Nitrogen effects on quantity, chemistry, and decomposability of Pinus densiflora and Quercus variabilis litters under elevated CO2 and warming

•High N increased litter biomass of oak, but not pine, regardless of CO2 × Tair.•High N changed litter chemistry for both pine and oak regardless of CO2 × Tair.•Changed N concentration, C/N, and lignin/N rarely affected litter decomposition.