Effects of elevated CO2 and N fertilization on plant and soil carbon pools of managed grasslands: a meta-analysis

Abstract

Elevated atmospheric CO2 levels and increasing nitrogen deposition both stimulate plant production in terrestrial ecosystems. Moreover, nitrogen deposition could alleviate an increasing nitrogen limitation experienced by plants exposed to elevated CO2 concentrations. However, an increased rate of C flux through the soil compartment as a consequence of elevated CO2 concentrations has been suggested to limit C sequestration in terrestrial ecosystems, questioning the potential for terrestrial C uptake to mitigate increasing atmospheric CO2 concentrations. Our study used data from 77 published studies applying elevated CO2 and/or N fertilization treatment to monitor carbon storage potential in grasslands, and considered the influence of management practices involving biomass removal or irrigation on the elevated CO2 effects. Our results confirmed a positive effect of elevated CO2 levels and nitrogen fertilization on plant growth, but revealed that N availability is essential for the increased C influx under elevated CO2 to propagate into below-ground C pools. However, moderate nutrient additions also promoted decomposition processes in elevated CO2, reducing the potential for increased soil C storage. An important role was attributed to the CO2 response of root biomass in soil carbon responses to elevated CO2, since there was a lower potential for increases in soil C content when root biomass increased. Future elevated CO2 concentrations and increasing N deposition might thus increase C storage in plant biomass, but the potential for increased soil C storage is limited.