Study On Physiological Characteristics Of Cold Resistance Of Kobresia Pygmaea In Qilian Mountains

Low temperature is one of the main limiting factors for plant growth in alpine regions.The unique plateau climate of the Qinghai-Tibet Plateau makes plants often suffer from sub-zero temperature and frost during the growth period,which seriously affects the quality and production of forage.Under the influence of low temperature,plants will undergo a series of physiological and biochemical reactions,which are mainly manifested in changes in cell membrane permeability,antioxidant enzyme activity,and osmotic adjustment substance content.Kobresia pygmaea is a high-quality forage grass with the widest distribution,largest area and higher feeding value in the alpine meadow of the Qinghai-Tibet Plateau.It has extremely high cold resistance.After long-term natural selection and genetic variation,Kobresia pygmaea has formed a physiological metabolic mechanism suitable for alpine environments.Therefore,studying the physiological characteristics of different organs during the growth season of Kobresia pygmaea under the change of altitude gradient and the cold resistance differences of different organs in different growth seasons under low temperature stress will help to understand the environmental adaptability of alpine plants and reveal their physiological mechanisms of cold resistance,and provide a reference for the improvement and domestication of alpine plants.In this study,Kobresia pygmaea in the Heihe River Basin of Qilian Mountains was used as the research object.By measuring the contents of malondialdehyde,soluble sugar,free proline,superoxide dismutase,peroxidase and catalase activity in the leaves and roots of Kobresia pygmaea in different growth seasons in the in-situ experiment(altitude3700m-4100m)and the control experiment(low temperature stress treatment),it is possible to systematically explore the osmotic adjustment substances and antioxidant system responses of Kobresia pygmaea in low temperature environments,and aim to clarify the physiological characteristics of Kobresia alpine meadow under the influence of low temperature and to explore the influencing factors of the plant defense stress mechanism,which can provide a clearer understanding on the physiological adaptation of Kobresia under the extreme environmental conditions of the Qinghai-Tibet Plateau.So as to improve the stress resistance of plants,cultivate low-temperature-tolerant alpine meadow varieties,and provide a reference for improving the quality of forage.The main findings are as follows:(1)The increase in altitude causes changes in plant habitats,resulting in changes in plant biomass.However,the above-ground and underground biomass of Kobresia pygmaea does not have a certain regularity with the increase in altitude.The above-ground biomass shows a downward trend as the phenological period changes,while the underground biomass shows an overall upward trend.It shows that significant changes in water and heat conditions have a greater impact on plant growth in alpine regions,and changes in niche changes with altitude have less impact on Kobresia pygmaea with strong environmental adaptability.(2)In in-situ experiments,the content of malondialdehyde in the leaves and roots of Kobresia pygmaea was greatly affected by the degree of plant development.The content of malondialdehyde in the leaves of Kobresia pygmaea showed an increasing trend with the growth and development of plants,while the content of malondialdehyde in the roots was higher in the early stages of plant development.Similarly,the free proline content in the leaves and roots of Kobresia pygmaea is also affected by the phenological period.The free proline content in the leaves reached the highest in the turning green stage,and the free proline content in the leaves was also significantly affected by the altitude.As the altitude increases,the free proline content in leaves of different phenological stages increased.The free proline content in roots increased to a certain extent in the later stages of plant development.The change of soluble sugar in leaves showed an obvious increasing trend with the change of phenological period and altitude,and the overall content of soluble sugar in roots was also higher in the decay period.It can be seen that plants are more susceptible to environmental stress in the later stages of development,which increases the content of malondialdehyde in the body.At the same time,the increase in free proline and soluble sugar alleviates the damage caused by the increase in malondialdehyde.Altitude and phenological changes have significant effects on the changes of enzyme activities in Kobresia pygmaea,and the changes of the three enzyme activities of Kobresia pygmaea are inconsistent,and changes with altitude do not have a certain regularity.The activity of superoxide dismutase in leaves is stronger in different phenological stages,while the enzyme activity in roots is stronger in the late green and withered stages.The peroxidase activity in the leaves of Kobresia pygmaea was significantly higher than that in the roots,and the enzyme activity in the leaves showed an overall downward trend with the change of phenological phase.The catalase activity in roots was significantly stronger than that in leaves in the late grass stage.It shows that different enzyme activities of different organs have different activation mechanisms when facing environmental stress,which may also be related to the synergistic effect of the three enzyme activities.