Effects Of Physiological Integration On Growth And Competitive Ability Of Clonal Plants

Clonal plants are very common in different ecosystems,such as grassland,tundra,wetland or aquatic ecosystem.Most of the clonal plants are dominant species and play very important roles in determining the structure and function of the ecosystems.Physiological integration in clonal plants is one of the most important features that differ from non-clonal plants and ecologists pay a lot of attention to the study of the effects of clonal integration under different conditions.Physiological integration can allow clonal plants to translocate resources between connected ramets,and then improves its growth and fitness.Many previous studies testing the role of clonal integration were conducted under heterogeneous environments.However,few studies test the role of clonal integration under homogeneous environments,and little direct evidence show the effects of clonal integration on the intra-and interspecific competition ability of clonal plants.We conducted a series of greenhouse experiments testing the effects of clonal integration on the growth and competitive ability of clonal plants.The main results are as follows:(1)We grew clonal fragments of Alternanthera philoxeroides and varied numbers of rooted versus unrooted ramets,connection between the apical and basal parts of fragments,and availability of nitrogen.Patterns of final size and mass of fragments did not support these hypotheses.By some measures,severance did reduce the growth of more apical ramets and increase the growth of less apical ones,consistent with net apical transfer of resources.Overall,the results indicate that physiological integration between ramets within clones in homogeneous environments can alter the allocation of resources between connected ramets even when it does not affect the total growth of clonal fragments.(2)We grew one(low density),five(medium density)or nine(high density)parent ramets of the floating invasive plant Pistia stratiotes in buckets,and newly produced offspring ramets were either severed(with fragmentation)or remained connected to parent ramets(no fragmentation).Increasing density reduced biomass of the whole clone(i.e.parent ramet plus its offspring ramets),showing intense intraspecific competition.Fragmentation decreased biomass of offspring ramets,but increased biomass of parent ramets and the whole clone,suggesting significant resource translocation from parent to offspring ramets when clones were not fragmented.There was no interaction effect of density x fragmentation on biomass of the whole clone,and fragmentation did not affect competition intensity index.Thus,clonal fragmentation does not alter intraspecific competition between clones of P.stratiotes,but increases biomass production of the whole clone.(3)Individual ramets of P.stratiotes and Eichhornia crassipes were grown in monoculture or in mixture,and new stolons bearing new offspring were severed or left intact.Fragmentation decreased the relative competitive ability of Pistia,but not that of Eichhornia.This was mainly because Pistia accumulated-30%less dry mass of offspring when fragmented and grown with Eichhornia than in other treatments.Offspring of Pistia were smaller than those of Eichhornia in all treatments.(4)We conducted a greenhouse experiment on Fragaria chiloensis crossed two treatments of connection between its ramets(intact or severed)with three treatments of competition with Bromus carinatus(none,uniform,or patch).Results show clear positive effects of clonal integration on the growth of F.chiloensis,but this was only true in patch treatments.The growth of plants was greatly suppressed when both its younger and older ramets grow in competition with the grass.Clonal integration had no significant effect on the growth of the plants when both its younger and older ramets grow in none or in uniform competition.It seems that the regime and pattern of clonal integration depends on plant species,and also the growth environment.Further researches are needed to provide more insights in understanding the role of clonal integration in order to make general conclusion.