Species Relationship Among Algae、Syntrichia Caninervis And Seed Plants In Biological-soil Crusts

Biological soil crusts (BSCs) are communites of diminutive but importantorganisms that may include bacteria, cyanobacteria, algae, fungi, lichens, liverworts,and mosses, which are intimately associated with the mineral soil surface, creating acohesive thin horizontal layer. They are widespread in arid and semi-arid regions inthe world. BSCs play significant functional roles in the desert ecosystem, includingthe process of soil formation, water and nutrient cycling, preventing soil erosion,influencing the establishment and performance of vascular plants. In differentsuccessional stages of BSCs and establishment of vascular plants, state of each stageand normal growth of the species have the closely relationship with the previous stage,especially interspecific relationship. In the thesis, several vascular plants and BSCs ofGurbantunggut desert were studied, the wild field sampling and indoor solid culturemethod were used for discuss the effect of four vascular plants. Some differences inspecies diversity, species composition and community structure of algae wereanalyzed by Shannon-Weaver index and t-test. The soil physical and chemicalproperties within and out of the riegulaea were determined by the conventionalanalysis method. In biological soil crusts, the indoor germination test were used fordiscuss the effect on germination of different plant seeds of moss crust andextracellular polysaccharides (EPS) secreted by cyanobacteria. Through the results,the relationship of cyanobacteria, moss and some vascular plant in BSCs wereexplored. The main results are as follows:To understand BSCs in the relationship between vascular plants and algae, theeffects of Ephedra distachya, Artemisia arenaria, Salsola collina and Ceratocarpusarenarius on algal distribution were investigated by culturing methods. The resultsshowed diversity, species composition and community structure of algae werechanged in different microenvironment. Some differences in species diversity of algaewere observed within and out of the riegulaea of E.distachya, A. arenaria and S. subcrass. Species richness and Shannon-Weaver index in the riegulaea of E.distachyawas lower significantly than that out of the riegulaea (P<0.05). However, algalrichness in the riegulaea of A. arenaria and S. subcrassa was higher significantly thanthat out of the riegulaea, and no difference in Shannon-Weaver index(P>0.05). Thechange of species composition of algae was mainly caused by dominant species anddominance degree of species. In community structure of algae, there was no obviousdifference within and out of the riegulaea of E.distachya and A. arenaria. However,Chroococcalcs and Oscillatoriales were dominant communities within and out of theriegulaea of E.distachya and in the herbs of C. arenarius, while others is low.Variations of some key species of algae were account for the change of communitieswithin and out of the three rirgulaea. Dominant species, community structure anddominance degree of algae was mainly caused by the difference of microenvironment.In biological soil crusts, extracellular polysaccharides (EPS) secreted bycyanobacteria have different effects on germination of different plant seeds. Theresults indicated that low concentration EPS of M. vaginatus, and S. ocellatuminhabited seed germination of Salsola subcrassa whereas high concentration EPSincreased seed germination of S. subcrassa. EPS of N. commune showed significanteffects on seed germination of S. subcrassa with high concentration (P<0.05). EPS ofM. vaginatus represented no obvious effects on seed germination of Nepetamicrantha, however, EPS of S. ocellatum, and N. commune had negative effects onseed germination of N. micrantha. EPS of M. vaginatus, S. ocellatum, and N.commune inhabited seed germination of H. pulchella. EPS of the differentcyanobacteria species had different effects on seed germination, which can beexplained by the differences of composition content of EPS and biological charactersof seeds. In addition, Cyanobacteria in biological soil crusts increase organic C and Nin soils by photosynthesis and N-fixing. Input of these nutrients into the soils mayplay important roles on growth and development of seed plant by decomposition of microorganism and transportation of nutrients by fungi hyphae.We investigated the effects of moss crust on seed germination of four desert plantspecies. The results indicated that germination rate of C. arenarius, S. subcrassa,Nepeta micrantha, H. pulchella on moss crust were lower significantly than on baresand, which can be explained by the physical barrier effect and strong suction force ofmoss.There exist complicated interspecific relationship among algae, moss and seedplants in biological soil crusts. The composition of spore plant species varies indifferent successional stages of biological soil crusts. They can secreteallelochemicals into the soil, which can produce certain allelopathy on growth andmetabolic processes of plant. However, the composition of allelochemicals and howthey play roles on interspecific relationship remains unknown and need further study.