Differences in physiological integration between invasive and noninvasive introduced clonal species of Carpobrotus

AimsClonal growth is associated with invasiveness in introduced plant species, but few studies have compared invasive and noninvasive introduced clonal species to investigate which clonal traits may underlie invasiveness. To test the hypothesis that greater capacity to increase clonal growthviaphysiological integration of connected ramets increases invasiveness in clonal plants, we compared the effects of severing connections on accumulation of mass in the two species of the creeping, succulent, perennial, herbaceous genusCarpobrotusthat have been introduced on sand dunes along the Pacific Coast of northern California, the highly invasive speciesCarpobrotus edulisand the co-occurring, noninvasive speciesCarpobrotus chilensis.     

Biomass partitioning in response to resources availability: A comparison between native and invaded ranges in the clonal invader Carpobrotus edulis

Identifying the mechanism underlying plant invasiveness is a fast-moving research topic in current ecology. Phenotypic plasticity has been pointed out as a trait that can contribute to plant invasiveness. This experiment examines the presence of rapid adaptive evolution favoring plastic biomass partitioning during the invasion process. With that aim, we tested differences in patterns of biomass allocation between populations of Carpobrotus edulis from South Africa (native area) and the Iberian Peninsula (invaded area) growing under different nutrient, water and light availabilities in a common garden experiment. Here we demonstrate that biomass partitioning in response to nutrient availability in C. edulis differs between populations from native and invaded ranges, indicating that this trait could be under selection during the invasion process. Thus, nutrient shortage significantly increased the proportional production of roots in populations from the invaded range, but not in populations from the native area. This plastic root-foraging response may contribute to the optimization of nutrient uptake by plants, and therefore could be considered as an adaptive strategy. Understanding the ecological implications of rapid evolution for plastic biomass partitioning is important in determining processes of plant adaptation to new environments, and contributes to disentangling the mechanisms underlying plant invasiveness.     

Effect of physiological integration in self/non-self genotype recognition on the clonal invader Carpobrotus edulis

Aims Biological invasions represent one of the most important threats to the conservation of biodiversity; however, the mechanisms underlying successful invaders remain unsolved. Many of the most aggressive invaders show clonal growth, and capacity for clonal integration has been pointed out recently as an important trait explaining the success of invasive plants. We aim to determine the role of physiological integration in the capacity for self/non-self genotype recognition in the clonal invader Carpobrotus edulis and the implications of this capacity for the expansion of this aggressive invader.Methods We used connected and severed ramets of identical or different genotype and we determined the capacity for self/non-self recognition by comparing changes in biomass partitioning to avoid competition for resources between pairs of ramets.Important findings Physiological integration allowed self/non-self genotype recognition in the invader C. edulis. Results showed a significant effect of physiological integration on the biomass allocated to roots by genetically identical ramets: older ramets specialize in acquisition of soil-based resources and younger ramets specialize in lateral expansion. This specialization could be considered a form of division of labour, which reduce intra-genotype competition. This is the first evidence that division of labour could be interpreted as a form of self/non-self recognition between genetically identical ramets. Capacity for self/non-self discrimination could contribute to increase the colonization capacity of the aggressive invader C. edulis. This is the first study showing an association between self/non-self recognition and invasiveness in a clonal plant.     

Effects of soil heterogeneity and clonal integration on Alternanthera philoxeroides populations with a radial ramet aggregation

Some clonal plants can spread their ramet populations radially, and soil heterogeneity and clonal integration may greatly affect the establishment of these types of populations. We constructed Alternanthera philoxeroides populations with a radial ramet aggregation, allowing old ramets of clonal fragments to concentrate in central pots and younger ramets to root in peripheral pots. The peripheral pots were supplemented either with three different levels (high, medium and low) of soil nutrients to simulate a heterogeneous soil environment, or only one medium level of soil nutrients to simulate a homogeneous environment. Stolon connections between the central older ramets and the peripheral younger ramets were left intact or severed to test the effect of clonal integration. The maintenance of stolon connection could induce the division of labor between different‐aged ramets, by increasing the root investment in central ramets and the above‐ground growth in peripheral ramets. The maintenance of stolon connection could improve the growth of the central and peripheral ramets, clonal fragments and even the whole population. However, the positive consequence in peripheral ramets and whole fragments was only detected in the high‐nutrient patch of heterogeneous treatment. In sum, in the population with the radial ramet aggregation, clonal integration can play a key role in the rapid recruitment of young ramets of A. philoxeroides fragments, as well as the expansion of the whole population. The magnitude of clonal integration also became more obvious in the peripheral young ramets and whole fragments that experienced high‐nutrient patches.     

