INTERACTIVE EFFECTS OF PH AND SUBSTRATE QUALITY ON THE FUNGAL-TO-BACTERIAL RATIO AND QCO(2) OF MICROBIAL COMMUNITIES IN FOREST SOILS

Microbiological and chemical properties of 40 North German spruce (Pic ea abies [L] K.) and beech (Fagus sylvatica L.) stands at either acidi c (similar to 3.0) or neutral (similar to 6.0) soil pH (A(h) horizon) were investigated to test the effects of pH, substrate type (forest ty pe) and the substrate x pH interactions on soil microbial communities. Soils of each pH set were selected to follow a normal distribution. T he percent fungal-to-bacterial respiratory ratio, as determined by the selective inhibition method, was significantly affected by type of fo rest substrate x pH interactions (P < 0.001). Soil pH influenced the p ercent fungal-to-bacterial ratio to a greater degree than substrate an d the effect of pH was more pronounced under beech than under spruce. Mean percent fungal-to-bacterial respiratory ratios (rounded) of 74-to -26 (beech) and 84-to-16 (spruce) were found at high pH (similar to 6) and ratios of 94-to-6 (beech) and 90-to-10 (spruce) were found at low pH (similar to 3.0), respectively. The metabolic quotient qCO(2) was strongly affected by soil pH (P < 0.001). Also, a strong substrate x p H effect was noted (P < 0 002). Particularly at low pH the qCO(2) was higher under spruce as compared to beech. A relationship emerged betwe en the qCO(2) and the fungal-to-bacterial ratio. With increasing funga l presence the qCO(2) declined. The C-mic- to-C-org ratio was only aff ected by pH (p < 0.001). (C) 1998 Elsevier Science Ltd. All rights res erved.