Implications of opposite phyllotaxis for light interception efficiency of Mediterranean woody plants

Opposite leaves lead to a greater leaf overlapping than leaves spirally arranged along a shoot, decreasing light interception efficiency (Ea, fraction of the light reaching the plant actually intercepted by the leaves) of the crown. However, Ea results from a whole suite of morphological traits. The interplay between phyllotaxis, crown architecture, leaf morphology and Ea was explored in 12 woody species from Mediterranean-type ecosystems, where the abundance of woody species with opposite phyllotaxis is unusually high. The three-dimensional model Y-plant was used to estimate Ea in unbranched, vertical shoots of each species encompassing the natural morphological variation found from moderate shade to open light environments. Ea exhibited significant interspecific differences, ranging from 0.25 in Daphne gnidium to 0.75 in Cistus ladanifer, Olea europaea and Salvia officinalis, decreasing with leaf inclination angle and leaf area ratio (LAR), and increasing with internode-to-leaf-length ratio and supporting biomass. Species with spiral vs. opposite phyllotaxis did not differ in their mean Ea. However, the former had higher Ea than the latter at short internode lengths. The natural range of variation in internode length had a larger effect on Ea than the natural range of leaf elevation angle. Principal component analysis segregated species with opposite phyllotaxis from those with spiral leaves because of their greater self-shading for high sun elevation angles (>45°); they were in turn distributed in two groups, one with high Ea, large investment in supporting biomass and long internodes, and another with low Ea and large LAR. Species with spiral phyllotaxis all had intermediate or low Ea and steep leaf elevation angles. Species with opposite phyllotaxis can compensate their less efficient leaf arrangement by decreasing leaf elevation angle and increasing internode length, but they may experience a real phylogenetic constraint for light interception when biomass allocation to supporting tissues (internodes and petioles) becomes very costly. This constraint could be involved in the shade intolerance of woody Mediterranean species exhibiting opposite phyllotaxis.     

披针叶茴香对变化光环境的表型可塑性

植物对变化光环境的表型可塑性大小影响其在林下生境中分布、生长和更新。为探讨披针叶茴香在不同光环境下的整体表型可塑性及其适应机制,采用遮荫试验模拟5种光照条件(100%、52%、33%、15%和6%相对光照强度),研究了不同光环境下披针叶茴香叶片形态、生理、解剖结构、根系形态以及生物量分配等的变化。结果表明:叶生物量在5种光照处理之间差异不显著,但叶面积和比叶面积均随光照强度减弱显著增加。遮荫处理增加了叶绿素a、叶绿素b和类胡萝卜素的含量,但叶绿素a/b比值随光照强度减弱而降低。遮荫降低了非结构性碳水化合物(淀粉和可溶性糖)和可溶性蛋白的含量,增加了叶片氮和磷含量,对叶片氮/磷比影响较小。在52%和33%相对光照处理下,叶片中硝酸盐含量最低,而在100%和6%相对光照处理下硝酸盐积累较多。根生物量、细根和粗根的长度、表面积以及比根长和比根表面积在5种光照处理之间均没有显著差异,根系氮含量在低光环境(15%和6%相对光照处理)中显著降低。随光照强度减弱,披针叶茴香采取保守生存策略,并没有增加叶生物量的分配,而是分配较多的生物量给枝条和树干,储存能量。综合来看,披针叶茴香具有较宽的光生态幅,在6%—100%光照强度下均能正常生长,遮荫有利于披针叶茴香地上和总生物量的积累,52%的相对光照条件下生长最佳。变化光环境下根系性状和整体结构的可塑性相对较低,叶片生理性状的可塑性在披针叶茴香适应光环境变化过程中发挥了主要作用。     

SEASONAL AND LIFETIME ALLOCATION PATTERNS OF THE WOODY GOLDENROD,SOLIDAGO PAUCIFLOSCULOSA MICHAUX. (COMPOSITAE)

Both seasonal and lifetime allocation patterns were determined for S. pauciflosculosa, a woody composite, by monitoring biomass loss and gain of each age class in a population for one year. Seasonal allocation patterns were typical of woody plants in stressed environments and did not differ significantly among different aged plants of the same reproductive status. The standing biomass of a mature individual was partitioned as follows: roots 15%, stems 55%, leaves 19%, and reproductive tissues 11%. Lifetime allocation to these particular tissues were 5%, 15%, 50%, and 30% respectively. Lifetime allocation to reproduction was similar to values for related annuals. The implications of these findings for energy allocation theory are discussed.     

