In situ detection of changes in soil bacterial and fungal activities by measuring 13C incorporation into soil phospholipid fatty acids from 13C acetate

Phospholipids in four types of soil incubated with 1-C-13 acetate for 24 h had much higher C-13 contents than neutral lipids or glycolipids. C-13 was mainly incorporated into 18:2 omega 6, 16:0 and 18:1 omega 9 phospholipids in a Low Humic Andosol and a Gray Lowland Soil. When soil was incubated with 1-C-13 acetate and cycloheximide, the incorporation of C-13 into 18:2 omega 6 could not be detected. Decrease of 18:2 omega 6 in phospholipids in soil suggested it was a component of soil fungi. The incorporation of C-13 into 18.1 omega 7, 16:1 omega 7, i15:0, a15:0, i17:0 and a17:0, the major fatty acid in many soil bacteria, could not be detected in a Gray Lowland Soil at pH 4.6. When soil pH was raised to 7 or 8. the incorporation of C-13 into phospholipids increased considerably and C-13 incorporation into 16:1 omega 7,18:1 omega 7 i15:0, a15:0, i17:0 and a17:0 in phospholipids increased in a Low Humic Andosol and a Gray Lowland Soil. This suggests that soil bacterial growth was inhibited at low soil pH and facilitated at pH 7 and 8. In conclusion, we have shown that measurement of C-13 incorporation into PLFAs from C-13 acetate can be used to detect changes in soil bacterial and fungal activities. (C) 1999 Elsevier Science Ltd. All rights reserved.