Effects And Mechanisms Of Biochar Derived From Different Feedstocks To Reduce Continuous Cropping Obstacles Of Panax Notoginseng

Continuous cropping obstacle of Panax notoginseng（PN）,a famous Chinese medicinal plant,has seriously restricted the development of Chinese medicine industry in Yunnan.A large number of studies have shown that biochar has a significant effect on improving soil physicochemical properties,regulating soil ecosystems,and enhancing disease resistance of crops.However,the effects and mechanisms of biochar on PN continuous cropping obstacle are still unclear.Therefore,in this study,a field experiment was conducted in Wenshan Sanqi Science Experiment Station,using biochar produced from rice hull,rubber wood and tobacco stalk,moreover,non-continuous cropping soil was selected as control.The biochar application rates were 0,9,12,15 and 18 t/ha.The survival rate,root rot incidence,and plant height of PN were measured and soil physicochemical properties,allelochemical phenolic acids,abundance of pathogenic Fusarium oxysporum,and microbial communities were tested to infer possible mechanisms,which aims to provide scientific basis for biochar application in soil improvement and reduction of PN continuous cropping obstacle.The main results are as follows:1.The effects of biochar produced from different materials on the growth and disease resistance of PN.After two years cultivation,when the application rate of rice husk and rubber wood biochar were 9 t/ha,and tobacco stalk biochar was 15 t/ha,the survival rate of PN was highest,which were 23%,51%,and 43%respectively,and the root rot incidence was lowest,which were 19%,12%,and 14%respectively.The survival rate of PN in continuous cropping soil was 0%,but up to 67%in non-continuous cropping soil.The application of rubber wood biochar promoted the growth of PN,but there was no significant difference in the plant height among the different biochar treatments.The results showed that the survival rate of PN treated with rubber wood biochar and tobacco stalk biochar were higher,the incidence root rot was lower,indicated the effects on promoting seedling growth and suppressing disease were better than that of rice husk biochar treatments.2.The effects of biochar produced from different materials on soil physicochemical properties under PN continuous cropping.Application of rice husk,rubber wood and tobacco stalk biochar significantly increased soil p H and the contents of available phosphorus（AP）and available potassium（AK）.Among the three kinds of biochar treatments with the highest survival rate,soil p H and organic matter（OM）contents were the highest under 9 t/ha rubber wood biochar application,which were6.22 and 16.67 g·kg^-1,respectively.The contents of NO₃^--N,AP,and AK were the highest under 15 t/ha tobacco stalk biochar application,which were 6.25、23.97 and265.81 mg·kg^-1,respectively.The survival rate of PN was significantly positively correlated with soil p H,NO₃^--N,AP,and OM contents（P<0.05）,and the plant height was significantly positively correlated with soil NO₃^--N,AP,AK,and OM contents（P<0.05）.The study showed that rubber wood biochar treatments were more effective than rice husk and tobacco stalk biochar in raising the p H of PN continuous cropping soil,rubber wood and tobacco stalk biochar treatments were more effective than rice husk biochar in reducing NH₄⁺-N and increasing AK and OM content,and tobacco stalk biochar treatment was more effective than rubber wood and rice husk biochar in increasing NO₃^--N and AP content.3.The effects of biochar produced from different materials on soil allelochemical phenolic acids.The contents of p-hydroxybenzoic acid,vanillic acid and syringic acid in the continuous cropping soil were decreased under three kind biochar application（P<0.05）,the contents of p-hydroxybenzoic acid,vanillic acid,and syringic acid were the lowest under 15 t/ha tobacco stalk biochar treatment,which were reduced by 19%,27%,and 30%respectively,compared with the continuous cropping soil.Furthermore,the contents of p-coumaric acid and ferulic acid were the lowest under 9 t/ha rubber wood biochar treatment,which were reduced by 10%and 19%respectively,compared with the continuous cropping soil.The results indicated that