Effects Of Two Typical Allelochemicals On Growth And Microorganism Of Lanzhou Lily

Lanzhou lily(Lilium davidii var.Unicolor)is a unique medicinal material found in Gansu Province.Due to particular climatic conditions,geographical environment and market demand,the perpetual cropping obstacle of the Lanzhou lily has become an important bottleneck restricting the sustainable development of the Lanzhou lily industry.Existing research shows that the accumulation of autotoxic substances is one of the reason that leading to the continuous cropping obstacle of Lanzhou lily.Previous studies confirmed that dibutyl phthalate(DBP)and 2,4-di-tert-butyl-phenol(2,4-DTBP)were the main autotoxic substances in root exudates of Lilium lancifolium.This study adopted a pot experiment applying DBP and 2,4-DTBP as autotoxic substances based on the interaction of plant-soil microorganisms.The changes in physiological characteristics,antioxidant pathway,and the osmotic pathway of the Lanzhou lily under various concentrations of DBP and 2,4-DTBP stress were studied.Based on the findings,the action mechanism of two typical autotoxic substances upon the growth and oxidative stress of the Lanzhou lily was clarified.Furthermore,the soil microbial diversity of the Lanzhou lily was studied by a BIOLOG microplate and high-throughput sequencing technology.The results showed that two self-toxic substances induced changes in the structure and function of the lily bulb alongside the soil microbial community in Lanzhou.Therefore,exploring the critical role of two typical self-toxic substances in the lily rhizosphere micro-ecosystem is of great significance to unravel the effect of allelopathicon soil microbial flora and the mechanism of soil micro-ecological imbalance mediated by self-toxic substances.In this paper,two typical self-toxic substances were used to act upon the Lanzhou lily.The mechanism of action of two typical self-toxic substances on physiology,biochemistry,and micro-ecology of the Lanzhou lily was analyzed.The main results were as follows:Under different concentrations of DBP and 2,4-DTBP,the two autotoxic substances showed significant effects on the growth and development of Lanzhou lily.Plant height,root length,and dry matter weight of underground parts were significantly affected.Still,the effects of DBP and 2,4-DTBP on different indexes were different with different concentrations and kinds of autotoxic substances,which showcased the phenomenon of low concentration promotion and high concentration inhibition.High concentration DBP(5.0 m M)and 2,4-DTBP(2.0 m M),plant height,stem diameter,and root length of Lanzhou lily showed marked autotoxicity,which decreased significantly compared with the control,with the highest decrease of39.65%and 24.42%,19.75%and 40.16%,45.88%,and 52.27%respectively.Two typical autotoxic substances also significantly reduced the increase of fresh weight and dry weight of bulbs.Through the analysis of the allelopathic response index(RI)of the Lanzhou lily under different treatments,DBP had the most significant inhibitory effect on root length.This indicates that autotoxic stress may hinder the root growth of the Lanzhou lily,the inhibition of root growth may hinder the growth and development of aboveground parts.This stunted growth,in turn,affects the formation of biomass and finally significantly reduces the increase of fresh weight and dry weight of bulbs at the harvesting parts of Lanzhou lily.While biomass was inhibited,DBP and 2,4-DTBP the quality of the Lanzhou lily were also significantly affected by2,4-DTBP treatment.Under the treatment of the two kinds of self-toxic substances,the total sugar content of Lanzhou lily markedly decreased,and the maximum increase of crude fiber content reached 41.06%.It can be inferred that the two kinds of autotoxic substances both hinder the growth of aerial parts and roots of Lanzhou lily,which causes the biomass and quality of the Lanzhou lily to decrease.Autotoxicity stress can lead to active oxygen accumulation and membrane lipid peroxidation damage by reducing the activity of plant protective enzymes.Under the treatments of DBP and 2,4-DTBP,the contents of O₂^-and H₂O₂in leaves of Lilium lancifolium significantly increased,which indicated the generation and elimination of O₂^-and H₂O₂.Then it caused the disorder of the antioxidant enzyme system and caused an oxidative stress reaction.Oxidative stress can equally change the antioxidant enzyme system.The enzyme activities of CAT,SOD,POD,APX,and GR and the contents of As A and GSH in leaves of Lilium lancifolium varied in degree under the influence of self-toxic substances.Still,the changing trend of these indexes is related to the types and concentrations of self-toxic substances.In addition,the change of reactive oxygen species will eventually lead to a significant increase in MDA content,resulting in membrane peroxidation and damage to the membrane system of Lilium lancifolium leaves.The MDA content under high concentrations of DBP(5.0 m M)and 2,4-DTBP(2.0 m M)increased by 67.19%and 50.67%,respectively,when compared with the control.DBP and 2,4-DTBP were also significantly affected the accumulation of osmotic adjustment substances,the proline content increased significantly,and soluble protein content decreased substantially under the treatment of autotoxic substances.Soluble sugar content first increased and then decreased with the increased concentration.It can be seen that DBP and2,4-DTBP altered the physiological metabolism and membrane system stability of the Lanzhou lily,which may account for one of the