Comparative Study On The Difference Of Mycorrhizal Fungi Between Terrestrial And Epiphytic Orchids

Orchidaceae is the second largest family in the plant kingdom.Its species are widely distributed in a variety of terrestrial ecosystems except for a few extreme environments in the world,and have strong ecological adaptability.According to their growth habits,orchids can be divided into terrestrial orchids,epiphytic orchids and lithophytic orchids.Under natural conditions,most orchid seeds depend on mycorrhizal fungi for nutrients to germinate,which affects the distribution and growth of orchids.Studies have shown that there are obvious ecological barriers between the mycorrhizal groups of different terrestrial orchids and epiphytic orchids,but there are few studies on the correlation between mycorrhizal fungi and the ecological adaptability of terrestrial orchids and epiphytic orchids.This study intends to compare the extracellular enzyme activity and optimal carbon and nitrogen sources of mycorrhizal fungi in terrestrial orchids and epiphytic orchids,trying to explain the ecological adaptability of mycorrhizal fungi to orchid plants from the perspective of fungal biology.And provide reference for the protection of orchid resources and the ecological restoration of endangered populations.The main conclusions of this paper are as follows:Using Illumina Miseq high-throughput sequencing to compare the mycorrhizal fungal community composition of 30 terrestrial and epiphytic and lithophytic Lparis spp.from Yunnan and Guangxi provinces,it was found that the fungi of the family Inocybaceae are the main groups of two life-forms of the Lparis spp..Data analysis shows that there is a significant difference in the composition of mycorrhizal fungal community between terrestrial and epiphytic and lithophytic Lparis spp.,indicating that ecological factors are the main factors that cause differences in the composition of fungal communities.Mycorrhizal fungi were isolated from 25 species of terrestrial orchids and 38 species of epiphytic orchids collected in Yunnan,Hainan,and Guangxi using the single hyphae and tissue mass separation method,and successfully separated from 8 species of terrestrial orchids and 18 species of epiphytic orchids.22 strains of Tulasnellaceae,4 strains of Ceratobasidiaceae and 3 strains of Serendipitaceae were isolated.The phylogenetic analysis showed that the isolated fungi of the Tulasnellaceae are scattered in different evolutionary branches and have a high diversity,which provides a source of strains for subsequent research on mycorrhizal biology.The activity of 5 extracellular enzymes of a total of 24 strains of terrestrial and epiphytic Tulasnellaceae fungi were determined,which are cellulase,xylanase,lignin peroxidase,laccase and superoxide dismutase.The results showed that the cellulase and xylanase activities of terrestrial OMF were significantly higher than those of epiphytic.OMF;meanwhile the cellulase activity of epiphytic OMF reached the highest value of enzyme activity faster,and at the same time,the rate of decline was also faster,which is related to the characteristics of two kinds of ecological environment and the seed germination characteristics of orchids.In addition,the activity of lignin peroxidase in epiphytic OMF is higher than that of terrestrial OMF,suggesting that epiphytic OMF has a stronger ability to degrade lignin.However,we found that the comparative analysis of laccase activity of the terrestrial and epiphytic OMF is extremely low,because Tulasnellaceae fungi may not have the ability to secrete laccase.In the analysis of superoxide dismutase activity,we found that the activity of epiphytic OMF superoxide dismutase was significantly higher OMF from the terrestrial suggests that epiphytic OMF is more resistant to active oxygen stress and can better adapt to the epiphytic environment.A comparative analysis of the most suitable carbon source for the fungi of the terrestrial and epiphytic OMF found that the ability of terrestrial OMF to utilize carboxymethyl cellulose is stronger than that of epiphytic OMF,while the ability of epiphytic OMF to utilize starch is significantly stronger than the terrestrial OMF.For terrestrial OMF,this result is consistent with the results of extracellular enzyme activity,indicating that terrestrial OMF has a stronger ability to degrade and utilize cellulose;Under natural conditions,the content of degradable cellulose in the living environment of epiphytic OMF is significantly lower than that of terrestrial OMF.Fungi obtain carbon source mainly through symbiosis with orchid plants to obtain plant photosynthetic products.Therefore,the corresponding epiphytic OMF has a stronger ability to utilize starch than the terrestrial OMF.This result shows that fungi's preference for carbon sources is closely related to fungi's survival mode.In the comparative study of the most suitable nitrogen source,it was found that the terrestrial and epiphytic OMF only had a significant difference in their ability to absorb and assimilate arginine.The epiphytic OMF has a stronger ability to use arginine as a nitrogen source.Previous studies have shown that arginine,as the most important form of nitrogen transportation and storage in the interaction between mycorrhizal fungi and plants,plays an important role in the symbiosis process.The results implied that epiphytic OMF has a strong nitrogen supply potential for plants,indicating that the preference of terrestrial orchids and epiphytic fungi for nitrogen sources is mainly related to the selectivity of host plants.The results herein show that terrestrial and epiphytic OMF with a significant difference in the extracellular enzyme activity and the use of carbon and nitrogen sources.Implicitly there are some differences between the terrestrial and epiphytic OMF.These differences can be explained by combining the two distinct environmental characteristics of terrestrial growth and epiphysis.Made a preliminary demonstration for the mycorrhizal fungi can improve the ecological adaptability of orchid plants.It is still necessary to further improve the research on the impact of mycorrhizal fungi on the ecological adaptability of orchids,including the exploration of the mechanism of fungi to improve plant resistance and the comparison of the interaction between orchids and fungi in a wider area.This will provide great help to the protection of orchid resources and the development and utilization of biological inoculants in the future.