Size-dependent allocation to sexual and vegetative reproduction in four clonal composites

Summary Populations of Silphium speciosum, Vernonia baldwinii, Solidago canadensis and Pityopsis graminifolia were studied to determine whether biomass allocation to sexual and vegetative reproduction and the balance between them were size-dependent and whether interpopulation differences in allocation patterns could be predicted from differences in population size distributions. All four species showed strong linear relationships between inflorescence mass and vegetative mass with negative y-intercepts. As a result, sexual reproductive effort (SRE) was a monotonically increasing function of ramet size. Genet size was a poor predictor of SRE. In each species, the regression parameters of these relationships differed significantly between burned and unburned habitats indicating size-independent interpopulation differences in patterns of reproductive effort as well as sizedependent effects. Interpopulation variation in vegetative reproductive effort (VRE) was greater than variation in SRE, but neither VRE nor the pattern of partitioning of VRE among daughter rhizomes showed significant relationships to plant size.     

Production of male flowers does not decrease with plant size in insect‐pollinated Sagittaria trifolia,contrary to predictions of size‐dependent sex allocation

Abstract It has been proposed that relative allocation to female function increases with plant size in animal‐pollinated species. Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size‐dependent sex allocation (SDS), throwing doubt on the generalization of SDS. Plant size, phenotypic gender, and flower production were measured in experimental populations of an aquatic, insect‐pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities. The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors. In the high‐density population, 48% of ramets were male without female flowers, but in the low‐density population all ramets were monoecious. We observed allometric growth in reproductive allocation with ramet size, as evident in biomass of reproductive structures and number of flowers. However, within both populations female and male flower production were isometric with ramet size, in contrast to an allometric growth in femaleness as predicted by SDS. Phenotypic gender was not related to ramet size in either population. The results indicated that large plants may increase both female and male function even in animal‐pollinated plants, pointing towards further studies to test the hypothesis of size‐dependent sex allocation using different allocation currencies.     

Habitat and sex specific differences in the dioecious weed Acetosella vulgaris (Polygonaceae)

Abstract Patterns of resource allocation, numbers of reproductive structures and sex ratios of flowering populations of the dioecious weed Acetosella vulgaris (Fourr.) were examined in the Kosciuszko alpine region of Australia. Specifically, the sex‐specific response of ramets was compared between a disturbed alpine habitat, in which weeds such as A. vulgaris are common (disturbed roadside/path‐edge), and a native alpine habitat in which weeds appear to have a limited capacity to germinate, grow and reproduce (undisturbed tall alpine herbfield). The disturbed habitat was generally more favourable for growth of A. vulgaris. Ramets of both sexes had greater total and vegetative biomass than ramets in native habitats. Although reproductive biomass was also greater in disturbed habitats, females had less reproductive biomass than males, which was not as predicted. Reproductive effort was not affected by habitat or gender. The disturbed habitat also favoured increased numbers of inflorescences per ramet and flowers per ramet, as expected. Whereas the gender of the ramet also influenced numbers of reproductive structures, again, this was not as predicted. Females had more flowers per ramet and more flowers per inflorescence than males. This may be because of factors associated with wind pollination. Females were taller in native habitats but there was no difference between the sexes in disturbed habitats. Sex ratios varied from all male populations to nearly all female populations among the 25 sites sampled irrespective of habitat. Factors such as time since last disturbance may have contributed to variation in the sex ratios of alpine populations of A. vulgaris in Australia.     

扎龙湿地不同生境芦苇分株的形态特征及生物量分配的异速关系

不同环境条件下的植物个体可以表现出形态特征的分异和物质分配的权衡与调整。采用大样本抽样调查与统计分析方法,比较研究扎龙湿地不同生境芦苇(Phragmites Australis)生殖株和营养株的形态特征以及生物量分配的异速关系。结果表明:在9月末,盐碱生境、旱生生境、湿生生境和水生生境芦苇分株的生长表现出较大的生态可塑性,株高和株重均以盐碱生境最小,水生生境最大,最大值与最小值的比值分别为1.3-3.3和1.8-5.1,分株生长在种群间的变异度高于种群内,与营养株相比,生殖株的变异度较低;分株的支持分配与生产分配的比值为1.8-4.2,生产分配以盐碱生境最高,以水生生境最低,而支持分配和生殖分配表现与生产分配相反的序位;生殖株的花序长和花序重与株高间呈直线函数形式增长,株高和株重低于种群平均值的20%和35%的分株不进行有性生殖;叶重、叶鞘和茎重以及分株重与株高间呈幂函数形式的异速生长关系。植物通过改变个体的形态特征以及调整构件间生物量分配适应不同环境,而受遗传因素控制的构件间生长关系却相对稳定。     

