- • The loss of carbon below-ground through respiration of fine roots may be modified by global change. Here we tested the hypothesis that a reduction in N concentration of tree fine-roots grown in an elevated atmospheric CO2 concentration would reduce maintenance respiration and that more energy would be used for root growth and N uptake. We partitioned total fine-root respiration (RT) between maintenance (RM), growth (RG), and N uptake respiration (RN) for loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua) forests exposed to elevated CO2.
- • A substantial increase in fine-root production contributed to a 151% increase in RG for loblolly pine in elevated CO2. Root specific RM for pine was 24% lower under elevated CO2 but when extrapolated to the entire forest, no treatment effect could be detected.
- • RG (< 10%) and RN (< 3%) were small components of RM in both forests. Maintenance respiration was the vast majority of RT, and contributed 92% and 86% of these totals at the pine and sweetgum forests, respectively.
- • The hypothesis was rejected because the majority of fine-root respiration was used for maintenance and was not reduced by changes in root N concentration in elevated CO2. Because of its large contribution to RT and total soil CO2 efflux, changes in RM caused by warming may greatly alter carbon losses from forests to the atmosphere.