根茎型植物扁秆荆三棱对光照强度和养分水平的生长响应及资源分配策略

自然界中光照和养分因子常存在时空变化,对植物造成选择压力。克隆植物可通过克隆生长和生物量分配的可塑性来适应环境变化。尽管一些研究关注了克隆植物对光照和养分因子的生长响应,但尚未深入全面了解克隆植物对光照和养分资源投资的分配策略。以根茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis)为研究对象,在温室实验中,将其独立分株种植于由2种光照强度(光照和遮阴)和4种养分水平(对照、低养分、中养分和高养分)交叉组成的8种处理组合中,研究了光照和养分对其生长繁殖及资源贮存策略的影响。结果表明,扁秆荆三棱的生长、无性繁殖及资源贮存性状均受到光照强度的显著影响,在遮阴条件下各生长繁殖性状指标被抑制。且构件的数目、长度等特征对养分差异的可塑性响应先于其生物量积累特征。在光照条件下,高养分处理的总生物量、叶片数、总根茎分株数、长根茎分株数、总根茎长、芽长度、芽数量等指标大于其他养分处理,而在遮阴条件下,其在不同养分处理间无显著差异,表明光照条件可影响养分对扁秆荆三棱可塑性的作用,且高营养水平不能补偿由于光照不足而导致的生长能力下降。光照强度显著影响了总根茎、总球茎及大、中、小球茎的生物量分配,遮阴条件下,总生物量减少了对地下部分根茎和球茎的分配,并将有限的生物量优先分配给小球茎。总根茎的生物量分配未对养分发生可塑性反应,而随着养分增加,总球茎分配下降,说明在养分受限的环境中球茎的贮存功能可缓冲资源缺乏对植物生长的影响。在相同条件下,根茎生物量对长根茎的分配显著大于短根茎,以保持较高的繁殖能力;而总球茎对有分株球茎的生物量分配小于无分株球茎,表明扁秆荆三棱总球茎对贮存功能的分配优先于繁殖功能。研究为进一步理解根茎型克隆植物对光强及基质养分环境变化的生态适应提供了依据。     

克隆植物的表型可塑性与等级选择

表型可塑性是指生物个体生长发育过程中遭受不同环境条件作用时产生不同表型的能力。进化的发生有赖于自然选择对种群遗传可变性产生的效力以及各基因型的表型可塑性。有足够的证据说明表型可塑性的可遗传性,它实际上是进化改变的一个成分。一般通过优化模型、数量遗传模型和配子模型来研究表型可塑性的进化。植物的构型是相对固定的,并未完全抑制表型可塑性。克隆植物因其双构件性而具有更广泛的、具有重要生态适应意义的表型可塑性。构件性使克隆植物具有以分株为基本单位的等级结构,从而使克隆植物的表型选择也具有等级性。构件等级一般包含基株、克隆片段或分株系统以及分株3个典型水平。目前认为克隆植物的自然选择有两种模式,分别以等级选择模型和基因型选择模型表征。等级选择模型认为:不同的等级水平同时也是表型选择水平,环境对各水平具有作用,各水平之间也有相互作用,多重表型选择水平的净效应最终通过繁殖水平——分株传递到随后的世代中。基因型选择模型指出:克隆生长引起分株的遗传变异,并通过基株内分株间以及基株间的非随机交配引起种子库等位基因频率的改变,产生微进化。这两种选择模式均突出强调了分株水平在自然选择过程中的变异性以及在进化中的重要性,强调了克隆生长和种子繁殖对基株适合度的贡献。基因型选择模型包含等级选择模型的观点,是对等级选择模型的重要补充。克隆植物的表型可塑性表现在3个典型等级层次上,由于各层次对自然选择压力具有不同的反应,其表型变异程度一般表现出“分株层次>分株片段层次>基株层次”的等级性反应模式。很多证据表明,在构件有机体中构件具有最大的表型可塑性,植物的表型可塑性实际上是构件而非整个遗传个体的反应。这说明克隆植物的等级反应模式可能具有普适性。如果该反应模式同时还是构件等级中不同“个体”适应性可塑性反应的模式,那么可以预测:1)在克隆植物中,分株层次受到的自然选择强度也最大,并首先发生适应性可塑性变化,最终引起克隆植物微进化;2)由于较弱的有性繁殖能力,克隆植物在进化过程中的保守性可能大于非克隆植物。克隆植物等级反应模式的普适性亟待验证。     

