Abstract: This paper studies the variation of soil fertility under pure artificial larch(Larix gmelinii) forest from as-pects of soil humus and enzyme activity. With increasing age of forest stand, soil fertility tends to de-crease, but soil enzyme activity tends to increase. Under forest with 20 years of age, the contents of soilhumus, humic acid and fulvic acid and the ratio of humic acid to fulvic acid are lowered, indicating thepoor decomposition of forest litters. Grey connectivity analysis and thorough analysis show that the orderof enzvme activities which directly affect soil organic matter dynamics are different under different ages offorest stand.

Key words: Citrus reticulata, Castanea henryi, soil respiration, soil temperature.