Soil organic matter pools under management intensification of loblolly pine plantations

Abstract Early thinning of loblolly pine plantations can potentially deliver sustainable feedstocks for biofuel/bioenergy. However, the management intensification for increased productivity and the removal of additional biomass from these plantations could reduce carbon (C) inputs belowground and therefore reduce overall ecosystem C storage. Increased fertilization could also affect C stocks, and their relative distribution between soil organic matter (SOM) fractions. We analyzed soil C stocks as a function of soil type and different pine plantation management systems across the Western Gulf region of the United States. Additionally, we analyzed SOM fractions with inherently different stabilization mechanisms and potential C persistence. We found no significant differences in bulk soil C stocks across management intensities or soil types. The early thinning treatment had no effect on the C distribution across each soil organic matter fraction. However, proportionally more C was found in mineral-associated organic matter and less in particulate organic matter in the more intensive management regime treatment, possibly due to higher below ground nutrient inputs and enhanced microbial activity. Our results suggest that management intensification to support biofuel production from loblolly pine plantations will not affect soil C stocks, but may increase their persistence. This study demonstrates that, from a soil C perspective, early thinning of intensively managed loblolly pine plantations has potential as a sustainable biofuel feedstock.