The effect of stolon fragmentation on the colonization of clonal invasive Carpobrotus edulis in a coastal dune system: a field test

Disturbances usually initiate processes of fragmentation in clonal plants, with the consequent division into portions of different size. The ability of these portions to survive and regrow after fragmentation plays an important role in the maintenance of populations and the colonization of new environments. In this field experiment we aim to determine the importance of stolons as reserve organs in the colonization of a coastal sand dune by a clonal invader. We simulated an event of fragmentation of clones of an aggressive invader into portions with short and long stolon sizes. Our results showed a reduction of biomass allocation to roots in the long stolon treatment that was balanced by an increase in the above‐ground growth; consequently, the area colonized by the invader was greater. We report evidence that stolons can contribute to buffering stressful conditions and allow expansion of the invader into a natural coastal sand dune.     

克隆植物对异质生境的适应对策研究进展

生境异质性是自然生态系统的基本特征,植物生长的必需资源和环境胁迫因子均存在着复杂的时间和空间异质性。克隆植物是指在自然条件下具有克隆特性的植物,即可通过与母株相连的芽、根茎、分蘖或枝条等繁殖体产生无性繁殖的植物,这些繁殖体一旦定居便可成为潜在的独立个体。克隆植物具有独特的生境适应策略(如形态可塑性、克隆整合、克隆分工、觅食行为、风险分摊等),面对异质性的生境条件,它可以通过调整自身的生理和形态结构来适应异质生境。目前,对于克隆植物在异质生境适应行为的研究已有很多报道,然而系统性的归纳和总结尚有欠缺。综述了克隆植物在不同资源异质生境(光照、养分、水分)和不同胁迫生境(盐碱胁迫、风沙胁迫、重金属胁迫)下独特的适应对策。最后,针对克隆植物对异质生境的适应对策,进行了总结并对未来的重点研究方向提出建议：(1)时间异质性尺度上的考量;(2)异质性生境中生物因子的调控作用;(3)克隆植物入侵机制;(4)克隆植物在生态修复中的应用潜力。     

Two types of division of labour in clonal plants: benefits, costs and constraints

Clonal plants spread vegetatively within their habitats by forming rooted ramets on stolons or rhizomes. Each of these ramets is capable of an independent existence after establishment. Nevertheless, ramets remain physically connected by stolon or rhizome internodes for variable periods of time, thereby allowing for resource movement and signal transduction within clones.Interconnected ramets of clonal plants, though potentially independent and totipotent, can specialize functionally in the performance of limited numbers of tasks such as the uptake of resources from above- vs below-ground sources, carbohydrate storage, vegetative spread and sexual reproduction. Such specialization and cooperation is comparable to a division of labour in economic systems or in colonies of social animals. The ecological significance of division of labour in clonal plants may be found in the increased efficiency of entire clones in exploiting their environments.Two different types of division of labour in clonal plants will be discussed in this review. The first type is an environmentally-induced specialization of ramets in the uptake of locally abundant resources (plastic division of labour), which can be found in several stoloniferous species. Evidence exists that this response increases resource uptake in spatially heterogeneous environments. The second type of division of labour, which occurs mainly in rhizomatous species, relates to a developmentally-programmed specialization and cooperation between interconnected ramets. This response pattern is thought to enhance plant performance by restricting the number of tasks for individual ramets and thereby significantly increasing the efficiency of task performance. In some plants, such an inherent division of labour is likely to contribute to nutrient extraction from poor and unpredictably variable sources.In this article not only benefits but also potential costs and constraints on division of labour in clonal plants are shown. The aim is to provide a review of existing knowledge and to develop concepts and hypotheses for future research.     