展毛翠雀花期繁殖特征和生物量分配对放牧的响应

生物量分配影响植物生长和繁殖,是植物生活史研究的重要内容。为了了解植物生活史性状对放牧的响应,该研究以青藏高原高寒草甸毒杂草展毛翠雀为对象,分析了放牧干扰对展毛翠雀的花期繁殖分配和性分配的影响。结果表明:放牧显著降低了展毛翠雀的总生物量、个体大小和繁殖投入; 放牧未改变展毛翠雀的营养部分与繁殖部分的等速生长关系,但显著增加了繁殖部分的生物量分配和总花数; 展毛翠雀的个体大小与总花数呈显著的正相关关系,但与性分配呈显著的负相关关系; 展毛翠雀的总花数与单花大小、单花的花瓣比例均表现出负相关关系,表明总花数与单花大小之间、总花数与单花的花瓣比例之间均存在权衡。因此,在放牧条件下,展毛翠雀的繁殖分配和性分配均表现出显著的可塑性。     

川西风毛菊果期资源分配对海拔的响应

以分布于青藏高原东缘的川西风毛菊为试验材料,研究了其不同海拔高度16个居群的果期资源分配。结果显示:1)随着海拔的升高,个体大小、繁殖器官生物量、营养器官生物量、根系质量、茎叶质量以及每株植物种子总数量均不断减小,但种子百粒重不断增加;2)繁殖分配和根系分配与海拔呈正相关关系,营养分配和茎叶分配与海拔呈负相关关系;3)果期繁殖分配和营养分配、根系分配和茎叶分配以及种子数量与百粒重之间均存在资源分配上的权衡。研究结论:1)海拔作为外界因子对川西风毛菊果期各生物量及资源分配有显著的影响;2)随着海拔的升高,川西风毛菊通过增加繁殖分配,根系分配以及种子百粒重来适应胁迫环境,提高自身的适合度。     

不同生境自交植物黄花大苞姜生殖分配的研究

为了探讨自交植物黄花大苞姜(Caulokaempferia coenobialis)对石壁附生这一特殊生境的生态适应,对其不同物候期和不同生境的生殖分配进行了对比研究。结果表明,在生殖生长过程中,黄花大苞姜种群用于营养生长的生物量分配占有绝对优势,而用于生殖的生物量分配比例较小(<13%)。在黄花大苞姜各构件的生物量分配中,根茎和叶的比重较大(24.22%~43.25%)。在光线较弱生境中的种群,为了提高资源获取能力,黄花大苞姜分配到叶的比重明显高于光线较强的种群,而分配给根茎的比例却明显低于光线较强的种群。随着物候期的推移,黄花大苞姜生殖分配的比例不断增加,到果期达到最大值。不同种群间和年度间黄花大苞姜分配给生殖构件的比例没有显著差异,推测其生殖分配可能受遗传因素控制。个体大小与根茎生物量呈极显著线性函数同速生长,而与生殖分配在云天海种群没有表现出相关性,在上坪和天堂顶种群表现为同速生长关系,但决定系数小于40%。因此,黄花大苞姜能有效调节其在不同生境的生物量分配以适应石壁附生的特殊生境,在光线较弱的种群提高叶的生物量分配并降低根茎的生物量分配以提高资源的获取能力。整体上投资到营养构件的生物量占比高达87%以上,生殖构件在居群间和年度间均保持稳定。这种繁殖策略,一方面较高的营养构件投资可以获得更多的资源,另一方面稳定的生殖投资可以保证种群的延续,各构件相互协调以更好适应石壁这一资源匮乏的生境。     

