Emergent plant presence and richness alter competitive interactions between two foating plants

Interactions between two plant species can be infuenced by the presence of other plant species and such an effect may change as the diversity of the other species increases.To test these hypotheses,we frst constructed aquatic communities consisting of 1,2 and 4 emergent plant species and then grew ramets of Lemna minor only,ramets of Spirodela polyrhiza only or ramets of both L.minor and S.polyrhiza within these aquatic communities.We also included controls with ramets of L.minor,S.polyrhiza or both but without any emergent plants.Biomass and number of ramets of L.minor and S.polyrhiza were signifcantly smaller with than without the emergent plants,but they did not differ among the three richness levels.The presence of S.polyrhiza did not signifcantly affect the growth of L.minor,and such an effect was not dependent on the richness of the emergent plant species.Without the emergent plant species,the presence of L.minor markedly reduced biomass(-92%)and number of ramets(-88%)of S.polyrhiza.However,such a competitive effect of L.minor on S.polyrhiza became much weaker in the presence of one emergent plant species(-46%biomass and-39%number of ramets)and completely disappeared in the presence of two or four emergent plant species.Therefore,both the presence and richness of emergent plant species can alter competitive interactions between the two duckweed species.These fndings highlight the importance of species diversity in regulating plant-plant interactions.

四大洲食用昼花属的比较入侵生态学:对养分和竞争的响应

入侵生物学的两个关键假设是,某些特征是外来物种入侵的基础,且这些特征是在引入期间或之后选择的。我们通过关注两个可能赋予入侵性的特征来检验这些假设,即营养增加引起的较高生长加速和竞争引起的较低生长减速。我们对采自非洲、澳洲、欧洲和北美洲的4个食用昼花属(Carpobrotus)品种进行了比较。为了测试高入侵物种莫邪菊(Carpobrotus edulis)对这些特征的选择,我们将原产于南非的植株与入侵其他3个地区的植株进行了比较。在一个同质园中繁殖植株。然后,在添加或不添加养分的情况下单独培育子代,并在不添加养分的情况下将子代与另一个食用昼花属品种一起、或与欧洲的一种共生本土物种马兰草(Ammophila arenaria)一起培育。不同品种的食用昼花属对营养物质的反应并无差异,在入侵性更强的物种中,竞争反应的负面性也没有减弱。然而,与本土莫邪菊相比,添加营养物质引起外来莫邪菊更高的生长加速。此外,在处理开始时,两种入侵物种每分株的鲜质量高于两种非入侵物种。我们的研究结果表明,引种可以选择入侵物种对营养富集的反应进行选择,也证明了外来植物的体积和入侵性之间的关联。

Effects of physiological integration on defense strategies against herbivory by the clonal plant Alternanthera philoxeroides

Aims The plant-herbivore interaction is one of the most fundamental inter-actions in nature.Plants are sessile organisms,and consequently rely on particular strategies to avoid or reduce the negative impact of herbivory.Here,we aimed to determine the defense strategies against insect herbivores in the creeping invasive plant Alternanthera philoxeroides.Methods We tested the defense response of A.philoxeroides to herbivory by a leaf-feeding specialist insect Agasicles hygrophila and a pol-yphagous sap-feeding insect Planococcus minor.We also tested the mechanisms triggering defense responses of A.philoxeroides by including treatments of artificial leaf removal and jasmonic acid application.Furthermore,we examined the effect of physiological integration on these defense strategies.Important Findings The combination of artificial leaf removal and jasmonic acid appli-cation produced a similar effect to that of leaf-feeding by the real herbivore.Physiological integration influenced the defense strat-egies of A.philoxeroides against herbivores,and increased biomass allocation to aboveground parts in its apical ramets damaged by real herbivores.Our study highlights the importance of physio-logical integration and modular plasticity for understanding the consequences of herbivory in clonal plants.

