Substrate quality is known to control leaf litter decay rates, yet linkages between leaf litter chemistry and overall soil carbon (C) balance are poorly resolved. High quality litter inputs enhance the turnover of litter-derived C and may prime decomposition of soil-derived C. Alternatively, high quality inputs could be stabilized in mineral-organic associations by promoting rapid microbial growth and turnover. Our goals were to 1) evaluate the effect of leaf litter chemical traits on soil carbon formation and decay and 2) determine the extent to which these effects are mediated by microbial growth and turnover. We conducted 215-d litter-soil incubations consisting of leaf litters from 16 different temperate broadleaf tree species spanning a gradient in litter quality, and soil with a distinct C isotopic signature. We quantified litter chemistry, monitored 13C-CO2 efflux, tracked litter-derived C into the mineral-associated organic matter, and measured indicators of microbial growth and turnover. We hypothesized that nutrient-rich litters with low lignin content would enhance the priming of soil-derived C, but would also enhance the stabilization of litter-derived C in mineral-organic associations.
Results/Conclusions
Leaf litter chemistry spanned a wide range and strongly influenced C mineralization in the microcosms. For example, lignin-to-nitrogen (N) spanned from ~9 to ~31 and was negatively correlated with total and litter-derived C mineralization. Preliminary results support the hypothesis that high quality leaf litter enhances litter-derived C stabilization. Specifically, high quality litters (i.e., those with low lignin:N) tended to accumulate more C in the mineral-associated organic matter fraction. However, these high-quality litters did not prime the decomposition of soil-derived C as hypothesized. Rather, we observed lower soil-derived CO2 efflux in the treatments with high-quality litter suggesting that microbes in the high-quality treatment preferentially decomposed litter inputs in lieu of soil organic matter. Taken together, our results provide empirical support for the emerging view that rapidly decomposing plant inputs favor the formation of mineral-associated organic matter. To the extent that this pool is protected from microbial decay, soil C in systems receiving high quality inputs may be more resistant to environmental change.