Reproductive allocation strategies in desert and Mediterranean populations of annual plants grown with and without water stress

Reproductive effort (relative allocation of biomass to diaspore production) was compared in matched pairs of Mediterranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Bromus fasciculatus C. Presl. and Brachypodium distachyon (L.) Beauv., grown under high and low levels of water availability in a common-environment experiment. Desert populations in all three species showed higher reproductive effort than corresponding Mediterranean populations, as expressed by both a reproductive index (RI= reproductive biomass/vegetative biomass), and a reproductive efficiency index (REI=number of diaspores/total plant biomass). Moreover, in E. hispanica and Brachypodium distachyon, inter-populational differences in reproductive effort were greater under water stress, the main limiting factor for plant growth in the desert. These results indicate that variability in reproductive effort in response to drought is a critical and dynamic component of life history strategies in annual species in heterogeneous, unpredictable xeric environments. When subjected to water stress the Mediterranean populations of E. hispanica and B. distachyon showed greater plasticity (e.g. had a greater reduction) in reproductive effort than the desert populations, while in Bromus fasciculatus both populations showed similar amounts of plasticity.     

唐古特雪莲花部特征及生殖分配的海拔差异

为探究高山植物生殖分配策略以及分析唐古特雪莲花部特征对海拔梯度的响应机制,该研究利用采样调查法和烘干称重法,对分布在青藏高原东缘不同海拔14个居群的唐古特雪莲花部特征和生殖分配进行了研究。结果表明:(1)繁殖分配随个体大小(地上生物量和株高)的增大呈线性递减趋势。(2)花期植株地上生物量、株高、管状小花数目、繁殖器官及营养器官生物量均随海拔升高呈线性递减趋势,管状小花生物量随海拔升高呈线性递增趋势。(3)花期管状小花数量及大小、繁殖器官生物量与营养器官生物量、雄蕊重量和雌蕊重量以及花粉数目与花丝长度之间均存在权衡现象。由此推论:(1)海拔作为外界因子对唐古特雪莲花部特征具有显著的影响,个体大小对其繁殖分配也存在潜在调控作用。(2)在不同海拔梯度上,唐古特雪莲有效地整合了有限的资源,其适应性特征之一就是通过减小个体大小来削弱营养生长以达到促进生殖生长的目的。     

Production of male flowers does not decrease with plant size in insect-pollinated Sagittaria trifolia, contrary to predictions of size-dependent sex allocation

It has been proposed that relative allocation to female function increases with plant size in animalpollinated species.Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size-dependent sex allocation (SDS),throwing doubt on the generalization of SDS.Plant size,phenotypic gender,and flower production were measured in experimental populations of an aquatic,insect-pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities.The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors.In the high-density population,48％ of ramets were male without female flowers,but in the low-density population all ramets were monoecious.We observed allometric growth in reproductive allocation with ramet size,as evident in biomass of reproductive structures and number of flowers.However,within both populations female and male flower production were isometric with ramet size,in contrast to an allometric growth in femaleness as predicted by SDS.Phenotypic gender was not related to ramet size in either population.The results indicated that large plants may increase both female and male function even in animal-pollinated plants,pointing towards further studies to test the hypothesis of size-dependent sex allocation using different allocation currencies.     

Costs of reproduction in life history of a perennial plant <Emphasis Type="Italic">Carex secalina</Emphasis>

We tested a hypothesis based on life history theory that examines reproductive costs incurred by individuals in consecutive years of their life. A multi-year dataset of resource allocation to vegetative and reproductive structures was analysed in Carex secalina — a perennial, monoecious sedge, reproducing only sexually. In a four-year garden experiment, we assessed above-ground biomass at the end of each season and reproductive allocation expressed as the total length of male and female spikes. The study was aimed at determining how size and age of a plant relates to its reproduction, and how the rate of reproduction affects the year-toyear biomass change in Carex secalina. We observed that after each reproductive episode, individuals had significantly smaller sizes and produced a lower number of generative tillers. The total production of reproductive structures decreased significantly with age in all populations. Moreover, the decrease in plant biomass was greater when more reproductive structures were produced in a previous year, which indicates that the plants incur costs of reproduction in terms of above-ground biomass production.     

