Data from: 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 soils, more C was allocated to roots at greater soil depth, with no
effect of air temperature. In P. mugo microcosms, assimilate partitioning
to roots increased with air temperature, but only when soils were at 9 °C.
Higher soil temperatures also increased the mean soil depth at which 14C
was allocated. Our findings highlight the dependence of C uptake, use, and
partitioning on both air and soil temperature, with the latter being
relatively more important. The strong temperature-sensitivity of C
assimilate use in the roots and rhizosphere supports the hypothesis that
cold limitation on C uptake is primarily mediated by reduced sink strength
in the roots. We conclude that variations in soil rather than air
temperature are going to drive plant responses to warming in cold
environments, with potentially large changes in C cycling due to enhanced
transfer of plant-derived C to soils.