Effects Of Piriformis Indica On The Growth And Physiology Of Phoebe Sheareri Under Salt-alkali Stress

Phoebe sheareri is a large evergreen tree of the genus Phoebe in the Lauraceae family,and is a Class II key protected tree species in China.Its natural distribution area is mainly located in low-altitude valleys and miscellaneous forests south of the Yangtze River,and the soil property is weakly acidic soil.However,the total area of saline-alkali land in China is 99.13 million hm²,accounting for about 10%of the country’s land area,it has seriously hindered the development of agriculture and forestry industry and the restoration of ecological environment in our country.Therefore,in order to promote the cultivation of Phoebe sheareri in weakly alkaline or saline soil,it is necessary to improve its salt and alkali resistance.In this study,two-year-old Phoebe sheareri seedlings were used as experimental materials,the effects of Piriformospora indica on the morphology and physiology of Phoebe sheareri seedlings inoculated with three alkaline concentrations（NaHCO₃:NaCO₃=1:1,0 mmol/L、100 mmol/L、200 mmol/L）were studied.This study cound lay a foundation for exploring the symbiosis mechanism between Phoebe sheareri and Piriformospora indica,improving Phoebe sheareri tolerance to saline alkali stress,and promoting the application of Phoebe sheareri in agriculture,forestry and landscaping.A total of 6 treatment groups were set up in the experiment,including CK group（normal management）,CK 100 group（100 mmol/L saline alkali stress）,CK200 group（200 mmol/L saline alkali stress）,PI group（normal management+inoculation with Piriformospora indica）,PI 100 group（100 mmol/L saline alkali stress+inoculation with Piriformospora indica）,and PI 200 group（200 mmol/L saline alkali stress+inoculation with Piriformospora indica）.The specific results are as follows:Inoculation of Piriformospora indica could alleviate the effect of saline alkali stress on the growth and development of Phoebe sheareri seedlings.According to leaf and root phenotypic health,the order was PI group>CK group>PI100 group>CK100group>PI200 group>CK200 group.As the concentration of saline-alkali increased,fresh weight（Above ground,Underground part）,plant height,ground diameter,leaf（thickness,dry weight,area）,root length（total length,surface area,volume,average diameter）,root activity,photosynthetic pigments（Chl a,Chl b,Total Chl,carotenoid）,and chlorophyll fluorescence parameters（y（II）,QP,QL,fvfm）decreased to different degrees,compared with the control group,the leaf tissue density increased in the treatment group after inoculation,while the leaf tissue density decreased.With the increase of salt alkali concentration,the SOD activity of Phoebe sheareri seedlings showed an upward trend in the inoculated treatment group,while in the non inoculated treatment group,it showed a trend of first increasing and then decreasing;POD activity and APX activity showed an upward trend in both inoculated and non inoculated treatment groups;The CAT activity showed a trend of first increasing and then decreasing in the vaccinated treatment group,while it showed an upward trend in the non vaccinated treatment group;The GR activity in the inoculated treatment group showed a trend of increasing first and then decreasing,while in the non inoculated treatment group,it showed an upward trend.The contents of GSH,H₂O₂,MDA,proline,soluble sugar,soluble protein,and relative electrical conductivity of Phoebe sheareri seedlings all showed an upward trend with the increase of salt and alkali concentration,while the As A content of the uninoculated group showed a first upward trend and then downward trend,while the As A content of the inoculated group showed a downward trend.Compared with the control group,the activities of SOD,CAT,POD,GR and the content of As A in the inoculated group were all increased in different degrees,while the activities of APX,the content of GSH and the content of soluble sugar were not significantly different,the content of H₂O₂and soluble protein decreased significantly under 200 mmol/l saline-alkali stress,the content of MDA decreased significantly under 100 mmol/l saline-alkali stress,the relative conductivity and the content of proline decreased significantly under saline-alkali stress（p<0.05）.The principal component analysis of 38 indexes of Phoebe sheareri seedlings in different treatment groups was carried out,photosynthetic pigment content,oxidoreductase Peroxidase content,osmotic adjustment substance proline content and biomass accumulation cound be used as comprehensive indicators to evaluate salt-alkali tolerance of Photinia.According to the score,the three treatment groups were in the order of PI group>PI100 group>PI200 group>CK100 group>CK200 group,the results showed that inoculation of Piriformospora indica could effectively increase the salt tolerance of Phoebe sheareri seedlings.