光照强度和基质养分对匍匐茎草本金戴戴克隆生长和克隆形态的影响

在深度遮光(光照强度为高光条件的6.25%,约为自然光照的5.3%)或低养分条件下,金戴戴(Halerpestes ruthenica Ovcz.)生物量、初级分株叶面积、分株总数、匍匐茎总数和总长度均显著减小,而比节间长和比叶柄长显著增加.在低养分条件下,金戴戴匍匐茎平均节间长显著增加,而匍匐茎分枝强度和分株数显著减小.这些结果与克隆植物觅食模型相符合,表明当生长于异质性生境中,金戴戴可能通过以克隆生长和克隆形态的可塑性实现的觅养行为来增加对养分资源的摄取.在深度遮光条件下,金戴戴平均间隔子长度(即平均节间长和平均叶柄长)均显著减小.这一结果与以往实验中匍匐茎草本间隔子对中度和轻度遮光(光照强度为高光条件的13%～75%,>10%的自然光照)的反应不同.这表明,在深度遮光条件下匍匐茎克隆植物可能不发生通过间隔子可塑性实现的觅光行为.光照强度和基质养分条件的交互作用对许多性状如总生物量、匍匐茎总数和总长度、二级和三级分株数、分株总数、初级分株叶面积以及分枝强度均有十分显著的效应.在高光条件下,基质养分对这些性状有十分显著的影响;而在低光条件下,基质养分条件对这些性状不产生影响或影响较小.这表明,光照强度影响金戴戴对基质养分的可塑性反应.在深度遮光或低养分条件下,金戴戴可能通过减小匍匐茎节间粗度(增加比节间长)来增加或维持其相对长度,从而更有机会逃离资源丰度低的斑块.     

Effects of four generations of density-dependent selection on life history traits and their plasticity in a clonally propagated plant

Life history evolution of many clonal plants takes place with long periods of exclusively clonal reproduction and under largely varying ramet densities resulting from clonal reproduction. We asked whether life history traits of the clonal herb Ranunculus reptans respond to density-dependent selection, and whether plasticity in these traits is adaptive. After four generations of exclusively clonal propagation of 16 low and 16 high ramet-density lines, we studied life history traits and their plasticities at two test ramet-densities. Plastic responses to higher test-density consisted of a shift from sexual to vegetative reproduction, and reduced flower production, plant size, branching frequency, and lengths of leaves and internodes. Plants of high-density lines tended to have longer leaves, and under high test-density branched less frequently than those of low-density lines. Directions of these selection responses indicate that the observed plastic branching response is adaptive, whereas the plastic leaf length response is not. The reverse branching frequency pattern at low test-density, where plants of high-density lines branched more frequently than those of low-density lines, indicates evolution of plasticity in branching. Moreover, when grown under less stressful low test-density, plants of high-density lines tended to grow larger than the ones of low-density lines. We conclude that ramet density affects clonal life-history evolution and that under exclusively clonal propagation clonal life-history traits and their plasticities evolve differently at different ramet densities.     

Differential influence of clonal integration on morphological and growth responses to light in two invasive herbs

Background and aims

In contrast to seeds, high sensitivity of vegetative fragments to unfavourable environments may limit the expansion of clonal invasive plants. However, clonal integration promotes the establishment of propagules in less suitable habitats and may facilitate the expansion of clonal invaders into intact native communities. Here, we examine the influence of clonal integration on the morphology and growth of ramets in two invasive plants, Alternanthera philoxeroides and Phyla canescens, under varying light conditions.

