Topographical and seasonal effects on soil fungal and bacterial activity in subtropical, perhumid, primary and regenerated montane forests

This study was conducted in subtropical, perhumid, montane forests of north-eastern Taiwan. The study sites were located along a slope from the 2100 m summit to the 1670 m lakeshore of a primary coniferous forest ecosystem and at three nearby regenerated forests. Soil ergosterol content, fungal and bacterial contributions to CO2 production (respiration rate) after glucose addition and hence ratios of fungal to bacterial respiration were evaluated. In the primary forest surface soils (depth 0–10 cm), ergosterol content and respiration rate increased from the summit to the lakeshore site, with the steep sloping shoulder site having the lowest level. At these sites, ergosterol content and CO2 production, calculated on a per gram basis, declined sharply with depth, being 10–1000 fold less in the deepest mineral horizon (>50 cm) as compared to the surface horizon. The soil total respiration rate was found to be significantly higher in summer than winter in the surface soil, but the fungal respiration rate and ergosterol content showed no significant difference between these two seasons. The primary coniferous forest had both a significantly higher respiration rate and ergosterol content than the regenerated Japanese cedar and regenerated broadleaf forest ecosystems, but not the regenerated false cypress forest. Ratios of fungal to bacterial respiration showed no significant differences between sites or soil layers. However, a significant positive correlation (r2=0.746) was exhibited between soil fungal ergosterol content and soil fungal respiration rate for all sampling sites.