Response Of Nutrient Stoichiometry And Microbial Community Of Karst Yellow Soil To Biochar Addition

Yellow soil is thin,poor fertility,and densely populated,which deteriorates the conflict between people and land.The yellow soil is widely distributed and is one of the most important soil types in the karst area of Southwest China.In order to maintain productivity,excessive application of fertilizer,pesticides and herbicides which is common in this area caused the soil degradation and severe soil erosion,and seriously damaged agriculture security and ecology sustainability.Biochar is a solid,highly aromatized product obtained by pyrolysis and conversion of biomass under anoxic conditions.In recent years,biochar has been widely used as a soil amendment and fertilizer slow-release carrier,and many researchs had been carried on the effect of biochar addition on soil carbon sequestration,greenhouse gas emission reduction,soil carbon and nitrogen cycling and nutrient retention.With the promotion of green agriculture and"double reduction"of pesticide and chemical fertilizer,the effect of biochar addition on agricultural soil improvement has received great attention.However,response between biochar addition with the characteristics of soil nutrients and soil ecosystems is still unclear,which has been the key constraint the application of biochar.However,as the most widely distributed zonal soil,the response of nutrient stoichiometry and microbial community to biochar addition has not been systematically studied,which is of important scientific significance and research value to clarify the response process and characteristics for improving yellow soil quality and maintaining soil ecosystem function in karst area.In view of this,indoor pot experiment and field plot experiment were conducted with the combination of different crop types(perennial ryegrass,day lily,corn),biological carbon addition content(0%,1%,3%,5%,7%and 9%mass ratio,0%as control)and adding day(120 days,240 days and 360 days)to determine the characteristics and coupled relationships among soil nutrient,stoichiometric and microbial community structure of yellow soil in karst area,which is helpful to clarify the mechanism of biochar addition to nutrient chemical cycling,soil microbial community,crop growth and yield of yellow soil.The main results of this study are as follows:(1)Biochar addition significantly increased the contents of soil organic matter(SOM),total nitrogen(N),total phosphorus(P),total potassium(K),available phosphorus(AP)and available potassium(AK)and improved the p H of soil,but significantly decreased the content of available nitrogen(AN).The contents of SOM,N,P,K,AP and AK were the highest and the effect on improving soil p H were better when biochar content amount was 7%?9%.The contents of soil SOM,N,P,K,AP and AK showed remarkable increase and soil p H showed significantly improvement with increasing biochar addition(P<0.05).The contents of SOM,N,P,K,AP and AK in 7%?9%biochar addition(P<0.05)were obviously higher than those in 0%,1%,3%and 5%biochar addition(P<0.05),while the contents of AN in 0%biochar addition were significantly higher than those in other treatments(P<0.05),indicating that the addition of biochar can reduce the content of AN.Under different crop types,that the maximum values of soil p H,SOM,N,P,K,AP and AK appeared when the biochar addition was 9%,and the minimum values appeared when the biochar addition was 0%.There were significant positive correlations among p H and the contents of SOC,N,P,K,AP and AK at 120,240 and360 days after biochar addition,while the AN were significantly negatively correlated with the above indexes(P<0.05).Under the treatments of different crops and biochar addition days,there were significant linear functional relationships between biochar addition and soil p H,the contents of SOM,N,P,K,AN,AP and AK(R²=0.748?0.994,P<0.05).It was found that biochar addition could effectively improve nutrients status of yellow soil,especially when the biochar addition amount among 7%?9%.(2)Biochar addition significantly affected the stoichiometry of C,N,P and K in yellow soil,and the addition days significantly affected C:K,N:P,N:K and P:K,while different crops significantly affected C:N,C:P,C:K and N:P.The results showed that biochar addition could influence the stoichiometric ratio of carbon and other nutrient elements,and was of great significance to regulate the nutrient cycle and carbon sequestration in yellow soil.C:N,C:P,C:K,N:P,N:K and P:K increased significantly with the increase of biochar(P<0.05),and the maximum values of C:N,C:P,C:K,and P:K appeared in 9%biochar addition,while the maximum values of N:P and N:K appeared at 7%biochar addition.In contrast,the values of AN:AP,AN:AK,AP:AK decreased significantly with the increase of biochar addition(P<0.05).Biochar addition days significantly affected soil nutrient stoichiometry characteristics.C:K,N:P,N:K,P:K increased significantly with longer biochar addition days,and the maximum of C:K,N:P,N:K,P:K showed at 360 days after biochar addition,while biochar addition days showed no significant influence on C:N,C:P,AN:AP,AN:AK,AP:AK.The results showed that different crop treatments significantly affected C:N,C:P,C:K and N:P(P<0.05),and the C:N,C:P,C:K and N:P under the crop treatments of ryegrass and daylily were significantly higher than those of the control.The interaction effect of Biochar addition amount and day on nutrient stoichiometry is significant(P<0.05),while considering combination crop factors with one of them,and the interaction effect on AN:AK was not significant.Under the treatments of different crops and biochar addition days,there were significant linear function between biochar addition and stoichiometry ratio of N,P and K(R²=0.725?0.979,P<0.05).Principal component analysis(PCA)showed that higher biochar addition(7%and 9%)and longer addition time(360 days)had the best effect on nutrient status improvement of yellow soil.