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

Author:
  • Birgit Wild
  • Jian Li
  • Johanna Pihlblad
  • Per Bengtson
  • Tobias Rütting
Publishing year: 2019
Language: English
Pages: 71-79
Publication/Series: Soil Biology and Biochemistry
Volume: 129
Document type: Journal article
Publisher: Elsevier

Abstract english

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.

Keywords

  • Geochemistry
  • Chitin
  • Decomposition
  • Extracellular enzymes
  • Lignin
  • Phospholipid fatty acids
  • Protein

Other

Published
  • MICCS - Molecular Interactions Controlling soil Carbon Sequestration
  • ISSN: 0038-0717
Per Bengtson
E-mail: per [dot] bengtson [at] biol [dot] lu [dot] se

Researcher

MEMEG

+46 46 222 37 60

E-F212

Sölvegatan 37, Lund

50

Research group

Microbial Ecology

Projects

Doctoral students and postdocs

PhD students, main supervisor

 

PhD students, assistant supervisor

Jian Li

Experimental setup