SEX RATIO,SEED PRODUCTION,BIOMASS ALLOCATION,AND THE COST OF MALE FUNCTION IN CUCURBITA FOETIDISSIMA HBK (CUCURBITACEAE)

In the gynodioecious plant Cucurbita foetidissima (Cucurbitaceae), females were common in all eight populations examined and made up 32% of adult plants. Females produced 1.5 (SE = 0.2) times as many seeds as did hermaphrodites. The observed difference in seed production alone is not great enough to explain the maintenance of females, especially at their current frequency. Females and hermaphrodites did not differ in number of nodes per stem, stems per plant, internode length, or size of leaves. Females produced more female biomass (fresh or dry weight) than hermaphrodites, but total investment in sexual biomass did not differ. Thus, the biomass of male flowers produced by hermaphrodites was about equal to the extra female biomass produced by females. The results support the existence of a trade-off between male and female reproduction.     

Biomass plasticity of the leaves and inflorescences of Acaena magellanica (Lam.) Vahl (Rosaceae) on Subantarctic Iles Kerguelen

Summary The relative allocation of biomass within monospecific stands of Acaena magellanica that vary in level of wind and water stress differ greatly. Populations in January 1983 varied in leaf biomass from 192 to 2373 g wet wt m^-2 (1105 to 10023 kJ m^-2) Inflorescences were not produced at either of these extremes of leaf biomass. In two populations with intermediate levels of leaf biomass (597 and 640 g wet wt m^-2, 3185 and 2664 kJ m^-2), inflorescent biomass was 104 and 273 g wet wt m^-2 (385 and 1127 kJ m^-2). The relative allocation to sexual reproduction is thus not constant in A. magellanica. The levels of energy in the leaves and inflorescences did not differ greatly despite differences in proximate composition.     

青藏高原露蕊乌头不同海拔居群的开花持续期与繁殖分配

对青藏高原东部3个不同海拔居群的露蕊乌头(Aconitum gymnandrum)(毛茛科)开花持续期和繁殖分配进行了野外观察和检测试验。结果表明:(1)随着海拔的升高,露蕊乌头的开花持续期时间延长,且不同居群间存在显著差异。(2)露蕊乌头的植株个体越大,繁殖投入越高。(3)露蕊乌头的繁殖分配在地上总生物量中所占的比例随海拔升高而增加。研究认为,露蕊乌头在高海拔地区较高的繁殖分配比例强调了有性繁殖在高山恶劣环境中的重要性,而高海拔地区开花持续期的延长补偿了传粉昆虫的减少并增加了对传粉昆虫的吸引能力。     

Variations in sexual and asexual reproduction of Scirpus mariqueter along an elevational gradient

In order to assess the importance of sexual and asexual reproduction during the life history of Scirpus mariqueter, its reproductive and growth characters were concurrently examined along an elevational gradient (from low elevation to high elevation). The proportions of flowering shoot and inflorescence mass, seed : flower ratio and seed weight were used to quantify the investment in sexual reproduction. The proportions of current-year shoot and rhizome mass were used to quantify the investment in asexual reproduction, and the proportion of corm mass was used for growth, respectively. It was found that vegetative propagation predominated at low elevation, whereas sexual reproduction predominated at high elevation; and that sexual reproduction increased with declining asexual reproduction along the gradient. The results suggest that asexual reproduction is relatively favored in the early life stage, whereas sexual reproduction is favored when the population becomes mature and aged, probably because of the functional differentiation between the two reproductive types. Sexual productive characters (i.e. the proportions of flowering shoot and inflorescence mass) were negatively correlated to both growth and asexual reproductive characters along the gradient, indicating there might exist some trade-offs among growth, sexual and asexual reproduction during the life history. However, no obvious pattern was found between asexual reproductive characters and growth characters along the elevational gradient, possibly because of the varied relationships between them at different life stages. The variations in sexual and asexual reproduction in the species and the relationship between them are thought to be of great significance for local population growth, species persistence and evolution.     

