| Northwest Sichuan is located on the southeastern edge of the Qinghai-Tibet Plateau and the northern section of the Hengduan Mountains.The region is rich in natural plateau wetlands.It is a very important water conservation area for the upper reaches of the Yellow River and the Yangtze River.It is known as the"Chinese National Water Tower"and its ecological location is extremely important.The hazards and impacts caused by land desertification are relatively serious and have aroused widespread concern in the whole society.The results of the"China Desertification and Desertification Status Bulletin"published in 2011 show that my country’s land desertification and desertification have been initially curbed,but the desertification and desertification of local areas such as the lower reaches of the Tarim River and northwest Sichuan are still expanding.The desertified land in Northwest Sichuan alone amounts to 822,000 hm~2,and this area is also home to ethnic minorities such as Tibetans.The desertification has affected the development of people’s livelihoods,livelihoods,and ecological security in this area.According to the impact of non-biological disasters and the actual situation of desertification and degradation,the main non-biological disaster factors affecting the alpine region of northwest Sichuan are:geological conditions,climatic factors and man-made causes.Among them,climatic factors are the main factors of land desertification,which are mainly reflected in the aspects of low temperature,strong sunshine and drought,which in turn result in poor site conditions,short plant growth periods,difficult vegetation restoration,and poor community structure stability.In view of the impact of non-biological disasters on desertified land,it is urgent to increase the protection of desertified ecosystems and forest resources,screen out a large number of sand-suitable shrubs,and provide the basis for desertified land prevention and control materials,and solve forestry production and ecological environmental protection.Technical difficulties caused by biological disasters.Based on the analysis of the fourth desertification monitoring data,this paper selects five typical counties,namely Ruoergai County,Aba County,Seda County,Litang County,and Daocheng County,which can represent the desertification control plant resources in Northwest Sichuan,as the core areas of this study.Line(square)method is used to investigate vegetation,find out suitable shrubs on sandy land,and select Salix cupularis(commonly known as"alpine willow")and Kangding willow(Salix paraplesia)according to the distribution width,niche width and suitability evaluation.Five shrubs including,Salix linearistipularis,Sibiraea angustata and Hippophae rhamnoides were used as test materials to carry out research on breeding techniques,drought stress control experiments on physiological and biochemical indicators,and transcriptome molecules.The main findings are as follows:(1)With the aggravation of desertification,the number of plant species in five counties decreased significantly.Among them,Litang County reduced from 20 species to 4species,a decrease of 80%.At the same time,the investigation found that there were significant differences in the dominant species of aboveground herbs in different desertification types.The dominant species in open sand were Kobresia alpina,Dendranthema parvifolium,Elymus nutans,etc.,the dominant species in fixed sand were Potentilla anserina,Polygonum nepalensis,Artemisia ordosica,etc.,and the dominant species in semi fixed sand were Anaphalis flavescens,Dendranthema parvifolium,Polygonum nepalensis,etc.For shrub communities,from open sand to semi fixed sand,the dominant species were S.kaempferi,H.rhamnoides,S.angustata,etc.,accompanied by some shrubs such as Rosa roxburghii,Spiraea alpina,Caragana microphylla,etc.In addition,the analysis of plant diversity of different desertification types showed that:with the aggravation of desertification degree,the species richness index,diversity index and evenness index showed a gradually decreasing trend,and when the open sand land degenerated to semi fixed sand land,the four diversity index values decreased significantly.The species richness index of open sand land and fixed sand land in each county was greater than 2,which indicated that open sand land and fixed sand land were rich in species,and their evenness index was also significantly higher than that of semi fixed sand land.At the same time,through the species distribution breadth and niche width,it is found that most of the desertified land is dominated by herbs,so with the aggravation of the degree of desertification,many herbs are gradually succeeding,and the dominant species change greatly.Although there are not many shrub distribution types,it plays a crucial role in the stability of the whole community,and the niche width is H.rhamnoides<S.paraplesia<S.angustata<S.linearistipularis<S.cupularis.Through field investigation,the current situation of vegetation in sandy land was found out.According to the comprehensive evaluation of distribution breadth,niche breadth and adaptability,five shrubs with strong niche breadth performance and adaptability were selected as test materials for further breeding and physiological and biochemical research.