| Global warming is an unquestionable fact and global climate change has become one of the major concerns for many scientists,policy-makers and communities.Under the future global warming background,permafrost is in a wide range of degradation.The upper reaches of the Heihe located in the Qilian Mountains area on the northwest region of the Qinghai-Tibet Plateau is an important ecological barrier in northwestern China.The widely developed permafrost and the extremely fragile alpine meadow ecosystem was highly sensitive to climate change and more susceptible to global warming.This study selected three different growth environments i.e.,elevation gradients,simulated warming experiments and thaw slump gradients.Kobresia pygmaea was used as the research object.The physiological characteristics of the K.pygmaea leaves including malondialdehyde(MDA),proline(Pro),Superoxide dismutase(SOD),peroxidase(POD),chlorophyll(Chl),etc.,were examined to revale the response,regulation and adaptation of physiological characteristics of K.pygmaea to environmental changes.This study is of great significance to reveal the physiological mechanism and strategy of K.pygmaea adapting to different growth environments and even global climate change.The main research conclusions are as follows:(1)With the increase of altitude,the degree of environmental stress increased,the content of MDA in the membrane lipid peroxidation products increased.In addition,the content of Pro increased,suggesting that the ability of K.pygmaea to resist low temperature stress increased.In the lower altitude area,the activity of SOD increased,the ability of active oxygen scavenging increased.In contrast,with the increase of altitude,the activity of SOD and POD decreased,and the resistance of K.pygmaea decreased with the increase of altitude.Chla,Chlb,and total chlorophyll content decreased,indicating photosynthesis decreased.With the changes in the growing season,under the influence of the decrease of the temperature and the natural aging of the vegetation,the MDA content in the leaves of K.pygmaea increased gradually.The Pro content decreased firstly and then increased,and the ability of regulating the permeability increased.In the end of the growing season,K.pygmaea aged seriously,the accumulation of active oxygen,the activity of SOD and POD increased gradually,and the ability of scavenging the active oxygen increased.The low temperature inhibited the synthesis of chlorophyll.The results showed that Chla,chlb,total chlorophyll content and photosynthetic capacity decreased.It was found that the change of water and heat conditions increased environmental stress of K.pygmaea.Temperature is the most important environmental factor that affects the change of its physiological characteristics.The aging of plants is also an important reason that affects the physiological characteristics of K.pygmaea.(2)The results showed that the MDA content of Kobresia in the warming plots was significantly lower than that of the control area,indicating the increase of temperature alleviated the stress of low temperature environment on K.pygmaea.At the same time,the increase of temperature also alleviated the water demand of Kobresia.The content of Pro decreased,and the ability of osmotic regulation decreased.Meanwhile,the increase of POD and SOD activity enhanced the ability of K.pygmaea to remove active oxygen.The results showed that the increase of temperature could alleviate the stress of environmental factors,promote the synthesis of chlorophyll and promote the growth of vegetation.With the change of the growing season,the MDA content of K.pygmaea leaves gradually increased,and the important reason for the increase of MDA content can be explained as the plant aging.The Pro content gradually decreased,and the osmotic adjustment ability weakened.There was no significant change in SOD activity during the process of plant aging,but the POD activity was not consistent,with an overall trend of decreasing,which indicated that SOD was still the main enzyme for scavenging active oxygen.The Chla,chlb,and total leaves in K.pygmaea is different.There are two trends of increasing firstly and then decreasing gradually.In the process of growing season,plant senescence may destroy the chlorophyll.The increase of temperature alleviated the low temperature stress under natural conditions,increased the surface temperature and soil temperature,and reduced the soil humidity.Among them,temperature is the most important environmental factor that affects the change of physiological characteristics.(3)After the permafrost collapse,the soil water and heat conditions changed,which increased the MDA content in the leaves of K.pygmaea in the collapse area,indicating that the collapse process lead to the environmental stress and the degree of membrane lipid peroxidation increased.In the slumping area,the soil water decreased,the content of Pro increased,and the concentration of cell fluid increased,the normal osmotic pressure was maintained.The activities of POD and SOD increased,the ability of K.pygmaea to scavenge the active oxygen was enhanced,and the occurrence of thermal collapse did not exceed the ability of K.pygmaea antioxidant enzyme system among environment stressors.The concentration of chlorophyll increased,the ability of photosynthesis was enhanced in the slumped areas,and these changes favor the vegetation growth.The MDA content of K.pygmaea leaves increased first and then decreased along with growing season.The soil water content increased first and then decreased,while the Pro content decreased first and then increased,indicating that the Pro content is closely related to the soil water.The SOD activity has no significant change,while the POD activity gradually decreased,indicating that the temperature decreased.In the process of plant senescence,the scavenging of active oxygen still plays the leading role of SOD,while the role of pod is gradually reduced,except for some cases.Chla,Chlb and Chlt content showed similar trends,which are the trend of increasing first and then decreasing.The results show that the change of physiological characteristics of K.pygmaea is mainly caused by the change of soil water and heat conditions caused by the thermakarst process of permafrost,temperature and soil moisture are the main environmental factors that affect the physiological characteristics of K.pygmaea.Taken together,this study shows that the effects of different environmental factors on the physiological characteristics of K.pygmaea.Temperature and soil water jointly affect the growth and development of K.pygmaea,which is a complex process.The growth of K.pygmaea is limited by low temperature in the high altitude area,and the effect of environmental stress on K.pygmaea is alleviated under the condition of increasing temperature.However,in the process of thermokarst,the soil water content decreases during the process of collapse,the water content increases after the formation of collapse landform,which is beneficial to the plant growth.From the change of vegetation physiological indices,the temperature rise caused by climate warming will be conducive to the growth of K.pygmaea in the future. |
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