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Stimulation of root growth under elevated CO2 has been hypothesized to enhance soil water uptake under water-limiting conditions. The objectives of this study were to quantify the effects of rising CO2 on root development and soil water uptake in Larrea tridentata and to quantify root proliferation into small water patches.

Seedling communities of L. tridentata were grown in rhizotrons under controlled environmental conditions at three CO2 concentrations (280, 360, and 600 mul l(-1) ). Patches of water were applied to small areas of the root systems in the rhizotrons and to L. tridentata shrubs in the field.

Rising CO2 significantly stimulated root length production, but only in the lower half of the soil profile. Stimulation of root production led to faster depletion of soil water. Neither mature shrubs nor seedlings responded to water-enriched soil patches via root proliferation.

The results of our study indicate that rising CO2 may accelerate seedling root growth in L. tridentata , could lead to proportionally greater investment of roots in deeper soil layers and may enhance water acquisition.