Soil respiration does not acclimatize to warmer temperatures when modeled over seasonal timescales

Soil warming studies have generally demonstrated an ephemeral response of soil respiration to warming suggesting acclimatization to increased temperatures. Many of these studies depict acclimatization as an empirical temperature-respiration model with data collected from late spring through early autumn. We examined the apparent temperature sensitivity of soil respiration in chronically warmed soils over three different timescales: annually, during the growing season, and seasonally during winter, spring, summer, and fall. Temperature sensitivity was evaluated by fitting exponential and flexible temperature functions as mixed effects models. From model coefficients, we estimated annual, growing season, and season-specific Q (10) values, and assessed the ability of model coefficients to predict daily soil respiration rates over a two-year period. We found that respiration in warmed soils can exhibit characteristics of acclimatized temperature sensitivity depending on the timeframe and the function (exponential or flexible) used. Models using growing season data suggested acclimatization while models using data collected in winter or spring indicated enhanced temperature sensitivity with 5 A degrees C of warming. Differences in temperature sensitivity affected predicted daily soil respiration rates, particularly in winter and spring. Models constructed over longer timescales overestimated daily respiration rates by as much 10-40 % whereas season-specific predictions were generally within 2 % of actual values. Failure to use season-specific models to depict changes in temperature dependence may over- or under-estimate carbon losses due to climate warming, especially during the colder months of the year.