5种毛茛科植物个体大小依赖的繁殖分配和性分配

 植物繁殖分配和性分配是生活史理论的核心问题,一直受到生态学家、进化生物学家们的关注。通过对青藏高原东部高寒草甸(3 500 m)及亚高山草甸(2 900 m)毛茛科5种虫媒两性花植物花期的繁殖分配和性分配的研究发现：1）个体越大,繁殖投入越高,繁殖分配越低,与以往研究结果一致;2）性分配是个体大小依赖的,大个体更偏向雌性器官的资源投入,花粉胚珠比与个体大小的关系较复杂,因种而异;3）花期雌雄功能之间存在资源分配上的权衡（Trade-off）,并且种群之间有差异,表明其受环境条件影响。     

Climate-driven changes in shoot density and shoot biomass in Leymus chinensis (Poaceae) on the North-east China Transect (NECT)

Aim Climate‐driven changes affecting ecosystem primary production have been well documented for many vegetation types, while the effects of climate on plant populations remains unclear. Herein, we address the relationships between climatic variables and shoot density, reproductive allocation and shoot biomass in Leymus chinensis on a large‐scale climatic gradient in 2000. Location Nine sites experiencing similar light regimes, but differing in longitude, precipitation and altitude were selected on the North‐east China Transect (NECT) from 115° to 124°E, around a latitude of 43.5°N. Methods Densities of total, vegetative and reproductive shoots and of shoot biomass were measured twice over the growing season in each site. Climatic data were taken from the climate database of the Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences and from the local weather stations throughout the NECT. Results Densities of total, vegetative and reproductive shoots increased significantly from the west to the east and from dry to moist along the NECT, and were strongly correlated with annual precipitation (r² = 0.934, 0.943 and 0.863, respectively) and an aridity index (r² = 0.809, 0.816 and 0.744, respectively). The average total shoot density at the east end (470/m²) was about three times that at the west (160/m²). Reproductive allocation and shoot biomass for both vegetative and reproductive shoots increased with precipitation and declined with the aridity index along the NECT. There were positive correlations between shoot biomass and annual precipitation for vegetative shoots (P < 0.05, R² = 0.604) and March precipitation for reproductive shoots (P < 0.05, R² = 0.533), respectively. Main conclusions These findings suggest that L. chinensis adjusts to decreasing precipitation/increasing aridity by alterations in shoot density, reproductive allocation and shoot biomass along the drought gradient of the NECT.     

Reproductive allocation in hermaphrodite and female plants of Sidalcea oregana SSP. spicata (Malvaceae) using four currencies

Reproductive allocation was investigated in female and hermaphrodite plants of gynodioecious Sidalcea oregana ssp. spicata. Total reproductive investment and partitioning of that investment was documented at the level of whole plants in terms of four ecologically relevant currencies: biomass, nitrogen, phosphorus, and potassium. Nutrient augmentations in the field confirmed that nutrients were limiting plant vegetative growth and propensity to flower; thus the use of these nutrients as currency was appropriate. Once the effects of plant size were removed, the sex morphs allocated similar total amounts of biomass, nitrogen, phosphorus, and potassium to reproduction, but partitioned those differentially. For any given individual size, females allocated larger proportions of their reproductive resource budgets to seeds. Hermaphrodites' reproductive investment in pollen and flowers was allocated at the expense of allocation to seeds. These data are relevant to the evolution of gynodioecy from hermaphroditism and support the hypothesis that females reallocate resources not spent on pollen to seeds.     