Methods

In a greenhouse experiment, branches, connected ramets and severed ramets of the same mother plant were exposed under full sun and 85% shade and their morphological and growth responses were assessed.

Key results

The influence of clonal integration on the light reaction norm (connection×light interaction) of daughter ramets was species-specific. For A. philoxeroides, clonal integration evened out the light response (total biomass, leaf mass per area, and stem number, diameter and length) displayed in severed ramets, but these connection×light interactions were largely absent for P. canescens. Nevertheless, for both species, clonal integration overwhelmed light effect in promoting the growth of juvenile ramets during early development. Also, vertical growth, as an apparent shade acclimation response, was more prevalent in severed ramets than in connected ramets. Finally, unrooted branches displayed smaller organ size and slower growth than connected ramets, but the pattern of light reaction was similar, suggesting mother plants invest in daughter ramets prior to their own branches.

Conclusions

Clonal integration modifies light reaction norms of morphological and growth traits in a species-specific manner for A. philoxeroides and P. canescens, but it improves the establishment of juvenile ramets of both species in light-limiting environments by promoting their growth during early development. This factor may be partially responsible for their ability to successfully colonize native plant communities.     

Effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions

异质光照条件下克隆整合对入侵植物南美蟛蜞菊化感作用的影响 植物入侵已成为全球生态系统最严重的威胁之一。当具有克隆生长能力的入侵植物入侵或定殖到新的生境时,它们相互连接的分株可能受到异质光照的影响。在异质光照条件下,克隆整合对入侵植物化感作用的影响尚不清楚。为研究异质光照条件下克隆整合对入侵植物南美蟛蜞菊(Wedelia trilobata) 化感作用的影响,采用两个连续分株的克隆片段进行了盆栽试验。较老的分株暴露在全光下,而年轻的分株则受到20%的全光照。同时,每个克隆片段的年轻分株与目标植株(一个番茄苗)在盆栽中相邻生长。南美蟛蜞菊的两个连续分株之间的匍匐茎设置切断和不切断两种处理。另外,两株番茄幼苗 (一株作为目标植株)在盆栽中相邻生长作为对照。研究结果表明,当与目标植物相邻生长的南美蟛蜞菊分株之间的匍匐茎保持完整时,目标植株的生物量积累、叶片叶绿素和氮含量、叶绿素荧光参数和净光合速率及其根长和活性相较于匍匐茎切断处理显著降低。异质光照条件下连续两个分株之间碳水化合物的运输或共享可以增强20%全光处理下年轻分株的化感作用。克隆整合在异质光照条件下对具有克隆生长能力的入侵植物的入侵或定殖具有重要意义。     

光照强度和基质养分对匍匐茎草本金戴戴克隆生长和克隆形态的影响

在深度遮光 (光照强度为高光条件的 6 .2 5% ,约为自然光照的 5.3% )或低养分条件下 ,金戴戴 (HalerpestesruthenicaOvcz.)生物量、初级分株叶面积、分株总数、匍匐茎总数和总长度均显著减小 ,而比节间长和比叶柄长显著增加。在低养分条件下 ,金戴戴匍匐茎平均节间长显著增加 ,而匍匐茎分枝强度和分株数显著减小。这些结果与克隆植物觅食模型相符合 ,表明当生长于异质性生境中 ,金戴戴可能通过以克隆生长和克隆形态的可塑性实现的觅养行为来增加对养分资源的摄取。在深度遮光条件下 ,金戴戴平均间隔子长度 (即平均节间长和平均叶柄长 )均显著减小。这一结果与以往实验中匍匐茎草本间隔子对中度和轻度遮光 (光照强度为高光条件的 1 3%～ 75% ,>1 0 %的自然光照 )的反应不同。这表明 ,在深度遮光条件下匍匐茎克隆植物可能不发生通过间隔子可塑性实现的觅光行为。光照强度和基质养分条件的交互作用对许多性状如总生物量、匍匐茎总数和总长度、二级和三级分株数、分株总数、初级分株叶面积以及分枝强度均有十分显著的效应。在高光条件下 ,基质养分对这些性状有十分显著的影响 ;而在低光条件下 ,基质养分条件对这些性状不产生影响或影响较小。这表明 ,光照强度影响金戴戴对基质养分的可塑性反应。在深度遮光     