长江口盐沼海三棱藨草在高程梯度上的生物量分配(英文)

海三棱草 (ScirpusmariqueterTangetZhang)是一种典型的先锋植物。它能占据于长江口盐沼的光滩上 ,生境非常恶劣。为探索该物种在高度环境胁迫下的生活史策略 ,测定了它在高程梯度上的生物量分配 ,以及有关形态学参数。结果发现海三棱草在中位高程时密度和单株生物量最高 ,生长最好。在由低及高的高程梯度上 ,球茎、根状茎的生物量分配比例逐渐下降 ,表明植物体在光滩前沿采取保守策略 ;而花序的比例则逐渐上升 ,表明植物在生活史过程中 ,由无性生殖向有性生殖的转变。这种转变可能有利于种群的扩散和生存。另外 ,相关分析表明 ,有性生殖性状与无性生殖、生长性状呈负相关 ,但无性生殖与生长性状间的关系难以确定 ,可能由于球茎在不同生活史阶段的不同功能引起。     

Biomass Allocation of Scirpus mariqueter Along an Elevational Gradient in a Salt Marsh of the Yangtse River Estuary

cirpus mariqueter Tang et Zhang is a typical pioneer plant colonizing the bare beaches of the Yangtse River estuary. To explore the life history strategy of the species with reference to environmental physical stress, the biomass allocations to different plant components and some related morphological parameters were examined along an elevational gradient within a salt marsh. Authors found that S. mariqueter performed best at medium elevation within the marsh, with relatively high density of shoot and individual ramet dry mass. Biomass allocation to corm was the highest at low elevations, and the least at high elevations, suggesting that a conservative strategy was adopted by the species to cope with the harsh physical conditions at the low elevation. The investment in rhizome decreased from low to high elevations, while the proportion of inflorescence mass increased, indicating that during the life history, the species shifts from predominant asexual reproduction to predominant sexual reproduction. This may be favourable for the species to colonize larger area, and to spread and persist at a meta-population level. Correlation analyses showed that sexual reproduction was inversely related to growth and asexual reproduction. However, it is difficult to determine the relationship between asexual reproduction and growth possibly because of the varied function of the corms of the species in different life history stages.     

PATTERNS OF BIOMASS ALLOCATION IN SPINACIA OLERACEA (CHENOPODIACEAE) ACROSS A SALINITY GRADIENT: EVIDENCE FOR A NICHE SEPARATION

Spinacia oleracea var. Americana was hydroponically grown across an experimental salinity gradient ranging from 0.0 to 6.0 grams NaCl/liter nutrient medium. Twenty male, 20 female, and 20 monoecious plants were randomly harvested from each treatment where possible. Root biomass (RTA), biomass allocated to leaves and stems (VA), and reproductive biomass (RA) were determined. Male, female, and monoecious plants were shown to have significantly different patterns of RTA, VA, and RA. Moreover, the treatments influenced allocation patterns of the sexes differently, i.e., a partial niche separation was observed among the sexes along the gradient with respect to RTA, VA, and RA. Additionaly, the sexes expressed different trade-offs between allocation of resources to the different tissues; most notably, under high salinity, RTA, and RA were strongly negatively correlated in females, but positively correlated in male and monoecious plants.     

Intraspecific variability of leaf cuticle alkanes in Sedum lanceolatum along an elevational gradient

Characterization of variability patterns in leaf n-alkanes isolated from Sedum lanceolatum field populations indicates little correlation with elevation gradients. Inherent variability is better explained by genetic constitution than phenotypic plasticity, thus suggesting that leaf wax samples isolated from field-collected specimens are suitable for use in elucidation of systematic relationships.     

Differences in carbon stocks along an elevational gradient in tropical mountain forests of Colombia

Tropical mountain forests provide an exceptional opportunity to evaluate the patterns of variation in carbon stocks along elevational gradients that correspond to well‐defined temperature gradients. We predicted that carbon stored in live aboveground biomass, aboveground necromass, and soil components of forests on the eastern flank of the Colombian Andes would change with elevation along this gradient extending from 750 to 2,800 m above sea level. The rationale was that the corresponding change in temperature (14–26°C) would influence tree growth and decomposition of organic matter. To address this hypothesis, we examined the carbon stored in these three components using data from 20 0.25‐ha plots located along this elevational gradient. The mean total carbon stock found in the study region was 241.3 ± 37.5 Mg C/ha. Aboveground carbon stocks decreased with elevation (p = 0.001), as did necromass carbon stocks (p = 0.016). Although soil organic carbon stocks did not differ significantly along the gradient (p = 0.153), they contributed proportionately more at higher than at lower elevations, counterbalancing the opposite trends in aboveground carbon and necromass carbon stocks. As such, total carbon stocks did not vary significantly along the elevational gradient (p = 0.576).     

