The Photoprotective Mechanisms Of Mosses In Different Habitat Types In Jiuzhaigou Under Temperature And Drought Stress

The Jiuzhaigou National Nature Reserve（hereinafter referred to as"Jiuzhaigou Reserve"）is located on the edge of the Qinghai-Tibet Plateau and is an important area for the protection of biodiversity.Bryophytes,as an important component of the ecosystem,plays an important role in maintaining ecosystem functions.Under natural conditions,moss plants are often subjected to rapid changes in light intensity.When the light intensity decreases,the photosynthetic rate of plants decreases rapidly,but the photosynthetic apparatus generally does not suffer damage;when the light intensity suddenly increases,the light-harvesting antenna absorbs a large amount of energy that cannot be consumed in time,and the excess excitation energy can easily cause damage to photosystem Ⅰ and photosystem Ⅱ,thereby affecting photosynthetic rate and growth and development.High temperature causes serious damage to PSI and PSⅡ,which cannot be quickly repaired in a short period of time,thereby inhibiting the linear electron（LEF）and cyclic electron（CEF）pathways.In a low-temperature environment,moss plants absorb and transfer excess light energy,generating a large amount of reactive oxygen species,which causes oxidative damage to the D1 protein of the PSⅡ reaction center and reduces the photochemical efficiency.Under drought stress,the electron balance between the receptor side and the donor side of PSⅡ is disturbed,which reduces the photochemical activity and electron transfer capacity of Photosystem Ⅱ.Mosses have experienced stress from high light,high/low temperature,and drought,and the FLV electron transfer mediated by flavodiiron protein（Flvs）and cyclic electron flow（CEF）around photosystem Ⅰ play an important role in the moss response to abiotic stress.This study investigated the moss plant resources in Jiuzhaigou Nature Reserve,and selected three species of mosses from different growth environments,namely Racomitrium japonicum,Hypnum plumaeforme,and Plagiomnium ellipticum.The study explored the photosynthetic physiological response mechanisms of the three mosses to fluctuating light intensity under high/low temperature and drought stress,providing new insights into the response strategies and abilities of moss plants to environmental stress.At the same time,it also provided a reference for the ecological restoration of bare rock slopes in Jiuzhaigou using moss plants.The main research results are as follows:（1）There are 211 species（including varieties）of moss plants belonging to 90 genera and 38 families in the Jiuzhaigou Reserve,with 7 dominant families.The floristic-geographical components of mosses in Jiuzhaigou are diverse and complex,with 10types in total,mainly distributed in East Asia,followed by the North Temperate Zone.The main habitats of moss plants are dead plants and epiphytes,and the main substrate types are humus,tree epiphytes,rock epiphytes,soil,and decaying plants.Through the comparison of floristic components and species composition,the similarity of moss plants in Jiuzhaigou to Gongga Mountain and Wanglang is high in terms of species similarity and floristic components,with the highest similarity coefficient to Gongga Mountain and close to Wanglang in floristic components.（2）The experimental results of three different habitat types of moss plants at different temperatures show that under high-temperature fluctuating light conditions,the FLV electron flow and CEF play an important role in light protection.Under low-temperature conditions,CEF is enhanced to compensate for the stopped FLV electron flow.Under fluctuating light and temperature stress,there is a synergistic relationship between FLV activity and CEF.Sun-loving mosses,Racomitrium japonicum and Hypnum plumaeforme,show high CEF,while shade-loving moss,Plagiomnium ellipticum,exhibits higher FLV activity.（3）Under dehydration conditions at 38℃,the PSⅡ of moss plants was severely damaged,mainly due to the deactivation of non-photochemical quenching（NPQ）.Dehydration also led to a large accumulation of O₂^-and H₂O₂.Racomitrium japonicum showed higher CEF and a positive correlation between CEF and FLV,indicating that CEF played a more important protective role in Racomitrium japonicum.The FLV is sensitive to environmental fluctuations and less stable than CEF,making it more likely to be lost during the colonization and evolution of seed plants on land.Based on the survey of moss resources in the Jiuzhaigou Reserve,this paper explores the photosynthetic response mechanisms of three different mosses to fluctuating light intensity under the stress of two environmental factors,temperature and drought.It was found that the cyclic electron transfer of Racomitrium japonicum was highly stimulated under high temperature,much higher than that of Hypnum plumaeforme and Plagiomnium ellipticum;the FLV of Plagiomnium ellipticum was highly stimulated under high temperature stress,but lost activity under high temperature-drought compound stress.