Clonal integration in Ranunculus reptans: by‐product or adaptation?

We studied fitness consequences of clonal integration in 27 genotypes of the stoloniferous herb Ranunculus reptans in a spatially heterogeneous light environment. We grew 216 pairs of connected ramets (eight per genotype) with mother ramets in light and daughter ramets in shade. In half of the pairs we severed the stolon connection between the two ramets at the beginning of the experiment. During the experiment, 52.7% of the ramet pairs with originally intact connection physically disintegrated. We detected significant variation among genotypes in this regard. Survival of planted ramets was 13.3% higher for originally connected pairs. Moreover, there was significant variation among genotypes in survival, in the difference in survival between plant parts developing from mother and daughter ramets, and in the effect of integration on this difference. In surviving plants connection between ramets decreased size differences between mother and daughter parts. Variation among genotypes was significant in growth and reproduction and marginally significant in the effect of physiological integration on growth and reproduction. Connected daughter ramets had longer leaves and internodes than daughters in severed pairs indicating that integration stimulated plant foraging in both the vertical and the horizontal plane. Observed effects of integration on fitness components in combination with genetic variation in maintenance and effects of connection indicate that clonal integration in R. reptans has the capability to evolve, and therefore suggest that clonal integration is adaptive. If genetic variation in integration is common, future studies on clonal integration should always use defined genetic material and many clones to allow extrapolation of results to population and wider levels.     

Trade-offs among growth, clonal, and sexual reproduction in an invasive plant Spartina alterniflora responding to inundation and clonal integration

The purpose of this article was to study the trade-offs among vegetative growth, clonal, and sexual reproduction in an aquatic invasive weed Spartina alterniflora that experienced different inundation depths and clonal integration. Here, the rhizome connections between mother and daughter ramets were either severed or left intact. Subsequently, these clones were flooded with water levels of 0, 9, and 18 cm above the soil surface. Severing rhizomes decreased growth and clonal reproduction of daughter ramets, and increased those of mother ramets grown in shallow and deep water. The daughter ramets disconnected from mother ramets did not flower, while sexual reproduction of mother ramets was not affected by severing. Clonal integration only benefited the total rhizome length, rhizome biomass, and number of rhizomes of the whole clones in non-inundation conditions. Furthermore, growth and clonal reproduction of mother, daughter ramets, and the whole clone decreased with inundation depth, whereas sexual reproduction of mother ramets and the whole clones increased. We concluded that the trade-offs among growth, clonal, and sexual reproduction of S. alterniflora would be affected by inundation depth, but not by clonal integration.     

Plant clonality: Biology and diversity

The current approaches to the study of clonal plants are reviewed. Most studies concentrate at the level of the ramet and clonal fragment exploring the “microscopic” view of clonal plants, dealing with the translocation of resources, clonal integration, plasticity of growth etc. The information gained, by this approach can be used in the understanding of higher levels of organization within the clonal system either with the help of spatially explicit modelling techniques, or by using means and distributions of size within a population instead of studying individual ramets separately. Plant scientists use the term clone with two meanings, viz. (a) a set of physiologically connected, but potentially independent ramets, and (b) a set of genetically identical, but potentially physically separated individuals. The overlap of these terms differs between individual plant species, depending on the extent of physical separation of the ramets and the degree of physiological integration between the ramets; the lower the frequency of ramet separation, the closer are the physiological and genetic concepts of the clone. Three critical areas seem to be neglected in clonal plant research: (a) the interrelationship between hierarchical levels in clonal plants, (b) the particular spatial structure of their environment, and (c) the importance of clonal plants in different ecological communities.     

