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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Long Term Decomposition: The Influence Of Litter Type And Soil Horizon On Retention Of Plant Carbon And Nitrogen In Soils

Margaret S. Torn
Lawrence Berkeley National Laboratory

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5/30/2017

Litter type affects initial decomposition rates, but soil horizon affects mechanisms of long-term soil carbon stabilization

The Science  
In one of the few studies examining litter decay over a decade, Berkeley scientists used stable isotope labels to trace plant litter-derived carbon and nitrogen as they decomposed and formed soil organic matter. They found that the litter type (needles or roots) and the soil environment (organic or mineral horizon) both affected decomposition, but at different timescales.

The Impact
This study helps bridge the gap between studies of litter decomposition and soil organic matter by tracing how litter becomes soil organic matter over a decade. The results back the recent paradigm shift in our understanding of soil carbon research be demonstrating that the long-term retention of litter-derived carbon and nitrogen soil is an ecosystem property dependent on the soil horizon in which the litter was placed.

Summary
We found that the legacy of the type of plant inputs (root or needle litter) affected total C and N retention over 10 years, but that soil horizon affected how the litter-derived SOM is stabilized in the long term. In the organic (O) horizon, litter was retained in the coarse particulate size fraction (>2 mm) over 10 years, likely due to conditions that limited its physical breakdown. In the mineral (A) horizon, litter-derived C and N were retained in a finer size fraction (<2 mm), likely due to association with minerals that prevent microbes from accessing the C and N. Litter type had no effect on the stabilization of litter-derived C and N in mineral-associated pools. After 10 years, 5% of initial C and 15% of initial N were retained in organo-mineral associations, which form the most persistent organic matter in soils. Very little litter-derived C moved vertically in the soil profile over the decade, but N was significantly more mobile.

Contacts (BER PM)
Dan Stover, TES Program Manager
301-903-0289
daniel.stover@science.doe.gov

PI Contact
Margaret S. Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Funding
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program under contract number DE-AC02-05CH11231.

Publications
Hicks Pries C, JA Bird, C Castanha, PJ Hatton, and MS Torn. 2017. Long term decomposition: the influence of litter type and soil horizon on retention of plant carbon and nitrogen in soils. Biogeochemistry. doi:10.1007/s10533-017-0345-6 (Reference link)

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