Mycorrhizal Synthesis Of Tuber And Their Effects On The Mycorrhizosphere Ecophysiology Of Host Plants

Tuber species are ectomycorrhizal fungi with important economic and ecological value.Many species of Tuber have high edible value,and can form ectomycorrhizae with numerous forest tree species.The rhizosphere is an important place for the formation and growth of Tuber mycorrhiza,as well as the development of fruiting bodies.The ecological environment in rhizosphere not only affects the colonization of Tuber,but also affects the growth and development of host plants.Mycorrhizal synthesis is the first step to obtain mycorrhizal seedlings,which can be used for artificial cultivation or ecological restoration.During the synthesis of Tuber mycorrhiza,rhizosphere nutrients have a great influence on mycorrhiza formation and host growth,especially the content of nitrogen directly affects the colonization rate of truffle.In addition,calcium amendments are commonly used in Tuber cultivation to adjust the soil environment for mycorrhizal seedlings growth and fruiting bodies development.However,the effect of calcium on Tuber colonization and host growth during mycorrhizal synthesis remians unexplored.High-quality mycorrhizal seedlings provide ecological benefits in arid and rocky desert areas,and bring economic benefits at the cultivation site.In this study,four Tuber species(T.indicum,T.pseudohimalayense,T.huidongense and T.lijiangense)of economic importance and six species of potential hosts(Castanea mollissima,Castanopsis rockii,Quercus variabilis,Q.aliena,Q.robur and Pinus armandii have been selected for mycorrhizal synthesis.The mycorrhiza morphological and anatomical character were described,the influence of different Tuber species colonization on the growth of host plants and rhizosphere ecophysiology,and the influence of nitrogen and calcium addition on the colonization of Tuber species and rhizosphere ecophysiology were studied.Additionally,in order to explore the adaptability of high-quality Tuber mycorrhizal seedlings to arid areas,the microbiome and metabolomics were employed to explore the mechanism of Tuber colonization improved drought resistance of host plants.Major results of the dissertation were summarized as follows:The compatibility of four Tuber species with six tree species were studied at controlled greenhouse-based mycorrhization trials.The results show that all the fungus-tree combination could form ectomycorrhizae.The mycorrhizae of T.indicum colonized with C.rockii and Q.robur,T.pseudohimalayense colonized with C.rockii,Q.variabilis and Q.robur,T.lijiangense colonized with C.rockii and P.armandii was first reported,and their morphological character was demonstrated.Furthermore,the effects of T.indicum and T.lijiangense colonization on host plant growth,physiological responses and mycorrhizosphere bacterial communities of C.rockii were compared.The results show that colonization of Tuber species colonization could significantly increase leaf photosynthetic rate,leaf P concentration and rhizosphere acid phosphatase activity,as well as richness of mycorrhizosphere bacterial communities of C.rockii seedlings.However,T.indicum colonization from a side significantly decreased tartrate content,bacterial acid phosphatase,pho C gene abundance in the mycorrhizosphere,and peroxidase(POD)activity of ectomycorrhizal root tips,but from the other,increased mycorrhizosphere p H and ECM superoxide dismutase(SOD)of ectomycorrhizal root tips,compared to T.lijiangense colonization.The relative abundance of the bacterium Agromyces cerinus have significant positive correlation with mycorrhizosphere acid phosphatase activity and leaf P concentration,suggesting that it might play an important role in P mobilization and acquisition.In addition,the effect of mycorrhization rate,plant growth and mycorrhizosphere physiology and bacterial communities of T.indicum and T.huidongense colonized with P.armandii and C.mollissima were compared under different N and Ca concentrations.The results showed that colonization rate of two Tuber species on the two host plants were significantly different.N concentration had no significant effect on the colonization rate of both Tuber species colonized with P.armandii,but had significant effect on T.huidongense colonized with C.mollissima.The higher concentration of Ca positively affect the colonization rate of T.indicum with P.armandii,while had negative effect on the colonization rate of T.huidongense.This study also found that under N and Ca application,most of the Top 20 abundant bacteria,especially A.cerinus,in the mycorrhizosphere were significantly correlated with mycorrhization rate.Finally,the plant physiological,mycorrhizosphere bacterial communities and root metabolites of P.armandii mycorrhizal seedlings colonized by T.indicum were analyzed under different substrate water capacity.The results showed that T.indicum colonization significantly reduced malondialdehyde content under severe water stress and increased proline content under moderate stress.In addition,there were no significant differences in mycorrhizosphere bacterial diversity and the community structure.However,T.indicum colonization significantly affected the root metabolites under different degrees of drought stress.The results indicated that Tuber colonization could stabilize the mycorrhizosphere bacterial community structure,via promote the metabolism of amino acids and sugars to obtain a large number of osmotic regulatory compounds to resist the damage from drought stress.The results obtained in this study can provide reference for the morphological study of Tuber mycorrhizae,give more host selection for the cultivation of truffle,and provide a new idea for the efficient cultivation of mycorrhizal seedlings.In addition,it can also provide theoretical support for the application of Tuber mycorrhizal seedlings in the ecological restoration of arid and rocky desertification areas.