| In order to explore the weed-suppressive mechanism of allelopathic rice in paddy field,the allelopathic rice accession PI-1 and its counterpart Lemont were used as cultured material by field tests under weed-removing mode and without weed-removing mode.The differentials of two rice accessions at seedlings stages(3-,5-and 7-leaf stage,respectively)in the allelopathic effect and physiological traits,the diversity and physiological characters of microbial in rice rhizospheric soils,and the related genes expression involved in secondary metabolisms and the contents of metabolites were compared and analyzed.The results were as follows:1.In the allelopathic effect and physiological traits of rice accessions,the highest of inhibitory rates of PI-1 rice seedlings was at 7-leaf stage,up to 85.82%on paddy weeds comparing to the control.The photosynthesis physiological indexes in PI-1 were higher than in Lemont,both in the two treated modes,but no rice seedlings at 3-leaf stage in weed-removing mode.The expression folds of genes related to photosynthesis were significant higher than in PI-1 than that in Lemont when comparing at the same leaf stage.The activity of protective enzymes in the leaves and roots of two rice accessions were significant higher in without weed-removing mode than that in weed-removing mode,however,and they were significant higher in PI-1 than that in Lemont,both in the two treated modes.The expression folds of genes related to nutrition transport were significant higher than in PI-1 than that in Lemont.The calorific values of rice tissues in two rice accessions were significant higher in without weed-removing mode than that in weed-removing mode,however,and they were significant higher in PI-1 than that in Lemont,both in the two treated modes.2.By DGGE and T-RFLP techniques,the microbial populations in the rhizospheric soils of PI-1 were all higher than that of Lemont.when comparing two rice accessions at the same treated modes and at the same leaf stages.And the quantity of bacteria in the rhizospheric soils of two rice accessions were significant higher in without weed-removing mode than that in weed-removing mode,however,no significant difference were found in the quantity of fungi and actinomyces.The 13 out of 19 T-RFs,which positively correlated to rice allelopathic potential were identified.They were 83 species microbes originated from 14 classes referring to five ecological functions such as metabolism about carbon,nitrogen and sulfur,the pathogen-inhibiting probiotics and pathogens.The abundance of these positive T-RFs were higher in the rhizospheric soils of PI-1 than that of Lemont,both in the two treated modes.The 7 out of 25 T-RFs,which negatively correlated to rice allelopathic potential were identified.They were 32 species microbes originated from 6 classes referring to four ecological functions such as metabolism about carbon and nitrogen,the pathogen-inhibiting probiotics and pathogens.The abundance of these negative T-RFs were higher in the rhizospheric soils of Lemont than that of PI-1,both in the two treated modes.3.In the physiological characters of microbials in rice rhizospheric soils,the weed-suppression potential of rhizospheric soils in PI-1 were significant higher than that in Lemont under without weed-removing mode.The microbial biomass carbon(MBC)and microbial respiration rate(MBR)of rhizospheric soils in PI-1 were significant higher than that in Lemont,both in the two treated modes and the highest was rice seedlings at the 5-leaf stage.The soil enzymes activities were increased as increasing of rice leaf stages,however,they were higher in without weed-removing mode than in weed-removing mode,as well as in PI-1 than in Lemont.The efficiencies of utilization for 6 carbon sources of PI-1 rhizospheric soils were higher in without weed-removing mode than that in weed-removing mode,and were also higher than that in Lemont rhizospheric soils.The phenolic acids and amides were the principal components by principal component analysis(PCA).4.In the genes expression involved in secondary metabolisms,the 6 genes related to phenolic acid metabolism in PI-1 leaves and roots were all up-regulation and expression folds were increased as increasing of rice leaf stages.However in Lemont leaves and roots,4 genes(Phenylalanine ammonia-lyase,Hydroxylase,Cinnamoyl-CoA,and Cinnamoyl alcohol dehydrogenase)were up-regulation and 2 genes(Cinnamate-4-hydroxylase and O-Methyltransferase)were down-regulation.The expression folds were significant higher in PI-1 than that in Lemont.Not significant differences were found in the genes expression of tepenoid metabolism,alkaloids metabolism and fatty acids metabolism between the two rice accessions,although they were all up-regulation.The inhibitory rates of phenolic extracts from the rhizospheric soils of PI-1 were significant higher in without weed-removing mode than in weed-removing mode,and were also significant higher than that of Lemont.However,the inhibitory rates of terpenoids extracts,alkaloids extracts and fatty acids from the rhizospheric soils were not significant difference between two rice accessions,although these inhibitory rates were increased as increasing of rice leaf stages.Corresponding to the phenolic extracts,the total contents of phenolic compounds and the contents of the phenolic allelochemicals in the rhizospheric soils of PI-1 were significant higher in without weed-removing mode than in weed-removing mode,and were also significant higher than that of Lemont.By simulation experiment,the inhibitory effect of mixed phenolic allelochemicals as results of PI-1 rhizospheric soils were significant higher than that of Lemont rhizospheric soils,and were significant higher of mixed phenolic allelochemicals as results of PI-1 rhizospheric soils in without weed-removing mode than that in weed-removing mode.In summary,the weed-suppressive mechanism of allelopathic rice accession in paddy fields could be(1)PI-1 can maintain and strengthen the traits and the dominant position in photosynthesis ability,enzymes,absorbance and transport of nutrients,and energy synthesis etc.;(2)by enhancing the genes expression of phenolic acids metabolism and promoting synthesis of phenolic compounds,PI-1 increased significantly the contents of phenolic allelochemicals in the rhizospheric soils,which driving the growth of soil microbial population in favor of phenolic acids and nitrogen,and increasing the species and amount of soil microbes more conducive for rice growth,such as enzymes activities and nutrient cycles about carbon,nitrogen and sulfur.(3)by regulating the microecological environment of the rhizospheric soils,PI-1 increased significantly the species and amount of soil pathogens against weeds growth,changed the ratios of allelopathy-positive soil microbes and allelopathy-negative soil microbes.Rice allelopathy in paddy fields had a high correlation with germplasm traits,up-expression of genes related to phenolic acids metabolism,thus changes of microbial population diversity and microecological environment in rice rhizospheric soils.In particular,the powerful expression of genes related to phenolic acids metabolism in allelopathic rice accession could increase the contents of phenolic allelochemicals,which driving the movements of microbial diversity and microecological environment in rice rhizospheric soils.The cooperative actions of allelochemicals and soil microbes were a principal mechanism for the weed-suppression of allelopathic rice accession. |
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