Tree species and soil textural controls on carbon and nitrogen mineralization rates

Terrestrial ecosystem models assume that high quality litter leads to the formation of high quality organic C and N in mineral soil, and that increased soil clay content decreases soil C and N mineralization rates. Few studies in forests, however, have examined the effects of initial litter quality and clay content on C mineralization rates (g C kg(-1) soil C) and net N mineralization rates (g N kg(-1) soil N) in soil. We used 16-mo laboratory incubations of mineral soil sampled from stands of lodgepole pine (Pinus contorta Dougl. ex loud ssp. latifolia Englem. ex S. Wats.) and aspen (Populas tremuloides Michx.) that varied in clay content (70 to 390 g kg(-1) soil) to examine how soil C and N mineralization rates relate to initial litter quality and soil texture. Aspen litter quality (C/N = 52-71; lignin/N = 26) was higher than pine litter quality (C/N = 82-111; lignin/N = 40-57), but pine soils released an average of 238 g C kg(-1) soil C over 16 mo compared with 103 g C kg(-1) soil C for aspen soils. Higher microbial biomass (mg kg(-1) soil C) under pine also indicates that pine soil C was of higher quality than aspen soil C. Net N mineralization rates did not relate to species or to soil C mineralization rates, and neither C nor N mineralization rates were related to soil clay content.