青藏高原东缘过路黄在资源交互斑块性生境中的克隆内资源共享

在青藏高原和四川盆地过渡带,分别于618m和1800m两个海拔高度上研究匍匐茎克隆植物过路黄(Lysimachia christinae)在资源交互斑块性生境中的克隆内资源共享及其对生长的影响.结果显示, 在海拔1800m处,与资源的空间同质性处理(Ⅰ) 和(Ⅱ)相比, 资源的空间异质性处理(Ⅲ)和(Ⅳ)下过路黄整个克隆片段的生物量和分株数均获得显著增加;在海拔618m处,与资源的空间同质性处理(Ⅰ) 和(Ⅱ)相比,资源的空间异质性处理(Ⅲ)和(Ⅳ)下过路黄整个克隆片段生物量显著增加.在海拔618m和1800m处,生长在低光高养条件下的远端分株, 若与高光低养的近端分株相连, 相比连接到低光高养的近端分株, 它们分配更多的生物量到地下部分;在海拔1800m处,生长在高光低养条件下的远端分株, 若与低光高养的近端分株相连, 相比连接到高光低养的近端分株, 它们分配更多的生物量到地上部分.在海拔618m和1800m处,生长在高光低养条件下的近端分株, 若与低光高养的远端分株相连, 相比连接到高光低养的远端分株, 它们分配更多的生物量到地上部分.处于资源交互斑块性生境中的过路黄发生了克隆内分工,依靠相连分株间的功能分化, 克隆植物能有效的利用异质性分布的资源, 缓解资源交互斑块性分布对克隆植物生长的不利影响.通过间隔子(匍匐茎或根状茎),相连分株间能够相互传递和共享由不同分株获得的资源,这种资源共享能够提高克隆植物在异质性生境中的存活与生长.同时,方差分析显示环境异质性和海拔的交互作用显著影响克隆片段的生物量和分株数.相比于海拔618m,在海拔1800m处克隆内资源共享对克隆植物生长表现的影响更大.     

Short‐term fitness benefits of physiological integration in the clonal herb Hydrocotyle peduncularis

Abstract We test whether physiological integration enhances the short‐term fitness of the clonal herb Hydrocotyle peduncularis (Apiaceae, R. Brown ex A. Richards) subjected to spatial variation in water availability. Our measures of fitness and costs and benefits are based on the relative growth rate of fragmented genets. Physiological integration over a gradient in soil moisture resulted in a highly significant net benefit to genet growth of 0.015 g g^?1 day^?1. This net benefit represents a significant enhancement of the average fitness of fragmented genets spanning the moisture gradient relative to the average of those growing in homogeneous moist or dry conditions. Sections of genet fragments growing in dry conditions in spatially heterogeneous treatments had significantly higher growth than the sections they were connected to that were growing in moist conditions. Within fragments, older (parent) sections growing in moist conditions experienced significant costs from connection to younger (offspring) sections growing in dry conditions. In contrast, offspring sections with ample water did not experience any costs when connected to parent sections growing in dry conditions. However, the net benefit of physiological integration was similar for parent and offspring sections, suggesting that parent and offspring sections contributed equally to the net benefit of physiological integration to genet growth and short‐term fitness.     