reasons that hindered the growth and development of Lanzhou lily.Under the influence of DBP and 2,4-DTBP,the soil environment of Lanzhou lily will become more complex.This change may be due to the substrate induction of DBP and 2,4-DTBP,therefore affecting the evolution of soil enzyme activity.Under the treatments of DBP and 2,4-DTBP,urease and polyphenol oxidase in the soil of Lanzhou lily showed a decreasing trend.The highest values of urease and polyphenol oxidase decreased by 38.09%and 33.22%,55.23%,and 50.57%,respectively,under the treatments of DBP(5.0 m M)and 2,4-DTBP(2.0 m M).Catalase gradually increased under DBP and 2,4-DTBP treatments and increased by 32.42%and 50.46%respectively under DBP(5.0 m M)and 2,4-DTBP(2.0 m M)treatments,while other soil enzymes showed an increasing trend at first and then decreased.The change of enzyme activity will eventually lead to the shift in soil microbial biomass.Microbial biomass nitrogen(MBN)showed a phenomenon that low concentration promoted high concentration inhibition under the action of two self-toxic substances.However,the microbial biomass carbon(MBC)showed different trends under the action of two self-toxic substances.However,MBC and MBN were significantly correlated with each other.Under DBP treatment,MBC was positively correlated with BG,urease,and CBH sucrase,while it was negatively correlated with catalase and NAG.Under2,4-DTBP treatment,MBC was positively correlated with urease,NAG,polyphenol oxidase,CBH,NAG,and sucrase.MBN was positively correlated with BG,CBH,NAG,and sucrase under DBP treatment,while MBN was positively correlated with sucrase and NAG under 2,4-DTBP treatment.Therefore,it is deduced that the decrease of most enzyme activities will limit the carbon source in the process of soil microbial metabolism and subsequently inhibit the growth and reproduction of microorganisms.This decrease will further inhibit the growth and reproduction of microorganisms and stimulating the inactivation of soil microbial biomass.A Biolog-ECO analysis showed that with the increase of the concentration of two typical autotoxic substances,soil microbial community structure,and carbon source metabolism characteristics have changed significantly.With the rise in DBP and 2,4-DTBP concentration,the average color change rate(AWCD)first increased and then decreased.A principal component analysis demonstrated that autotoxic substances changed the utilization of microbial carbon sources in the rhizosphere soil of Lanzhou lily,changed the metabolism of the microbial community,and interfered with the function and structure of the soil microbial community.The composition and structural diversity of soil microbial colonies were significantly changed.DBP and 2,4-DTBP have marked autotoxic effects on microorganisms in soil and lily bulbs;this effect varies with different concentrations and types of autotoxic substances.There are significant differences between the�common'and�unique'microbial communities in soil and bulb under different concentrations.With the change of the concentration of self-toxic substances,the fungi increase with the increase of the concentration,which demonstrates a strong inhibitory effect on bacteria.5.0 m M DBP and 2.0 m M 2,4-DTBP promoted the production of pathogenic fungi in soil and bulbs,and Fusarium and Ascomycetes responded most conspicuously to DBP and 2,4-DTBP.It is also positively correlated with the increase of the concentration of self-toxic substances.The results of the RDA analysis of enzyme activity in antioxidant system,soil enzyme activity,and microorganisms in soil and bulb showed that the abundance,composition,and diversity of microorganisms are linked to enzyme activity.Therefore,the change sustained by microorganisms in soil is faster than the change in plants,which leads to the shift in the microbial community in plants in the process of interaction between microorganisms and enzymes,and a series of reactions occur during this process.Concisely,typical autotoxic substances DBP and 2,4-DTBP changed the rhizosphere microbial system,and it indirectly changed the microbial community in the Lanzhou lily bulb.The increase of pathogenic bacteria may lead to the decline of the quality and yield of the Lanzhou lily.As per the aforementioned research results,through the correlation analysis among plant,soil,and microorganism,it can be concluded that the mechanism of continuous cropping obstacle caused by self-toxic substances may be the result of comprehensive action of numerous factors.The self-regulation ability of Lanzhou lily plants is reduced due to the accumulation of autotoxic substances,oxidative stress,osmotic stress,etc.,which lead to the poor growth and development of plants,ultimately leading to the decline of the lily quality.On the other hand,by altering the soil enzyme activity and deteriorating rhizosphere micro-ecological structure,the proliferation of some pathogenic bacteria in soil microflora is stimulated,and the pathogenic bacteria are continuously accumulated,thus infecting host plants.The structural composition and diversity of microorganisms in the bulb were induced to change.Therefore,it is speculated that the cell membrane system could potentially be destroyed following the changes sustained by the root system due to autotoxic substances.This change makes the plant more prone to diseases,resulting in a decline in the quality and yield of the Lanzhou lily.It is of great significance to comprehend the relationship between self-toxicity and obstacles in the long-term continuous cropping process of the Lanzhou lily.