Study On The Competition-coexistence Pattern Of Phragmites Communis And Phalaris Arundinacea Based On Niche Theory

In this paper,Zhenjiang Waterfront Wetland in lower reaches of the Yangtze Riverwas taken as the experimental site and the Phalaris arundinacea and Phragmites communis in the relatively long-term stable competition coexistence status of the wetland were used as the experimental materials.Based on the theory of niche,the difference of the temporal(growth period)and spatial(the vertical distribution of aboveground plants and the underground root)niche of P.arundinacea and P.communis was studied.Then,based on the difference,the compensation and utilization of light resources about P.arundinacea below the community and the complementary utilization of nutrient resources at different level between P.arundinacea and P.communis was studied.This study is not only of great significance for revealing the mechanism of relatively long-term stable competition coexistence pattern between the two dominant species in the P.arundinacea-P.communis community but also provides theoretical guidance and technical support forstability maintenance of artificial wetland plants with predominant decontamination plants of P.arundinacea and P.communis.The main conclusions of this study are as follows:(1)Temporal niche distribution characteristics based on differences of growth period: there was a significant separation and overlap between the growth period of the P.arundinacea and P.communis.Growth periods of them were about 270 days and every growth stages of the P.arundinacea were earlier than those of P.communis.The separation of growth periods of them occurred before mid-March and after late May,about 190 days;the overlap of the growth period occurred between mid-March and late May,about 80 days,and in early May,the shading effect of the P.communis to P.arundinacea is the most obvious.(2)Spatial niche distribution characteristics based on plant height and root distribution: there were significant differences about the growth dynamics of plant height between the P.arundinacea and P.communis.The plant height of P.arundinacea was higher than that of P.communisin from early February to early April.Then the two plant height gap was getting smaller and smaller and at the beginning of April the two reached the same height(about 0.7m).After that the plant height of P.communis was always higher than that of P.arundinacea.There were significant differences about root biomassat different layer between the P.arundinacea and P.communis.The root of the P.arundinacea was mainly distributed in the 0-20 cm layer and the root biomass of the 0-20 cm layer accounted for 98.12% of the total root biomass of the grass layer 0-30 cm;The roots of the P.communis were mainly distributed in the 0-50 cm layer and 0-50 cm layer root biomass accounted for 97.69% of the root biomass of reed 0-60 cm.Root biomass of P.communiswas the highest in 20-30 layer,accounting for 27.65% of total root biomass and root biomass at 0-20 layer only accounted for 36.83% of the total root biomass.(3)Light energy compensation utilization characteristics of P.arundinacea in the P.arundinacea-P.communis community: The surface canopy of P.arundinacea below Phragmites australis has obvious light energy compensation utilization effect and the effect is all-weather in the normal growth stage(grouting period)that Phragmites australis has the most obvious shade effect on P.arundinacea and the light energy compensation utilization efficiency decreased gradually with the density increasing of Phragmites australis population.When the Phragmites australis density was changed in a certain range,the extinction rate of Phragmites australis on the surface canopy of P.arundinacea was not significantly improved,and the light energy utilization efficiency of P.arundinacea under Phragmites australis was not significantly reduced.However,if the density of the Phragmites australis exceeded the threshold,the shading effect of Phragmites australis on the canopy of P.arundinacea was very serious and the light energy compensation efficiency of P.arundinacea below Phragmites australis was significantly reduced.(4)Complementary utilization characteristics of nutrient resources of two species in the P.arundinacea-P.communis community:The complementary utilization of P.arundinacea and P.communis to soil nutrients is mainly manifested in two aspects.On the one hand,in the vertical direction,P.communis had compensation utilization effectthe 20-50 cm layer soil nutrients and the minimum compensation utilization rateof ammonium nitrogen,nitrate nitrogen and available phosphoruson was 50.39%,50.65% and 50.06% respectively;On the other hand,grass can use nutrients in the soilin advance and the absorption and utilization of ammonium nitrogen,nitrate nitrogen and available phosphorus reached 79.92%,62.92% and 60.23% of the minimum requirement of these nutrients,greatly alleviating the fierce competition for ammonium nitrogen,nitrate nitrogen and available phosphorus between them in the 0-20 cm soil layer.