| Research background and purpose:Lamiophlomis rotata(Benth.)Kudo is an important medicinal resource plant distributed in the alpine grassland of the Qinghai-Tibet Plateau.In recent years,the growing demand for medicinal materials and the growing of grassland degradation have led to the reduction of L.rotata's wild medicinal resources.To achieve the sustainable use of L.rotata resources,the impact of grassland degradation on L.rotata population and the response pattern of this plant to the alpine grassland degradation require in-depth study.This study compares the population ecology,plant physiology and morphological structure of L.rotata in grass with different degrees of degradation,with a view to explaining the growth strategy of L.rotata to degraded grasslands.Then scientific basis can be provided to the wild tending and artificial large-scale planting of L.rotata and promote the sustainable use of L.rotata medical resources.At the same time,it can provide a reference for the ecological adaptability research of other wild medicinal plants in plateaus.Materials and Methods:The research area is located in Ruokehe Ranch of Aba County,Aba Tibetan and Qiang Autonomous Prefecture,Sichuan Province.The survey area was divided into mildly degraded grassland,moderately degraded grassland,and extremely degraded grassland according to the four-level classification criteria for grassland degradation.We statistically measure the number of L.rotata,the plant leaf spread(length and width),and number of L.rotata in the breeding period(flowering)in the different degraded plots.SPSS19.0 statistical software was used to analyze the above indicators,compare the differences of L.rotata population characteristics in different degraded grasslands,and analyze the L.rotata population distribution rule and reproduction strategy based on the results.L.rotata of similar size were selected from different degraded grasslands and the leaves were collected and stored in FAA fixative.Transverse sections of leaves and leaf epidermal cell mounts used for microscopic observation were made by hand-held slicing method.The leaf thickness,epidermal cells,cuticle thickness,palisade tissue arrangement,and palisade tissue / sponge tissue values of grassland with different degrees of degradation were observed and compared using leaf cross sections to calculate leaf compactness(CTR)and leaf looseness(SR).Leaf epidermal cells were used to observe and compare the stomatal density and glandular scale density of different degraded grasslands,and the stomatal index was calculated.The differences of leaf micro-structures in different degraded grasslands were compared,and the adaptive strategies of L.rotata's morphology and structure under grassland degraded background were analyzed.For the determination of physiological indicators of leaves,L.rotata of similar size were selected from different degraded grasslands and the leaves were collected and stored in Liquid nitrogen tank.Then take it back to the laboratory and store in the refrigerator at-80 ?.Ultraviolet spectrophotometry was used to determine the content of physiological and biochemical indexes of leaf stress resistance,including superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),malondialdehyde(MDA),candied Seven determination indexes of lysine(Pro),soluble sugar(SS)and soluble protein(SP).The fuzzy membership function method was used to evaluate the unique resistance of grassland with different degrees of degradation.Analyze physiological adaptation strategies of L.rotata in the context of grassland degradation.Results:1.According to the statistics of L.rotata in the different habitats,the plant density of the moderately degraded grassland is significantly higher than that of the mildly degraded grassland and the extremely degraded grassland;the proportion of flowering plants in the mildly degraded grassland is significantly higher than that in the other grades.The plant spread of the mildly degraded grassland is significantly greater than that of the moderately degraded grassland and the extremely degraded grassland.The standard deviation of the spread of L.rotata in extremely degraded grassland is large,and from our field observation,some large plants were scattered on the bare land,and their spread is even greater than that in the mildly degraded grassland.2.With the increase in the degree of degradation,the thickness of the leaves of L.rotata gradually decreases as well as the thickness of stratum corneum increases,the morphology of upper epidermal cells tends to b e regular,and the arrangement tends to be neat and tight.The amount of phosphorus in the same field of view increases,and the pores are mostly infinite or unequal types.The leaf thickness and thickness of stratum corneum on upper epidermis of the mildly degraded grassland have significant differences to those samples from the moderately degraded grassland and the extremely degraded grassland(P<0.05).The density of glandular phosphorus in all the different habitats is significantly different(P<0.05)and increases with the aggravation of degradation.The stomata index of leaves from the extremely degraded grassland is the highest.The palisade tissue of leaves in the mildly degraded grassland is obviously irregularly curved,arranged loosely with obvious cell space.The palisade tissue of leaves in the moderately degraded grassland and the extremely degraded grassland is arranged regularly,and the cells are organized in 2 to 3 columns,forming a regular strip.The samples taken from the extremely degraded grassland are slightly thicker than those from the moderately degraded grassland.3.Among the seven physiological indicators,the contents of SOD and POD in the three habitats were significantly different(P<0.01),the MDA,Pro and SS contents in the samples from the moderately degraded grassland were significantly different from those from the mildly degraded grassland and the extremely degraded grassland(P<0.01).There is no significant difference between CAT and SP content.A certain correlation existed between the stress resistance indexes in the leaves of L.rotata.A significant positive correlation existed between the SOD and POD,and between the SOD and MDA content.There is no significant difference between CAT and SP content.The correlations between the Pro and SS,and the SP and SS are negative.Calculated by fuzzy membership function method,L.rotata of the moderately degraded grassland showed the strongest resistance,followed by the mildly degraded grassland,and the extremely degraded grassland was the smallest.Conclusions:1.L.rotata does not have a competitive advantage due to plant height or population size in slightly degraded grassland,and does not become a dominant plant;In response to the degradation of alpine grassland on the Qinghai-Tibet Plateau,the L.rotata population and biomass distribution in the underground parts have increased,enhancement of content of physiological indexes(SOD?POD?CAT)and enhanced structure resistance,etc.,indicating adaption to the moderately stressed habitats;In extremely degraded habitats,the population is significantly reduced,which is related to the extreme instability of the microenvironment,that is caused by habitat degradation,and seriously affects the maturity of the seeds and the formation of seedlings.2.Morphologically,the developed root system,thicker cuticle,increasing stomatal density and number of glandular scales,more closely arranged epidermal cells,and palisade organization are all L.rotata morphological and structural responses to degraded grassland.3.Physiologically,the protective enzyme system is a L.rotata adaptation strategy for degraded grasslands;and from the perspective that the three degraded grasslands have not accumulated a large amount of Pro,it fully shows that L.rotata has physiologically produced adaptability to degraded grasslands.4.This study can provide a reference for breeding and ecological planting of L.rotata,suggests that in the nursery stage,the moderately degraded grassland should be chosen for ecological breeding to enhance the survival rate of seedlings.While after large-scale planting,reasonable community interventions should be used to simulate the P.fruticose + F.rubra community which is the mildly degraded grassland to increase the yield of medicinal materials. |
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