Study On The Interaction Between The Expansion Of Stellera Chamaejasme L.and Soil Microorganisms In Degraded Grassland

Stellera chamaejasme L.,a poisonous perennial weed,is widely distributed on grasslands in China.With the gradual degradation of natural grasslands,S.chamaejasme population spreads continuously and the growth area has increased,which impairs ecological stability and reduces the area of grazing grasslands,posing detrimental impact on the development of animal husbandry.Plant growth is often affected by the physiochemical properties of the soil,as well as the interaction with the microbial community of the soil.Therefore,the plant-soil-microorganism is indivisible and dependent on each other.For example,plant soil feedback(PSF)can explain the mechanism of plant invasion and the maintenance of ecological niche to some extent.Focused on the relationship between plants,soil and microorganisms during the spread of S.chamaejasme,this study aimed to answer two questions.First,whether the growth of S.chamaejasme is related to differences in soil physicochemical properties and microbial community composition in different geographical areas.Ssecond,whether soil microbial environment from where S.chamaejasme grows has a feedback effect on the growth of other plants.By answering the above two questions,evidence could be provided for the expansion mechanism of S.chamaejasme.Therefore,first this study focused on two typical distribution areas with different climates and grassland types: the Inner Mongolia Plateau and the Qinghai-Tibet Plateau,where rhizosphere soil and non-rhizosphere soil of S.chamaejasme at 26 sites were collected,respectively.Three soil cores were taken as biological replicates,with a total number of 156 samples.The physicochemical properties and microbial diversity of the collected soil samples were measured to compare possible differences and search for the connection between them and S.chamaejasme between them.Secondly,the PSF of S.chamaejasme rhizosphere soil microorganisms on itself and its common associated species Leymus chinensi,Agropyron cristatum,Allium mongolicum,Sanguisorba officinalis,Plantago asiatica,Saussurea runcinata were measured by indoor pot experiment to determine possible feedback effect.The main results of this study are as follows:1.The expansion of S.chamaejasme population was related to the changes of soil nutrients,but the differences depended on different regions.Paired t-test showed that the contents of total carbon,total nitrogen and ammonium nitrogen in the rhizosphere soil of S.chamaejasme were greatly higher than those in the non-(S.chamaejasme)-rhizosphere soil(p < 0.01)in the Qinghai Tibet Plateau.The total phosphorus content of the rhizosphere soil was significantly higher than that of the non-rhizosphere soil(p < 0.05)in the Inner Mongolia Plateau.In other aspects,the soil nutrients of the rhizosphere soil increased compared with the non-rhizosphere soil,but the difference was not statistically significant.Comparing the soil characteristics of the two regions,it was found that the soil nutrients of the Qinghai Tibet Plateau are higher than those of the Inner Mongolia Plateau.Furthermore,two-way ANOVA showed that the regional influence on the change of soil nutrients was higher than that caused by S.chamaejasme itself.2.High-throughput Pac Bio full-length sequencing of bacterial 16 s and fungal ITS amplicons of the rhizosphere soil and non-rhizosphere soil samples showed that,the abundance and diversity of bacterial and fungal microbial communities in the rhizosphere soil were higher than that in the non-rhizosphere soil.The dominant bacteria in the soil are Actinobacteria,Proteobacteria and Firmicutes.The abundance of Firmicutes in the rhizosphere soil was lower than that in the non-rhizosphere soil.The dominant fungi were Ascomycota,Basidiomycota and Mortierellomycota.When comparing the bacterial diversity at the genus level between the rhizosphere soil with the non-rhizosphere soil,it was found that the abundance of the main dominant bacteria Rubrobacter,Bacillus and Gaiella were lower,and there were significant differences among the four groups(the rhizosphere soil and non-rhizosphere soil in the Qinghai Tibet Plateauand Inner Mongolia plateau).At the level of fungal genus,the relative abundance of Penicillium and Fusarium in the rhizosphere soil was significantly lower than that in the non-rhizosphere soil.3.The feedback experiment showed that there were differences in fungal diversity between the rhizosphere and non-rhizosphere soil.Although the abundance of AMF in the rhizosphere soil was lower than that in the non-rhizosphere soil,the difference was not significant.After inoculation with the S.chamaejasme rhizosphere microorganisms,a positive feedback on the growth of itself and four other forbs,Allium mongolicum,Sanguisorba officinalis,Plantago asiatica,Saussurea runcinata,and a negative feedback on the growth of two grasses,Leymus chinensi and Agropyron cristatum were found.The root to shoot ratio of S.chamaejasme growing in its own soil microbial community increased significantly.