Movement of Isotopically Depleted Face Log C into Mineral Soil after Six Years of Decomposition

Document Type

Conference Proceeding

Publication Date

1-8-2019

Department

College of Forest Resources and Environmental Science

Abstract

Dead wood can be a significant forest C pool, and understanding the extent and mechanisms regulating its incorporation into stable mineral soil C fractions is important for assessing the effects of climate change and forest management practices on ecosystem C sequestration. However, C from wood decomposition cannot easily be differentiated from other soil C using standard analyses. We addressed this problem using the depleted wood 13C signature in loblolly pine, trembling aspen and paper birch logs grown at Free-Air Carbon dioxide Enrichment (FACE) experiments. Logs of the species were placed in nine forests across the U.S. in 2011. After four and six years of decomposition in the field, we sampled the forest floor and mineral soil beneath the decomposing logs. For the year six sampling, soil adjacent to the logs was also sampled. Samples were analyzed for C and 13C, as were samples from control soil distant from FACE logs. Two end-member mixing models were used to estimate the proportion of soil C that originated from the decomposing FACE logs. The amount of wood C that could be found in soil beneath the logs increased greatly from the fourth to sixth year of decomposition, doubling to quadrupling at most sites. On average, about 3% of the C originally in the logs could be found in the top 10 cm of soil beneath the logs after six years, with an approximately equal amount of wood C existing in surface mineral soil within 30 cm adjacent to the logs. There were clear species differences, with aspen and birch having faster movement of wood C into soil at most sites. Through six years, climate has been a strong driver of decomposition rate and movement of wood C into mineral soil, with rates being fastest for warm, moist sites.

Publication Title

Soil Science Society of America International Soils meeting

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