The Effect Of Psammophilic Shrubs Communities On Soil Multi-fractal And Geochemical Elements Spatial Distribution

Soil wind erosion is regarded as a mainly process and pattern in Ulan Buh Desert,and surface erosion materials are not only used to reflect physicochemical properties of soil erosion matters from near-source and far-source dust storm region,but also be capitalized to reveal interception and deposit capability of psammophilic shrubs on sand flow and aeolian particles.In order to study contents and distribution status of soil particles and geochemical elements,and make sure of influence of psammophilic shrubs on PSD multi-fractal parameters,SOC contents and distribution as well as heavy metals contents and pollution status,aeolian sandy soil samples were collected,and soil samples were collected respectively depth of 0-100 cm（0-10,>10-20,>20-30,>30-40,>40-60,>60-80,>80-100 cm）from 5shrubs（Ammopiptanthus mongolicus,Hedysarum scoparium,Oxytropis aciphylla,Nitraria tangutorum and Haloxylon ammodendron）and that of mobile dune in Ulan Buh Desert.In addition,multi-fractal theory were used to determine soil PSD,and w（Mn）,w（Zn）,w（Cr）,w（Cu）,w（Pb）,w（Ni）,w（As）,w（Cd）,w（SOC）and distribution status were measured in lab and correlations between PSD,SOC and heavy metal contents were analyzed to show soil structure and heavy metal pollution.In addition,Index of Geoaccumulation(I_geo)and Pollution Load Index（PLI）were capitalized to assess heavy metals pollution status comprehensively.Results showed that:（1）Different shrubs in Ulan Buh Desert can enlarge soil particle distribution range,especially,AmmopiptanthusmongolicuscommunitiesandHedysarumscoparium communities can entrap and deposit fine particles such asφ（clay）,φ（silt）andφ（extremely fine sand）in sand flow to make surface soil layer condition around shrubs decent,and improve PSD status of different soil layers,such as enlarging range of PSD and increasing PSD concentration degree in dense area,as well as increasing PSD heterogeneity,finally make soil filled with fine and coarse particles simultaneously.Hence,Ammopiptanthus mongolicus communities and Hedysarum scoparium communities will improve soil PSD status better than other psammophilic shrubs.（2）w（SOC）of different soil layers of different sites ranked as Ammopiptanthus mongolicuscommunities>Hedysarumscopariumcommunities>Oxytropisaciphylla communities>Haloxylonammodendroncommunities>Nitrariatangutorum communities>mobile dune,and this regular was approximately similar with even value of soil D₁/D₀,and w（SOC）of aeolian sandy soil under different psammophilic shrubs all significantly different from that of mobile dune（P<0.05）.w（SOC）of aeolian sandy soil under Haloxylon ammodendron shrubs communities and that of mobile dune all showed regular that increasing first and decreasing later with augment of soil layer,and this regular between 0-40cm soil layer was extremely intensive.In addition,both of which were minimum in 0-10 cm surface soil,values were 11.635 and 11.698 g·kg^-1,respectively.Summit w（SOC）of aeolian sandy soil under Ammopiptanthus mongolicus communities were located in>20-30 cm and>60-80 cm soil layer,and values were 11.958 and 11.928 g·kg^-1,respectively.（3）All heavy metals contents showed positive relations withφ（clay）andφ（silt）,and that were more intensive withφ（silt）thanφ（clay）.Except w（Cr）,others all showed negative relationships withφ（medium coarse sand）,and other correlations between heavy metals contents and other particles did not showed coincident relations.Meaning thatφ（clay）andφ（silt）were determining fine and coarse particles respectively,in aeolian sandy soil.And correlations between heavy metals contents and multi-fractal parameters were similar with that ofφ（clay）,φ（silt）andφ（medium coarse sand）,hence,multi-fractal parameters can also well describe correlations between heavy metals and determining soil particles.Correlations betweenφ（clay）,φ（silt）and D₁,D₀ were extremely positive（P<0.01）,and that between D₁/D₀were extremely negative positive（P<0.01）,and increasing of range as well as homogeneous degree of PSD showed increasing ofφ（clay）andφ（silt）,but increasing of dispersion degree of PSD showed decreasing ofφ（clay）andφ（silt）.Correlation of w（SOC）betweenφ（clay）andφ（silt）all showed extremely positive（P<0.01）,but D₁,D₀ and??all showed extremely positive relation between w（SOC）,and correlation value were higher than that ofφ（clay）andφ（silt）.And D₁,D₀ and??also be used to reflected SOC contents well which results were better than particles diameters classification.（4）Heavy metals contents of aeolian sandy soil under different shrubs ordered as w（Mn）>w（Zn）>w（Cr）>w（Cu）>w（Pb）>w（Ni）>w（As）>w（Cd）,entirely.Heavy metals contents of0-10 cm aeolian sandy soil under different shrubs all higher than that of mobile dune,except Cu.Meaning,shrubs will intercept fine particles with heavy metals in sand flow to deposit that around shrubs and increase heavy metals contents in aeolian soil to decrease heavy metals pollution in down-wind cities.Average I_geoeo value of other heavy metals all less than 0,and subdued to non-pollution degree,except Cu,Zn and Ni.Contents of Ni were subdued to non-pollution to medium pollution,Cu and Zn subdued to medium pollution degree.I_geoeo even value of Cu were distributed inside interval of 0 to 3,and that of degree were distributed between non-pollution,medium pollution and medium pollution to intensive pollution.I_geoeo value of 0-10 cm soil layer was higher than that of other soil layers,and that of Ammopiptanthus mongolicus communities and Hedysarum scoparium communities were significantly higher than that of mobile dune and other shrubs（P<0.05）.Zn and Mn pollution status were similar,I_geoeo value all distributed inside interval of 0 to 3,but I_geoeo value of all soil layers of mobile dunes distributed inside intervals of 1 to 2,which subdued to medium pollution degree,and maximum value was 1.809,in 0-10 cm surface soil layers（P<0.05）.Pollution of Ni were lower than Cu and Zn,I_geoeo value distributed between interval of 0 to 2,which subdued to non-pollution and medium pollution,and I_geoeo value of Ni in various soil layers were less than 1,average I_geoeo value of Ammopiptanthus mongolicus communities and Hedysarum scoparium communities were 0.958 and 0.972 respectively,which were higher than that of mobile dunes and other shrubs.（5）PLI value of aeolian sandy soil of different sites showed that heavy metals pollution existing in all soil layers of mobile dunes and different shrubs,and that distributed inside intervals of 1 to 2 and subdued to medium pollution degree.Maximum PLI value of aeolian sandy soil of mobile dune and Ammopiptanthus mongolicus communities were both located in0-10 cm surface soil layer,which were 1.559 and 1.856,respectively.However,maximum PLI value of aeolian sandy soil under Hedysarum scoparium communities and Nitraria tangutorum communities were not existing in 0-10 cm surface soil layer,and located in>10-20 cm（1.837）and>30-40 cm（1.549）soil layer,respectively,and minimum value located in>30-40 cm（1.503）and>60-80 cm（1.081）,respectively.And average PLI value of every sites were ranked as Hedysarum scoparium communities（1.619）>Ammopiptanthus mongolicuscommunities（1.593）>Oxytropisaciphyllacommunities（1.505）>mobile dunes（1.434）>Nitraria tangutorum communities（1.374）>Haloxylon ammodendron（1.302）,and were divided into 2 significantly different categories（P<0.05）,which were Hedysarum scoparium communities,Ammopiptanthus mongolicus communities,Oxytropis aciphylla communities and mobile dunes,Nitraria tangutorum communities,Haloxylon ammodendron communities.