Recent (<4 year old) leaf litter is not a major source of microbial carbon in a temperate forest mineral soil

Christiane Kramer; Susan Trumbore; Mats Fröberg; Luz Maria Cisneros Dozal; Dachun Zhang; Xiaomei Xu; Guaciara M. Santos; Paul J. Hanson

doi:10.1016/j.soilbio.2010.02.021

Recent (<4 year old) leaf litter is not a major source of microbial carbon in a temperate forest mineral soil

Christiane Kramer, Susan Trumbore, Mats Fröberg, Luz Maria Cisneros Dozal, Dachun Zhang, Xiaomei Xu, Guaciara M. Santos, Paul J. Hanson

Environmental Sciences Division

Research output: Contribution to journal › Article › peer-review

123 Scopus citations

Abstract

Microbial communities in soil A horizons derive their carbon from several potential sources: organic carbon (C) transported down from overlying litter and organic horizons, root-derived C, or soil organic matter. We took advantage of a multi-year experiment that manipulated the ¹⁴C isotope signature of surface leaf litter inputs in a temperate forest at the Oak Ridge Reservation, Tennessee, USA, to quantify the contribution of recent leaf litter C to microbial respiration and biomarkers in the underlying mineral soil. We observed no measurable difference (<∼40‰ given our current analytical methods) in the radiocarbon signatures of microbial phospholipid fatty acids (PLFA) isolated from the top 10cm of mineral soil in plots that experienced 3 years of litterfall that differed in each year by ∼750‰ between high-¹⁴C and low-¹⁴C treatments. Assuming any difference in ¹⁴C between the high- and low-¹⁴C plots would reflect C derived from these manipulated litter additions, we estimate that <∼6% of the microbial C after 4 years was derived from the added 1-4-year-old surface litter. Large contributions of C from litter<1 year (or >4 years) old (which fell after (or prior to) the manipulation and therefore did not differ between plots) are not supported because the ¹⁴C signatures of the PLFA compounds (averaging 200-220‰) is much higher that of the 2004-5 leaf litter (115‰) or pre-2000 litter. A mesocosm experiment further demonstrated that C leached from ¹⁴C-enriched surface litter or the O horizon was not a detectable C source in underlying mineral soil microbes during the first eight months after litter addition. Instead a decline in the ¹⁴C of PLFA over the mesocosm experiment likely reflected the loss of a pre-existing substrate not associated with added leaf litter. Measured PLFA Δ¹⁴C signatures were higher than those measured in bulk mineral soil organic matter in our experiments, but fell within the range of ¹⁴C values measured in mineral soil roots. Together, our experiments suggest that root-derived C is the major (>60%) source of C for microbes in these temperate deciduous forest soils.

Original language	English
Pages (from-to)	1028-1037
Number of pages	10
Journal	Soil Biology and Biochemistry
Volume	42
Issue number	7
DOIs	https://doi.org/10.1016/j.soilbio.2010.02.021
State	Published - Jul 2010

Funding

Funding for the EBIS project was provided by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research, as a part of the Terrestrial Carbon Processes Program. Work at the Oak Ridge National Laboratory (ORNL) is managed by UT-Battelle, LLC, for the DOE under contract DE-AC05-00OR22725. We thank John Greaves of the UCI Physical Sciences Mass Spectrometry Facility for help with compound identification and the W.M Keck Carbon Cycle Accelerator Mass Spectrometry Facility at UC Irvine. We also thank Margaret Torn, Chris Swanston, Julie Jastrow and Gerd Gleixner for access to data and helpful comments, and two anonymous reviewers for helpful suggestions to improve the manuscript.

Funders	Funder number
U.S. Department of Energy
Office of Science
Biological and Environmental Research
Oak Ridge National Laboratory	DE-AC05-00OR22725

Keywords

C
EBIS
Heterotrophic respiration
Isotope
Microbial carbon
Microbial respiration
PLFA
Phospholipid fatty acid
Radiocarbon
Soil respiration

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@article{94e294b9c1e7413ba3f4048d7fdd0a58,

title = "Recent (<4 year old) leaf litter is not a major source of microbial carbon in a temperate forest mineral soil",

abstract = "Microbial communities in soil A horizons derive their carbon from several potential sources: organic carbon (C) transported down from overlying litter and organic horizons, root-derived C, or soil organic matter. We took advantage of a multi-year experiment that manipulated the 14C isotope signature of surface leaf litter inputs in a temperate forest at the Oak Ridge Reservation, Tennessee, USA, to quantify the contribution of recent leaf litter C to microbial respiration and biomarkers in the underlying mineral soil. We observed no measurable difference (<∼40‰ given our current analytical methods) in the radiocarbon signatures of microbial phospholipid fatty acids (PLFA) isolated from the top 10cm of mineral soil in plots that experienced 3 years of litterfall that differed in each year by ∼750‰ between high-14C and low-14C treatments. Assuming any difference in 14C between the high- and low-14C plots would reflect C derived from these manipulated litter additions, we estimate that <∼6% of the microbial C after 4 years was derived from the added 1-4-year-old surface litter. Large contributions of C from litter<1 year (or >4 years) old (which fell after (or prior to) the manipulation and therefore did not differ between plots) are not supported because the 14C signatures of the PLFA compounds (averaging 200-220‰) is much higher that of the 2004-5 leaf litter (115‰) or pre-2000 litter. A mesocosm experiment further demonstrated that C leached from 14C-enriched surface litter or the O horizon was not a detectable C source in underlying mineral soil microbes during the first eight months after litter addition. Instead a decline in the 14C of PLFA over the mesocosm experiment likely reflected the loss of a pre-existing substrate not associated with added leaf litter. Measured PLFA Δ14C signatures were higher than those measured in bulk mineral soil organic matter in our experiments, but fell within the range of 14C values measured in mineral soil roots. Together, our experiments suggest that root-derived C is the major (>60%) source of C for microbes in these temperate deciduous forest soils.",

