Relation between respiration, ATP content, and Adenylate Energy Charge (AEC) after incubation at different temperatures and after drying and rewetting

Abstract

Temperature, drying, and rewetting are important climatic factors that control microbial properties. In the present study we looked at the respiration rates, adenosine 5'-triphosphate (ATP) content, and adenylate energy charge, (AEC) as a measure for energy status of microbial biomass in the upper 5 cm of mineral soils of three beech forests at different temperatures and after rewetting. The soils differed widely in pH (4.0 to 6.0), microbial biomass C (92 to 916 mug (g DW)(-1)) and ATP content (2.17 to 7.29 nmol ATP (g DW)(-1)). The soils were incubated for. three weeks at 7 degreesC, 14 degreesC, and 21 degreesC. After three weeks the microbial properties were determined, retaining temperature conditions. The temperature treatment acid not significantly affect AEC or ATP content, but respiration rates increased significantly with increasing temperature. In a second experiment the soils were dried for 12 hours at 40 degreesC. Afterwards the soils were rewetted and microbial properties were monitored for 72 hours. After the drying, respiration rates dropped below the detection limit; but within one hour after rewetting respiration rates increased above control level drying reduced AEC by 16 % to 44 % and ATP content by 47 % to 7.8 %, respectively. Rewetting increased AEC and ATP content significantly as compared to dry soil, but after 72 hours the level of the controls was still not reached. The level of AEC values indicated dormant cells, but ATP content increased. These results indicate that he microbial carbon turnover was not directly linked to microbial growth or microbial energy, status. Furthermore our results indicate that AEC may describe an average energy status but does not reflect phases of growing, dormant, or dying cells in the complex microbial populations of soils.