SAPROPHYTIC FUNGAL-BACTERIAL BIOMASS VARIATIONS IN SUCCESSIONAL COMMUNITIES OF A SEMIARID STEPPE ECOSYSTEM

A major goal in attempting to understand plant succession is to assess the implications of fungal and bacterial biomass changes over time as plant-soil systems develop. In this study, the soil fungal and bacter ial biomass of three successional semi-arid steppe communities, sample d 4, 12, and 38 years after cultivation ended, were compared with an u ncultivated native plant community using microscopic procedures. In th e course of the succession, significant increases in fungal hyphal len gths occurred, reaching a maximum in the oldest successional (38-year) community. Active (cytoplasm filed) hyphae decreased along the chrono sequence, with the native plant community having the lowest values. Si milar decreases in active bacterial biomass values occurred. In contra st, microscopically determined total bacterial numbers did not differ in soils associated with the 4-year-old and native plant communities. The ratio of active bacterial to fungal biomass, which increased over the chronosequence tested in this study, appears to provide a valuable integrative measure of plant-soil resource system development and eco system maturity.