Application Of Biofertilizer From Spent Mushroom Substrate In Remediation Of Saline-alkali Soil And Phytoextraction Of Zn,Cu,Ni,Cr Contaminated Soil

Tianjin Binhai New Area,on the east coast of Tianjin,China,is characterized as saline-alkali soil with low nutrient and high salinity unsuitable for crop growth.Spent mushroom substrate(SMS)is a kind of agricultural waste in mushroom industry.In this work,a salt-and pH-tolerant PGPR consortium composing of Azotobacter chroococcum N1,Bacillus subtilis K3 and Pichia farinosa FL7 was used convert SMS into stress-tolerant biofertilizer and applied to reclaim saline-alkali soil from different sites under greenhouse conditions.We studied the dynamics of soil pH,EC1:5,N,Pi,K fractions,soybean growth and phytouptake in soil-plant system to characterize the reclamation efficiency under effects of biofertilizer.Results showed that regardless of site,the concentrations of soil inorganic N,labile P,available K were significantly improved by PGPR inoculation.Inoculation of PGPR consortium could protect against salt stress and promote plant growth and nutrient uptake.The high-efficient phosphate-solubilization yeast P.farinosa FL7 could regulate organic acid production according to the P source in presence.The addition of biofertilizer influenced the partition of soil N,Pi and K fractions.Further analysis showed that inoculated PGPR consortium increased N availability by stimulating nitrification as well as N2 fixation.The primary phosphate transfer mechanism of phosphate-solubilization was the dissolution of stable Pi more than the translocation of NaOH-Pi and HCl-Pi.The main potassium transfer mechanism mineral K dissolution was the translocation of structural K into available and non-exchangeable K.Phosphate-solubilizing yeast P.farinosa FL7 in combination with N2-fixing bacteria A.chroococcum N1 and potassium-solubilizing bacteria B.subtilis K3 was used to prepare biofertilizer from SMS and applied to the phytoextraction of Zn,Cu,Ni,Cr contaminated soil.All strains showed high heavy metal tolerance and P.farinosa FL7 could directly solubilize phosphorous from metal phosphates more than 10 folds greater than the control without inoculation.The results of pot experiments revealed that the addition with biofertilizer significantly increased the extent of Zn,Cu,Ni,Cr accumulation in Brassica juncea.The total biomass of B.juncea was promoted by the inoculation treatment,which increased from 0.23~0.24 g to 0.34~0.36 g.The changes of metal speciation indicated that inoculation of biofertilizer increased the immobilization of soluble metals in soluble metal spiked soil and that inoculation of biofertilizer increased the bioavailability of metals in insoluble metal phosphate spiked soil.The present study may provide an effective way for the improving phytoextraction of Zn,Cu,Ni,Cr contaminated soils.