The Effect Of Urbanization On The Concentration And Distribution Of Soil Phosphorus

Urbanization has a major role in changing the configuration of green space in urban area,substantially impact levels of soil nutrients as well as the cycling of soil phosphates?P?.Thus,estimating the effects of urbanization on changes of urban green space landscape and soil P is crucial for urban green land management and improving soil P use efficiency.In the current study,We selected the central city-suburb-exurban satellite gradient belt in Chengdu,China as our study area,and then divided the urban green space into 7 types?Park green space,Residential green space,Public green space,Traffic green space,Industry green space and Cultivated and Forest land?.We analyzed the soil samples to test the effects of distance from urban center,construction and road density,green space type and landscape pattern index on the distribution of soil total P?TP?and its fractions?Water-Pi?Water-Po?NaHCO₃-Pi?NaHCO₃-Po?NaOH-Pi?NaOH-Po?HCl-Pi?HCl-Po?Residual-P?.The main research results as following:?1?The percentage of greenery coverage were 22.55%,56.64%,49.36%in central urban,suburban and satellite city,respectively.The residential,public and traffic green space were the main green space in central urban;suburban was covered by cultivated and forest land primarily;and cultivated and forest land,and the residential and traffic green space were the main green space in exurban satellite.In central urban,the land patch number of residential,traffic and public green space were much higher than other green space types,the index of LSI,PDL,LPI index of those three green space types were small,and the LPI index of cultivated and forest land was higher than the LPI index in suburbs and exurban satellite.The index of LPI is highest in park green space in suburban areas.Comparing the landscape pattern indexes among the soil sample point buffer,the index of NP,PD,LSI,SHEI and DIVISIONH in the central urban were higher than exurban satellite and suburban areas.The index of LPI and CONTAG were highest in the exurban satellite,and then in suburban and central urban.The landscape diversity in the study area was not high,and the distribution of the green space landscape in this gradient was slightly unequal with no obvious advantage landscape.?2?The values of soil TP concentrations ranged from 0.51-1.23 g/kg,with a mean value of 0.83 g/kg,higher than the soil P back value in Chengdu plain.The variation coefficient of TP was 31%,belong to medium variation.The inorganic phosphorus were the main form of soil P,and the percent of each soil P fractions were:HCl-P?46.54%?>Residual-P?41.07%?>NaOH-P?10.12%?>NaHCO₃-Pi?1.26%?>Water-P?0.63%?.?3?The concentrations of soil TP is decreased from center city to suburban,and then increased from suburban to exurban satellite,the concentrations of soil Water-P and NaHCO₃-P were significantly higher in the north central urban than other areas,and the concentration of Water-Pi was high around the outer ring road.The concentrations of soil NaOH-Pi and HCl-Pi were higher in exurban satellite than suburban area,while the NaOH-P and HCl-P content were higher in central urban than other area.Analysis the relationship between the landscape index in the buffer and soil P content,in addition to Water-Pi,the concentrations of soil TP and other P showed significantly positive correlation with the index of PD,LSI,DIVISION and SHEI,and showed negative correlation with LPI and CONTAG.While the correlation of SHDI and soil P was not significant.Besides,the relationships of Water-Pi and landscape indexes were not significant,and disagree with other P fractions.?4?In the current study,soils further away from the urban center had lower P concentrations,and the construction and road densities were significantly positively correlated with soil TP and its fractions except Residual-P.The increase in the NaOH-Pi concentrations was best explained by construction density,while the increase in the NaHCO₃-Pi concentrations was best explained by road density.The concentrations of TP,NaHCO₃-P,NaOH-P and HCl-P showed similar trends in that residential and traffic green spaces soils showed higher concentrations,whereas industry green space soils had the lowest concentrations,and in soils from park green spaces,Water-Pi and Water-Po values were significantly higher than in other green spaces.?5?The R² values of the stepwise multiple regression models ranged from 0.224to 0.472,After eliminating nonsignificant factors,distance from urban center,construction and road densities,green space types and CONTAG,SHDI,SHEI were included in the regression models.The road density was a significantly positive impact factor for Water-Pi,Water-Po,NaHCO₃-Pi and NaHCO₃-Po.The construction density was a significantly positive impact factor for NaOH-Pi.The CONTAG was a significantly positive impact factor for NaOH-Pi?NaOH-Po and HCi-Po,the SHDI was a significantly positive impact factor for HCl-Pi,and the SHEI was a significantly positive impact factor for HCl-Po.