关键词: 科尔沁沙地, 土壤微生物量碳和氮, 潜在净氮矿化速率, 潜在净硝化速率, 土壤酶活性, 土壤有效磷

Abstract: Seasonal variations of epiphytic microflora on apple phylloplane were studied by washing and centrifugating during its growing season in 1991 in natural and disease-control orchards.The results indicate that－the population and number of species of both epiphytes and pathogens vary significantly during the sea-son. Under natural condition,the total amount of epiphytic bacteria peaks earlier than that of fungi.Both of the peaks emerge later than that of pathogens,The populations of epiphytes and pathogens are signifi-cantly affected by precipitation and fungicides. 358 isolates of epiphytes are indentified into 36 fungus-species and at least 4 bacterium genera,Dominant species of epiphytes in early season Rreatly differ from those in late season .but some epiphytes present consistently during the season. There are no obvious differences among populations of epiphytes in different ecological regions.Biological control of pathogens in orchards is discussed.

Key words: Keerqin Sandy Land, soil microbial biomass C and N, potential net N mineralization rate, potential net nitrification rate, soil enzyme activity, Olsen-P.