Dominant Plants In The Drawdown Zone In The Middle Section Of The Three Gorges Reservoir - Distribution Characteristics Of Phosphoru

Phosphorus cycling in the soil of the Three Gorges Reservoir Area has an important impact on reservoir environmental security,but the distribution characteristics of phosphorus between plants and rhizosphere soil are not clear.In this study,three primary tributaries-Ganjing River in Zhongxian County,Zhuxi River in Wanzhou,and Pengxi River in Yunyang-were selected in the middle section of the Three Gorges Reservoir Area,A gentle slope zone（around 25°）was selected at the mouth of each tributary.Four dominant plants,Cynodon dactylon,Xanthium sibiricum,Bidens pilosa Collection of Polygonum hydropiper plants and rhizosphere soil.Total phosphorus（TP）in the aboveground and underground parts of plants,phosphorus occurrence patterns in rhizosphere soil,and various physical and chemical properties of soil were measured.In order to further explore the distribution characteristics of phosphorus between plants and soil under different conditions in this reservoir section,this study conducted multiple analyses of the measured results based on the classifications of plants,main river and tributary,elevation,section,and other conditions.The results are shown as below:Based on the classifications of plants,there was a significant difference in TP content in the rhizosphere soil of the four plants(P;The content of Fe,Al,P（Fe/Al P）in Xanthium sibiricum was significantly higher than that in bermudagrass rhizosphere soil（P<0.01）;There were significant differences in the aboveground and underground TP contents among the four plants（P<0.05）,and the aboveground TP content was greater than the underground TP content.The transport coefficient E of the four dominant plants was greater than 1,and the aboveground phosphorusenrichmentcoefficientofBidensbipinnata>Xanthium sibiricum>Bermudagram>Polygonum hydropiper was significantly different(P.There was a negative correlation between the aboveground TP,underground TP,E transport,and E integration of plants and the content of available nitrogen in the rhizosphere soil（P<0.05）.Based on the classifications of main and branch rivers,there were significant differences in soil physical and chemical properties between the main and branch streams,except for TN and TK（P>0.05）.Other physical and chemical properties such as TP,AP,TN,AN,AK,etc.,had significant differences（P<0.05）.The TP content of the aboveground parts of the four species of plants in the main stream is greater than that in the tributaries.In terms of soil phosphorus occurrence patterns,there are significant differences between IP and OP in the main and tributaries（P<0.05）,and the difference in Ca-P content in the main and tributaries is consistent with that of IP.There were significant differences among different plants in E_transport,E aboveground,E underground,and E entire plant in the main and branch streams（P<0.05）,and E transport was greater than 1 in all settings,There was a significant positive correlation between E underground and E entire plants and their rhizosphere Fe/Al-P content in tributary settings.Based on the classifications of elevation,the contents of TN,AN,and AP in the elevation sections 145-160m and 160-175m in the hinterland of the Three Gorges Reservoir area have significant differences among plants（P<0.05）,and the distribution of TP,TK,and AK in the elevation sections is relatively uniform;The difference in phosphorus enrichment per unit of aboveground parts of different plants is small at the same elevation and different elevations for the same plant;There were significant differences in the contents of OP,IP,and Fe/Al-P in different plant phosphorus occurrence forms at the same elevation（P<0.05）,while there was no significant difference in Ca-P;Soil AN content was significantly correlated with plant E transport.Based on the classifications of section,there were significant differences in TP content among the four plants in Yunyang section（P<0.05）.There were significant differences in TP content in the rhizosphere soil of each plant in different sections（P<0.05）.There were significant differences in the AP content in the rhizosphere soil of the four plants in Wanzhou and Yunyang sections（P<0.05）,while no significant difference in the AP content was detected in the rhizosphere soil of the different plants in Zhongxian section（P>0.05）.There were significant differences in the AN content of the rhizosphere soil of the four plants in Zhongxian and Yunyang sections(P There were significant differences among Polygonum hydropiperus（P<0.05）.There was no significant difference in TK content of rhizosphere soil among different plants in Zhongxian,Wanzhou,and Yunyang sections（P>0.05）.The TP content in the aboveground part of the four dominant plants in different sections was significantly higher than that in the underground part The E transport of different plants in Zhongxian section are Bermudagrass>Bidens bipinnata>Xanthium sibiricum>Polygonum hydrophylum.Among them,Bermudagrass E_transport is the highest,while E transport of Polygonum hydrophylum is the lowest.There was no significant difference of E transport among the four plants（P>0.05）.In the Yunyang section,there was a significant difference in Etransport between Bidens bipinnata and Polygonum hydrophylum（P<0.05）,while there was no significant difference between Bermudia root and Xanthium sibiricum（P>0.05）.In different segments,the E transport of bermudagrass and Bidens bipinnata,was the highest in Zhongxian segment,while the Etransport of Xanthium sibiricum and Polygonum hydrophila were the highest in Wanzhou segment,and there was no significant difference in E transport of the same plant in each segment（P>0.05）.There was no significant difference between E aboveground and E underground in different plants and different sections（P>0.05）,but it can be seen that both E aboveground and E underground of Xanthium sibiricum were the highest among the four plants.The size relationship of different plants E on the ground in Zhongxian County is as follows:Xanthium sibiricum>Bidens bipinnata>Polygonum hydrophylum,Xanthium sibiricum>Bidens bipinnata>Polygonum hydrophylum in Wanzhou section,Xanthium sibiricum>Wanzhou section>Yunyang section.There was a significant positive correlation between E transport and TK content in Yunyang section（P<0.05）,a positive correlation between E underground and E whole plants and Fe/Al-P content in Yunyang section（P<0.05）.No correlation between E transport E above ground was detected,as well asamong E whole plants,soil physicochemical properties and phosphorus occurrence forms in rhizosphere soil in other sections（P>0.05）.