keywords = "C, EBIS, Heterotrophic respiration, Isotope, Microbial carbon, Microbial respiration, PLFA, Phospholipid fatty acid, Radiocarbon, Soil respiration",

author = "Christiane Kramer and Susan Trumbore and Mats Fr{\"o}berg and {Cisneros Dozal}, {Luz Maria} and Dachun Zhang and Xiaomei Xu and Santos, {Guaciara M.} and Hanson, {Paul J.}",

year = "2010",

month = jul,

doi = "10.1016/j.soilbio.2010.02.021",

language = "English",

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T1 - Recent (<4 year old) leaf litter is not a major source of microbial carbon in a temperate forest mineral soil

AU - Kramer, Christiane

AU - Trumbore, Susan

AU - Fröberg, Mats

AU - Cisneros Dozal, Luz Maria

AU - Zhang, Dachun

AU - Xu, Xiaomei

AU - Santos, Guaciara M.

AU - Hanson, Paul J.

PY - 2010/7

Y1 - 2010/7

N2 - Microbial communities in soil A horizons derive their carbon from several potential sources: organic carbon (C) transported down from overlying litter and organic horizons, root-derived C, or soil organic matter. We took advantage of a multi-year experiment that manipulated the 14C isotope signature of surface leaf litter inputs in a temperate forest at the Oak Ridge Reservation, Tennessee, USA, to quantify the contribution of recent leaf litter C to microbial respiration and biomarkers in the underlying mineral soil. We observed no measurable difference (<∼40‰ given our current analytical methods) in the radiocarbon signatures of microbial phospholipid fatty acids (PLFA) isolated from the top 10cm of mineral soil in plots that experienced 3 years of litterfall that differed in each year by ∼750‰ between high-14C and low-14C treatments. Assuming any difference in 14C between the high- and low-14C plots would reflect C derived from these manipulated litter additions, we estimate that <∼6% of the microbial C after 4 years was derived from the added 1-4-year-old surface litter. Large contributions of C from litter<1 year (or >4 years) old (which fell after (or prior to) the manipulation and therefore did not differ between plots) are not supported because the 14C signatures of the PLFA compounds (averaging 200-220‰) is much higher that of the 2004-5 leaf litter (115‰) or pre-2000 litter. A mesocosm experiment further demonstrated that C leached from 14C-enriched surface litter or the O horizon was not a detectable C source in underlying mineral soil microbes during the first eight months after litter addition. Instead a decline in the 14C of PLFA over the mesocosm experiment likely reflected the loss of a pre-existing substrate not associated with added leaf litter. Measured PLFA Δ14C signatures were higher than those measured in bulk mineral soil organic matter in our experiments, but fell within the range of 14C values measured in mineral soil roots. Together, our experiments suggest that root-derived C is the major (>60%) source of C for microbes in these temperate deciduous forest soils.

AB - Microbial communities in soil A horizons derive their carbon from several potential sources: organic carbon (C) transported down from overlying litter and organic horizons, root-derived C, or soil organic matter. We took advantage of a multi-year experiment that manipulated the 14C isotope signature of surface leaf litter inputs in a temperate forest at the Oak Ridge Reservation, Tennessee, USA, to quantify the contribution of recent leaf litter C to microbial respiration and biomarkers in the underlying mineral soil. We observed no measurable difference (<∼40‰ given our current analytical methods) in the radiocarbon signatures of microbial phospholipid fatty acids (PLFA) isolated from the top 10cm of mineral soil in plots that experienced 3 years of litterfall that differed in each year by ∼750‰ between high-14C and low-14C treatments. Assuming any difference in 14C between the high- and low-14C plots would reflect C derived from these manipulated litter additions, we estimate that <∼6% of the microbial C after 4 years was derived from the added 1-4-year-old surface litter. Large contributions of C from litter<1 year (or >4 years) old (which fell after (or prior to) the manipulation and therefore did not differ between plots) are not supported because the 14C signatures of the PLFA compounds (averaging 200-220‰) is much higher that of the 2004-5 leaf litter (115‰) or pre-2000 litter. A mesocosm experiment further demonstrated that C leached from 14C-enriched surface litter or the O horizon was not a detectable C source in underlying mineral soil microbes during the first eight months after litter addition. Instead a decline in the 14C of PLFA over the mesocosm experiment likely reflected the loss of a pre-existing substrate not associated with added leaf litter. Measured PLFA Δ14C signatures were higher than those measured in bulk mineral soil organic matter in our experiments, but fell within the range of 14C values measured in mineral soil roots. Together, our experiments suggest that root-derived C is the major (>60%) source of C for microbes in these temperate deciduous forest soils.

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KW - EBIS

KW - Heterotrophic respiration

KW - Isotope

KW - Microbial carbon

KW - Microbial respiration

KW - PLFA

KW - Phospholipid fatty acid

KW - Radiocarbon

KW - Soil respiration

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VL - 42

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JO - Soil Biology and Biochemistry

JF - Soil Biology and Biochemistry

IS - 7

ER -

Recent (<4 year old) leaf litter is not a major source of microbial carbon in a temperate forest mineral soil

Abstract

Funding

Keywords

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