rubber wood and tobacco stalk biochar treatments were moer effective than rice husk biochar in reducing vanillic acid and syringic acid,while rice husk biochar treatments were better than rubber wood and tobacco straw biochar in reducing ferulic acid content in soil.4.The effects of biochar produced from different materials on soil microbial diversity.Application of rice husk,rubber wood and tobacco stalk biochar significantly increased soil fungal and bacterialαdiversity in the continuous cropping soil of PN,moreover,there was a significant positive correlation between PN survival rate and microbial diversity（P<0.05）.The fungalαdiversity was highest under 9 t/ha rubber wood biochar treatment,however,the bacterialαdiversity was the highest under 15t/ha tobacco stalk biochar treatment.Compared with the continuous cropping soil,the Chao1 index of fungal and bacterial community increased by 78%and 24%,respectively.The study showed that rubber wood biochar treatment was more effective than rice husk and tobacco straw biochar in improving soil fungalαdiversity and tobacco stalk biochar treatment was more effective than rice husk and rubber wood biochar in improving soil bacterialαdiversity.5.The effects of biochar produced from different materials on the pathogenic and beneficial microorganisms.After rice husk biochar treatment,the relative abundance of potential pathogenic Alternaria and F.oxysporum decreased by 0.05-0.27%and 14.37-32.34%,respectively,while the beneficial Mortierella,Penicillum,and Chaetomium increased by 2.85-25.42%,0.16-1.84%,and 0.43-1.83%,respectively.After rubber wood biochar treatment,the relative abundance of potential pathogenic Fusarium,Plectosphaerella,and F.oxysporum decreased by 5.76-6.94%,1.62-2.49%,and 0.89-19.40%,respectively,and the potential beneficial Mortierella,Penicillum,Trichoderma,and Chaetomium increased by 17.53-26.00%,6.05%-18.78%,17.48-18.78%,and 2.45-6.23%,respectively.The relative abundance of potential pathogenic Fusarium,Alternaria,and F.oxysporum were decreased by 4.15-4.32%,0.16-0.88%,and 0.03-4.05%,respectively,and the beneficial Mortierella and Trichoderma increased by 10.53-12.40%and 0.43～2.84%,respectively after tobacco straw biochar treatment.Among biochar produced from different feedstocks,more beneficial species were enriched in soil under rubber wood biochar treatment.In addition,the soil phenolic acids were positively correlated with relative abundance of pathogenic microorganisms,and could promote the growth of pathogenic fungi,such as F.oxysporum,F.solani,and Alternaria panax.6.The effects of biochar produced from different materials on microbial community.A distinct distribution pattern of microbial community was observed under different biochar treatments,with rubber wood biochar application at 9 t/ha restoring soil microbial community similar to non-continuous cropping soil.Besides,under the treatments of rubber wood biochar and tobacco stalk biochar,the average connectivity of soil fungi-bacteria interaction network was 20.3 and 18.9,and the closeness centrality was 46 and 50,the positive cohesion of the network was significantly lower and the negative cohesion was significantly higher than that of the application of rice husk biochar（P<0.05）.Moreover,changes in soil properties caused by biochar application dominated the succession of microbial community.This study indicated that rubber wood and tobacco stalk biochar are effective on alleviating the continuous cropping obstacles of PN,however,the effect of rice husk biochar was relatively small.The application of rubber wood and tobacco stalk biochar effectively increased soil p H,NO₃^--N,available P,available K,and OM content,and the relative abundance of beneficial microorganisms,decreased soil pathogenic microbial abundance,improved soil microbial diversity and ecological stability,altered microbial community structure,and consequently improved the survival rate of PN under continuous cropping.The application of 9 t/ha rubber wood biochar was most effective in alleviating the continuous cropping obstacles of PN.This study provides theoretical and experimental basis for the effective utilization of agricultural and forestry wastes and the reduction of PN continuous cropping obstacles.