Environmental stress and the evolution of dioecy: Wurmbea dioica (Colchicaceae) in Western Australia

Stressful ecological conditions have been implicated in the evolution of separate sexes in plants. Gender dimorphic species are often found in drier habitats than their sexually monomorphic relatives, and gynodioecious populations appear closer to a dioecious state as resources, particularly water, become limiting. This pattern could result if dry conditions decrease the relative seed fitness of cosexual plants, allowing female plants to become established in monomorphic populations. We studied geographical variation in gender expression and biomass allocation among 12 monomorphic and dimorphic populations of Wurmbea dioica along a latitudinal precipitation gradient in southwestern Australia to provide insight into mechanisms by which aridity might favor transitions between sexual systems. Plants in monomorphic and dimorphic populations exhibited contrasting gender expression and patterns of biomass allocation in areas with different levels of precipitation. Among dimorphic populations, lower precipitation was associated with a higher frequency of female plants, and reduced allocation to female function by hermaphrodites during flowering. In contrast, stress conditions had no effect on female allocation at flowering in monomorphic populations. Across latitudes, unisexuals and cosexuals exhibited consistent differences in above ground traits, with cosexuals having larger leaves, taller stems and larger flowers. Although all plants were smaller under drier conditions, cosexuals decreased above ground allocation to vegetative and reproductive structures with decreasing latitude. In contrast, unisexuals increased allocation to reproduction in drier areas at the expense of below ground size. Aridity was associated with reduced flower size among all gender classes, but not with changes in flower number. These data do not support the hypothesis that resource limitation of female allocation in cosexual populations favors the establishment of gender dimorphism in W. dioica. Alternative hypotheses, involving higher selfing rates and enhanced survival of unisexuals relative to cosexuals under resource-limited conditions, are discussed as possible explanations for the origin of dioecy in W. dioica. This revised version was published online in August 2006 with corrections to the Cover Date.     

SEXUAL DIMORPHISM IN BIOMASS ALLOCATION AND CLONAL GROWTH OF XANTHOXYLUM AMERICANUM

Reproduction can have a high resource cost. It has been suggested that greater investments in sexual reproduction by female dioecious plants leads to a lower rate of vegetative growth in females than in males. In this study, we investigated sexual dimorphism in biomass allocation and genet growth of the dioecious clonal shrub, northern prickly ash (Xanthoxylum americanum). The allocation of biomass over the course of one growing season to reproductive tissue, leaves, and growth of aboveground first-year wood, was compared in 18 clones growing in fields and six clones in woods in southeastern Wisconsin during 1985 and 1986. In addition, the number of shoots per clone, and weight of nonfirst-year wood (accumulated biomass) above- and below-ground were estimated. In open field sites, male clones allocated more biomass to new wood and less to reproduction than females, although males allocated more to flowers alone. Accordingly, male clones had significantly more shoots and more accumulated biomass both above- and below-ground than female clones. In the woods, where fruit set was near zero, there were few significant differences between male and female clones in either biomass allocation or accumulated biomass. These results support the hypothesis that the high resource investment in fruit production by females reduces their vegetative growth relative to males.     

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。     

The effects of seed weight on growth and competitive ability of Rumex acetosella from two successional old-fields

Summary The effects of seed size on growth, biomass allocation and competitive ability of Rumex acetosella plants grown either individually or in competition were studied in two populations (6 months and 15 years old respectively) sampled from a postcultivation successional gradient. For plants grown individually there were highly significant effects of seed weight on growth after 43 days, with a higher relative growth rate (RGR) observed for plants raised from heavier seeds. However at the end of the experiment, seedlings developed from lighter seeds had a RGR 2 times greater than those from heavier seeds. Final biomass of the two types was not significantly different after 73 days of growth. When plants were grown individually, there were only slight differences between populations, but when grown in monocultures of 4 plants per pot, plants from the old population had higher root and leaf biomass per pot whereas those from the young population had a higher reproductive effort per pot. This suggests that a trade-off between allocation to sexual and vegetative reproduction occurs over successional time. In mixtures of light and heavy seeds, plants from light seeds were shorter, had fewer leaves and lower biomass than plants from heavy seeds, which were also taller and produced more dry matter than plants grown from heavy seeds in monoculture. The significant effects of seed weight and population on biomass parameters persisted unit the end of the experiment. Seedlings from heavy seeds were strong competitors: those from the young population grew better in the presence of neighbors than in monoculture and those from the late successional population suppressed the more the growth of their partners. Seedlings from light seeds were subordinate competitors. These results suggest that seedlings from seeds of different sizes benefit from contrasting ecological conditions and that selection acts on reproductive output along successional gradients.     

