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Title: The relative importance of exogenous and substrate-derived nitrogen for microbial growth during leaf decomposition

Author: Cheever, B.M.; Webster, J. R.; Bilger, E. E.; Thomas, S. A.;

Date: 2013

Source: Ecology 94(7):1614–1625

Publication Series: Scientific Journal (JRNL)

Description: Heterotrophic microbes colonizing detritus obtain nitrogen (N) for growth by assimilating N from their substrate or immobilizing exogenous inorganic N. Microbial use of these two pools has different implications for N cycling and organic matter decomposition in the face of the global increase in biologically available N. We used sugar maple leaves labeled with 15N to differentiate between microbial N that had been assimilated from the leaf substrate (enriched with 15N) or immobilized from the water (natural abundance 15N:14N) in five Appalachian streams ranging in ambient NO3-N concentrations from about 5 to 900 μg NO3-N/L. Ambient NO3- concentration increased sugar maple decomposition rate but did not influence the proportion of microbial N derived from substrate or exogenous pools. Instead, these proportions were strongly influenced by the percentage of detrital ash-free dry mass (AFDM) remaining. Substrate-derived N made up a large proportion of the microbial N after the first 24 h in all streams. Detrital and microbial isotopic 15N signatures approached that of the water as decomposition progressed in all streams, suggesting that exogenous N may be the predominant source of N for meeting microbial requirements even when exogenous N concentrations are low. Our results support predictions of more rapid decomposition of organic matter in response to increased N availability and highlight the tight coupling of processes driving microbial N cycling and organic matter decomposition.

Keywords: 15N, assimilation, chloroform fumigation, heterotrophic microbes, immobilization, nitrogen availability, nitrogen cycling, organic matter decomposition, streams

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Cheever, B.M.; Webster, J. R.; Bilger, E. E.; Thomas, S. A. 2013. The relative importance of exogenous and substrate-derived nitrogen for microbial growth during leaf decomposition. Ecology 94(7):1614–1625. http://dx.doi.org/10.1890/12-1339.1

 


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