Trans-generational effects in the clonal invader Alternanthera philoxeroides

Aims Recent studies have revealed heritable phenotypic plasticity through vegetative generations.In this sense,changes in gene regulation induced by the environment,such as DNA methylation(i.e.epigenetic changes),can result in reversible plastic responses being transferred to the offspring generations.This trans-generational plasticity is expected to be especially relevant in clonal plants,since reduction of sexual reproduction can decrease the potential for adaptation through genetic variation.Many of the most aggressive plant invaders are clonal,and clonality has been suggested as key to explain plant invasiveness.Here we aim to determine whether trans-generational effects occur in the clonal invader Alternanthera philoxeroides,and whether such effects differ between populations from native and non-native ranges.Methods In a common garden experiment,parent plants of A.philoxeroides from populations collected in Brazil(native range)and Iberian Peninsula(non-native range)were grown in high and low soil nutrient conditions,and offspring plants were transplanted to control conditions with high nutrients.To test the potential role of DNA methylation on trans-generational plasticity,half of the parent plants were treated with the demethylating agent,5-azacytidine.Important Findings Trans-generational effects were observed both in populations from the native and the non-native ranges.Interestingly,trans-generational effects occurred on growth variables(number of ramets,stem mass,root mass and total mass)in the population from the native range,but on biomass partitioning in the population from the non-native range.Trans-generational effects of the population from the native range may be explained by a‘silver-spoon’effect,whereas those of the population from the non-native range could be explained by epigenetic transmission due to DNA methylation.Our study highlights the importance of trans-generational effects on the growth of a clonal plant,which could help to understand the mechanisms underlying expansion success of many clonal plants.

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 aggres-sive 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 physi-ological integration in the capacity for self/non-self genotype recog-nition 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 gen-otype 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 recogni-tion 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 acqui-sition 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 inter-preted 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.

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

Aims Clonal 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 growth via physiological 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 genus Carpobrotus that have been introduced on sand dunes along the Pacific Coast of northern California,the highly invasive species Carpobrotus edulis and the co-occurring,noninvasive species Carpobrotus chilensis.Methods Pairs of ramets from four mixed populations of the species from California were grown in a common garden for 3 months with and without severing the stem connecting the ramets.To simulate the effect of clones on soils in natural populations,the older ramet was grown in sand amended with potting compost and the younger in sand alone.Important Findings Severance decreased net growth in mass by~60%in C.edulis and~100%in C.chilensis,due mainly to the negative effect of severance on the shoot mass of the younger ramet within a pair.Contrary to the hypothesis,this suggests that physiological integration increases growth more in the less invasive species.However,severance also decreased allocation of mass to roots in the older ramet and increased it in the younger ramet in a pair,and the effect on the younger ramet was about twice as great in C.edulis as in C.chilensis.This indicates that the more invasive species shows greater phenotypic plasticity in response to physiological integration,in particular greater capacity for division of labor.This could contribute to greater long-term growth and suggests that the division of labor may be a trait that underlies the association between clonal growth and invasiveness in plants.

Resource-sharing strategies in ecotypes of the invasive clonal plant Carpobrotus edulis: specialization for abundance or scarcity of resources

Aims Carpobrotus edulis(L.)N.E.Br.is known to invade many coastal ecosystems around the world,and it has been considered as one of the most severe threats to numerous terrestrial plant communi-ties.Therefore,the study of the relationships between life-history traits that may favour its invasiveness and the invasibility of the environments is necessary to improve our knowledge about inva-sion success.In this research,we specifically tested the effects of physiological integration in genotypes from contrasting habitats,where the importance of integration is expected to differ.Thus,the main objective of this work was to detect the presence of adaptive plasticity in the capacity for clonal integration in this aggressive invader.Methods In a greenhouse experiment,we compared the performance,in terms of growth and photochemical efficiency,of two C.edulis ecotypes.Connected and severed ramet pairs from coastal sand dunes and rocky coast habitats were grown in substrates of different quality and heterogeneity.Important Findings Our study clearly indicates that clonal integration improves growth and photosynthetic efficiency in the aggressive invader C.edulis.Two differ-ent aspects of clonal integration determine site-specific strategies in this species in order to optimize its successful propagation in a particular habitat.We demonstrated that the adaptation of C.edulis to local envi-ronments has led to a differential selection of two complex clonal traits associated with the capacity for clonal integration.In patchy sand dunes,C.edulis has evolved ecotypes with ramets highly plastic in patterns of biomass allocation,which allows ramets to specialize in the acquisi-tion of the resource that is locally most abundant,i.e.,a spatial division of labour among ramets.However,in the harsher rocky coast habitats,local adaptation produced highly integrated ecotypes,where resource sharing is not combined with a specialization of resource acquisition.