DEVELOPMENT CHARACTERISTICS AND DISTRIBUTION OF MICROORGANISMS WITHIN 3-YEAR-OLD ARTIFICIAL ALGAL CRUSTS IN HOPQ DESERT

In this study,development characteristics and distribution of microorganisms within four different types of artificial algal crusts were investigated.The results showed that:(1) artificial algal crusts came into being,when desert cyanobacteria were inoculated onto surface of dunes,with their average thickness of 2.23-5.36mm,highly black and sage green,and coverage of artificial algal crusts over 70% when artificial algal crusts underwent growth and development of three years.As to the four artificial algal crusts,Salix cheilophila Schneid.2Aneurolepidium chinensis-algal crust(SAA)was found to gain the best developments and reached the most biomass,and arrived at the succession of moss crust at the same time.Plenty of desert plants occurred at the locations of artificial algal crusts,such as A.squarrosum,E.dahuricus,S.collina and A.chinensis,etc.,and the coverage of vegetation accounted for 60%-90%.Algal compositions of artificial algal crusts at four different stations were entirely very single,and the quantities of algal species varied inapparently.M.vaginatus was found to be still utterly dominant,whereas,S.javanicum kept secondary.Moreover,different species of algae were discovered to inhabit distinct ecological niche.It was shown in our study that artificial algal crusts could bear high compressive strength,and compressive strength commonly achieved 35-70 N/m2.Cyanobacteria forming artificial algal crust was found to own abundant filamentous growth forms that could band and felt soil particles by compact and high mechanical force,and simultaneously,they exude polysaccharide with their filaments to hasten soil aggregation and cement soil particles together.All those meant compressive strength of artificial crusts was able to be maintained due to the presence of filamentous cyanobacteria.The observation to ultra-microstructures of algal crusts indicated that abundant filamentous growth forms occurred between the sand soils within algal crusts during growth and development of 3 years in the fields.A great deal of filamentous growth forms were observed to band up and felt sand particles,which may be contributed to cementation process of artificial algal crusts.(-) Change trend of the total number of microorganisms was: SAAGAAASACK.Changes of biomass of artificial algae crusts accorded with that of the total number of microorganisms.Of all main microorganism groups,the quantities of bacteria,actinomyces and fungi within different types of artificial algae crusts were consistent with that of the total number of microorganisms.Concerning the four artificial algae crusts,the ratio of bacteria quantities to the total number of microorganisms was distinctly more than that of actinomyces and fungi.The percentage of bacteria quantities to the total number of microorganisms increased sharply in turn,while the percentage of actinomyces quantities to the total number of microorganisms decreased evidently.Need to mention that it took on very small ratio of fungi quantities to the total number of microorganisms,and differences of the ratios varied very little.