群贡献最大;根茎贮藏力除个别月份以3a、4a最高外,两群落大部分以2a最高,在生长季后期,1a根茎物质积累的速率最快。     

扎龙湿地异质生境芦苇种群根茎动态及年龄结构

无性系植物根茎不仅具有营养繁殖和扩展种群的功能,也是无性系家族中芽和分株生理整合的通道。采用单位土体挖掘取样,对扎龙湿地单优种群落芦苇种群根茎进行调查,比较了湿生生境和水生生境根茎长度、生物量和干物质贮量的季节变化。结果表明:芦苇种群根茎长度、生物量和干物质贮量均以湿生生境显著大于水生生境;8月前,根茎长度缓慢增加,8月后,根茎长度迅速增加,以3龄最长,6龄最短;根茎生物量、干物质贮量先下降后上升,8月最低,至10月休眠期均已超过营养生长初期,生物量以3龄最大,1龄最小,干物质贮量以5龄最高,1龄最低;不同龄级根茎长度及年龄谱与月份间呈线性相关(R~20.81,P0.05),不同龄级根茎生物量与月份间呈二次曲线关系(R~20.98,P0.05),生物量年龄谱与月份间呈线性相关(R~20.80,P0.05),5个生育期根茎干物质贮量与龄级之间呈二次曲线关系(R~20.86,P0.05)。芦苇种群根茎长度、生物量、干物质贮量有着相同的季节变化规律,不同龄级根茎的寿命与养分的输出消耗和养分的再输入补偿密切相关。整个生育期内,生境异质性对芦苇种群根茎动态及年龄结构的影响均存在,且引起的差异也相对较稳定。     

黑龙江扎龙湿地芦苇种群构件数量特征及其相关性

采用刈割和挖土取样,对扎龙湿地旱生、湿生、水生和盐碱生境芦苇种群分株、根茎和根茎芽进行调查。结果表明:6—10月,4个生境芦苇种群分株密度、根茎长度和根茎芽库存量、输入量、休眠量均以湿生生境最大,盐碱生境最小;根茎芽输出量均以水生生境最大,盐碱生境最小,构件间的差异及其差异序位均相对稳定,构件种群均存在明显的环境效应,构件水平上存在较大的可塑性;构件间又均表现出一定的协同进化性,其中分株密度与根茎长度、根茎芽库存量和输入量之间呈显著或极显著正相关,与根茎芽休眠量之间呈显著负相关;根茎芽库存量、输入量和输出量与根茎长度之间呈显著或极显著正相关;芦苇分株均由根茎芽萌发形成,根茎芽对分株的贡献率为100%,80%以上的根茎芽萌发形成新根茎,根茎的生长又可形成更多的根茎芽,不同构件形态结构的更替改变维持着种群的稳定和持续更新。     

Contrasting bud bank dynamics of two co-occurring grasses in tallgrass prairie: implications for grassland dynamics

Because most shoot recruitment in perennial grasses occurs from belowground axillary buds, bud dynamics determine plant population dynamics and meristem limitation to population growth. Therefore, grassland vegetation responses to environmental change or disturbance may be influenced by interspecific differences in bud banks and the patterns and environmental controls of bud development and demography. We examined bud bank dynamics in Andropogon gerardii and Dichanthelium oligosanthes in tallgrass prairie by enumerating and classifying buds throughout 15?months to determine whether grass buds live for multiple years and accumulate; whether bud natality, dormancy and outgrowth are synchronous or variable; and whether bud bank dynamics differ between these co-occurring species. Andropogon gerardii (a C₄ species) maintained a larger dormant bud bank, showed synchrony in bud development and transition to tiller, and its buds lived for multiple years. Thus, multiple previous years?? bud cohorts contributed to recruitment. By contrast, D. oligosanthes (a C₃ species) maintained a smaller dormant bud bank, had asynchronous bud development with active buds present year-round, and its buds lived for 1?year. Buds played different roles in the dynamics of each species, allowing A. gerardii to over-winter and recruit new spring tillers and D. oligosanthes to survive and recruit new tillers following summer dormancy. These differences in bud bank age structure, phenology, and dynamics between these species suggest greater demographic buffering and time-lag effects in A. gerardii populations. Interspecific differences in bud bank structure and dynamics may explain and help predict grassland responses to environmental change.     