(3)Biochar addition increased the abundance of soil microbial community,improved the structure of microbial community and microbial growth promoting crop growth,and inhibited the reproduction and growth of crop pathogens,which was conducive to biological control.Furthermore,biochar addition improved the carbon metabolism capacity of yellow soil microorganisms in different crop types.Increased biochar addition promoted the abundance of soil microbial community,and the abundance was highest when the biochar addition was 5%?7%,under the treatments of ryegrass and daylily,the soil microbial abundance increased by 0.92%?8.77%and 1.27%?6.26%,respectively,compared with the control,and quadratic function could be used to describe the relationship between biochar addition and soil microbial abundance which is significant(R²=0.891?0.927,P<0.05).Biochar addition affected the structure of soil microbial community,and Actinobacteria,Proteobacteria and Chloroflexi are the dominant bacteria phyla,and Ascomycota,Basidiomycota,and Mucoromycota are the dominant fungal phyla.Actinobacteria and Proteobacteria increased with biochar addition,Ascomycota and Basidiomycota changed with biochar addition.Biochar addition significantly affected the diversity and richness of soil microbial community(P<0.05).Alpha diversity analysis showed that the richness and diversity of soil microbial community in the treatments of 7%biochar addition were significantly higher than the other treatments(P<0.05).Beta diversity analysis showed the structure and diversity of soil microbial communities in different crops under low-addition(1%and 3%)treatments and high-addition(7%and 9%)treatments had great differences.The relative abundance of carbon metabolism genes increased with the increasing biochar addition in ryegrass and daylily treatments,while decreased with the increasing biochar addition in control.It shows that addition biochar positively affected the functional genes of soil carbon metabolism with crops that the two crops had the highest abundance of functional genes of carbon metabolism when the biochar addition was 5%?9%.Principal component analysis(PCA)suggested that biochar addition could significantly affect soil microbial community structure and functional genes,showing that soil microorganism community was positively correlated with soil p H,C:N and the content of soil AK,AP,but negatively correlated with the content of soil AN,AP:AK,AN:AP,AN:AK.Soil microbial functional metabolic genes were positively correlated with soil p H,C:N and the content of soil P,while negatively correlated with the content of soil N,K,C:P and N:P.(4)Biochar addition(C),biochar combined with compound fertilizer(CF),and compound fertilizer treatment(F)significantly affected the growth,physiological characteristics,and yield traits of corn.Compared with the control(CK),the contents of SOC,N,P,K,AN,AP and AK generally significantly increased,and soil p H improved,while C:K,N:K,P:K,AN:AP,AN:AK and AP:AK generally significantly decreased(P<0.05)under different fertilization treatments(only biochar addition(C),combined addition of biochar and compound fertilizer(CF),only compound fertilizer addition(F).C,CF and F treatments significantly increased the growth and physiological index of crops compared with the control,and the growth indexs including plant height,ground diameter,leaf area index(P<0.05),and physiological indexs including chlorophyll a,chlorophyll b content,total chlorophyll content,Leaf SPAD value,leaf carboxylation efficiency,maximum net photosynthetic rate,CO₂ saturation point and photorespiration rate.Compared with the control,the weight of dry root,stem,leaf and fruit of crops and the yield indexes including ear weight,ear length,ear diameter,ear grain weight,ear row number,row number and unit yield were significantly increased by C,CF and F(P<0.05).The results showed there were positive correlation among soil p H,C,N,P,K and stoichiometric ratios,growth indexes,yield indexes,and physiological indicators.Grey correlation analysis shows that the improved effects of fertilization(C,CF,F and CK)on soil nutrients,nutrient stoichiometry,and the indicators of crop growth,physiology and yield could be ranked as follows:CF(0.7498)>F(0.7064)>C(0.6163)>CK(0.4088),suggesting the combined application of biochar and compound fertilizer is the optimum treatment on increasing the nutrients status and promoting crop growth and yield in yellow soil.This study analyzed the effects of biochar addition on the characteristics of p H,C,N,P,K,of yellow soil by indoor control experiments,discussed the interaction effect and balanced relationships of biochar addition on C,N,P,K elements and its stoichiometric characteristics of yellow soil,studied the effect of biochar addition on the structure,abundance and diversity of soil microbial communities,and analyzed the effect of biochar addition on functional microorganisms.Based on laboratory experiments,this study also combined field experiments to reveal the characteristics of crops growth and yield with biochar addition.In short,combined indoor simulation with field verification indicating that appropriate addition of biochar can improve the nutrient status and microbial communities of yellow soil in karst.In sum,appropriate amount of biochar addition has a certain beneficial effect on the nutrients and microbial communities in karst yellow soil.The research results will provide scientific reference and theoretical basis for the biochar application in agricultural production in karst areas.