Adenylate energy charge of a glucose-treated soil without adding a nitrogen source

Soil microorganisms were metabolically activated by addition of glucose in one large initial ration or eight repeated additions without adding a nitrogen source. We tested whether the adenylate energy charge (AEC=(ATP+0.5×ADP)/(AMP+ADP+ATP) reflects this physiological activation. We compared the effects of glucose addition on adenylates with the development of microbial biomass C and biomass N from 6 h onwards during an 8 d incubation at 25 °C. Initial addition of 1600 μg glucose C g−1 soil increased microbial biomass C within 24 h from 152 to a maximum value of 469, dropping to 291 μg g−1 soil. In the treatment with daily addition of glucose, i.e. 8×200 μg glucose C g−1 soil, microbial biomass C increased within 24 h to roughly constant 325 mg g−1 soil throughout the experiment. Microbial biomass N showed a smaller increase than biomass C after glucose addition, leading to increased microbial biomass C/N ratios after glucose addition, especially in the treatment with initial glucose addition. The ATP-to-microbial biomass C ratio varied in our treatments between 3.2 and 10.1 μmol g−1 C and showed a significant negative relationship with the microbial biomass C/N ratio (r=−0.70, P<0.0001). The average ATP-to-microbial biomass C ratios in the different treatments were 5.1 (initial glucose addition), 6.9 (daily glucose addition) and 8.9 (control) μmol g−1. It was not possible to increase the AEC with glucose addition. The AEC was very similar in unamended and amended soils, in agreement with previous results.