Does soil heterogeneity and compaction in ingrowth-cores affect growth and morphology of black spruce fine-roots?

Ingrowth-cores are commonly used in studies of fine-root production in forest stands. However, some concerns have been expressed regarding changes in root growth in the artificial soil environment created in ingrowth-cores, In this study, the effects that homogenization and compaction of soil might have on fine-root growth and morphology of black spruce (Picea mariana Mill.) were examined. Fine-root (<2mm) morphology was characterized by diameter and internode length. There was no difference in fine-root biomass and morphology between conventional ingrowth-cores (soil sieved and homogenized) and compacted cores (soil density increased by one third). However, fine-root biomass was substantially higher in ingrowth-cores in which the soil was distributed in layers of different fertility (patchy treatment) and both diameter and internode length values were closer to that found in the undisturbed soil cores. In the heterogenous treatment, the root internode length and biomass was significantly higher in rich patches than in poor patches, Our results indicate that fine-root production assessment using conventional ingrowth-cores where the soil is sieved and homogenized may underestimate the true production found in undisturbed soil, Fine-root architectural parameters in the patchy treatment were more similar to those found in the undisturbed soil cores. This study suggests that stratification or increased patchiness of the ingrowth-core growing medium should better mimic the conditions associated in undisturbed soils.