Study On The Mechanism Of Biological Fertilizer In Controlling The Replanting Disease Of Pseudostellaria Heterophylla

Consecutive monoculture problem is a widespread replanting disease for crops that seriously hinders the sustainable development of agriculture.The reasons for replanting disease to occur are as follows:decline of soil fertility,the autotoxicity of root exudates and the imbalance of the rhizosphere micro-ecology.Pseudostellaria heterophylla(P.heterophylla)is one of the most important traditional Chinese herbs in Fujian Province,and there exists serious replanting disease in the continuous cropping system.After years of research on replanting disease of P.heterophylla,its mechanism has become clear gradually.Based on our previous studies,16s rRNA amplifier sequencing,DGGE and qPCR techniques were used to study the biological process of environmental catastrophe in rhizosphere soil under continuous cropping regime of P.heterophylla.In addition,on the basis of our previous research on the single and mixed microbial fertilizers to control the replanting disease of P.heterophylla,we further optimized the microbial fertilizer(beneficial microbiome),and then its remediation effect was evaluated.At last,we optimized the best biological fertilizer and studied its remediation mechanisms using 16s rRNA amplifier sequencing,DGGE,qPCR,metatranscriptome and transcriptome sequencing.Main results of this study are as follows:1)Consecutive monoculture problem of P.heterophylla is closely associated with the change of microbiota in rhizosphere ecosystem.Consecutive monoculture system of P.heterophylla can cause changes in structure of microbial community,which ultimately results in the deterioration of microbial structure in rhizosphere soil with fewer beneficial microorganisms(including microbes relating to soil nutrient cycle)and an increase in pathogenic microbes.This imbalanced rhizosphere microecological system consequently leads to serious consecutive monoculture problems in continuous cropping system of P.heterophylla.2)After applying different microbial fertilizers,the BM treatment showed the best effect.The net photosynthesis rate(Pn)and the relative chlorophyll content(SPAD)increased by 1.41 and 1.61 times as much as those of replanting P.heterophylla,respectively.The root weight and total yield increased by 1.75 and 2.69 times as much as those of replanting P.heterophylla,respectively.3)The beneficial microbial fertilizer BM can increase the diversity and richness of microbial community and change the structure of rhizosphere microbal community,showing an increase in beneficial bacteria and a decrease in harmful bacteria in rhizosphere soil of replanting P.heterophylla.It also effectively inhibited the fungal diseases of P.heterophylla.The microorganism structure in rhizosphere soil of P.heterophylla tended to be favorable to the growth of P.heterophylla to alleviate the replanting disease of P.heterophylla.4)Compared to that in newly planting soil,the differentially expressed genes in replanting soil are down-regulated mainly in ribosome,two-component system,flagellum assembly and so on,so many metabolic pathways in replanting soil were blocked.At the same time,the replanting P.heterophylla reduces the populations of many microorganisms and their vitality in replanted soil,and further affects the microbiome structure of rhizosphere soil,and finally influences the growth of P.heterophylla.BM treatment could promote many metabolic pathways in rhizosphere soil of replanting P.heterophylla especially in two-component system,flagellum assembly,ribosome,bacterial secretion system,oxidative phosphorylation,chlorocyclohexane and chlorobenzene metabolism,phosphate metabolism and lipoic acid metabolism,and up-regulate the related genes expression which increased populations of the total microbial community in rhizosphere of replanting P.heterophylla and improved the activity of photosynthetic bacteria,carbon and nitrogen cycle,and energy cycle in rhizosphere soil of replanting P.heterophylla.This is also an important mechanism of BM microbial fertilizer to alleviate the replanting disease of P.heterophylla.5)BM could significantly increase the pH value of rhizosphere soil and transform the nutrient elements into a form that is easy to be used by P.heterophylla,and directly promote the absorption and utilization of soil nutrient elements by P.heterophylla.So it in turn alleviates the replanting disease of P.heterophylla.6)The results of P.heterophylla transcriptome analysis showed that the expression of some important enzymes,such as nitrate reductase and pyruvate kinase,decreased after replanting,which can reduce nitrogen assimilation and energy metabolism of P.heterophylla.There were significant differences in photosynthesis related pathway in nitrogen metabolism and jasmonic acid synthesis pathway of P.heterophylla after BM treatment.The results showed that BM treatment could promote photosynthesis of P.heterophylla,and it also can regulate jasmonic acid pathway to make P.heterophylla adapt to the replanting environment,which is an important mechanism of BM fertilizer to alleviate the replanting disease of P.heterophylla.Based on this study,the author further summarizes the causes of replanting disease of P.heterophylla and the mechanism that BM controls the replanting disease of P.heterophylla.At the same time,these results also prove that the imbalance of rhizosphere microecology(especially the rhizosphere microbiome structure)of P.heterophylla is a vital cause for replanting disease of P.heterophylla.This study will provide an important theoretical basis and technical support for the final solution to control the replanting disease of P.heterophylla.This result also provides a reference to overcome the replanting disease of other crops.