Effect Of Biochar On Soil Fertility Of Continuous Cropping And Root-rot Pathogens Of Panax Notoginseng

Panax notoginseng is a valuable traditional Chinese herb with high medicinal value in China.However,continuous crop disorder can lead to reduced yield or even extinction of panax pseudoginseng,which seriously limits the development of panax pseudoginseng cultivation.Biochar,as a soil amendment,can effectively improve soil quality and reduce the impact of succession disorder on Panax pseudoginseng,but there are still many unclear points regarding the mechanism of biochar’s action in it.The effects of biochar on soil fertility and microbial community structure of Panax notoginseng,especially whether biochar inhibits the activity of pathogenic bacteria of Panax notoginseng diseases and what is its mechanism of action,need to be further clarified.Therefore,this study was conducted to investigate the mechanism of biochar abatement in Panax notoginseng continuous crop disorder through field trials and indoor culture trials.In the field experiment,the effects of different types of biochar on the fertility,soil enzyme activity,microbial carbon metabolism and microbial community of the inter-root soil of Panax pseudoginseng were investigated by applying tobacco straw biochar,rice husk biochar and rubber wood biochar,with no biochar applied as the control,In addition,in a pot experiment with modified biochar,rubber wood biochar and iron-modified rubber wood biochar were used at 1%and 3%mass fractions,and no added biochar was used as the control to investigate the effects of modified biochar on the growth traits,leaf enzyme activity and inter-root soil physicochemical properties of Panax notoginseng plants.The effects of modified biochar on the growth traits,leaf enzyme activity and inter-root soil physicochemical properties of Panax notoginseng plants were investigated.The main findings of the study are as follows:（1）The results of the field trial showed that the survival rate of Panax notoginseng seeds in the treatment groups increased after the application of biochar,with the rice husk biochar（RB）,tobacco straw biochar（TB）and rubber wood biochar（WB）treatments increasing by 3.3,3.1 and 6.5 times respectively compared to the control（CK）.Soil pH and effective phosphorus content increased significantly（P<0.05）and soil ammonium nitrogen content decreased significantly（P<0.05）after the application of the three biochar types.The effect of different types of biochar on soil enzyme activity varied,with rice husk biochar（RB）application significantly（P<0.05）reducing sucrase activity in continuous cropped soil by 48.9%compared to CK.Soil urease and acid phosphatase activities were significantly lower（P<0.05）with the application of tobacco straw biochar（TB）,reducing by 22.7%and 65.5%,respectively,compared to CK,but soil sucrase activity was significantly lower with the biochar application treatment,averaging 60.3%lower than CK（P<0.05）.Structural model analysis showed that pH（0.746***）,effective phosphorus（0.698***）,microbial mass carbon and effective potassium had a facilitative effect on Panax notoginseng survival and ammonium nitrogen（-0.845***）had an inhibitory effect on Panax ginseng survival after biochar application.（2）Biochar also enhanced the activity of microbial utilisation of carbon sources by modulating soil environmental factors.The application of biochar enhanced the utilisation of 31 carbon sources by soil microorganisms,increasing utilisation by12.9%,16.13%and 9.07%respectively.Further analysis showed that soil microorganisms were most significantly affected by biochar application on A-D-lactose,β-methyl D-glucoside,glucose-1-phosphate,D-malic acid of carboxylic acid and phenethylamine of amine after biochar application（P<0.05）.（3）The abundance of soil bacterial communities increased after the application of biochar treatment.Among them,the TB treatment had the most significant effect on the abundance of Proteobacteria,with a significant increase of 142.93%compared to the CK group（P<0.01）;the WB treatment had the most significant effect on the abundance of Acidobacteria and Actinobacteria,with a significant increase of 168.89%and 175.12%compared to the CK group（P<0.01）.All three treatment groups significantly reduced the abundance of Bacteroidetes,and the WB treatment had the most significant effect in reducing the abundance of Bacteroidetes,with a significant reduction of 67.30%compared to the CK group（P<0.01）.The treatment with biochar significantly increased the abundance of photosynthetic bacteria such as Chloroflexi（P<0.05）and increased the diversity of soil carbon sequestering bacterial community,with the TB treatment having the most significant effect on the abundance of Bradyrhizobium,which increased by 45.85%compared to CK（P<0.05）.（4）The diversity of the soil fungal community increased with the application of biochar.The relative abundance of Ascomycota was significantly higher and that of Basidiomycota and Mortierellomycota was significantly lower（P<0.05）.At the genus level,RB treatment had the greatest effect on Mortierella,Fusarium and Aspergillus,with significant reductions of 51.22%,8.99%and 12.0%,respectively（P<0.05）;RB treatment had a greater effect on Alternaria,with a significant reduction of 34.05%（P<0.05）.Fusarium abundance was significantly reduced by 8.19%（P<0.05）and Aspergillus abundance was significantly increased by 46.15%（P<0.01）compared to the CK group.（5）The application of biochar was able to inhibit the mycelial growth of Panax notoginseng pathogens.3%rice husk biochartreatment had the most significant effect on the mycelial growth rate of Fusarium oxysporum,with 82.64%reduction compared to CK（P<0.01）;.Rubber biocharhad the best virulence effect on Fusarium oxysporum with an EC₅₀ of 0.1120 mg·ml^-1 and the optimal inhibition effect was as follows:3%WB（53.69%）>3%RB（53.13%）>0.5%TB（44.86%）;Similarly,rubber wood biochar had the best virulence effect on F.solani.with an EC₅₀of 0.0194 mg·ml^-1 and the optimal inhibition effect was as follows:3%WB（53.69%）>3%RB（53.13%）>0.5%TB（44.86%）.The adsorption tests showed that there was a dynamic adsorption process of biochar on both strains of pathogens and that the different biochars showed convergence towards the pathogens.（6）Indoor pot trials showed that application of iron-modified biochar significantly affected soil conductivity,water content,microbial load carbon and nitrogen content and plant height（P<0.05）.The application of 1%iron-modified biochar treatment significantly increased SOD enzyme activity of Panax notoginseng leaves by 283.11%（P<0.01）and POD enzyme activity by 16.84%（P<0.05）compared to the control CK.The application of Fe modified biochar resulted in more resistant Panax notoginseng plants.In conclusion,the application of different biochar treatments improved the survival rate of Panax notoginseng seeds,improved soil physicochemical properties and microbial community structure,and produced direct inhibition of root rot-causing bacteria.Therefore,the improved soil fertility and reduced abundance of pathogenic bacteria in the biochar treatment were important factors in the reduction of continuous crop barriers in Panax notoginseng.This study can provide a technical reserve for soil improvement and reduction of continuous crop barriers in Panax notoginseng.