Modelling compensatory regrowth with bud dormancy and gradual activation of buds

Many plants show compensatory regrowth after herbivory and dormant buds often have an important role in compensatory responses. Theoretical models have shown that herbivore damage may select for a bud bank, i.e., a pool of dormant buds that are protected from herbivory and that are activated after herbivore damage. Earlier models assumed that undamaged plants cannot activate their dormant buds without damage, although they apparently have sufficient resources for successful seed production through the additional shoots dormant buds could produce. However, many plants are able to gradually activate buds over an extended period of time without any cue from damage. The aim of this study was to analyze how herbivory imposes selection for gradual mobilization of the bud bank. I assume that selection pressures that affect the fraction of buds active at each time point include damage by herbivores, time left to the end of season, and the opportunity costs of dormant buds. I modelled bud dynamics with gradual activation when there is a single damage event and (i) when the seed set of a shoot is not dependent on the time it is active, or (ii) when the seed set of a shoot diminishes with later activation. In addition, I analyzed how (iii) risk of repeated herbivory affects selection for gradual activation. Under these models, gradual activation is optimal over a wide range of herbivory pressures. Selection appears to favour activation of all buds at the beginning of the season only when herbivore pressure is weak and when early shoots have a higher seed set than late shoots. Alternatively, strong herbivore pressure and late damage may select for a large bud bank throughout the growing season, without gradual activation; the bud bank is only mobilized after damage. In this case, damaged plants can overcompensate, i.e. they have a higher seed set than undamaged plants with the same bud activation pattern. Selection for overcompensation demands a stronger herbivore pressure in this current model than in earlier bud bank models. The model never predicts selection for overcompensation when there is a risk of repeated herbivory. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of fire frequency and grazing on tallgrass prairie productivity and plant composition are mediated through bud bank demography

Periodic fire, grazing, and a variable climate are considered the most important drivers of tallgrass prairie ecosystems, having large impacts on the component species and on ecosystem structure and function. We used long-term experiments at Konza Prairie Biological Station to explore the underlying demographic mechanisms responsible for tallgrass prairie responses to two key ecological drivers: fire and grazing. Our data indicate that belowground bud banks (populations of meristems associated with rhizomes or other perennating organs) mediate tallgrass prairie plant response. Fire and grazing altered rates of belowground bud natality, tiller emergence from the bud bank, and both short-term (fire cycle) and long-term (>15 year) changes in bud bank density. Annual burning increased grass bud banks by 25% and decreased forb bud banks by 125% compared to burning every 4 years. Grazing increased the rate of emergence from the grass bud bank resulting in increased grass stem densities while decreasing grass bud banks compared to ungrazed prairie. By contrast, grazing increased both bud and stem density of forbs in annually burned prairie but grazing had no effect on forb bud or stem density in the 4-year burn frequency treatment. Lastly, the size of the reserve grass bud bank is an excellent predictor of long-term ANPP in tallgrass prairie and also of short-term interannual variation in ANPP associated with fire cycles, supporting our hypothesis that ANPP is strongly regulated by belowground demographic processes. Meristem limitation due to management practices such as different fire frequencies or grazing regimes may constrain tallgrass prairie responses to interannual changes in resource availability. An important consequence is that grasslands with a large bud bank may be the most responsive to future climatic change or other global change phenomena such as nutrient enrichment, and may be most resistant to exotic species invasions.     

Increases in cytokinin levels in Scots pine in relation to chilling and bud burst

Levels of isopentenyladenosine and zeatin riboside were monitored in buds and needles of Scots pine ( Pinus sylvestris L.) seedlings grown under controlled climatic conditions and in field-grown trees. Extracts were purified by immunoaffinity chromatography and high-performance liquid chromatography. Cytokinin levels were quantified with an enzyme-linked immunosorbent assay. The cytokinin content was low in buds and needles of dormant seedlings but increased during dormancy release, reaching peak values in buds just before resumption of shoot growth. Samples collected in the field also showed a marked increase in the levels of cytokinins just prior to bud burst. Further, the biological activity of applied cytokinins in activating the dormant buds of Scots pine is shown. The results indicate a probable role of cytokinins in seedlings during dormancy release.     

The effect of glyphosate on frond regeneration, bud development and survival, and storage rhizome starch content in bracken

In addition to very effectively suppressing bracken frond regeneration for two years at levels of 2.24 kg a. i./ha and above, glyphosate had considerable effects on the rhizome system. Dry weight of frond-bearing rhizomes, number of living apices and developed buds, number and viability of dormant buds and starch content of storage rhizomes were all markedly reduced. The effects on dormant buds and starch content are particularly important when considering frond regeneration and as a consequence of these, glyphosate is likely to give long lasting control of bracken. Low levels of glyphosate (0.02 and 0.07 kg a. i./ha) did not stimulate bracken growth, while the addition of NH₄SCN apparently inhibited the action of the sub-lethal rate of 0.56 kg a. i./ha.     

