Differential nutrient uptake responses to CO{sub 2} enrichment in three desert species

Differences in species capacity to absorb nutrients may be a crucial factor determining species and ecosystem responses to CO{sub 2} enrichment. In a phytotron study, we examined responses of three dominant species from the Chihuahuan Desert-Prosopis glandolusa and Larrea tridentata (C{sub 3} shrubs) and Bouteloua gracilis (a C{sub 4} perennial grass)-to a doubling of atmospheric CO{sub 2}, with special emphasis on rates of root NO and PO, uptake. Seedlings were grown in pots at CO{sub 2} partial pressure of either 35 or 70 pa. Rates of root NO{sup {minus}}{sub 3} and PO{sup 3{minus}}{sub 4} uptake were determined on three month old individual seedlings or tussocks using depletion rates of these ions from {1/4} strength Hoagland solutions over a 4h period. Root uptake rates of both NO{sup {minus}}{sub 3} and PO{sup 3{minus}}{sub 4} more than doubled in response to CO{sub 2} enrichment in Bouteloua but did not significantly respond in Prosopis. High CO{sub 2} also did not significantly affect rate of PO{sup 3{minus}}{sub 4} uptake in Larrea but inhibited NO{sup {minus}}{sub 3} uptake rate. Biomass increased an average of 36% in the shrubs and 25% in the grass. A positive biomass response to CO{sub 2} in C{sub 4} species has beenmore » observed in several other studies but the potential mechanism for such an enhancement is still nuclear. Our data suggests that such an enhancement may result from improved root nutrient uptake capacity.« less