Carbon allocation in Larrea tridentata plant-soil systems as affected by elevated soil moisture and N availability

Background and Aims Global change will likely express itself in southwestern United States arid lands through changes in amounts and timing of precipitation in response to elevated CO₂ concentrations. In addition, increased nitrogen (N) deposition may occur due to increased urban development. This study addressed the effects of water and N availability on C allocation in arid land soil-plant systems. Methods Columns filled with Mojave Desert topsoil containing Larrea tridentata seedlings with two treatment levels each of N and soil moisture were labeled by exposure to ¹³C-enriched CO₂. Results Increased soil moisture increased plant biomass, total ¹³C uptake, ¹³C levels in leaves, soil organic matter, and soil respiration, decreased relative C allocation to stems but increased allocation to soil organic matter. Increased soil N availability increased N uptake but decreased C allocation to soil respiration presumably due to decreased substrate supply for microbes. There was no detectable label in carbonate C, suggesting that this pool does not significantly contribute to ecosystem C fluxes. Conclusions Our study indicates that increased water availability causes increased C uptake with increased C allocation to soil organic matter in Larrea tridentata dominated communities while increased N deposition will have a minimal impact on C sequestration.