| It is still a blank on germplasm innovation and variety breeding of grasses through using Epichlo? endophyte in China.In the current study,an important turf-type perennial ryegrass(Lolium perenne)infected with endophyte Epichlo? festucae var.lolii was selected as the material.The new material(E+)was obtained based on high endophyte infection rate and excellent agronomic characters through greenhouse and field selection.The physiological and molecular mechanisms of Epichlo? endophyte enhancing growth and survival of L.perenne under low nitrogen stress,and increasing soil nutrients by litter addition were studied in this study.The main results obtained are as follows:1.The new material(E+)with high endophyte infection rates and excellent agronomic characters was obtained,and a screening process for plant population with high endophyte infection rates was established.After three years of field screening and indoor detection,average endophyte infection rates in the tillers and seeds of E+ plant population were 93.6% and 96.5%,respectively.Mean value of crown width,number tillers and panicle number of E+ plants were 48.3 cm,206,and 186.6,respectively.Withering period was postponed,regrowth period was advanced and over-wintering rate was increased significantly(P<0.05)in the new material compared with the control material(E-).2.The results showed that high Epichlo? endophyte infection rates improved the growth,and increased survival rate of new materials in a short time(45-90 days)under low fertility conditions.Endophyte infection significantly increased the survival rate,root metabolic activity and dry weight in leaf and root of new material(P<0.05)under low fertility conditions.The contents carbon,nitrogen and phosphorus were increased significantly(P<0.05)by endophyte infection,thereby improving the survival rate of new materials.In addition,the contents of potassium,calcium,magnesium,iron,manganese,zinc and copper of E+ plants were higher significantly than of E-plants.3.The effects of high Epichlo? endophyte infection rate on amino acid metabolism and endogenous hormone secretion of the new material under low fertility conditions were clarified.Endophyte infection significantly increased contents of aspartic acid,serine,alanine,glycine,lysine,proline,methionine,arginine,phenylalanine and total amino acids contents(P<0.05),while have no significant effect on threonine,glutamic acid,cystine,valine,isoleucine,leucine,leucine and histidine under low fertility conditions at 45 days(P>0.05).The contents of cytokinin and indoleacetic acid contents of E+ seedlings were higher than that of E-seedlings(P<0.05),with a relative increase of 33.46%,34.26% and 16.71%,23.06%.Endophyte infection significantly reduced abscisic acid content(P<0.05),while increased the content of gibberellin in ryegrass under low fertility conditions(P< 0.05).4.The results of low nitrogen stress experiment showed that Epichlo? endophyte infection significantly improved plant growth and biomass of the new materials(P<0.05)through significant altering host nutrient content,rhizosphere soil nutrient contents,and regulating abundance and diversity of the AOB-amo A,nir K,nos Z and nif H genes involved in soil nitrification,denitrification and nitrogen fixation(P<0.05).Endophyte infection significantly reduced the uptake of organic carbon,total nitrogen and total phosphorus in leaves(P<0.05)and total phosphorus in roots(P<0.05)under low nitrogen stress.Epichlo? infection significantly increased the accumulation of H+,S2+,organic carbon,ammonium nitrogen,nitrate nitrogen and total phosphorus in rhizosphere soil(P<0.05),but significantly decreased the p H,C/N ratio and nitrous oxide emissions under low nitrogen stress(P<0.05),thus changing the biomass allocation of host plants.Under 0.05 mol/L N treatment,Epichlo? infection significantly increased the relative abundance of nif H and nos Z functional genes,and the diversity of AOB-amo A,nif H,nir K and nos Z functional gene communities in the rhizosphere soil of E+ plants(P<0.05),but significantly decreased the relative abundance of nir K functional genes(P<0.05).IV 5.The results of litter incorporation experiment showed that Epichlo? infection improved sorganic carbon conten by changing the litter quality,soil nutrient,abundance and diversity of the AOB-amo A,nir K and nos Z functional genes involved in nitrification and denitrification in the soil nitrogen cycle.The presence of Epichlo? endophyte altered the contents of organic matter,total nitrogen and total phosphorus in the new materials.Compared with litter without endophyte,Epichlo?-containing plant litter significantly increased the contents of soil total nitrogen,ammonium nitrogen,nitrate nitrogen and total phosphorus,as well as the contents of soil microbial biomass carbon and nitrogen,and significantly decreased soil p H(P<0.05).The absolute abundance of the AOB-amo A functional gene at second litter incorporation(S1)and fourth sampling(S3)times were significantly higher in soil with Epichlo?-containing litter compared to soil with Epichlo?-free litter at S1 and S3 times(P<0.05).The absolute abundance at S1 and S3 and diversity at S3 of the nir K functional gene,and the absolute abundance at S1 to S3 and diversity at S1 of the nos Z functional gene were significantly lower in soil with litter containing Epichlo? endophyte than that of soil with litter without the endophyte(P<0.05).In conclusion,the first new material of L.perenne with high endophyte infection rate,excellent agronomic characters,and low nitrogen tolerance was obtained,and preliminarily determined the mechanisms that Epichlo? endophyte improved the growth and survival of new materials under low nitrogen stress,and increased soil nutrient.However,future work should further explore the mechanism of nutrition distribution between endophyte and host plants,and lay a foundation for the promotion and application of new material. |
PDF Full Text Request