异质性水分环境中克隆整合对活血丹生物量分配及叶片结构特征的影响

喀斯特石漠化环境有着高度的生境异质性,异质性生境中土被不连续,土壤瘠薄,岩溶漏斗上的土壤保水性差,严重制约着喀斯特植被的生长及分布。为探究克隆植物在喀斯特地区的适应策略,本研究以喀斯特黄色石灰土为基质,选用克隆植物活血丹（Glechoma longituba）,以一个节间连接的两个分株为材料,保持节间连接或切断,种植于相邻花盆中,并施以不同浇水量,以明确不同水分可用性水平下克隆整合对活血丹生物量积累、生物量分配、叶片气孔及叶片组织特征的影响。结果显示,克隆整合显著促进活血丹生物量的积累及对根、叶的生物量分配;增加了活血丹叶气孔导度,降低了气孔指数;叶海绵组织受克隆整合影响较小,但栅栏组织及栅海比（栅栏组织/海绵组织）表现为非整合分株高于整合分株。本研究表明,克隆整合可增加活血丹胁迫分株对根、叶的投资,并以更佳的叶气孔、组织适应策略提高其在喀斯特生境中的生存与适应。     

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。     

Effects of Frankia on field performance of Alnus clones and seedlings

Field performance of tissue cultured clones and seedlings of Alnus viridis ssp. crispa, A. glutinosa, A. incana, and A. japonica was assessed five years after outplanting in central Ontario. Half the individuals were inoculated with a mixture of four Frankia isolates prior to planting. Inoculation produced significant increases (25% to 33%) in biomass production of two clones of A. glutinosa and one of A. incana. Woody biomass increments for the first five years, averaged across all clones and seedlings, were highest in A. japonica and A. incana (4.3 and 3.7 Mg ha^–1 yr^–1, respectively). Individual tree growth improved markedly in lower slope positions, but total plot biomass did not show similar gains in downslope positions owing to higher mortality and aphid (Paraprociphilus tessellatus) infestation. Aphids occurred in 22% of Frankia-inoculated individuals, and 15% of non-inoculated individuals. The fastest growing species, A. incana and A. japonica, were most susceptible to aphid attack. Growth of the best clones of A. glutinosa and A. incana exceeded seedling growth by 51% and 76%, respectively. The high growth variation in clones of the same species with similar geographic origins and the excellent performance of tissue cultured stock suggest that rapid genetic gains in an Alnus breeding program might be obtained by clonal propagation.     

Effects of light on the growth and clonal reproduction of Ligularia virgaurea

Ligularia virgaurea is a perennial herb that is widely distributed in the alpine meadow on the eastern Qinghai-Tibet plateau.We investigated the patterns of growth and reproduction of L.virgaurea under two contrasting levels of light conditions for two continuous growing seasons.Our results showed that the light affects on the maximum relative growth rate,the shoot weight ratio and the root weight ratio differed between the two growing seasons.L.virgaurea reproduced initially through rhizome in the second growing season,rather than sexual reproduction.The proportion of genets with clonal reproduction decreased under shaded conditions.A minimum genet size should be attained for clonal reproduction to begin under the shaded conditions.There was a positive linear relationship between clonal reproduction and genet size.Light level affected the allocation of total biomass to clonal structures,with less allocation under the full natural irradiance than under the shaded conditions.There seemed to be a trade-off between vegetative growth and clonal reproduction under the full natural irradiance,in terms of smaller relative growth rates of genets with clonal reproduction than those without clonal reproduction.L.virgaurea emphasized clonal reproduction under the full natural irradiance,while the plant emphasized vegetative growth under the shaded conditions.     

施肥对毛竹种群不同年龄分株间胸径大小关系的影响

克隆植物不同年龄分株间可以通过生理整合作用相互传递资源, 实现资源共享。施肥可以改变林地资源状况, 进而可能影响分株间的整合作用及不同年龄分株间的生长关系。该文采用标准主轴(SMA)估计法和多元回归分析, 对不同施肥管理下大型克隆植物毛竹(Phyllostachys edulis)种群不同年龄分株(1年生分株、3年生分株和5年生分株)间的胸径(DBH)关系进行了研究, 探讨毛竹不同年龄分株DBH大小关系对施肥的响应。结果表明: 连续5年施肥有效地增加了毛竹1年生分株的DBH, 而施肥1年处理下, 1年生分株DBH与3年生分株和5年生分株平均DBH差异不显著(p > 0.05)。1年生分株与3年生分株和5年生分株DBH之间的SMA斜率为0.88-1.10, 均与1.00不存在显著差异(p > 0.05), 表现为等速生长关系。施肥1年和连续施肥5年没有改变不同年龄分株DBH之间的SMA斜率, 但连续5年施肥导致SMA的y轴截距显著增大(p < 0.001), 即在3年生分株和5年生分株DBH相同的情况下, 连续5年施肥使1年生分株具有更大的DBH增长量。采用多元线性逐步回归分析发现, 毛竹1年生分株的DBH大小在很大程度上受3年生分株DBH大小的影响, 而连续5年施肥可增强5年生分株对1年生分株DBH大小的影响。     