The effect of local resource availability and clonal integration on ramet functional morphology in Hydrocotyle bonariensis

Summary Within a physiologically integrated clone, the structure and functioning of an individual ramet is determined by: 1) the response of that ramet to its local environment and 2) its response to resource integration within the clone. In a multifactorial experiment, Hydrocotyle bonariensis ramets were grown in limiting resource environments with and without the benefit of basipetal resource movement from another branch of the clone. Ramets were analyzed for their morphological responses to variation in local light, water and nitrogen availability and to the superimposed effect of resource integration on these conditions. The expression of ramet morphology, from induction to development, was highly plastic in response to variable local resource availability. Resource integration changed a ramet's local response in a variety of ways depending on the resource(s) being translocated and the character involved. Among leaf characteristics (leaf weight, petiole height, blade area), resource translocation into the shade resulted in an enhancement of the local response. Similarly, the translocation of nitrogen and water generally increased clonal proliferation and sexual reproduction among ramets. In contrast, the translocation of water reversed the effect of local low water conditions on ramets by inhibiting root production. Some characters such as internode distance and leaf allometry were unaffected by integration. The maintenance of connections between ramets as a Hydrocotyle clone expands allows for resource sharing among widely separated ramets and can result in an integrated morpological response to a resource environment that is patchy in time and space.     

On plastic and non-plastic variation in clonal plant morphology and its ecological significance

Morphological plasticity in clonal plants has received wide attention because localized plastic changes in spacer length, branching intensity and branching angle may enable clonal plants to place ramets selectively in the more favourable microhabitats within a heterogeneous environment. These responses have been interpreted in terms of foraging behaviour. Studies of morphological plasticity in clonal plants are usually carried out with one or two genotypes of a species, or with material of unknown genetic origin. Based on the concept of phenotypic plasticity, it is argued that such studies do not reveal whether plasticity in a population can be modified by natural selection. In addition, responses are often evaluated at two environmental conditions only, which may underestimate plasticity. Hence, our information on the ecological and evolutionary significance of morphological plasticity in clonal plants is still very incomplete. Two examples are given to show that stolon internode and rhizome lengths may vary considerably within an individual plant. Only a minor part of this variation may be plastic, i.e. the variation is hardly changed by the environmental conditions to which the plants are subjected. Hence, non-plastic variation in clonal morphology may exceed the degree of morphological plasticity. The non-plastic variation seems to originate from species-specific patterns of stolon and rhizome development. Marked non-plastic variation may obscure the effects of morphological plasticity on the placement pattern of ramets in the field, suggesting that plasticity in clonal morphology may not be very effective in terms of foraging for favourable patches. Possible reasons for the low levels of plasticity of clonal spacers are discussed.     

Heterogeneous light supply affects growth and biomass allocation of the understory fern Diplopterygium glaucum at high patch contrast