(2)The cutting time,transplanting method and transplanting density of five shrubs,S.cupularis,S.paraplesia,S.linearistipularis,H.rhamnoides and S.angustata were studied.The results showed that the cutting survival rate of S.cupularis was the highest,that of H.rhamnoides was relatively low,and that of S.angustata was the lowest.According to the survival rate of transplanting seedlings of several sand control shrubs,the survival rates of S.cupularis,S.paraplesia and S.linearistipularis are much higher than those of H.rhamnoides and S.angustata in terms of transplanting time,mode and density,but there is no significant difference in the survival rate of the three willows.Generally speaking,compared with seabuckthorn and Sibiraea angustata,the survival rate of the three willows is higher than that of H.rhamnoides and S.angustata,which shows that the adaptability of willow is stronger,and it has certain promotion value in sand control.(3)The drought stress and drought resistance test of five sand fixing plants showed that there were differences in several indexes of five shrub species,i.e.S.cupularis,S.mandshurica,S.linearistipularis,H.rhamnoides and S.angustata,which indicated that the drought resistance of the five species showed diversity.Drought stress significantly reduced the water content of leaves,increased the cell membrane permeability,increased the activities of peroxidase(POD)and superoxide dismutase(SOD),and the contents of pro and MDA in leaves changed correspondingly,which indicated that the five shrubs had different drought resistance under drought stress.Comprehensive evaluation of drought resistance showed that the subordinate value of S.linearistipularis was 0.346 higher than that of other sand fixing plants,and S.angustata was the lowest after 5 days of water shortage;the subordinate value of H.rhamnoides was 0.544 higher than that of other sand fixing plants,and S.cupularis and S.paraplesia were close;on the 15th day under drought stress,the subordinate value of H.rhamnoides was 0.621 higher than that of other sand fixing materials,and the drought resistance of S.linearistipularis was improved,Under drought stress,the subordinate value of H.rhamnoides was significantly higher than that of other sand fixing materials.Finally,the membership mean of seabuckthorn was the largest and S.angustata was the smallest.According to the mean value of membership and the membership value of severe drought,the drought resistance of sand fixing plants was ranked as follows:H.rhamnoides>S.cupularis>S.paraplesia>S.linearistipularis>S.angustata.(4)The niche of H.rhamnoides,S.cupularis,S.paraplesia,S.linearistipularis and S.angustata in desertification control in Northwest Sichuan Province was evaluated by principal component analysis(PCA).In the final comprehensive score of 5 shrubs,the highest was H.rhamnoides and S.cupularis were similar,which were significantly higher than S.paraplesia,S.linearistipularis and S.angustata.Although H.rhamnoides has strong drought resistance,its niche width is narrow,and S.cupularis is not only higher than that of H.rhamnoides,but also higher in seedling survival rate.In addition,in recent years,a large number of scholars have carried out systematic research on H.rhamnoides,including physiology and biochemistry,transcriptome molecules,etc.,while the research on S.cupularis mainly focuses on morphology and physiology,while there are few reports on drought resistance genes of S.glauca.In addition,in recent years,S.cupularis has been widely promoted,and the effect of desertification control is obvious.Therefore,comparative transcription of S.cupularis is carried out Group study.After treated with distilled water(T1)and polyethylene glycol(PEG)stress(T2)for 15 days,65228 unigenes were constructed.Among them,16192 unigenes were>1 KB,accounting for 24.82%of the total unigenes library.The gene structure of Uni Gene database was analyzed,including ORF prediction,SSR Analysis and inter sample SNP analysis.Finally,6779 SSR markers were identified.At the same time,using RNA SEQ to compare the differential expression genes of T1 and T2,a total of 4289 genes were identified,including 2340 up-regulated genes and 1949 down-regulated genes.Go analysis divides genes into three categories:cell components,molecular functions and biological processes.Analysis of KEGG pathway enrichment of DEGs between T1 and T2 showed that the top 20 metabolic pathways of KEGG were mainly porphyrin and chlorophyll metabolism,photosynthesis,phenylpropanol biosynthesis of phenylalanine metabolism,mutual transformation of pentose and gluconate,and sugar chain degradation.These metabolic pathways can adapt to the changes of external environment through a series of hormone changes such as abscisic acid(ABA),auxin(IAA)and ethylene,and then resist the external drought conditions.At the same time,KEGG enrichment showed that chlorophyll metabolism and Photosynthesis and other metabolic pathways can significantly affect the drought resistance of plants.In order to further understand the chloroplast genome of five shrubs,through the analysis of published chloroplast genome,it was found that some scholars have sequenced the chloroplast genome of H.rhamnoides Therefore,the whole genome sequencing analysis was carried out.