青藏高原东缘星状风毛菊生殖分配对海拔的响应

通过采样调查法和烘干称量法, 检测了青藏高原东缘不同海拔20个居群星状风毛菊(Saussurea stella)的花部特征, 研究其花部特征对海拔及个体大小的响应。结果表明: 1)繁殖分配是依赖个体大小的, 个体越大, 繁殖分配越小; 2)花期繁殖器官和营养器官的生物量、头状花序的数量及大小、雌雄功能以及雄性内部花丝与花粉之间均存在资源分配上的权衡; 3)星状风毛菊通过花部特征的变异响应海拔的变化。研究发现, 星状风毛菊通过花部特征的变异, 特别是花柱和花丝的伸长及投入更多资源于吸引结构花瓣, 以此来补偿该种在高海拔地区因传粉者减少、活动频率降低和花粉数减少等因素对传粉带来的影响, 使其能够在高海拔的胁迫环境下有效地传粉, 完成有性繁殖。     

Pollen-Ovule Ratio and Gamete Investment in Pedicularis （Orobanchaceae）

The Pedicularis species provides ideal materials to study floral evolution because of their substantial flower variation based on a narrow genetic basis, even though they are almost exclusively pollinated by bumblebee. These traits allow us to detect the evolutionary trends of floral parameters without considering genetic background and the difference of pollination vectors. The pollen-ovule ratio is widely used to estimate the pattern of resource investment in two sexual functions in flowering plants. Forty species representing all of the corolla types in Pedicularls were used to study pollen-ovule ratio, gamete investment, and their correlations. Results show that pollen-ovule ratio does not differ among both different corolla types and taxonomic groups. It is therefore suggested that pollen-ovule ratio should be a parallel evolution. The correlations between pollen-ovule ratio and pollen size （-）, and ovule size （＋） can be successfully explained in terms of sex allocation theory. The biological significance of such relationships was also discussed. Additionally, we analyzed the pattern of resource investment into female gamete, which has been somewhat neglected, and found that plants have different patterns of gamete investment between the two sexual functions.     

Flowering phenology and sexual allocation in single-mutation lineages of Arabidopsis thaliana

We investigated the relationship between flowering time and sexual allocation in wild-type Arabidopsis thaliana and in genetically similar lineages with single-locus mutations of floral induction genes. We examined whether the mechanisms of growth and development that govern resource investment would permit the independent evolution of reproductive phenology and sexual allocation, or whether constraints, manifested as pleiotropic effects of the single mutations, would link these two life-history traits. Flowering times differed significantly among genotypes, and, as expected, later flowering times were associated with larger vegetative size. Later flowering genotypes produced heavier floral parts (larger petals, in particular), and allocated a significantly lower proportion of biomass to androecia, especially in final allocations that included fruit biomass. At least part of this pleiotropic covariation of flowering time and sexual allocation is likely to be mediated by vegetative size and the rate of resource supply to growing reproductive tissues, because the larger fruits of late-flowering genotypes required the same time, or proportionately less time than the difference in biomass, to mature. Because fruit mass is considered an investment in female function, sexual allocation measured at the end of a growing season tends to be highly female biased in angiosperms. We consider the implications of the pleiotropic association of flowering time, vegetative size, and sexual investment for the theory of sex allocation, and suggest that the idiosyncratic phenology of sexual investment in flowering plants creates a departure from a central assumption of Fisher's seminal sex allocation argument.     

Genetic and phenotypic variation,dispersal limitation and reproductive success in the invasive herb Eschscholzia californica along an elevation gradient in central Chile

Background: Reductions of genetic diversity and phenotypic changes in invasive plants are often observed to occur at high elevations. Genetic/phenotypic changes of invasive plants along elevation help to understand mechanisms of the presumed resistance of mountain ecosystems to invasion.

Aims: To assess genetic variability and phenotypic plasticity along an elevation gradient of Eschscholzia californica in the Andes, central Chile.

Methods: Eleven microsatellites were used to describe the genetic structure and the allelic diversity individuals, distributed at three elevations and two sites. We assessed the number of flowers per plant, floral biomass, leaf area, number of leaves, vegetative biomass and plant height of plants at each elevation.

Results: Genetic diversity as genetic structure did not decrease with elevations. Plant height and flower numbers decreased while leaf number and vegetative biomass increased with elevation. The ratio of the number of flowers to vegetative biomass, decreased significantly with elevation.

Conclusions: Strong genetic differences among elevations and similar genetic diversity along elevation do not suggest dispersal limitation to higher elevation. Reduction of reproductive and vegetative traits concomitantly with an increase of the reproductive cost suggests reproductive stress with increasing elevation, reducing the invasiveness of this species to higher elevation.