Effects Of Nitrogen Level And Reciprocal Neighbour Density On Competition Between Suaeda Salsa And Suaeda Glauca In The Yellow River Delta

Nitrogen deposition is increasing gradually due to human activities,which the elevated nitrogen content in the soil environment.Plant response to enhanced soil nitrogen?N?availability differently,which may change interspecific competition relationship.To reveal the impacts of increasing soil N supply on the competition between congeners,a competition experiment in a target-neighbor design was conducted in the Yellow River Delta,with two typical dominant congenetic species,Suaeda salsa and Suaeda glauca,as target plant and neighbor plant reciprocally.Three N supply levels(low,0 g·m^-2;medium,15 g·m^-2;high,30 g·m^-2)and three neighbor plant densities?0 plants,2 plants,and 4 plants per pot,respectively?were set up in a factorial design.The effects of nitrogen levels and neighbor densities on the growth characters,biomass and competitiveness of S.salsa and S.glauca were analysed to provide reference for the prediction of palnt community changes in the Yellow River Delta under increasing nitrogen input circmustances.The results showed that:?1?N levels and neighbor densities had no significant effect on the height of S.salsa,while they affected that of S.glauca significantly.the height of S.glauca increased firstly and then decreased with N level increasing and decreased with the density increasing of S.salsa.The canopy breadth of both species was significantly affected by the N levels and neighbor densities.Increased N level promoted the canopy breadth of S.salsa more strongly,while the neighbor concomitant density inhibited canopy breadth of S.salsa more significantly.The infulence trend of N levels and neighbor densities on the growth rates of plant height and canopy breadth of the two species were consistant to their effects on the plant height and canopy breadth respectively.The leaf dry matter content?LDMC?of S.salsa was affected significantly by the neighbor density of S.glauca,with significant interactive effect with N level.However,it had no significant difference between low and high neighbor S.glauca density at all N levels designed in the expreiment,indicated that high neighbor S.glaua density didn't reduce the resource acquisition ability of S.salsa.The LDMC of S.glauca was only significantly affected by the density of S.salsa,which was significantly lower at high-density S.glauca circumstance than that at low-density S.glauca circumstance,indicated that high density of S.salsa reduced the resource acquisition ability of S.glauca.?2?N levels and neighbor densities had significant effects on the total biomass of the two species.The total biomass of S.salsa increased continuously with the increase of the N levels,while the total biomass of S.salsa had almost no increase between medium and high nitrogen conditions.The biomass of both species decreased with the increase of neighbor density.Increased N level promoted the S.salsa biomass more strongly under the same conditions.N level and neighbor density had no significant effect on the leaf biomass ratio of S.salsa,while had significant effects on the leaf biomass ratio of S.glauca.However,there was no significant relationship between the changes of the leaf biomass ratio of S.glauca and its biomass.The root-shoot ratio of the two species was affected by the N levels and neighbor densities with same tendency,both decreased with increasing N level and increased with the increasing neighbor densities.Compared with S.glauca,S.salsa can adjust the above-ground and underground biomass allocation more rapidly to respond to resource competition and ensure maximum absorption of limited resources.?3?The relative competition intensity of the height of the S.salsa was not significantly affected by N levels and densities of S.glauca.However,that of S.glauca was significantly affected by both,increasing with the N levels and neighbor densities.With the increase of N level,the relative competition intensity of canopy breadth of S.salsa decreased,while that of S.glauca increased.The relative competitive intensity?CIr?of the biomass of both species was significantly affected by the N level and density.With the increase of N level,the inhibition of S.salsa on S.glauca increased significantly,while the reverse decreased.The relative crowding effect of S.glauca was higher than that of S.salsa,and the interaction strength per unit biomass was relatively lower than that of S.salsa.With increasing N level,the interaction strength per unit biomass of the two species both declined;however,the relative crowding effect of S.salsa increased while that of S.glauca decreased.Changes of reciprocal relative competition intensity between two congeners under different N levels depended on the variaton of relative crowding effect?Dr?.?4?At the both low and high neighbor density designed in the study,the reciprocal relative competition intensity of the two congeners had no significant difference at low N level;however,the relative competition intensity that S.salsa suffered from S.glauca was signifincantly lower than the reverse at medium and high N level.The inhibition effect of S.salsa on S.glauca increased wihle the reverse decreased with increasing N level,indicating that S.salsa may become dominant gradually in the mixed communities.