Root litter decomposition slows with soil depth

Journal Article · Thu Jul 12 00:00:00 EDT 2018 · Soil Biology and Biochemistry

DOI:https://doi.org/10.1016/j.soilbio.2018.07.002· OSTI ID:1477394

Hicks Pries, Caitlin E. ^[1]; Sulman, Benjamin N. ^[2]; West, Corinna ^[3]; O'Neill, Caitlin ^[4]; Poppleton, Erik ^[5]; Porras, Rachel C. ^[6]; Castanha, Cristina ^[6]; Zhu, Biao ^[7]; Wiedemeier, Daniel B. ^[8]; Torn, Margaret S. ^[6]

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1. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Dartmouth College, Hanover, NH (United States)
2. Princeton University, NJ (United States); University of California, Merced, CA (United States)
3. University of Wisconsin, Madison, WI (United States)
4. University of Illinois, Urbana-Champaign, IL (United States)
5. Arizona State University, Tempe, AZ (United States); Tufts University, Medford, MA (United States)
6. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
7. Peking University, Beijing (China)
8. University of Zurich (Switzerland)

Even though over half of the world's soil organic carbon (SOC) is stored in subsoils (>20 cm deep), and the old ages of subsoil OC indicate its cycling differs from surface SOC, there are few studies examining in situ decomposition processes in deep soils. Here, we added 13C-labeled fine roots to 15, 55, and 95 cm depths of a well-characterized coniferous forest Alfisol and monitored the amount of root-derived C remaining over 6, 12, and 30 months. We recovered the root-derived C in microbial phospholipid fatty acids (PLFAs) after 6 months and in coarse (>2 mm) particulate, fine (<2 mm) particulate, and dense, mineral-associated pools after 6, 12, and 30 months. Overall, root decomposition in the first 6 months was similar among all depths but significantly diverged at 30 months with faster decomposition at 15 cm than at 95 cm. There were more fungal and Gram negative-associated PLFAs at 15 cm than at 95 cm, and13C analysis revealed those microbial groups preferred the added root carbon to native SOC. Mineral-associations were not the cause of slower decomposition at depth because similar amounts of applied root C was recovered in the dense fraction at all depths. The largest difference among depths was in the amount of root C recovered in the coarse particulate fraction, which was greater at 95 cm (50%) than at 15 cm (15%). Slower decomposition of the particulate pool at depth likely contributed to the increase in C:N ratios and depletion of δ13C values below 60 cm depth in our soil profiles. Simulations of these soils using the CORPSE model, which incorporates microbial priming effects and mineral stabilization of SOC, reproduced patterns of particulate and mineral-associated SOC over both time and depth and suggested that a lack of priming by root exudates at depth could account for the slower decomposition rate of particulate root material. Decomposition of deep particulate SOC may increase if root exudation or dissolved OC transport to depth increases.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1477394
• Alternate ID(s): OSTI ID: 1548083
• Journal Information: Soil Biology and Biochemistry, Journal Name: Soil Biology and Biochemistry Journal Issue: C Vol. 125; ISSN 0038-0717
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

13C
59 BASIC BIOLOGICAL SCIENCES
PLFA
carbon
decomposition
density fractionation
fine root
soil depth
soil organic matter