Short-term impacts of soil amendments on belowground C cycling and soil nutrition in two contrasting Pinus taeda L. genotypes

We monitored two Pinus taeda L. genotypes, planted in 170 L lysimeters, subjected to different combinations of fertilization and logging residue (LR) incorporation for 1 year. The objectives were to elucidate how soil amendments modified soil biological properties and belowground C cycling, and secondly, to determine if planting of contrasting genotypes have a detectable impact on total soil CO2 efflux (FS). LR incorporation resulted in decreased bulk density, increased total soil porosity, and increased total soil C and N contained within the fine-soil fraction. For most of the experiment we found no consistent differences between genotypes; however, on the final two sampling dates a pattern emerged of one clone showing greater FS. If this pattern continues or becomes stronger with increased occupation of soil by roots it may have an influence on total site net C exchange. Increased C loss by way of FS and soil leaching made up approximately 7% of total C incorporated as LR. Conservative estimates using a constant rate of decomposition showed that it would take a minimum of 15 years to fully decompose the incorporated LR. Our data suggest that moderate rates of LR incorporation following harvesting over multiple rotations could increase SOM without negatively impacting plant growth, which could increase soil C sequestration.

► We compare addition of logging residue and fertilization on soil respiration.
► Logging residue could increase long-term soil C.
► Soil amendments influenced soil respiration and microbial populations.
► Difference in soil respiration among clones emerged at the end of study.