(5)Through the dynamic analysis of vegetation restoration process and physical properties of sandy soil before and after sandy land treatment,it was found that the plant species,coverage and density increased after ecological restoration in both fixed and semi fixed sandy land.The soil index of the restored sandy land is obviously better than that of the non restored sandy land.The soil sand decreased gradually,the soil particles and clay increased gradually,the soil water content also increased,and the soil structure tended to be stable.Through the comparison of different restoration measures of fixed sand,it can be seen that with the increase of restoration years,a series of physical properties such as soil bulk density,water content and total porosity have changed correspondingly.In addition,the soil fertility and structure have been greatly improved in the fixed sandy land which has never been restored.With the establishment of artificial vegetation,the vegetation coverage and soil fertility show an increasing trend,and the ecological benefits are obvious.In a word,vegetation and soil are two important parts of ecosystem,and they are closely related to grassland degradation.Ecological restoration indirectly affects the soil physical properties by planting seedlings and grasses,because there is frequent material exchange between soil and plants,and finally achieves a stable community structure.To sum up,from the perspective of species distribution and niche breadth,most of the desertified land in Northwest Sichuan is dominated by herbs.With the aggravation of desertification,many herbs are gradually succeeding,the dominant species change greatly,and the species diversity index difference is obvious.Although the distribution of shrub species is not many,it plays an important role in the stability of the whole community structure.From the analysis of distribution breadth and niche breadth,it can be seen that S.cupularis,S.paraplesia,S.linearistipularis,S.angustata,H.rhamnoides all rank at the top,but Salix cupularis has the largest niche breadth and H.rhamnoides has the smallest.The survival rate of Salix was higher than other H.rhamnoides and S.angustata.According to the subordinate values of drought resistance indexes of various tree species,H.rhamnoides has the strongest drought resistance ratio,and Salix is second only to H.rhamnoides.The comprehensive evaluation of the availability of H.rhamnoides,S.cupularis,S.paraplesia,S.linearistipularis and S.angustata in the control of desertification in Northwest Sichuan was conducted from three aspects:niche width,seedling difficulty and physiological drought resistance.The highest comprehensive score was H.rhamnoides,followed by S.cupularis.After comprehensive analysis,comparative transcriptome analysis was carried out in S.cupularis.Through KEGG pathway enrichment analysis of DEGs between T1 and T2,it was found that the top 20 metabolic pathways of KEGG were porphyrin and chlorophyll metabolism,photosynthesis,phenylpropanol biosynthesis of phenylalanine metabolism,mutual transformation of pentose and gluconate,sugar chain degradation and other metabolic pathways.These metabolic pathways can adapt to the changes of external environment through a series of hormones such as abscisic acid(ABA),auxin(IAA)and ethylene,so as to resist external drought conditions.At the same time,the chloroplast genome sequencing of S.cupularis and S.angustata was carried out to further understand the relationship between photosynthesis and drought resistance.At last,the application of S.cupularis in desertification land management was analyzed,mainly from two aspects of vegetation and soil.The results showed that the plant species,coverage and density increased after ecological restoration.The soil index of the restored sandy land is obviously better than that of the non restored sandy land.The soil sand decreased gradually,the soil particles and clay increased gradually,the soil water content also increased,and the soil structure tended to be stable.These results lay a foundation for the restoration of abiotic disasters,and also provide a theoretical basis for forest ecological protection and Drought Resistance Research of desert control shrubs. |
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