Ramet demography and ecological attributes of the perennial river corridor plant Cnidium dubium (Schkuhr) Thell. (Apiaceae)

Cnidium dubium is a highly endangered, perennial river corridor plant in Central Europe. Here we summarise a 4-year field study of its ramet demography, growing in two different flood meadows in the Lower Havel River Valley in northeastern Germany, emphasising the influence of site-specific abiotic factors, mowing and the summer flood of 2002.We recorded 1658 ramets at densities between 2 and 180 ramets m⁻², which varied over area and time, indicating a high small-scale turnover of this species within grasslands. The half-life of the different ramet cohorts was estimated to range from 0.1 to 1.3 years, but single ramets of more than 4 years old were also found. Ramets are monocarpic: they propagate only once in their life. The highest probability of a vegetative ramet becoming a flowering stalk was 11.6%. Ramet density, cumulative number of newly produced ramets per year, leaf length, leaf age, reproductive growth and recovery from the summer flood of 2002 varied, depending on site. C. dubium had a higher performance at sites in intermediate zones of the overall flooding gradient compared with higher zones. Flooding stress is the controlling factor for the lower limit of its performance, while there was no evidence for an upper limit controlled by summer drought. Mowing slightly increased the cumulative number of leaves per ramet, but it decreased the size of new leaves and also the summer above-ground biomass per ramet. As a consequence, the most marked effect was that fewer ramets entered the generative life stage, but the plants were able to keep their overall reproductive performance on a level independent of mowing. Knowledge of basic growth patterns of C. dubium in natural populations could help to explain the species rareness, and may also suggest appropriate strategies to manage its survival.     

Soil temperature drives elevational patterns of reproductive allometry in a biodiversity hotspot

Understanding the geographic patterns of reproductive allocation helps in clarifying the selective forces that shape the reproductive strategies of plants. However, studies on the elevational patterns of reproductive allocation remain limited. Moreover, although soil attributes have long been suspected to drive elevational patterns of reproductive allocation, few studies have explored this relationship. Delaying reproduction and allocating a high proportion of biomass to vegetative organs may be risky for plants living under high-elevation habitats, as these two processes can potentially lead to plant reproductive failure due to the low temperatures and short growing seasons at high elevations. Thus, we hypothesize that reproductive effort will increase with elevation and the elevational pattern of reproductive allocation will be largely driven by soil attributes, given their covariation with elevation. To test these hypotheses, we determined the vegetative and reproductive biomass of individual Impatiens arguta (Balsaminaceae) plants across 12 populations in the Gaoligong Mountains (China), and collected data on soil temperature, nutrients, moisture, and pH for each population. Based on standard major axis regression and linear regression models, we found that (1) both vegetative and reproductive biomass decreased with elevation; (2) all populations demonstrated significant allometric slopes (i.e., linear coefficients of log[reproductive biomass]???log[vegetative biomass] regressions)?>?1; (3) allometric slopes decreased with elevation; and (4) soil temperature was a better predictor of the allometric slope than elevation, i.e., the allometric slope decreased with soil temperature. These results suggest that plant species growing at high elevation invest proportionately more resources to reproduction as an adaptation to low-temperature environments, and reproductive output is heavily dependent on vegetative growth. This study provides the first evidence of soil temperature driving reproductive allocation patterns, which suggests that plant species will favor allocation to growth under increasing soil temperatures with climate warming.

     

天津沿海滩涂互花米草种群生殖分株数量特征及生殖分配研究

通过对天津沿海滩涂单优群落的取样调查,研究了互花米草种群生殖分株的数量特征和生殖分配规律。结果表明,在籽实成熟期,互花米草种群单个生殖分株重为15.62±9.26 g,穗和种子重分别为2.68±2.08和1.39±1.12 g,小穗和种子数分别为537.7±362.2和490.2±376.3个,生殖分配Ⅰ和生殖分配Ⅱ分别为15.02±5.83和7.62±3.8%,结实率为81.9 ±28.6%。穗和种子的形成分别需要分株积累3.2和3.6 g以上的生物量。穗长、穗重、种子数、小穗数、生殖分配Ⅰ和生殖分配Ⅱ分别与分株高度呈极显著(p<0.01)的正相关关系。穗重、小穗数、种子重、种子数、生殖分配Ⅰ和生殖分配Ⅱ分别与分株重呈极显著(p<0.01)的线性正相关关系。种子数、小穗数、生殖分配Ⅰ和生殖分配Ⅱ分别与茎和叶鞘生物量分配呈极显著(p<0.01)的负相关关系。穗各构件在空间上的分布也存在较强的规律性。     

