Effects of Detrital Inputs and Roots on Carbon Saturation Deficit of a Temperate Forest Soil

Abstract

Soil C sequestration has been proposed as a tool for addressing climate change. However, models used to predict soil C sequestration do not account for C saturation and functional differences among soil C pools. In this study, we examined differences in soil C pool content of a forest soil in Pennsylvania following 20 yr of detrital manipulation (i.e., control, no roots, no leaf litter, no inputs, double leaf litter). Detrital input treatments had a highly significant (ANOVA, F = 10.6, p < 0.0001) effect on soil C in the 0- to 5-cm soil depth. However, soil C pools responded differently to the different treatments: the intra-microaggregate silt + clay, intra-microaggregate particulate organic matter (POM), and silt + clay within large macroaggregates in plots receiving no detrital inputs had significantly lower C concentrations (1.1, 2.5, and 0.4 g C kg−1 soil, respectively) than the control, double-leaf-litter, and no-roots plots. Carbon in coarse POM within small macroaggregates was significantly lower in double-leaf-litter (4.5 g C kg−1 soil) and no-leaf-litter plots (6.6 g C kg−1 soil) than all other treatments (15.3–28 g C kg−1 soil). The intra-microaggregate fractions in double-leaf-litter plots had greater C concentrations than in the control plots; along with moderate C concentrations in all bulk soil samples, this suggests that the soil is not yet approaching C saturation. This study reinforces the use of microaggregates within large macroaggregates as a diagnostic fraction for changes in soil C content and demonstrates that altering the organic matter source and quantity significantly affects soil C sequestration dynamics. Consideration of these factors will enable improved assessment of soil C sequestration capacity and management.