Interspecific Competition Modulates Nitrogen Utilization Strategy Of An Invasive Plant,Flaveria Bidentis

Because of the strong reproductive and competitive capabilities invasive plants can often threaten the native biodiversity seriously of invaded areas.At present,Flaveria bidentis invades many areas across the North China,causing serious damages to ecological environment,agricultural production and economic development ect.Invasive plant species can alter their resource utilization strategies thus get better resource competitive advantages over native species.Nitrogen is playing an important role in the promotion of invasive plant.However,it’s unclear how the nitrogen utilization strategies of an invader alter under competition among invasive plants and native species,and the plant-soil feedback mechanisms underlying this process is generally unknown.Therefore,we aimed to test the effect of the addition of different nitrogen forms at two levels on the nitrogen-preference of F.bidentis,where it grown together with either native Amaranthus retroflexus or Bidens maximowicziana at various growing proportions.Furthermore,we conducted a sreen house study to investigate its nitrogen uptake pattern,affected by AM fungi and interspecific competition.The main results in our studies are as follows:We found that the biomass of F.bidentis was higher than that of the natives under nitrogen addition,especially under NH₄⁺-N addition.However,the response of two natives to different nitrogen forms were not significant.And with the increase of culture patterns of F.bidentis to two natives（1:3,2:2,3:1）,the biomass of each F.bidentis was decreasing,which indicated that the interspecific competition was lower than intraspecific competition.The competitive density determined the degree of dependence of F.bidentis on nutrients.Under the co-occurring condition between the exotic and native species,the RII value of F.bidentis are all greater than 1,which also indicated that F.bidentis can promote its invasion ability under the condition of co-occurring with natives.However,the competitiveness of F.bidentis are greatly competitor-dependent,which highlight the feasibility of manipulating soil nutrient types and amounts,as well as selecting competitive resident plants for ecological restoration of habitats degraded by invasive plants.F.bidentis is AMF symbiotic plant,and in this study,the sterilization treatment promoted F.bidentis biomass accumulation and showed positive feedback to F.bidentis,which suggested that the AMF can have pathogen parasitic behavior to F.bidentis under a certain condition.Also under the un-sterilization treatment,when co-occurring with B.maximowicziana,the RY value of F.bidentis was greater than 1 and A.retroflexus was lower than 1.This also can indicate that the F.bidentis had competition identity selection.Our results showed that association with AM fungi was costly to plants regardless of the presence of competing resident species,but the magnitude of the suppressive effect of AM fungi was related to the mycorrhizal dependency of natives with which F.bidentis compete.Furthermore,all test species showed strong preference for NO₃^-over NH₄⁺and glycine irrespective of mycorrhizal status when growing in monoculture,whereas F.bidentis significantly increased NH₄⁺-N or glycine-N uptake,showing much more plasticity in resource use than natives when competitors were present.Specially,the reduction of AM fungi association lead to even higher NH₄⁺-N recovery with F.bidentis.Taken together,our findings has implications that AM fungi might act as a biotic filter limiting invasion of F.bidentis,and that competition plays an important role in driving the partitioning of soil N between plant species.Above all,the nitrogen acquisition strategy of F.bidentis can be variation with its competition identity and competition density.The result can provide powerful supports to its control.