Spatial heterogeneity in resource supply is common and responses to heterogeneous resource supply have been extensively documented in clonal angiosperms but not in pteridophytes. To test the hypotheses that clonal integration can modify responses of pteridophytes to heterogeneous resource supply and the integration effect is larger at higher patch contrast, we conducted a field experiment with three homogeneous and two heterogeneous light treatments on the rhizomatous, understory fern Diplopterygium glaucum in an evergreen broad-leaved forest in East China. In homogeneous treatments, all D. glaucum ramets in 1.5 m×1.5 m units were subjected to 10, 40 and 100% natural light, respectively. In the heterogeneous treatment of low patch contrast, ramets in the central 0.5 m×0.5 m plots of the units were subjected to 40% natural light and their interconnected ramets in the surrounding area of the units to 100%; in the heterogeneous treatment of high patch contrast, ramets in the central plots were subjected to 10% natural light and those in the surrounding area to 100%. In the homogeneous treatments, biomass and number of living ramets in the central plots decreased and number of dead ramets increased with decreasing light supply. At low contrast heterogeneous light supply did not affect performance or biomass allocation of D. glaucum in the central plots, but at high contrast it increased lamina biomass and number of living ramets older than annual and modified biomass allocation to lamina and rhizome. Thus, clonal integration can affect responses of understory ferns to heterogeneous light supply and ramets in low light patches can be supported by those in high light. The results also suggest that effects of clonal integration depend on the degree of patch contrast and a significant integration effect may be found only under a relatively high patch contrast.     

莲草直胸跳甲取食对空心莲子草和莲子草克隆整合的影响

很多外来入侵植物都具有克隆生长习性,探究克隆整合特性与外来克隆植物入侵性间的关系对阐明其生态适应性及入侵机制具有重要的意义。本研究以入侵植物空心莲子草及其本地同属种莲子草为研究对象,比较在生防昆虫莲草直胸跳甲的取食下,克隆整合对两种植物先端分株、基端分株及整个克隆片段生长和生物量分配的影响。结果表明: 在莲草直胸跳甲取食下,有克隆整合的空心莲子草先端分株的叶片数、茎长、分株数及整个克隆片段的地径均显著高于无克隆整合植株,其基端分株及整个克隆片段的地下生物量和总生物量相较于无克隆整合植株分别降低了78.2%、60.9%和48.7%、37.2%;有克隆整合的莲子草先端分株的地径及整个克隆片段的叶片数与无克隆整合植株相比显著增加,其基端分株数显著降低了21.7%,而其先端分株、基端分株及整个克隆片段的生物量均无显著差异。耗益分析表明,在莲草直胸跳甲取食下,空心莲子草先端分株的分株数与生物量及莲子草先端分株的分株数均能通过克隆整合显著受益,而两种植物基端的分株数、生物量的耗益则不受克隆整合处理的影响。这些结果表明,克隆整合虽能在一定程度缓解莲草直胸跳甲对于两种植物先端分株的取食压力,且空心莲子草的克隆整合作用要强于莲子草,但在整个克隆片段水平上,两种植物并不能通过克隆整合显著获益。     

Arbuscular mycorrhizal fungi reduce effects of physiological integration in Trifolium repens

Background and Aims

One of the special properties of clonal plants is the capacity for physiological integration, which can increase plant performance through mechanisms such as resource sharing and co-ordinated phenotypic plasticity when plants grow in microsites with contrasting resource availabilities. However, many clonal plants are colonized by arbuscular mycorrhizal fungi (AMF). Since AMF are likely to reduce contrasts in effective resource levels, they could also reduce these effects of clonal integration on plasticity and performance in heterogeneous environments.

Methods

To test this hypothesis, pairs of connected and disconnected ramets of the stoloniferous herb Trifolium repens were grown. One ramet in a pair was given high light and low nutrients while the other ramet was given high nutrients and low light. The pairs were inoculated with zero, one or five species of AMF.

Key Results

Pairs of ramets grown without AMF developed division of labour and benefited from resource sharing, as indicated by effects of connection on allocation to roots, accumulation of mass, and ramet production. Inoculation with five species of AMF significantly reduced these effects of connection, both by inhibiting them in ramets given high nutrients and inducing them in ramets given high light. Inoculation with one species of AMF also reduced some effects of connection, but generally to a lesser degree.

