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Decoupling of priming and microbial N mining during a short-term soil incubation

Wild, Birgit; Li, Jian LU ; Pihlblad, Johanna; Bengtson, Per LU and Rütting, Tobias (2019) In Soil Biology and Biochemistry 129. p.71-79
Abstract

Soil carbon (C) and nitrogen (N) availability depend on the breakdown of soil polymers such as lignin, chitin, and protein that represent the major fraction of soil C and N but are too large for immediate uptake by plants and microorganisms. Microorganisms may adjust the production of enzymes targeting different polymers to optimize the balance between C and N availability and demand, and for instance increase the depolymerization of N-rich compounds when C availability is high and N availability low (“microbial N mining”). Such a mechanism could mitigate plant N limitation but also lie behind a stimulation of soil respiration frequently observed in the vicinity of plant roots (“priming effect”). We here compared the effect of increased... (More)

Soil carbon (C) and nitrogen (N) availability depend on the breakdown of soil polymers such as lignin, chitin, and protein that represent the major fraction of soil C and N but are too large for immediate uptake by plants and microorganisms. Microorganisms may adjust the production of enzymes targeting different polymers to optimize the balance between C and N availability and demand, and for instance increase the depolymerization of N-rich compounds when C availability is high and N availability low (“microbial N mining”). Such a mechanism could mitigate plant N limitation but also lie behind a stimulation of soil respiration frequently observed in the vicinity of plant roots (“priming effect”). We here compared the effect of increased C and N availability on the depolymerization of native bulk soil organic matter (SOM), and of 13C-enriched lignin, chitin, and protein added to the same soil in two complementary ten day microcosm incubation experiments. A significant reduction of chitin depolymerization (described by the recovery of chitin-derived C in the sum of dissolved organic, microbial and respired C) upon N addition indicated that chitin was degraded to serve as a microbial N source under low-N conditions and replaced in the presence of an immediately available alternative. Protein and lignin depolymerization in contrast were not affected by N addition. Carbon addition enhanced microbial N demand and SOM decomposition rates, but significantly reduced lignin, chitin, and protein depolymerization. Our findings contrast the hypothesis of increased microbial N mining as a key driver behind the priming effect and rather suggest that C addition promoted the mobilization of other soil C pools that replaced lignin, chitin, and protein as microbial C sources, for instance by releasing soil compounds from mineral bonds. We conclude that SOM decomposition is interactively controlled by multiple mechanisms including the balance between C vs N availability. Disentangling these controls will be crucial for understanding C and N cycling on an ecosystem scale.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Chitin, Decomposition, Extracellular enzymes, Lignin, Phospholipid fatty acids, Protein
in
Soil Biology and Biochemistry
volume
129
pages
9 pages
publisher
Elsevier
external identifiers
  • scopus:85056833495
ISSN
0038-0717
DOI
10.1016/j.soilbio.2018.11.014
language
English
LU publication?
yes
id
029e236a-399c-4d9f-8f40-d93ecf03a3e9
date added to LUP
2018-11-29 11:13:56
date last changed
2019-01-06 14:17:54
@article{029e236a-399c-4d9f-8f40-d93ecf03a3e9,
  abstract     = {<p>Soil carbon (C) and nitrogen (N) availability depend on the breakdown of soil polymers such as lignin, chitin, and protein that represent the major fraction of soil C and N but are too large for immediate uptake by plants and microorganisms. Microorganisms may adjust the production of enzymes targeting different polymers to optimize the balance between C and N availability and demand, and for instance increase the depolymerization of N-rich compounds when C availability is high and N availability low (“microbial N mining”). Such a mechanism could mitigate plant N limitation but also lie behind a stimulation of soil respiration frequently observed in the vicinity of plant roots (“priming effect”). We here compared the effect of increased C and N availability on the depolymerization of native bulk soil organic matter (SOM), and of <sup>13</sup>C-enriched lignin, chitin, and protein added to the same soil in two complementary ten day microcosm incubation experiments. A significant reduction of chitin depolymerization (described by the recovery of chitin-derived C in the sum of dissolved organic, microbial and respired C) upon N addition indicated that chitin was degraded to serve as a microbial N source under low-N conditions and replaced in the presence of an immediately available alternative. Protein and lignin depolymerization in contrast were not affected by N addition. Carbon addition enhanced microbial N demand and SOM decomposition rates, but significantly reduced lignin, chitin, and protein depolymerization. Our findings contrast the hypothesis of increased microbial N mining as a key driver behind the priming effect and rather suggest that C addition promoted the mobilization of other soil C pools that replaced lignin, chitin, and protein as microbial C sources, for instance by releasing soil compounds from mineral bonds. We conclude that SOM decomposition is interactively controlled by multiple mechanisms including the balance between C vs N availability. Disentangling these controls will be crucial for understanding C and N cycling on an ecosystem scale.</p>},
  author       = {Wild, Birgit and Li, Jian and Pihlblad, Johanna and Bengtson, Per and Rütting, Tobias},
  issn         = {0038-0717},
  keyword      = {Chitin,Decomposition,Extracellular enzymes,Lignin,Phospholipid fatty acids,Protein},
  language     = {eng},
  pages        = {71--79},
  publisher    = {Elsevier},
  series       = {Soil Biology and Biochemistry},
  title        = {Decoupling of priming and microbial N mining during a short-term soil incubation},
  url          = {http://dx.doi.org/10.1016/j.soilbio.2018.11.014},
  volume       = {129},
  year         = {2019},
}