Effect Of Pyroligneous Acid Co-applied With Cow Manure On Chemical Properties And Microbial Community Structure In Saline-alkali Soil

As a soil buffer zone between land and ocean,coastal saline soil has important role in ecological environment protection,and improving coastal saline soil is an important work.In the process of coastal saline soil improvement,soil microbial community structure can react relatively quickly and is used as one of the indicators of soil remediation effect.At present,most scholars pay attention to the changes of soil physical and chemical properties in the process of soil improvement,and the study of soil microbial community structure has not been well known.In order to investigate the effects of pyroligneous acid and cow manure on the chemical properties and microbial community structure of coastal saline soil,soil bacteria,Gram-positive bacteria,gram-negative bacteria,fungi and actinomycetes were determined by phospholipid fatty acid biolabeling(PLFA).In this study,11 treatments were used in soil culture experiment,including blank control(CK)without pyroligneous acid and cow manure,3 pyroligneous acid,namely,P1,P2,P3(The ratio of pyroligneous acid concentrate and water volume were 1:100,1:50 and 1:20.The application of pyroligneous acid were 7.5 t·time-1·hm-2),3 cow manure,namely,C1,C2,C3(The concentration of cow manure were 20.0,50.0 and 100.0 g·kg-1,respectively.)and 4 pyroligneous acid and cow manure(C1P1,C1P3,C3P1,C3P3).The results showed that:(1)The application of pyroligneous acid and cow manure could significantly increase the content of soil carbon,nitrogen and available phosphorus,and significantly reduce the pH value of coastal saline soil.The content of organic carbon,water soluble organic carbon,oxidizable carbon,total nitrogen,ammonium nitrogen and nitrate nitrogen in coastal saline soil reached the maximum under C3P3 treatment,which were 16.61g·kg-1,226.30 mg·kg-1,1049.65 mg·kg-1,1.79 g·kg-1,2.79 mg·kg-1 and 9.54 mg·kg-1,respectively.(2)The microbial community structure of coastal saline soil was significantly different under different pyroligneous acid and cow manure treatments.Under the combined application of pyroligneous acid and cow manure,the PLFA marker contents of soil Gram-positive bacteria,Gram-negative bacteria,bacteria,fungi,actinomycetes and microorganisms reached the maximum under C3P3 treatment,with the values of 100.14 nmol·g-1,120.16 nmol·g-1,228.59 nmol·g-1,62.73 nmol·g-1,33.48 nmol·g-1,and 554.26 nmol·g-1,respectively.From fungi/bacteria ratio,C3P1 treatment had a relatively high ratio of 0.32.The average chemical properties and microbial PLFA marker content of soil under different pyroligneous acid,cow manure and combined application treatments basically reached significant levels.(3)The diversity index of soil microbial community varied with the application of pyroligneous acid with different dilution times and cow manure with different concentration.The variation of microbial diversity index was relatively large when pyroligneous acid solution P3 was applied alone.Diversity index of soil microbial community in cow manure treatment was higher than CK treatment.Shannon-Wiener diversity index(H)of C1P1,C3P1 and C3P3 were 3.34,3.26 and 3.28 which were 0.47,0.39 and 0.41 units higher than CK,respectively;Pielou evenness index(J)was 1.09,1.07 and 1.07 times of CK;Simpson dominance index(D)of C3P1 was the highest,which was 0.95.(4)Contents of Soil carbon and nitrogen were the main factors driving the change of soil microbial community structure under different combination of pyroligneous acid and cow manure.The contents of PLFA markers of Gram-positive bacteria,Gram-negative bacteria,bacteria,fungi,actinomycetes and microorganisms in coastal saline soil were positively correlated with soil organic carbon,water-soluble organic carbon,readily oxidized carbon,total nitrogen,ammonium nitrogen and available phosphorus.In conclusion,the application of pyroligneous acid and cow manure can not only improve the chemical properties of coastal saline soil,but also improve the microbial activity,and the effect of mixed application is more significant than that of single application.From the principal component analysis,the comprehensive score of C3P3 treatment was the highest,with a value of 1.99.C3P3 may be the best mixing method.