放牧格局和生境资源对矮嵩草（Kobresia humilis）分株生物量分配和补偿性生长的影响

为研究密集型克隆植物对放牧扰动和生境资源变化的生物量分配和补偿生长响应特性,验证克隆植物的觅食模型和3个有关植物个体补偿反应的假说(①放牧优化假说,grazing optimization hypothesis,GOH;②反应连续谱假说,continuum of responses hypothesis,CRH;③增长率模型,growth rate model,GRM),在具有不同放牧利用格局和土壤养分水平的高寒矮嵩草草甸(Ⅰ.畜圈草地:重度放牧、资源丰富;Ⅱ.牧道草地:中度放牧、资源贫乏;Ⅲ.封育草地:不放牧、资源贫乏)中通过设置扣笼/无扣笼样方对其建群种矮嵩草(Kobresia humilis)进行了研究.结果表明不论当年解除家畜放牧与否,春季采摘率越高(畜圈草地),分株生物量向生长的投入越少,向贮藏器官的投入越多.繁殖分配在中度采摘下最高(牧道草地),扣笼内外分株各部分的生物量分配无差异.矮嵩草分株在中度采摘×资源贫乏条件下产生了超补偿响应,在重度采摘×资源丰富条件下为等量补偿,重度采摘导致分株密度显著减少.生物量分配格局与觅食模型的预测不符.补偿生长响应特性证实了GOH和GRM的预测,但与CRH的预测不符.这说明在研究地区放牧扰动格局对克隆植物矮嵩草分株的生物量分配和补偿生长具有重要影响,适度放牧利用更利于引起超补偿,而重度利用可能会对该种群的长期保持产生不利影响.     

A simple model for the influence of habitat resource availability on lateral clonal spread

Plant clonal spread is ubiquitous and of great interest, owing both to its key role in plant community assembly and its suitability for plant behaviour research. However, mechanisms that govern spreading distance are not well known. Here we link spacer costs and below-ground competition in a simple model of growth in a homogeneous below-ground environment, in which optimal distance between ramets is based on minimizing the sum of these costs. Using this model, we predict a high prevalence of clonal growth that does not employ spacers in resource-poor environments and a nonlinear increase in spreading distance in response to increasing below-ground resource availability. Analysis of database data on clonal growth in relationship to below-ground resource availability revealed that patterns of the spread based on stolons is compatible with the model''s predictions. As expected, model prediction failed for rhizomatous species, where spacer sizes are likely to be selected mainly to play roles other than spread. The model''s simplicity makes it useful as a null model in testing hypotheses about the effects of environmental heterogeneity on clonal spread.     

两种践踏胁迫下克隆整合对入侵植物空心莲子草生长的影响

研究了两种践踏胁迫下克隆整合对入侵植物空心莲子草生长的影响.结果表明:(1)切断分株间的匍匐茎连接,会降低先端分株的生物量、分株数、总匍匐茎长度和总叶片数,但会显著增强基端分株的生物量.(2)对先端分株的践踏胁迫会显著降低先端分株叶片的叶绿素相对含量,对基端分株的践踏胁迫会显著降低基端分株的生物量和总匍匐茎长度.(3)对于基端分株的分株数、总匍匐茎长度和总叶片数来说,当进行基端分株践踏胁迫时,匍匐茎连接对其影响不大,而当进行先端分株践踏胁迫时,则明显对其不利.(4)对于整个克隆片段,践踏胁迫的差异和匍匐茎是否切断对其生长没有显著影响.