Belowground bud banks and meristem limitation in tallgrass prairieplant populations

Rhizome meristem populations were sampled in tallgrass prairie to quantify the size, grass?:?forb composition, and temporal and spatial variability of the soil bud bank and to compare fire effects on bud bank and seed bank composition. Soil cores (10.5 cm diameter, 15 cm deep) were collected from replicate annually and infrequently burned tallgrass prairie sites, and intact rhizomes and rhizome buds were censused. Bud bank densities ranged from approximately 600 to 1800 meristems/m(2) among sites and had high spatial and seasonal variability. In annually burned prairie, the total bud bank density was two-fold greater and the grass?:?forb meristem ratio was more than 30-fold greater than that of infrequently burned prairie. These patterns are opposite those observed in soil seed banks at this site. The rhizome population in annually burned prairie was 34% larger than the established aboveground tiller population. By contrast, the bud bank density in unburned prairie was significantly lower than aboveground stem densities, indicating possible belowground meristem limitation of stem density and net primary production on infrequently burned prairie. The patterns observed in this study suggest that the densities and dynamics of tallgrass prairie plant populations, as well as their response to disturbance (e.g., fire and grazing) and climatic variability, may be mediated principally through effects on the demography of belowground bud populations. Patterns of seed reproduction and seed bank populations have little influence on short-term aboveground population dynamics of tallgrass prairie perennials.     

Effects of endogenous ABA levels and temperature on cedar (Cedrus libani Loudon) bud dormancy in vitro

Axillary and apical buds of in-vitro-propagated cuttings of Cedrus libani are unable to burst at 24 °C, but this inhibition was overcome at 30 °C. Here we have used cedar microcuttings to investigate whether the levels of endogenous hormones vary with bud dormancy and temperature. We analysed the levels of abscisic acid, indole-3-acetic acid, zeatin, isopentenyladenine and their major metabolites using HPLC purification and fractionation of the samples coupled to an ELISA method for hormonal quantitation involving several antibodies elicited against each hormonal family. Abscisic acid levels in microcuttings with dormant buds were higher than those in microcuttings with growing buds. At 24 °C, needles accumulated more abscisic acid than at 30 °C. In addition, when needles were removed, but growth release was achieved at 24 °C. Abscisic acid supplied at 30 °C induced the formation of dormant buds. These results suggest that abscisic acid accumulation in the needles can explain the bud dormancy of cedar microcuttings at 24 °C. Received: 14 November 1997 / Revision received: 16 January 1998 / Accepted: 5 May 1998     

Branch construction and bud defence status at the canopy surface of a West African rainforest

Branch specimens were collected from the very tops of tropical tree crowns in southern Cameroon, West Africa. An analysis of branching patterns revealed a consistency of form across unrelated taxa. All specimens showed evidence of rhythmic growth cither due to the regular occurrence of dormant terminal buds or due to sympodial growth with loss or flowering of terminal buds. Study of bud anatomy revealed an extensive array of protective devices associated with drought tolerance and herbivore defence. Normally a considerable excess of dormant, well protected axillary buds were present which (almost without exception) existed in a viable state. In very many instances the large dormant bud population was due to the presence of accessory buds, i.e. > 1 bud in the axil of each leaf. The microclimate at the outer surface of a tropical rainforest may experience a daily increase in temperature and associated depression in humidity; the canopy surface characteristics are more akin to chaparral shrub vegetation than to familiar rainforest understorey vegetation.     

Point pattern analysis of different age-classes of Larix principis-rupprechtii in Luya Mountain Reserve, Shanxi Province, China

Larix principis-rupprechtii forest is an important vegetation formation and has a large distribution area in Luya Mountain Reserve,China.Spatial pattern analysis on individual trees in different age-classes of Larix principisrupprechtii was made in this paper.Here,we employed the technique of point pattern analysis,which could analyze patterns under all scales along a gradient.It was based on spatial mapped points of individual distribution.The results of this study showed that the densities of the five age-classes varied in the order:age-class 3＞age-class 4＞age-class 5＞age-class 2＞age-class 1.Although age-classes 1 and 2 have much fewer individuals than other three age-classes do,the population was stable at present.However,it would be necessary to take some measures for improving population regeneration for a long-time view.The individuals of all age-classes focused on clumping distribution in space;however,their distribution pattern varied with the change of scale.This mainly depended on biological features of Larix principis-rupprechtii and forest environments,but it also meant that the scale was an important factor in controlling spatial distribution pattern of tree individuals.The feature of clumping distribution became more significant with the increase of age.The relationships between individuals in different age-classes were almost all significantly correlated with each other.These associations became more significant within the older age-classes.This suggested that the individuals of different age-classes were interdistributed,by which the population could get benefits in resource utilization.The technique of point pattern analysis is effective and easy to be used in species pattern study.Its results are more closer to the reality,especially for community structure.