Marie-Anne De Graaff and Johan Six. Plant Sciences, UC-Davis, One Shield avenue, Davis, CA 95616
Free Air Carbon dioxide Enrichment (FACE) and Open Top Chamber studies (OTC) are valuable tools for evaluating the impact of elevated atmospheric CO2 on terrestrial ecosystems. Using the statistical tool Meta analysis, we summarized the results of 105 CO2-fumigation studies on plant growth and soil nutrient cycling conducted in managed ecosystems. With this analysis we aimed at determining how elevated CO2 affects the interactions between plant growth and soil nutrient cycling, and what the implications are for soil C sequestration. Elevated CO2 stimulated above- and belowground plant production by 20% and 30%, respectively. Concurrently, soil C input increased, which enhanced soil microbial C contents and respiration by 17.3% and 7.5%, respectively. Despite the rise in microbial activity, soil C contents increased by 0.94% per year, suggesting that stimulated soil C input had counterbalanced the increase soil C output under elevated CO2. However, when comparing experiments receiving low versus high N fertilization rates, plant growth and soil C contents increased only under elevated CO2 in experiments receiving the high N fertilization rates. Also, N2 fixation was stimulated by elevated CO2 (+51%) only when additional mineral nutrient fertilizer was supplied. The increase in gross N immobilization (+22%) reduced the plant growth response to elevated CO2 in low resource environments. Concurrently, soil C sequestration did not increase in these systems. These results suggest that soil C sequestration under elevated CO2 constrained by the availability of nutrients.
