Changing Characteristics Of Phosphorus And Potassium In The Rhizosphere And Bush Soil Of The Xeromorphic Shrubs

In this paper,seven native xeromorphic shrub species inhabiting in the Alashan desert, including Nitraria tangutorum,Zygophyllum xanthoxylum,Reaumuria soongorica, Ammopiptanthus mongolicus,Atraphaxis bractata,Haloxylon ammodendron and Ceratoides lateens,are used to compare differences in contents of total P,total K,available P,available K and P fractions in bulk,rhizosphere,under shrub,the edge of shrub and between shrubs soils.The purpose of the work is to reveal the mechanism of shrubs effective utilization of soil nutrients,as well as the role of shrubs in process of restoration in the arid desert ecological environment.The research results provided a theoretical basis and effective measures for the protection of valuable plant resources and biodiversity in Alashan areas.The result showed that:1) There was a higher available P concentration in the rhizosphere soil than in the bulk soil of all seven shrubs,but concentrations of total P are lower in the rhizosphere soil than in the bulk soil in all shrubs except A.bracteata;The soil pH decreased in rhizosphere of all shrubs except H.ammodendron,Regression analyses indicated a significant relationship between available P concentration and pH,but no significant relationships were found between total P concentration and pH in both the rhizosphere and bulk soils.2) The H₂O-P concentration was lower in the rhizosphere soil than in the bulk soil in all shrubs except H.ammodendron,whereas concentrations of NaHCO₃-Pi,DHCl-Pi and HHCl-Pi were lower in the rhizosphere soil than in the bulk soil in C.lateens; concentrations of DHCl-Pi and HHCl-Pi were lower in the rhizosphere soil than in the bulk soil in all shrubs except A.bracteata.;the NaOH-Po concentration was lower in the rhizosphere soil than in the bulk soil in all shrubs except A.mongolicus,as well as the HHCl-Po concentration was lower in the rhizosphere soil than in the bulk soil in all shrubs.3) In the rhizosphere soil,there was a significant relationship between available P and H₂O-P as well as NaHCO₃-Pi,and between NaOH-P.However,there was a significant relationship between available P and NaHCO₃-Po,DHCl-Po,H₂O-P, NaHCO₃-Pi,NaOH-Pi and NaOH-Po in bulk soil.NaHCO₃-Pi and NaHCO₃-Po were main factors which influenced the P availability in rhizosphere and bulk soils.4) There was no significant difference in total K concentration between the rhizosphere soil and bulk soil,but the concentrations of available K are higher in the rhizosphere soil than in the bulk soil in Z.xanthoxylum,A.bracteata and H.ammodendron.The trend of the concentrations of available K in rhizosphere soil was:Z.xanthoxylum＞C.lateens＞A.mongolicus＞N.tangutorum＞R.soongo rica＞A.bracteata＞H.ammodendron.5) The shrub caused enrichments of soil total phosphorus,total potassium and available potassium were not obvious,however,enrichment of soil available P was obvious.For all of 0-10cm,10-20cm,20-30cm soil depths,along the horizontal direction,the concentration of soil available P tended to increase from the under to the edge and to the between shrubs canopy(under shrub＞edge of shrub＞between shrubs).In 0-10cm soil depth,available P content under the shrub canopy is 117.94%and 134.45%, respectively,compared with the edge of shrub canopy and between shrubs canopy. For all of the under,edge and between of shrub canopies,along the vertical direction from 0-10cm to 10-20cm and to 20-30cm soil depths,the concentration of soil available P tended to decrease(0～10cm＞10～2Ocm＞20～30cm).Under the shrub canopy,the concentrations of soil available P in 0-10cm soil depth is140.2%and 173.3%,respectively,compared with in 0-20cm soil depth and 20-30cm soil depth.