Effects Of Clonal Fragmentation And Environmental Factors On Growth And Competitive Ability Of Floating Plant

Floating plants are key components of many wetland ecosystems and play an important role in the maintenance of their structure and function.Most floating plants are clonal and produce connected ramets(asexual individuals)along rhizomes or stolons.Disturbance is ubiquitous in wetland ecosystems and can easily break connected clones into fragments of different sizes.Disturbance-mediated clonal fragmentation can affect the growth of floating plants,and further affect their intraspecific or interspecific competition.Such effects may also change with environmental conditions(e.g.nutrients and space).In this study,four greenhouse experiments were conducted with three widely distributed floating plants(Spirodela polyrhiza,Salvinia natans and Azolla imbricata).The aim is to test the effects of clonal fragmentation,nutrient levels and physical space on the growth and competitive ability of floating plants.Plants of S.polyrhiza with three levels of initial density(i.e.1,4,16 ramets)were grown at two levels of nutrients(low or high)and subjected to two levels of fragmentation(connections between parent and offspring ramets were severed or not).Clonal fragmentation increased the growth and changed the leaf size of S.polyrhiza,but did not affect its intraspecific competition intensity.However,high nutrients increased the intraspecific competition intensity.S.natans and S.polyrhiza were grown in monoculture or in mixture at two nutrient levels(low or high),and at the same time three levels of clonal fragmentation(no,low or high)were applied on S.natans.Clonal fragmentation decreased biomass and ramet number of S.natans,but did not affect the competitive effect of S.polyrhiza.However,high nutrients increased the interspecific competitive ability of S.natans to S.polyrhiza.Four fragment sizes(clonal fragments initially consisting of 1,2,3,or 6 ramets)of S.natans were grown at two levels of nutrient(low or high)with competition or not(in the presence or absence of A imbricata).Fragments with more initial ramets produced more biomass and ramets,but the relative growth rate was decreased.Competitive ability was stronger in larger fragments in low nutrients,but high nutrients increased interspecific competitive ability of smaller fragmentsEither one or four clonal fragments of A.imbricata were grown at four levels of nutrients(1%,4%,10%,and 40%Hoagland solution)and with three types of cylindrical containers which differ in diameter and height/volume.Biomass of A imbricata was higher in the container with larger diameter,but height/volume did not affect the growth.Container type,nutrients,initial density,and all interactions significantly affected the growth of A imbricata,but container type did not affect the intraspecific competition.High nutrients reduced growth and intraspecific competition.These suggest that nutrients can alter intraspecific competitive ability of floating plants,but physical space may not.In summary,clonal fragmentation affected neither intraspecific competition of S.polyrhiza nor the interspecific competitive ability of S.natans to S.polyrhiza,but nutrients could affect the competitive ability of floating plants.Therefore,both biological characteristics of floating plants and roles of environmental factors should be considered when selecting floating plants as measures for restoration of degraded wetlands.