Microbial Physiology And Soil Co2 Efflux After 9 Years Of Soil Warming In A Temperate Forest - No Indications For Thermal Adaptations

Abstract

Thermal adaptations of soil microorganisms could mitigate or facilitate global warming effects on soil organic matter (SOM) decomposition and soil CO2 efflux. We incubated soil from warmed and control subplots of a forest soil warming experiment to assess whether 9ￂﾠyears of soil warming affected the rates and the temperature sensitivity of the soil CO2 efflux, extracellular enzyme activities, microbial efficiency, and gross N mineralization. Mineral soil (0￢ﾀﾓ10ￂﾠcm depth) was incubated at temperatures ranging from 3 to 23ￂﾠￂﾰC. No adaptations to long￢ﾀﾐterm warming were observed regarding the heterotrophic soil CO2 efflux (R10 warmed: 2.31ￂﾠￂﾱￂﾠ0.15ￂﾠￎﾼmolￂﾠm￢ﾈﾒ2ￂﾠs￢ﾈﾒ1, control: 2.34ￂﾠￂﾱￂﾠ0.29ￂﾠￎﾼmolￂﾠm￢ﾈﾒ2ￂﾠs￢ﾈﾒ1; Q10 warmed: 2.45ￂﾠￂﾱￂﾠ0.06, control: 2.45ￂﾠￂﾱￂﾠ0.04). Potential enzyme activities increased with incubation temperature, but the temperature sensitivity of the enzymes did not differ between the warmed and the control soils. The ratio of Cￂﾠ:ￂﾠN acquiring enzyme activities was significantly higher in the warmed soil. Microbial biomass￢ﾀﾐspecific respiration rates increased with incubation temperature, but the rates and the temperature sensitivity (Q10 warmed: 2.54ￂﾠￂﾱￂﾠ0.23, control 2.75ￂﾠￂﾱￂﾠ0.17) did not differ between warmed and control soils. Microbial substrate use efficiency (SUE) declined with increasing incubation temperature in both, warmed and control, soils. SUE and its temperature sensitivity (Q10 warmed: 0.84ￂﾠￂﾱￂﾠ0.03, control: 0.88ￂﾠￂﾱￂﾠ0.01) did not differ between warmed and control soils either. Gross N mineralization was invariant to incubation temperature and was not affected by long￢ﾀﾐterm soil warming. Our results indicate that thermal adaptations of the microbial decomposer community are unlikely to occur in C￢ﾀﾐrich calcareous temperate forest soils.