What was done
Circular FACE plots (30-m diameter) maintained at atmospheric CO2 concentrations of 365 and 565 ppm were established in a 13-year-old loblolly pine plantation in North Carolina, USA, to determine the long-term effects of elevated CO2 on this forest ecosystem.  Since the initial planting, a deciduous understorey was naturally established from nearby hardwood forests.  In this paper, the authors report the effects of elevated CO2 on total plantation leaf litter chemistry and decomposition following two complete years of atmospheric CO2 enrichment.

What was learned
Elevated CO2 had little effect on green leaf and leaf litter nitrogen contents.  In addition, elevated CO2 did not significantly affect the efficiency of nitrogen retranslocation prior to leaf senescence.  Moreover, lignin and total nonstructural carbohydrate contents in leaf litter remained unchanged by atmospheric CO2 enrichment.  Thus, in general, elevated CO2 did not alter leaf litter chemistry; and, consequently, decomposition of leaf litter remained unaffected by elevated CO2 in this pine forest ecosystem.

What it means
As the air's CO2 content increases, it is likely that loblolly pine forests will display persistent increases in net primary productivity that will lead to greater dry matter production.  However, the overall carbon and nitrogen budgeting of forest leaves and leaf litter is not likely to change, as indicated in this study.  Thus, decomposition rates of CO2-enriched litter will largely remain unchanged from rates currently occurring in such forests exposed to ambient levels of atmospheric CO2.  Consequently, net mineralization rates of nitrogen from such litter and its availability to plant roots will likely stay the same as they are now.