(3)In the indoor control experiment,with the change of temperature,the expression of physiological indexes of Kobresia pygmaea under different phenological periods was different.The electrical conductivity changes as follows: the electrical conductivity of the leaves and roots showed an overall upward trend in June,the electrical conductivity changes more steadily with temperature changes in July and August,and the electrical conductivity of the leaves and roots decreased overall when the temperature decreased in September.It shows that the electrical conductivity of plants is affected by the degree of plant development.In the early stage of plant growth and development,plant bodies are more susceptible to temperature changes.The changes of osmotic adjustment substances are: the changes of malondialdehyde in Kobresia pygmaea leaves and roots in June showed an overall increasing trend with the decrease of temperature,July and August were relatively gentle,and the overall content of 0?in September was lower.The content of free proline in leaves and roots in June,July and August changed differently and fluctuated greatly.The content of free proline in leaves and roots in September showed an overall increasing trend with the decrease of temperature.The changes of soluble sugars in leaves and roots were similar to those of malondialdehyde content,both increased in June as the temperature decreased,and decreased in September as the temperature decreased.It shows that the changes of osmotic adjustment substances are affected by the phenological phase,and mature plants have stronger adaptability to the cold stress.The enzyme activity changes as follows: In June,the superoxide dismutase activity in Kobresia pygmaea roots fluctuates more than that of leaves.In July,the superoxide dismutase activity in leaves has a significant decrease,and in August,roots show a significant decline at different temperatures.The overall change trend of leaves and roots with the decrease of temperature in September is opposite.From June to August,the peroxidase activity in the leaves and roots of Kobresia pygmaea alternate with temperature changes.When the leaves change smoothly,the roots will fluctuate.However,in September,the peroxidase of leaves and roots fluctuated greatly at different temperatures.The catalase activity in leaves and roots fluctuates greatly at 4°C in June,and the enzyme activity in leaves and roots increases at 0°C in July and August.In September,the catalase activity in leaves and roots fluctuated significantly under different temperature gradients.It shows that the development degree of organs and organs affects changes in enzyme activity in the body,and thus exhibits different responses under different temperature stresses.(4)Correlation analysis of Kobresia pygmaea in in-situ experiments showed that the correlations of different physiological indicators are different,and they are affected by organs.Multivariate analysis of variance confirmed this point.Organs,phenological phases,organ-phenological phases,and the interaction of the three have significant effects on various physiological indicators.It shows that organs can actively respond to changes in the phenological phase,and the interaction between the two has a greater impact on the growth and development of plants than altitude.The correlation analysis of the physiological indexes of Kobresia pygmaea in the control experiment shows that there is a certain correlation between the same physiological index and different physiological indexes.Principal component analysis showed that malondialdehyde,proline and soluble sugar in roots,superoxide dismutase,peroxidase and catalase in leaves accounted for a higher proportion of the first principal component.Soluble sugar in leaves and peroxidase in roots accounted for a higher proportion of the second main component.The electrical conductance in the root occupies a higher proportion in the third principal component.It further shows that organs have a significant influence on changes in osmotic adjustment substances and enzyme activities.The combination of temperature and time with the highest comprehensive efficiency of various physiological factors of Kobresia pygmaea in leaves is 4? stress for 3h.The roots were stressed at 0? for 24 h.The comparison results of the cold resistance of Kobresia pygmaea in different phenological periods under different temperature stresses are: September>June>July>August.Therefore,the normal physiological metabolic development of plants in alpine regions has inconsistent responses at different time periods,which may be a manifestation of their adaptation to the alpine environment.(5)From the correlation analysis and clustering relationship heat map of environmental factors and physiological indicators,it can be seen that the soluble sugar,malondialdehyde in the osmotic adjustment substance and the peroxidase activity in the antioxidant system are mostly positively correlated with the physical and chemical properties of the soil and mostly negatively correlated with meteorological factors.The free proline in osmotic regulators and the activities of superoxide dismutase and catalase in the antioxidant system are mostly positively correlated with meteorological factors,and mostly negatively correlated with soil physical and chemical properties.Principal component analysis shows that soil moisture content,total nitrogen and p H have a greater impact on plant physiological indicators than other factors.It can be seen that different physiological indicators have different sensitivity to different environmental factors,and the osmotic adjustment substances and antioxidant systems in plants respond to changes in environmental factors together.In summary,the results of in-situ experiments and control experiments show that plant physiology is affected by changes in organs,phenological phases,and plant development,and the interaction of many environmental factors also has a significant impact on the physiology of Kobresia pygmaea.It shows that Kobresia pygmaea has strong adaptability in response to changes in growth conditions.The osmotic adjustment substances and antioxidant systems between organs can actively respond to environmental changes,coordinate the metabolic system in the plant,and ensure the normal development of the plant.The changes of physiological indicators respond to changes in different environmental factors.The sensitive physiological characteristics of plants in alpine regions may also be a physiological mechanism for their adaptation to the alpine environment.