Conclusions

The results show that AMF can significantly modify the effects of clonal integration on the plasticity and performance of clonal plants in heterogeneous environments. In particular, AMF may partly replace the effects and benefits of clonal integration in low-nutrient habitats, possibly more so where species richness of AMF is high. This provides the first test of interaction between colonization by AMF and physiological integration in a clonal plant, and a new example of how biotic and abiotic factors could interact to determine the ecological importance of clonal growth.Key words: Arbuscular mycorrhizal fungi, biomass allocation, clonal plant, division of labour, environmental heterogeneity, light availability, nutrients, white clover     

异质光环境下克隆整合对白夹竹光合氮分配格局的影响

采用盆栽试验,以单轴散生型竹类植物——白夹竹(Phyllostachys bissetii)克隆片段为对象,使近端分株处于自然光照环境,远端分株处于遮荫环境中,对根状茎作切断或不切断处理,研究克隆整合对远端分株和近端分株光合氮分配格局的影响。结果表明:(1)根状茎保持连接的远端分株较根状茎切断的远端分株具有更高的最大净光合速率、叶片氮含量、光合色素含量、叶片光合氮分配系数。(2)相对根状茎切断处理,根状茎保持连接的远端分株将更多的氮分配到光合系统的羧化系统、生物力能学组分,而分配至捕光系统组分的比例较小。(3)比较处于自然光照条件的近端分株,比叶重、叶片氮含量等并没有因根状茎切断与否表现出显著性差异,根状茎连接的近端分株部分指标甚至高于根状茎切断的近端分株。研究认为,克隆整合作用影响处于遮荫环境的白夹竹远端分株的光合氮分配格局,使得处于遮荫生境中的克隆分株依旧维持较高的光合能力,保证了处于逆境条件下克隆分株的生存与生长。     

Clonal Integration of Fragaria orientalis in Reciprocal and Coincident Patchiness Resources: Cost-Benefit Analysis

Clonal growth allows plants to spread horizontally and to experience different levels of resources. If ramets remain physiologically integrated, clonal plants can reciprocally translocate resources between ramets in heterogeneous environments. But little is known about the interaction between benefits of clonal integration and patterns of resource heterogeneity in different patches, i.e., coincident patchiness or reciprocal patchiness. We hypothesized that clonal integration will show different effects on ramets in different patches and more benefit to ramets under reciprocal patchiness than to those under coincident patchiness, as well as that the benefit from clonal integration is affected by the position of proximal and distal ramets under reciprocal or coincident patchiness. A pot experiment was conducted with clonal fragments consisting of two interconnected ramets (proximal and distal ramet) of Fragaria orientalis. In the experiment, proximal and distal ramets were grown in high or low availability of resources, i.e., light and water. Resource limitation was applied either simultaneously to both ramets of a clonal fragment (coincident resource limitation) or separately to different ramets of the same clonal fragment (reciprocal resource limitation). Half of the clonal fragments were connected while the other half were severed. From the experiment, clonal fragments growing under coincident resource limitation accumulated more biomass than those under reciprocal resource limitation. Based on a cost-benefit analysis, the support from proximal ramets to distal ramets was stronger than that from distal ramets to proximal ramets. Through division of labour, clonal fragments of F. orientalis benefited more in reciprocal patchiness than in coincident patchiness. While considering biomass accumulation and ramets production, coincident patchiness were more favourable to clonal plant F. orientalis.     

The effects of clonal integration on morphological plasticity and placement of daughter ramets in black locust (Robinia pseudoacacia)

We studied the field response of Robinia pseudoacacia L. to light, total soil nitrogen, available soil phosphorus and soil pH. Results indicated that there was very strong clonal integration between mother and daughter ramets. Mother ramets can provide nitrogen and phosphorus to daughter ramets sufficient for their continued growth through strong clonal integration, but cannot provide enough photosynthate. With clonal integration, soil nitrogen and phosphorus availability had no effect on biomass allocation to roots, number of ramets and length of connection roots. Biomass allocation to roots increased markedly and responded to nitrogen and phosphorus availability, when the connections were severed. Light had a significant effect on the percent of biomass allocation to leaves and number of ramets, but no effect on the length of connection roots. Daughter ramets allocated more resources to leaves, and clones placed more daughter ramets in high light patches than in low light patches. Soil pH had a significant effect on ramet number and connection root length. Clones concentrated in alkaline patches and escaped from acid patches through selective placement of daughter ramets and changing the length of connection roots. We suggest that the clonal integration may be very strong and provide sufficient soil resources to daughter ramets, then affect the daughter ramets’ morphology and placement, if the size of a specific ramet is significantly larger than the other ramets in an arbor clone.     

