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Short-term carbon input increases microbial nitrogen demand, but not microbial nitrogen mining, in a set of boreal forest soils

Wild, Birgit; Alaei, Saeed LU ; Bengtson, Per LU ; Bodé, Samuel; Boeckx, Pascal; Schnecker, Jörg; Mayerhofer, Werner and Rütting, Tobias (2017) In Biogeochemistry 136(3). p.261-278
Abstract

Rising carbon dioxide (CO2) concentrations and temperatures are expected to stimulate plant productivity and ecosystem C sequestration, but these effects require a concurrent increase in N availability for plants. Plants might indirectly promote N availability as they release organic C into the soil (e.g., by root exudation) that can increase microbial soil organic matter (SOM) decomposition (“priming effect”), and possibly the enzymatic breakdown of N-rich polymers, such as proteins, into bio-available units (“N mining”). We tested the adjustment of protein depolymerization to changing soil C and N availability in a laboratory experiment. We added easily available C or N sources to six boreal forest soils, and determined... (More)

Rising carbon dioxide (CO2) concentrations and temperatures are expected to stimulate plant productivity and ecosystem C sequestration, but these effects require a concurrent increase in N availability for plants. Plants might indirectly promote N availability as they release organic C into the soil (e.g., by root exudation) that can increase microbial soil organic matter (SOM) decomposition (“priming effect”), and possibly the enzymatic breakdown of N-rich polymers, such as proteins, into bio-available units (“N mining”). We tested the adjustment of protein depolymerization to changing soil C and N availability in a laboratory experiment. We added easily available C or N sources to six boreal forest soils, and determined soil organic C mineralization, gross protein depolymerization and gross ammonification rates (using 15N pool dilution assays), and potential extracellular enzyme activities after 1 week of incubation. Added C sources were 13C-labelled to distinguish substrate from soil derived C mineralization. Observed effects reflect short-term adaptations of non-symbiotic soil microorganisms to increased C or N availability. Although C input promoted microbial growth and N demand, we did not find indicators of increased N mobilization from SOM polymers, given that none of the soils showed a significant increase in protein depolymerization, and only one soil showed a significant increase in N-targeting enzymes. Instead, our findings suggest that microorganisms immobilized the already available N more efficiently, as indicated by decreased ammonification and inorganic N concentrations. Likewise, although N input stimulated ammonification, we found no significant effect on protein depolymerization. Although our findings do not rule out in general that higher plant-soil C allocation can promote microbial N mining, they suggest that such an effect can be counteracted, at least in the short term, by increased microbial N immobilization, further aggravating plant N limitation.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Ammonification, Boreal forest, Microbial N mining, N mineralization, Organic N, Priming, Protein depolymerization
in
Biogeochemistry
volume
136
issue
3
pages
261 - 278
publisher
Springer
external identifiers
  • scopus:85032358644
  • wos:000416325100003
ISSN
0168-2563
DOI
10.1007/s10533-017-0391-0
language
English
LU publication?
yes
id
fd8df779-510f-4a39-96d1-38280253dabc
date added to LUP
2017-11-07 13:14:31
date last changed
2018-02-19 02:06:52
@article{fd8df779-510f-4a39-96d1-38280253dabc,
  abstract     = {<p>Rising carbon dioxide (CO<sub>2</sub>) concentrations and temperatures are expected to stimulate plant productivity and ecosystem C sequestration, but these effects require a concurrent increase in N availability for plants. Plants might indirectly promote N availability as they release organic C into the soil (e.g., by root exudation) that can increase microbial soil organic matter (SOM) decomposition (“priming effect”), and possibly the enzymatic breakdown of N-rich polymers, such as proteins, into bio-available units (“N mining”). We tested the adjustment of protein depolymerization to changing soil C and N availability in a laboratory experiment. We added easily available C or N sources to six boreal forest soils, and determined soil organic C mineralization, gross protein depolymerization and gross ammonification rates (using <sup>15</sup>N pool dilution assays), and potential extracellular enzyme activities after 1 week of incubation. Added C sources were <sup>13</sup>C-labelled to distinguish substrate from soil derived C mineralization. Observed effects reflect short-term adaptations of non-symbiotic soil microorganisms to increased C or N availability. Although C input promoted microbial growth and N demand, we did not find indicators of increased N mobilization from SOM polymers, given that none of the soils showed a significant increase in protein depolymerization, and only one soil showed a significant increase in N-targeting enzymes. Instead, our findings suggest that microorganisms immobilized the already available N more efficiently, as indicated by decreased ammonification and inorganic N concentrations. Likewise, although N input stimulated ammonification, we found no significant effect on protein depolymerization. Although our findings do not rule out in general that higher plant-soil C allocation can promote microbial N mining, they suggest that such an effect can be counteracted, at least in the short term, by increased microbial N immobilization, further aggravating plant N limitation.</p>},
  author       = {Wild, Birgit and Alaei, Saeed and Bengtson, Per and Bodé, Samuel and Boeckx, Pascal and Schnecker, Jörg and Mayerhofer, Werner and Rütting, Tobias},
  issn         = {0168-2563},
  keyword      = {Ammonification,Boreal forest,Microbial N mining,N mineralization,Organic N,Priming,Protein depolymerization},
  language     = {eng},
  number       = {3},
  pages        = {261--278},
  publisher    = {Springer},
  series       = {Biogeochemistry},
  title        = {Short-term carbon input increases microbial nitrogen demand, but not microbial nitrogen mining, in a set of boreal forest soils},
  url          = {http://dx.doi.org/10.1007/s10533-017-0391-0},
  volume       = {136},
  year         = {2017},
}