Depth-dependency of trembling aspen and paper birch small-root responses to eCO2 and eO3

Background and Aims

Projected changes in the atmospheric concentrations of CO₂ and tropospheric O₃ over the next 50?years are of significant concern due to the linkages in the cycling of carbon and water in forested ecosystems. Responses of tree roots to elevated CO₂ (eCO₂) and O₃ (eO₃) have been characterized primarily by studies of relatively shallow roots, yet deeper roots often play a disproportionately large role in water acquisition relative to their biomass. We undertook the present study to determine if there were significant root responses to eCO₂ and eO₃ below the maximum soil depths typically studied.

Methods

In the current study, we characterized small root biomass and morphometric responses to eCO₂ and eO₃ at the Aspen-FACE Experiment in Rhinelander, Wisconsin down to a depth of one meter.

Results

Elevated CO₂ caused relatively undifferentiated growth stimulation. Elevated O₃ stimulated root growth in the AA community at depth, while in the AB community there was a reduction in root growth in the shallow soil layer that was reversed in the deeper layers.

Conclusions

Root responses below depths typically studied were qualitatively similar than those within shallower soils for eCO₂, but were sometimes compensatory for eO₃.