Role of Clonal Integration among Different Environmental Conditions (A Review)

Most of the ecosystems are dominated by clonal species. The most unique feature of clonal plants is their capability for clonal integration (translocation of vital resources among connected ramets), implying that integration may play an essential role in their success. However, a general effect of clonal integration on plant performance is lacking. We conducted a text review on the effects of clonal integration on different habitats and species. Overall, clonal integration increased performance of clonal plants in different habitats. However clonal integration has also some limitations under stressful environments. Benefits of clonal integration may lack somehow when environmental stress increases. But connected ramets placed in unfavorable patches benefited more from integration compared to severed ramet placed in nutrient rich patches. Climate change and temperature increase have positive effects on biomass of clonal species.

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

Plant invasion is one of the most serious threats to ecosystems worldwide.When invasive plants with the ability of clonal growth invading or colonizing in new habitat,their interconnected ramets may suffer from heterogeneous light.Effects of clonal integration on allelopathy of invasive plants are poorly understood under heterogeneous light conditions.To investigate the effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions,a pot experiment was conducted by using its clonal fragments with two successive ramets.The older ramets were exposed to full light,whereas the younger ones were subjected to 20%full light.The younger ramets of each clonal fragment were adjacently grown with a target plant(one tomato seedling)in a pot.Stolon between two successive ramets was either severed or retained intact.In addition,two tomato seedlings(one as target plant)were adjacently grown in a pot as contrast.Compared with severing stolon,biomass accumulation,foliar chlorophyll and nitrogen contents,chlorophyll fluorescence parameters and net photosynthetic rates of the target plants as well as their root length and activity,were significantly decreased when stolon between interconnected ramets of W.trilobata retained intact.Under heterogeneous light conditions,transportation or sharing of carbohydrate between two successive ramets enhanced allelopathy of the young ramets subjected to 20%full light treatment.It is suggested that clonal integration may be important for invasion or colonization of invasive plants with ability of clonal growth under heterogeneous light conditions.

Effects of salinity and clonal integration on the amphibious plant Paspalum paspaloides:growth,photosynthesis and tissue ion regulation

Aims Clonal integration can increase performance of clonal plants suffer-ing from environmental stress,and clonal plants in many wetlands commonly face stress of flooding accompanied by salinity.However,few studies have tested roles of clonal integration in amphibious plants expanding from terrestrial to aquatic saline habitats.Methods Basal(older)ramets of clonal fragments of Paspalum paspaloides were grown in soil to simulate terrestrial habitats,whereas their apical(younger)ramets were placed at the surface of saline water containing 0,50,150 and 250 mmol l^(−1)NaCl to mimic different salinity levels in aquatic habitats.Stolons connecting the apical and basal ramets were either intact(connected)to allow clonal integra-tion or severed(disconnected)to prevent integration.Important Findings Increasing salinity level significantly decreased the growth of the apical ramets of P.paspaloides,and such effects on the leaf growth were much higher without than with stolon connection after 60-day treatment.Meanwhile,leaf and total mass ratios of the connected to the disconnected apical ramets were higher at high than at low saline treatments.Correspondingly,Fv/Fm and F/Fm′of the apical ramets were higher with than without stolon connection in highly saline treatments.The results suggest that clonal integration can benefit the spread of apical ramets from terrestrial soil into saline water,and that the positive effects increase with increasing salinity.However,clonal integration did not significantly affect the growth of the whole frag-ments.Due to clonal integration,Na^(+)could be translocated from the apical to the basal ramets to alleviate ion toxicity in apical ramets.Our results suggest that clonal integration benefits the expansion of P.paspaloides from terrestrial to aquatic saline habitats via maintained photosynthetic capacities and changed biomass allocation pattern.

Clonal integration affects growth and sediment properties of the first ramet generation,but not later ramet generations under severe light stress

Clonal integration benefits clonal plants by buffering environmental stress and increasing resource extraction efficiency.However,the number of connected ramet generations that benefit from clonal integration in a clonal system has received relatively little attention.A pot experiment was conducted to evaluate the extent of physiological integration within the clonal system of Vallisneria natans consisting of a mother ramet and three sequentially connected offspring ramets.Mother ramets were grown in full sunlight,and offspring ramets were heavily shaded with limited light availability.Stolons between mother ramets and offspring ramets were severed or connected,but connection among the three offspring ramets remained.The photosynthetic ability of unshaded mother ramets of V.natans was significantly enhanced,but their biomass accumulation was greatly reduced when connected to shaded offspring ramets.Clonal integration significantly increased biomass accumulation,C and N availabilities,extracellular enzyme activities and microbial biomass of the first ramet generation(adjacent ramet),but not later ramet generations.Our results indicate that support from the mother ramet of V.natans may be limited to the adjacent offspring ramet in a clonal system under severe light stress,implying an effect of ramet generation.Our results contribute to a better understanding of the hierarchy and segmentation of clonal plants.These findings suggest that the extent of clonal integration plays a vital role in ecological interactions of the ramet population.

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.

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.

Responses of Hedysarum Laeve,a guerrilla clonal semi-shrub in the Mu Us Sandland,to local sand burial

In arid and semi-arid inland deserts,one of the environmental stresses for plants is recurrent sand burial,which can influence the physical and biotic microenviron-ments of the plants and soil.Previous studies have shown that different levels of sand burial have different effects on plants.Slight sand burial could increase the height increment,leaf biomass and the number of new ramets of the plants while heavy sand burial could impair the growth of the plants and even decrease their chances of survival.In other words,below a certain threshold level of burial,the growth of plants is stimulated probably because of multiple factors.However,as the level of burial increases,the positive response starts to decline until it becomes a negative value.Arid and semi-arid inland deserts are frequently colonized and stabilized by many rhizomatous clonal plants.Clonal physiological integration often helps clonal plants buffer local environmen-tal stress encountered by ramets.A rhizomatous clonal semi-shrub,Hedysarum laeve(H.laeve),is the dominant plant species and important for vegetation restoration in the Mu Us sandland.To investigate whether clonal integration can increase the threshold of sand burial and help rhizomatous H.laeve tolerate heavy sand burial,we conducted a field experiment.The results showed that slight sand burial could accelerate ramet growth and enhance leaf biomass,stem bio-mass and shoot biomass,while heavy sand burial reducesed the biomass of the plant and impairs survival and growth of the ramets.Clonal integration increased the threshold of sand burial.Under heavy sand burial,ramets connected to other ramets not buried in sand were more in terms of height increment,stem biomass,leaf biomass and shoot biomass compared to the ramets encountering sand burial but disconnected from other ramets.It suggested that clonal physiological integration could help H.laeve ramets tolerate relatively heavy sand burial.We also discussed that clonal integration plays a role in H.laeve presence in the Mu Us sandland.