| As the "third pole" of the Earth and a sensitive area for global climate change,the Qinghai-Tibet Plateau has a complex geography and extreme climatic environment,but also nurtures rich and special biological resources,and its biodiversity and response to global climate change are of global interest.The Androsace tapete Maxim.is the most representative cushion plant on the Qinghai-Tibet Plateau.To explore the mechanism of their adaptability to extreme environmental temperature,in order to provide data support and theoretical reference for the study of the adaptability of matted plants and even plateau plants.To reveal the adaptability of A.tapete from several aspects,surrounding "Does the mat structure of the A.tapete have a heat preservation effect? How do the microorganisms symbiotic with the A.tapete affect their adaptability? How do A.tapete in high altitude populations,which are more susceptible to extreme temperature stress,adapt to their environment through internal molecular regulation?" three scientific questions,starting from the three aspects of insulation effect of morphological structure,interaction with microorganisms and molecular regulation.The specific research content and results are in the following three sections.(1)In order to investigate the thermal insulation effect of the A.tapete and the factors that determine it,the temperature inside the living and dead individuals of the A.tapete was measured with a thermometer,and the diurnal variations of the surface,internal,nearby air and soil temperatures of the A.tapete were recorded with a temperature logger in summer and winter respectively.Analysis of the recorded temperature data revealed that there was no significant difference(P > 0.05)between the internal temperatures of surviving and dead individuals;during the diurnal temperature variation,the surface temperature of the A.tapete varied much more than the air temperature,while the internal temperature varied similarly to the soil temperature and much less than the air temperature;after the low temperature treatment simulating hailstorm,the surface temperature plummeted to 0°C,but the internal temperature was still maintained at 10°C or more.The results show that the thermal insulation of A.tapete is mainly due to its structural properties and is less influenced by altitude differences,its own metabolic activity and cold domestication.Its thermal insulation capacity is slightly weaker than that of the soil layer at 5 cm,which can significantly buffer the dramatic diurnal temperature difference on the plateau,effectively reduce the stress of high daytime temperatures in summer and low temperatures in winter or at night,and resist frostbite and mechanical damage caused by sudden hailstorms in the summer without cold domestication.(2)To investigate the diversity of culturable microorganisms between and phyllospheric and endophytic of A.tapete and the differences in microorganisms between individuals in different states of survival,and to obtain cold-tolerant cellulolytic strains among them.Bacteria,yeasts and filamentous fungi were isolated and purified from phyllospheric and intrafoliar of three different regions of A.tapete by pure culture method,and screened for cold-tolerant cellulolytic strains using CMC solid medium and CMC-Congo Red solid culture at 4°C and 15°C,respectively.The final results were 350 phyllospheric microorganisms,identified as 22 genera and49 species,with the dominant species being Penicillium sajarovii,and 274 endophytic microorganisms,identified as 19 genera and 45 species,with the dominant species being Bacillus mycoides;the dominant genus of both was Penicillium.There were 52 strains,14 genera and 32 species of coldresistant cellulolytic strains,including 3 species of bacteria,9 species of yeasts and 20 species of filamentous fungi.The relative cellulase activity of the cold-tolerant cellulolytic strains was high and was represented by Didymella pomorum,Aureobasidium pullulans,Penicillium goetzii and P.griseoroseum.The α-diversity of microorganisms was mostly not significantly different between phyllospheric and intrafoliar and between individuals in different states of existence,and there was overlap in membership between communities,but there was significant spatial heterogeneity in species composition.The results show that the phyllospheric and intrafoliar of the A.tapete are rich in culturable microbial resources,and the species composition of microorganisms from individuals in different survival states or different parts of the leaf varies greatly,but the relative cellulase activities of cold-tolerant cellulolytic strains do not differ significantly,and that the selection preferences of microorganisms for different environments result in different community patterns.A high proportion of shared strains also existed between microbial communities of different origins,and the heterotrophic mode and ecological niche of these shared strains were not fixed,and could survive both symbiotically and saprophytically,with no clear boundaries for survival space.These highly active cold-tolerant cellulolytic strains can effectively decompose litter in cushion structures,promote carbon cycling,and play an important role in the adaptation of A.tapete to extreme environments and perform the function of ecosystem engineers.(3)To investigate the adaptive mechanisms at the molecular level of A.tapete under different altitude environments,several A.tapete from three regions were selected as samples with an altitude gradient of about 500 m.Transcriptome sequencing and untargeted metabolome determination were performed to analyze the differentially expressed genes and differentially expressed metabolites.The results showed that with increasing altitude,there was a tendency for gene expression in both leaves and roots of A.tapete,with many differential genes and differential metabolites enriched.In leaves,pathways that were significantly enriched and consistently upregulated were MAPK signaling pathway-plant,cutin,suberine and wax biosynthesis,plant-hormone signal transduction,and plant-pathogen interaction.The pathways that were significantly enriched and consistently down-regulated were: plant-pathogen interaction and photosynthesis.In roots,the pathways that were significantly enriched and consistently upregulated were plant-pathogen interaction,and the pathways that were significantly enriched and consistently down-regulated were MAPK signaling pathway-plant and photosynthesis.In the metabolomic analysis,with increasing altitude,the differential metabolites were significantly enriched in the metabolic pathways of starch and sucrose in roots and in the propane biosynthetic pathway in leaves.The combined transcriptomic and metabolomic analyses showed that the Starch and sucrose metabolism pathway is a KEGG co-enrichment pathway for differentially metabolised and differentially expressed genes,and that A.tapete accumulates soluble sugars(alpha-D-Glucose 1,6-bisphosphate)by enhancing the metabolism of starch and sucrose to withstand the low temperatures at high altitudes.Various extreme environments such as the Qinghai-Tibet Plateau are an integrated effect on plants and plant adaptation to such environments is all-encompassing.In this study,the A.tapete showed adaptability to the highland environment in terms of morphological structure,microbial and molecular regulation.The insulation of its cushion structure provided a relatively mild environment for itself and its symbiotic microbes;its interstitial cellulose-degrading strains could effectively decompose litter in the cushion structure at low temperatures,releasing nutrients for the soil below and reducing the inhibition of its growth by litter accumulation;At higher altitudes,A.tapete enhances its stress tolerance by up-regulating the expression of a number of genes associated with abiotic stresses and regulating metabolites.The interconnectedness of the various aspects has enabled A.tapete to cope with the extreme environmental temperatures of the Qinghai-Tibet plateau and to survive as one of the highest altitude seed plants. |
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