Effects Of Seasons And Storage Conditions On The Physiological Characteristics And Vegetative Propagation Of Desiccation-tolerant Mosses

Biocrusts are widely distributed in arid and semiarid ecosystems and play important roles in soil surface stabilization,soil fertility enhancement,and soil hydrology regulation.As later successional biocrusts,the moss crust has enormous potential for ecological restoration.Thus,researchers have artificially cultured moss biocrusts in the laboratory.Vegetative propagation is a dominating reproduction mode of bryophytes in dryhabitats,so that fragments of moss gametophyte often are used for inoculum of moss crust.However,lack of knowledge regarding relation between physiological characteristics and vegetative propagation of mosses hinder artificial cultivation of moss crust.To reveal the influences of seasons and storage conditions on the physiological characteristics and vegetative propagation of vegetative propagule of moss(fragment),three desiccation-tolerant mosses,Barbula unguiculata,Didymodon vinealis,and Didymodon tectorum,which are the dominant desiccation-tolerant mosses in moss crust in the Loess Plateau semiarid region,were investigated in the paper.We study effects of seasons(before rain season,rain season and after rain season),storing environment and storage time on physiological indices(the contents of chlorophyll,soluble sugar,soluble protein and MDA,MDA is abbreviation of malondialdehyde)and germination parameters(gametophyte germination percentage,gametophyte increment,gametophyte germination index and gametophyte vigor index).Based on the results,we analyze the relation between physiological indices and germination parameters,and then reveal the mechanism of influences of seasons and storage conditions on the vegetative propagation of desiccation-tolerant mosses.These conclusions can provide theoretical support for artificially culturing moss biocrusts,which are as follow:(1)Effects of seasonal variation on the physiological characteristics and vegetative propagation of desiccation-tolerant mosses are significant and the degree to which season effects mosses relate to species.The capacity of vegetative propagation both of B.unguiculata and D.tectorum is higher before rain seasonand after rain seasonthan in rain season.No significant differences in four germination parameters of D.vinealis are found among the three seasons.The MDA contents of B.unguiculata and D.tectorum in rain season are significantly lower than before rain season and after rain season.The contents of chlorophyll,soluble sugarand soluble protein of the two species are significantly higher in the season than other seasons,meanwhile the vigor index of both of the two species is significantly lower than other seasons.There is only a physiological index,MDA content,have significant correlation with germination parameters(the increment and vigor index).(2)Effects of storage temperature on the physiological characteristics and vegetative propagation of desiccation-tolerant mosses are significant.After storage at 0?,4?,17?,25? and 30?,the capacity of vegetative propagation of each of the three mosses increase and decrease thereafter when storage temperature increasing from 0 to 30?.The maximum value of the vigor index of B.unguiculatais shown at 4?,and the maximum values of D.vinealis and D.tectorum are shown at 17?.The MDA contents of desiccation-tolerant mosses decrease with increasing temperature from 0 to 17?,accompanied by an increase in soluble sugar content as well as the vigor index and chlorophyll content.The MDA content increase when storage temperature is more than 17?,meanwhile the vigor index and the contents of chlorophyll and soluble sugar decrease.The vigor index of B.unguiculata after storage is decreased by 18.81% at 4?.The vigor index of both of D.vinealis and D.tectorum after storage is decreased by 32.86% and increase by 57.32% at 17?,respectively.(3)Effects of storage light intensity on the physiological characteristics and vegetative propagation of desiccation-tolerant mosses are significant and the degree to which light intensity effects mosses relate to species.After storage at 0Lux,20 Lux and 4000 Lux,the vigor index of both of B.unguiculata and D.vinealis after storage show maximum value at 4000 Lux.The maximum value of the vigor index of D.tectorum after storage is shown in the shade.The contents of chlorophyll,soluble sugar and soluble protein of desiccation-tolerant mosses decrease with increasing light intensity.The vigor index of B.unguiculata after storage is decreased by 12.12% at 4000 Lux.The vigor index of D.vinealis after storage is decreased by 22.37% at 4000 Lux.The vigor index of D.tectorum after storage is increase by 8.28% at 0 Lux.(4)Changes of the physiological indices and germination parameters of desiccation-tolerant mosses relate to storage time.The variation trends of the physiological indices and germination parameters with storage time are similar among the three moss species.After 0,40,89,127 and 197 days of storage,the chlorophyll contents of desiccation-tolerant mosses decrease with storage time increasing,meanwhile their contents of soluble sugar and MDA increase.The capacity of vegetative propagation of each of the three mosses decrease when storage times increasing.After storage 197 day,the vigor index of B.unguiculata,D.vinealis and D.tectorum is 4.26%,57.83% and 86.70%,respectively.(5)The physiological characteristics of desiccation-tolerant mosses relate closely to their vegetative propagation.Different reponse of the physiological characteristics of desiccation-tolerant mosses to seasons and storage conditions cause changes of the capacity of vegetative propagation after rehydration.Oxidative injury ofmoss cell increase with increasing storage time,meanwhile storage temperature and light intensity also can affect oxidation levels and permeability of moss cell membrane.These physiological changes cause different capacity of vegetative propagation after storage.The physiological characteristics of desiccation-tolerant mosses vary seasons,and possible change reponses of mosses to oxidative stress.Thus,same storage conditions caused different results of moss regeneration in different seasons.The capacity of vegetative propagation of desiccation-tolerant mosses is the highest at 4? or 17? before rain season and after rain season,and the maximum is shown at 0? in rain season.