Effect Of Coumarin On Physiological Characteristics And Rhizosphere Microecology Of Annual Ryegrass

In order to elucidate the allelopathy mechanism of coumarin for weed control,and provide a theoretical basis for the development of coumarin compounds as biological pesticides,in the current research,potexperiments were carried to determine the effect of different concentrations of coumarin on plant height,root length,biomass,antioxidant enzymes(SOD,POD and CAT),osmotic adjustment substances(soluble sugar and soluble protein),hormones(IAA and ABA)content and chlorophyll fluorescence of annual ryegrass were determined after 20 days of treatment.Then root metabolites and bacterial community in rhizosphere soil of annual ryegrass were also analyzed with treatment of coumarin(200 mg/kg).And the main findings are as follows:1.Coumarin can inhibit the growth of annual ryegrass,and this inhibition will strengthen with the coumarin concentration increase.The results of allelic comprehensive effect showed that the concentration of 100 mg/kg had little effect on ryegrass,and the inhibitory effect on above-ground or underground parts were same(-0.04).However,at 200 mg/kg concentration,plant height,root length and biomass of ryegrass significantly decreased(P<0.01).MDA content,POD activity,CAT activity and ABA content in above-ground were significantly increased(P<0.01).SOD activity and soluble sugar content significantly increased(P<0.05)whereas soluble protein content significantly decreased(P<0.05).In underground part,the contents of MDA and ABA were significantly increased(P<0.01).And POD activity,CAT activity and IAA content were significantly decreased(P<0.01).The contents of soluble sugar and soluble protein were significantly decreased(P<0.05).Thus,200 mg/kg coumarin can inhibit the growth of annual ryegrass by changing the activity of antioxidant enzymes,and regulating the content of osmotic substances and endogenous hormones.Moreover,200 mg/kg coumarin has a stronger effect on the allelopathic inhibition of underground(-0.48)than that of above-ground(-0.13).2.The 100 mg/kg concentration had a lighter effect on the annual ryegrass photosynthetic system compared with 200 mg/kg,and in the 200 mg/kg coumarin treatment,chlorophyll a,chlorophyll b and total chlorophyll content were significantly reduced(P<0.01),OJIP fluorescence transient curve were significantly reduced,and the antenna pigments were structurally changed or degraded.JIP test results showed that in the treatment of 200 mg/kg coumarin,the initial fluorescence and maximum fluorescence values of the leaves decreased,the PI quantum yield and efficiency decreased while the specific energy flux increased,and the PIABS and PItotal values decreased significantly(P<0.01).The results of slow fluorescence parameters showed that under the treatment of 200 mg/kg coumarin,the Fv/Fm,Y(Ⅱ)and ETR values significantly decreased(P<0.01),but the photochemical quenching parameters(qP and qL),Y(NPQ)and Y(NO)significantl rose(P<0.05).Therefore,200 mg/kg coumarin can cause irreversible damage to the annual ryegrass photosynthetic system3.The 200 mg/kg coumarin had little effect on the bacterial species of annual ryegrass rhizosphere,but it had a significant effect on its abundance.Under coumarin allelopathy stress,annual ryegrass can stimulate the relative abundance of beneficial flora in the rhizosphere to resist allelopathy stress,but certain pathogenic bacteria such as the pathogenic endemic genus Aquicella multiply in large numbers,which also may be an important reason for the sharp decline in annual ryegrass biomass and even death.Metabolomics results showed that 200 mg/kg coumarin treatment produced a total of 351 significantly different metabolites,of which 284 metabolites were significantly higher than the CK group,only 67 metabolites were significantly lower than that of the CK group(P<0.05),and the differential metabolites were mainly enriched in 20 metabolic pathways such as Pentose phosphate pathway,Carbon metabolism,Anthocyanin biosynthesis,Acridone alkaloid biosynthesis,Tyrosine metabolism,Tryptophan metabolism,Isoquinoline alkaloid biosynthesis,Phenylpropane biosynthesis,Flavonoid biosynthesis,Glutathione metabolism and so on.Correlation analysis of rhizosphere soil bacterial communities and root metabolites revealed that some bacterial communities and metabolites had a great correlation.The change in abundance broke the balance of the rhizosphere micro-ecosystem and indirectly regulated the root metabolites,but their specific relationship still needs further study.