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| Titel |
Stoichiometry constrains microbial response to root exudation- insights from a model and a field experiment in a temperate forest |
| VerfasserIn |
J. E. Drake, B. A. Darby, M.-A. Giasson, M. A. Kramer, R. P. Phillips, A. C. Finzi |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 2 ; Nr. 10, no. 2 (2013-02-07), S.821-838 |
| Datensatznummer |
250017503
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| Publikation (Nr.) |
 copernicus.org/bg-10-821-2013.pdf |
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| Zusammenfassung |
| Plant roots release a wide range of chemicals into soils. This process,
termed root exudation, is thought to increase the activity of microbes and
the exoenzymes they synthesize, leading to accelerated rates of carbon (C)
mineralization and nutrient cycling in rhizosphere soils relative to bulk
soils. The nitrogen (N) content of microbial biomass and exoenzymes may
introduce a stoichiometric constraint on the ability of microbes to
effectively utilize the root exudates, particularly if the exudates are rich
in C but low in N. We combined a theoretical model of microbial activity
with an exudation experiment to test the hypothesis that the ability of soil
microbes to utilize root exudates for the synthesis of additional biomass
and exoenzymes is constrained by N availability. The field experiment
simulated exudation by automatically pumping solutions of chemicals often
found in root exudates ("exudate mimics") containing C alone or C in
combination with N (C : N ratio of 10) through microlysimeter "root
simulators" into intact forest soils in two 50-day experiments. The
delivery of C-only exudate mimics increased microbial respiration but had no
effect on microbial biomass or exoenzyme activities. By contrast,
experimental delivery of exudate mimics containing both C and N
significantly increased microbial respiration, microbial biomass, and the
activity of exoenzymes that decompose low molecular weight components of
soil organic matter (SOM, e.g., cellulose, amino sugars), while decreasing
the activity of exoenzymes that degrade high molecular weight SOM (e.g.,
polyphenols, lignin). The modeling results were consistent with the
experiments; simulated delivery of C-only exudates induced microbial
N-limitation, which constrained the synthesis of microbial biomass and
exoenzymes. Exuding N as well as C alleviated this stoichiometric
constraint in the model, allowing for increased exoenzyme production, the
priming of decomposition, and a net release of N from SOM (i.e.,
mineralization). The quantity of N released from SOM in the model
simulations was, under most circumstances, in excess of the N in the exudate pulse,
suggesting that the exudation of N-containing compounds can be a viable
strategy for plant-N acquisition via a priming effect. The experimental and
modeling results were consistent with our hypothesis that N-containing
compounds in root exudates affect rhizosphere processes by providing
substrates for the synthesis of N-rich microbial biomass and exoenzymes.
This study suggests that exudate stoichiometry is an important and
underappreciated driver of microbial activity in rhizosphere soils. |
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