Global change in the root zone: lessons from soil moisture dynamics in a multifactor climate manipulation experiment

Assessing the future of water resources in terrestrial biomes is contingent on observations from climate-manipulation experiments. Global change in the Anthropocene could produce various permutations of warming, atmospheric carbon levels, and moisture availability; however the impact on ecosystem hydrology is largely studied individually (e.g., elevated CO₂ or temperature) rather than interactively. We sought to specify how various combinations of  drought, elevated CO₂ (+150 ppm, +300 ppm) and warming (+1.5°C and + 3°C) may alter the partitioning of soil moisture in the root zone of mountain grassland. Using spectral techniques, we transformed these high resolution data (i.e., 4 soil depths and every 15 min) into the frequency domain to study the interactive effects of climate change on sub-hourly to seasonal soil moisture signals. Diurnal moisture signals in heated plots (+3°C in air temperature) were up to 3x stronger (in amplitude) during summer drawdown compared to plots receiving heat and elevated CO₂ (+300 ppm). This preliminary analysis suggests that elevated atmospheric carbon may buffer heat-driven soil moisture losses in grassland root zones by reducing transpiration fluxes during seasonal dry periods.