See more from this Session: Microbe, Plant , and Soil Interactions (Includes Graduate Student Poster Competition)
As expected, SOC depth gradients were greater in the native grassland than the no-till soil, a feature consistent across all fractions, but attenuated in the mineral and aggregate protected SOC fractions. Depth gradients for lignin/OC or cutin+suberin/OC differed across fractions or treatments. Cutin + suberin/SOC concentrations remained consistent with depth in all fractions from the no-till soil, while decreasing significantly with depth in all grassland fractions. Lignin/OC concentrations exhibited opposing depth effects, remaining consistent with depth in the mineral and aggregated grassland fractions and decreasing with depth in the no-till mineral and aggregate fractions. When not protected, coarse POM lignin/OC was depleted with depth in the grassland, but did not change in the no-till soil. These results point to distinct differences in biochemical-specific protection or degradation of SOM components with no-till cultivation. The strong cutin+suberin/SOC gradient reflects the root architecture of grassland soils, with increased root density and surface area in the upper 5 cm leading to increased cutin+suberin SOC concentrations. Relict effects of tillage prior to no-till adoption in 1978 as well as lesser root density gradients explain the less pronounced SOC and cutin + suberin/SOC gradients in the no-till soil, but fail to clarify the contrasting treatment effects of lignin/SOC protection with depth in these two systems.