荒漠植物白刺属4个物种的生殖分配比较

选定乌兰布和沙漠地区白刺属4种植物为研究对象,通过对其样株在花期的各生殖构件的数量特征及生物量调查,系统研究了唐古特白刺(Nitraria tangutorum Bobr.)、西伯利亚白刺(Nitraria sibirica Pall.)、大白刺(Nitraria roborowskii Kom.)和泡泡刺(Nitraria sphaerocarpa Maxim.)4种白刺属植物在生殖枝水平上的生殖分配。结果表明:不同白刺属植物在分株高度、生殖枝长、生殖枝基径、单枝花数、花序干重、枝叶干重等生殖构件的数量性状方面均有显著差异,其中泡泡刺的各生殖构件的数量均最小;除了西伯利亚白刺的生殖分配值达到44.51%外,其余3种白刺的生殖分配值均没有超过20%。经统计分析,4种白刺种群的生殖枝长分别与分株高度呈显著(P<0.05)的直线性正相关关系;生殖枝花序干重与分株高显著正相关;4种白刺的生殖分配随着分株生殖枝生物量的增加而减少,即白刺的个体大小与生殖分配之间呈现负相关关系。这种生殖分配特点反映了不同白刺植物对生长环境的资源利用、与克隆繁殖的权衡及对生态适应的策略。     

Mineral allocation to reproduction in Sorhum bicolor and Sorghum halepense in relation to parental nutrient supply

Summary This experiment investigated the effect of parental nutrient shortage on the allocation of five nutrients to seeds and rhizomes in Sorghum halepense, a perennial, noxious weed, and to seeds in Sorghum bicolor, an annual, cultivated species. Plants from both species were grown from seeds and supplied with fertilizer at three concentrations. The allocation of biomass and nutrients (N, P, K, Ca and Mg) to reproductive and vegetative parts was determined. Relative biomass allocation to reproduction (either sexual or vegetative) remained constant in S. halepense in spite of large differences in total plant weight. In S. bicolor, however, biomass allocation to sexual reproductive structures decreased significantly with decreasing nutrient supply. Individual seed weight was not modified by parental nutrient supply in S. halepense, but it increased with decreasing nutrient availability in S. bicolor. Important differences in mineral allocation to seeds were found between the two species. While S. bicolor seeds were largely buffered from the differences in parental nutrient status, concentration of nutrients in S. halepense seeds decreased significantly with decreasing supply for all the nutrients analyzed except Ca. However, mineral nutrient concentration in S. halepense rhizomes remained remarkably constant despite differences in the external supply, evincing the priority given to vegetative reproduction at the expense of sexual reproduction. Overall, the pattern of nutrient allocation in S. bicolor seeds under different nutrient supply resembled the pattern observed in S. halepense rhizomes, but it had little resemblance to the pattern of nutrient allocation in S. halepense seeds. The results are discussed in terms of differences and similarities in the reproductive strategy of these two species.     

The importance of clonal growth to the recovery of Gaultheria procumbens L. (Ericaceae) after forest disturbance

We investigated the importance of clonal growth to the recovery of a common eastern North American sub-shrub, Gaultheria procumbens L. (Ericacea), after clearcut logging. Changes in vegetative growth and development of G. procumbens clones and clonal populations were examined in a chronosequence of logged stands representing different stages of successional development after clearcutting (open habitat, young regenerating forest, closed regenerating forest) and in neighboring undisturbed late-successional forests representative of presettlement conditions. We specifically quantified seedling presence and above-ground ramet production, demographic condition (e.g., sexual vs. vegetative stems), belowground rhizome growth and spread, and assessed the degree of intraspecific variation in clonal morphology and biomass allocation in stands differing in their disturbance history and degree of successional development. Recovery in G. procumbens was largely driven by the “release growth” of pre-existing clonal bud-banks in response to canopy removal. Release growth was expressed as greater ramet initiation, rhizome branching and clonal spread. Conversely, we found no evidence of sexual establishment in the species, although production of reproductive biomass (e.g., inflorescence mass, number of flowering shoots) was significant. These findings support a deterministic model of vascular resistance and resilience to catastrophic disturbance, in which recovery of forest plant communities derives from the life-history characteristics of constituent species.