Quorum Sensing Signal AHLs--Based Interaction Regulation Mechanism Between Bacterial Community In Poplar Rhizosphere And Fine Root Growth

Poplar is an important timber tree species,especially widely cultivated in China.The healthy management and productivity maintenance of poplar plantation is an important subject in forestry research.Based on the close relationship between fine roots and stand productivity,fine roots of Poplar Plantation have become an important research content.Therefore,it was very important to understand the relationship between fine root growth and development and environmental factors.There were many biotic and abiotic factors affecting root growth and development.The interaction between rhizosphere microorganisms and roots plays a key role in plant growth.In the process of plant root growth,microbial communities can be recruited and assembled by creating a specific rhizosphere microenvironment to meet the functional needs.Besides rhizosphere microorganisms can use their quorum sensing molecules and ecological functions to find a good niche and make a significant impact on plant.At present,most studies have proposed the interaction mechanism that plants drive the composition of rhizosphere microbial community through root exudates and rhizosphere microorganisms affect plant growth by their ecological functions.However,there are few studies on the interaction mechanism of rhizosphere Microbial quorum sensing molecule affecting plant root growth.Therefore,it is important to study the interaction mechanism between rhizosphere soil microorganisms and roots for understanding and improving fine root growth.In this study,we investigated the Populus × eurameicana 'Neva' to explore the interaction between fine root growth process and rhizosphere bacterial community.Firstly,scanning electron microscopy(SEM)was used to observe the morphology and structure of fine roots in three growth stages(new white root WR,mature yellow root YR and aging brown root BR).High-throughput sequencing and phospholipid fatty acid(PLFA)were used to accurately analyze the rhizosphere bacterial community in three stages,and to study the correlation among rhizosphere nutrients(carbon composition,nitrogen,phosphorus nutrients),fine root growth and rhizosphere soil bacterial community.Then,the positive bacteria of quorum sensing signal in different growth stages of rhizosphere were isolated,and the expression of AHLs was detected.Through the control experiment of exogenous addition of AHL,the effect of AHL on the growth and development of fine roots was explored.The main results of this study are as follows:(1)According to the OTU classification statistics of rhizosphere bacterial community,it was found that the bacterial abundance in new rooting was the highest.There were significant differences in biomarker bacteria in rhizosphere at each growth stage.Bacteria have 11 dominant genera with a relative abundance over 1%,of which,four genera of the bacteria(Bacillus,Burkholderia,Ralstonia and Dyella)differ in abundance among the WR,YR and BR soil compartments.The bacteria in the primary stage of fine root growth(new root rhizosphere)are related to nutrient assimilation.The bacteria in the mature stage(mature root rhizosphere)are mainly biological control and promote growth,while the bacteria in the old stage(aging root rhizosphere)are mainly biological control and disease prevention.(2)Total soil carbon(TC)in rhizosphere soil increased with root growth,while dissolved organic carbon(DOC)decreased with root growth.With the change of rhizosphere dissolved organic carbon,39 species of rhizosphere bacteria in the top 50 were significantly related to rhizosphere DOC.NTI and ?NTI of rhizosphere microbial community showed that the evolution process of bacterial community composition in rhizosphere from new root to aging root was randomness,deterministic and dominated randomness.Moreover,there was a significant linear correlation between ?NTI and Rhizosphere dissolved organic carbon(DOC),indicating that the change of carbon component(DOC)in poplar root system driven the differentiation of rhizosphere microbial community.(3 We isolated and purified 10 species of quorum sensing signal positive bacteria in each growth stage of rhizosphere.The correlation between QS positive bacteria and soil nutrients showed that B3 belonging to Burkholderia had a linear correlation with dissolved organic carbon in soil.In addition,there was a significant linear positive correlation between rhizosphere AHLs and Burkholderia.This shows that C8-HSL produced by QS positive bacteria is closely related to the growth and development of fine roots.(4)Study on the effects of exogenous addition of C8-HSL on the growth and development of fine roots of poplar.The results showed that C8-HSL had dual effects on the growth of fine roots of poplar.Firstly,in terms of morphological traits,10 n M treatment significantly promoted root growth,but did not change root configuration.There was no significant change in fine root growth under 10 n M to 10?M treatment.Under the treatment of more than 100?M,the fine root growth of poplar was significantly inhibited and showed a significant concentration dependence.There was no significant change in root tip meristem at 10 n M,root hairs increased and grew,root tip and root crown aged and fell off significantly at 100?M,cortical cells shrank,root hairs were few and incomplete,lateral root development was also significantly inhibited,large vacuoles appeared in root tip meristem cells,and organelles were damaged.Then,in terms of physiological characteristics,the root activity of fine roots under10 n M treatment was significantly higher than that of other groups.Although the antioxidant enzyme activity of fine roots increased significantly at 1?M,it began to decrease with the increase of AHL concentration.However,under the treatment of 100?M,the fine root DNA was broken irregularly and some cells were necrotic.Finally,there were significant differences in fine roots of transcription and metabolism between 10 n M and 100 ?M treat.Compared with the CK,MYB46 transcription factor and calmodulin(Ca M)played an important role in the regulation of root morphology and structure of poplar fine roots under high concentration treatment.However,the promotion of fine root growth at low concentration is closely related to plant auxin indoleacrylic acid and the hydrolysis of AHL.In conclusion,our results show that the growth of poplar fine roots shapes the composition and structure of rhizosphere bacterial community.The quorum sensing positive bacteria in the bacterial community can regulate the growth of fine roots by N-acyl homoserine lactone.To explore the interaction mechanism between poplar fine root growth and rhizosphere microorganisms can deeply understand the ecological process and mechanism of forest root-soil.At the same time,it also provides a theoretical reference for exploring the regulation of rhizosphere process and productivity maintenance technology of plantation.