Physiological Response Of Mycorrhizal Seedlings Of Xingan Larch(Larix Gmelinii) To Drought And Pathogenic Stress

Due to the accelerated industrialization,a combination of biotic and abiotic stresses,represented by drought and pathogenic bacteria,is seriously endangering the forest system in the Daxinganling Mountains and other areas,affecting plant growth and development and thus causing damage to the ecosystem.The use of ectomycorrhizal mycorrhizae to form symbiosis with plants to enhance plant resistance has become a hot application because of its low cost,environmental friendly,non-polluting,wide range of application and good effect.In this study,annual seedlings of Larix gmelinii were grown in pots to study the response mechanisms of drought,Fusarium oxysporum,and inoculation of ectomycorrhizal fungi(Ectomycorrhizal fungi)in response to biotic and abiotic stresses.The effects of drought,Fusarium oxysporum and Ectomycorrhizal fungi(ECMF)inoculation on the growth and physiology of Xingan larch seedlings were investigated in a pot experiment to explore the alleviating effects of ECMF inoculation on Xingan larch seedlings under single and combined stresses of drought and pathogens and the similarities and differences between combined and single stresses on Xingan larch seedlings.This paper provides a theoretical basis for the restoration of forest vegetation in the Daxingan Mountains through the use of plant-microorganism interactions.The main findings of the paper are as follows:(1)Under drought and Fusarium acanthoides stress,both blood red riveted mushroom(Gomphidius rutulus,Gr)and delicious boletus(Boletus edulis,Be)using mixed inoculation and single inoculation were able to form good symbiosis with seedlings of Xing’an larch,with infestation rates of 15.28%～68.33%,and the effects showed that mixed inoculation Gr +Be >Gr alone > Be alone,indicating that Be and Gr have different affinities for Xing’an larch,but can synergistically infest Xing’an larch.(2)The combined stresses of drought and Fusarium acuminatum caused more severe damage to seedlings than single stresses,showing a cumulative effect.ANOVA showed significant interaction of seedling POD activity and other indicators with drought × Fusarium acuminatum.(3)Under the single and combined stresses of drought and Fusarium acuminatum,ECMF promoted seedling growth,significantly increased the plant height and biomass of Xing’an larch,and reduced the specific root length and increased the root-to-crown ratio of seedlings,and the mycorrhizal effect was positively promoted,alleviating the inhibitory effect of drought and Fusarium acuminatum stress on seedling growth.Among them,mixed inoculation of Gr+Be showed the best performance in promoting seedling growth.The biomass of seedlings inoculated with ECMF was 1.67-11.07 times higher than that of CK under single and combined stresses.(4)Inoculation of ECMF significantly increased photosynthetic pigment content,net photosynthetic rate,intercellular CO2 concentration,stomatal conductance,transpiration rate,maximum photochemical quantum yield of PSII,actual photochemical quantum yield of PSII and photochemical burst coefficient of seedlings of Xingan larch under drought and Fusarium acuminatum single and combined stresses.Under the drought-pathogen complex stress treatment,the net photosynthetic rates of plants with Be,Gr,and Gr+Be applied increased by0.90%～13.46%,6.63%～17%,and 11.51%～19.41%,respectively,compared with CK.It indicates that ECMF can alleviate the inhibition of photosynthesis of plants by stress.(5)Under drought,Fusarium acuminatum single and compound stresses,ECMF inoculation significantly increased SOD,CAT,POD activity and proline,soluble protein content and soluble sugar content of Xing’an larch,reduced MDA content in seedlings,and enhanced their uptake and accumulation of nutrient elements.Under MD+Fu treatment,the SOD activity,CAT activity,POD activity,proline,soluble protein content,soluble sugar and MDA content of seedlings inoculated with Gr+Be were 2.5,8.27,1.19,1.4,1.34,2.34 and 0.66 times higher than those of CK,respectively.It showed that ECMF could maintain the stability of oxidative system balance by increasing the antioxidant enzyme activity,maintain cell expansion pressure by up-regulating the content of osmoregulatory substances,and alleviate the damage to cell membrane by stress by decreasing the MDA content.In conclusion,there was a cumulative injury effect of drought and pathogen compound stress on plants,and there was a significant interaction in some indicators.The principal component analysis showed that ECMF mainly responded to single and compound adversity stresses by enhancing photosynthesis,promoting seedling growth and nutrient uptake to alleviate adversity injury,and the combined analysis of D values indicated that the effect of ECMF to improve resistance of Xing’an larch was Gr+Be>Gr>Be>CK.