Effects of loblolly pine litter, forest floor, and root exclusion on mineral soil carbon in a Florida Spodosol

Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for assessing the potential for carbon sequestration of managed pine forests. This study used a sequential exclusion of aboveground litter inputs (L, litter exclusion) and aboveground plus belowground inputs (LR, litter and root exclusion) to segregate carbon sources contributing to the development and maintenance of SOC in the surface soil supporting juvenile loblolly pine (Pinus taeda L.) in its rapid growth phase. The study spanned the 7th to 10th year of stand growth. Soil physical size fractions (>2 mm, <= 2 mm, 2000-250 mu m, 250-150 mu m, 150-53 mu m, and <53 mu m) were used to investigate the change in native SOC over time in the untreated control plots (UC, untreated control) and the effects of exclusion treatments. An accretion rate of 4.6 Mg SOC.ha(-1) of soil.year(-1) was observed in the fine earth fraction (<= 2 mm), reflecting the rapid phase of stand growth. The accretion was primarily observed in the upper 10 cm of the soil. Treatment effects were most apparent in soil bulk density, SOC of the fine earth, and 150-53 mu m size fractions. In general, changes in SOC observed in the L treatment was an intermediate increase between the UC and LR treatments, where only the removal of roots provided no change in SOC and was significantly different from the control (p = 0.05). We conclude that a major contributor to the maintenance and increase of SOC in this fast-growing pine ecosystem was due to root turnover (60%), with 40% due to aboveground litter inputs.