The Effects Of Biochar-based Fertilizer Application On The Soil Microbial Community Structure Of Karst Calcareous Soil In Southwestern China

Karst ecosystems are vulnerable to degradation and constitute a significant proportion(550,000km~2)of southwestern China.Here,we explored the amendment of karst soils with biochar in combination with swine manure compost and chemical fertilizer with the aim of improving the microbial community structure and soil nutrient status of these soils.A pot experiment was conducted with twelve treatments:the control(CK),NPK fertilizer(F),compost(M),compost plus NPK fertilizer(MF),2%wood biochar(W2;the percentage is the biochar addition rate by the weight ratio of biochar to soil,same below),2%wood biochar plus NPK fertilizer(W2F),2%wood biochar plus compost(W2M),2%wood biochar plus compost and NPK fertilizer(W2MF),1%wood biochar plus compost and NPK fertilizer(W1MF),4%wood biochar plus compost and NPK fertilizer(W4MF),2%bamboo biochar plus compost and NPK fertilizer(B2MF)and2%rice husk biochar plus compost and NPK fertilizer(RH2MF).Each treatment,except for CK,was kept equal for added N,P,K nutrients content.The treatments were divided into three parts:(1)CK,MF,W2MF,B2MF and RH2MF,in order to show the effects of biochar-based fertilizer with biochar derived from different materials,i.e.wood,bamboo and rice husk,on the soil microbial community structure,diversity,and soil nutrients content;(2)CK,F,M,MF,W2,W2F,W2M and W2MF,in order to illustrate the effects of biochar and organic compost added into biochar-based fertilizer on the soil microbial community structure and composition;(3)CK,MF,W1MF,W2MF and W4MF,in order to reveal the effects of the addition rate of biochar in biochar-based fertilizer.The results showed that:(1)Different kinds of biochar-based fertilizer W2MF,B2MF and RH2MF increased the contents of SOM(soil organic matter,164.76%-198.10%),AN(soil available nitrogen,45.66%-54.40%),AP(soil available phosphorus,629.49%-725.75%)and AK(soil available potassium,210.32%-217.81%)respectively compared to CK.The soil nutrients content in biochar-based fertilizer treated soil(W2,W2F,W2M and W2MF)were 76.47%(SOM),13.38%(AN),21.64%(AP)and 13.51%(AK)higher than in the no-biochar treated soil(CK,F,M and MF),and the compost-treated soil(M,MF,W2M and W2MF)were also 75.00%(SOM),21.63%(AN),162.99%(AP)and 88.99%(AK)higher than in the no-compost treated soil(CK,F,W2 and W2F).The soil nutrients content increased following the increase of biochar addition rate in biochar-based fertilizer,with the highest value at W4MF treatment increasing by 300.95%(SOM),52.98%(AN),702.28%(AP)and 224.69%(AK)respectively compared to CK.Biochar-based fertilizer treatment increased the plant dry biomass by 41.66%-97.79%compared to CK.(2)The cluster and LEf Se analyses showed that biochar-based fertilizer treatments had distinct bacterial and fungal community structure and composition compared to the control treatment.The different kinds of biochar-based fertilizer treatment group(W2MF,B2MF and RH2MF)had significant different bacterial and fungal community structure from the control treatment CK(P=0.003).The bacterial and fungal community structure were mainly grouped into the compost(M,MF,W2M and W2MF)and no-compost treated group(CK,F,W2 and W2F),and the biochar(W2,W2F,W2M and W2MF)and no-biochar treated group(CK,F,M and MF)(P<0.01,except for the bacterial community between biochar and no-biochar treated group with the P=0.441).Biochar-based fertilizer addition increased the bacterial phylum Acidobacteria and Planctomycetes abundance but decreased the phylum abundance of Proteobacteria,Bacteroidetes and Firmicutes compared to CK;for the fungal composition,they increased the fungal phylum Rozellomycota and Zygomycota abundance and decreased the phylum Ascomycota abundance.(3)The wood biochar-based fertilizer treated soil had higher bacterial and fungal diversity than the other two kinds of biochar derived from bamboo and rice husk but had the same microbial community structure and microbial biomass carbon(MBC),nitrogen(MBN)and phosphorus(MBP)(P<0.05).(4)Biochar and biochar-based fertilizer treatments(W2,W2F,W2M and W2MF)had higher bacterial and fungal diversity(Simpson and Shannon)and microbial biomass(increased by 10.22%-MBC,11.98%-MBN and 27.01%-MBP respectively)compared to the corresponding no-biochar treatments(CK,F,M,MF),and treatments with compost(M,MF,W2M and W2MF)had 18.06%(MBC),22.07%(MBN)and 40.74%(MBP)higher values than no-compost treatments(CK,F,W2 and W2F).(5)The microbial network structure in biochar treated group(biochar network,W2,W2F,W2M and W2MF)had a higher number of nodes,links and modules than that in no-biochar group(no-biochar network,CK,F,M and MF),and the microbial network in compost treated group(compost network,M,MF,W2M and W2MF)had more complexity than that of no-compost treatments group(no-compost network,CK,F,W2 and W2F).And soil variables(p H,SOM,AN,AP and AK)significantly influenced the bacterial biochar and the no-biochar networks,whereas there was no significant correlation with bacterial compost or no-compost networks.Soil variables significantly influenced the fungal compost and no-biochar networks.(6)The fungal high-biochar network(W2MF and W4MF)had higher amounts of nodes,links and modules than the low-biochar network.The bacterial low-biochar network(MF and W1MF)had higher amounts of nodes,and modules than the high-biochar network(W2MF and W4MF),however the difference of the modularity didn't reach to the significance(P>0.05).(7)The soil p H and nutrients content were significantly correlated with soil microbial taxa,i.e.the bacterial phylum Acidobacteria,Nitrospirae,Chloroflexi,Planctomycetes,Actinobacteria and Cyanobacteria were positively related to soil nutrients content(SOM,AN,AP and AK),and The fungal phylum Zygomycota,Rozellomycota and Glomeromycota were positively related to soil nutrients content and p H.In conclusion,biochar-based fertilizer induced microbial correlation network complexity and diversity increases and improved the soil nutrients,indicating biochar-based fertilizer had great benefits on restoration of karst degraded soil.Biochar-based fertilizer addition increased soil nutrients content,so that it could support the plant growth and biomass increase.Biochar-based fertilizer application caused the changes in the soil bacterial and fungal community structure and increase soil bacterial and fungal diversity and biomass.Increased microbial diversity and network correlation complexity illustrated more steady soil microbial ecosystems after biochar-based fertilizer amendment.And this means the microorganisms with higher diversity could deal with severer soil environment to support the plant grouth.The wood biochar-based fertilizer treated soil had the higher bacterial and fungal diversity due to its higher porosity than the other two kinds of biochar derived from bamboo and rice husk.So wood biochar had a better promoting potential in improving karst soil in the future field research.Biochar and compost addition into the biochar-based fertilizer could increase microbial community network structure complexity,indicating that the biochar-compost-NPK fertilizer mixed amendment could improve soil microbial ecosystem then benefit in the soil nutrien cycling.Although there are so many benefits of biochar,the microbial diversity and network complexity did not increase all the time following the increasing biochar addition rate.The microbial diversity reached to the highest value at W2MF treated soil.So the appropriate addition rate of biochar should be taken into consideration in the future to keep a sustainable and stable soil microbial environment.