Trans-generational effects in the clonal invader Alternanthera philoxeroides

近年的研究已经揭示出表型可塑性可以通过营养世代遗传。从这个意义上讲,环境诱导的基因调控变化(例如DNA甲基化,即表观遗传变异)会导致可逆的塑性反应传递给后代。这种跨世代的可塑性在克隆植物中尤其重要,因为有性繁殖减少会降低通过遗传变异进行适应的可能性。许多最具侵略性的植物入侵者都具有克隆性,而且克隆性被认为是植物入侵性的关键。本研究中,我们的目标是确定在克隆入侵者喜旱莲子草(Alternanthera philoxeroides)中是否发生了跨代效应,以及这种效应在本地和非本地群落之间是否存在差异。在同质园实验中,我们将采自巴西(原产地)和伊比利亚半岛(非原产地)的喜旱莲子草种群分别种植在养分高和低的土壤中,后代植株被移植到高养分条件下作为对照。为了检验DNA甲基化对跨代可塑性的潜在作用,一半的母株用去甲基化剂5-氮杂胞苷处理。在来自原产地和非原产地的种群中均观察到了跨代效应。有趣的是,在原产地种群的生长变量(分株数、茎生物量、根生物量和总生物量)中发现了跨代效应,而在非原产地种群中发现了生物量分配具有跨代效应。在原产地种群中出现的跨代效应可以用“银勺”效应来解释,而非原产地种群的跨代效应可以归因于DNA甲基化引起的表观遗传传递。本研究强调了跨代效应对克隆植物生长的重要性,这有助于理解众多克隆植物能够成功繁殖扩张的机制。     

Functional specialization of ramets in Scirpus maritimus – Splitting the tasks of sexual reproduction, vegetative growth, and resource storage

Clonal plant species can be considered as populations of interconnected ramets which are basically identical in form and function, and potentially independent from each other. Experimental studies and field observations suggest that an intra-clonal specialization of ramets with different roles (division of labour) can increase the performance of clonal systems under heterogeneous conditions. This paper explores structural and functional variation in the emergent macrophyte Scirpus maritimus, which forms ramets that specialize in three main activities: sexual reproduction, photosynthetic assimilation and vegetative growth, and reserve storage. The main question asked in this study is whether such specialization is a developmentally programmed syndrome in this species, and whether environmental conditions can alter the pattern of ramet differentiation along rhizome systems.We analyzed clonal fragments collected from a population in the field, and grew clones individually in pots of two sizes to simulate different degrees of crowding and shoot density. Specialization of ramets was largely predictable from their position along the rhizome system, indicating that specialization is an inherent feature (developmentally programmed) of clone ontogeny in S. maritimus. In the field, sexual ramets were always situated at the base of rhizome systems, vegetative ramets were in first and intermediate positions, and shoot-less storage ramets were almost always formed distally on rhizomes (terminal ramets). In the pot experiment flowering ramets were observed in all positions along rhizome systems, suggesting that specialization for sexual reproduction shows a plastic response to environmental conditions.S. maritimus can adjust the relative numbers of ramets with and without above-ground shoots when grown in different shoot densities, i.e. the frequency of individual ramets responsible for a certain functional or developmental process can be adjusted to environmental conditions and internal needs. In S. maritimus, the density-dependant regulation of storage versus vegetative growth and sexual reproduction may represent a mechanism to limit shoot competition in crowded populations.