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 1-13C acetate for 24 h had much higher 13C contents than neutral lipids or glycolipids. 13C was mainly incorporated into 18:2ω6, 16:0 and 18:1ω9 phospholipids in a Low Humic Andosol and a Gray Lowland Soil. When soil was incubated with 1-13C acetate and cycloheximide, the incorporation of 13C into 18:2ω6 could not be detected. Decrease of 18:2ω6 in phospholipids in soil suggested it was a component of soil fungi. The incorporation of 13C into 18:1ω7, 16:1ω7, 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 13C into phospholipids increased considerably and 13C incorporation into 16:1ω7 ,18:1ω7 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 13C incorporation into PLFAs from 13C acetate can be used to detect changes in soil bacterial and fungal activities.