Disentangling effects of air and soil temperature on C allocation in cold environments: a 14C pulse labelling study with two plant species

Carbon cycling responses of ecosystems to global warming will likely be stronger in cold ecosystems where many processes are temperature-limited. Predicting these effects is difficult because air and soil temperatures will not change in concert, and will affect above and belowground processes differently. We disentangled above and belowground temperature effects on plant C allocation and deposition of plant C in soils by independently manipulated air and soil temperatures in microcosms planted with either Leucanthemopsis alpina or Pinus mugo seedlings. Daily averages temperatures of 4 or 9 °C were applied to shoots and independently to roots, and plants pulse-labelled with 14CO2. We traced soil CO2 and 14CO2 evolution for four days, after which microcosms were destructively harvested and 14C quantified in plant and soil fractions. In microcosms with L. alpina, net 14C uptake was higher at 9°C than at 4°C soil temperature, and this difference was independent of air temperature. In warmer...