Effects of grazing on microbial functional groups involved in soil N dynamics

A. K. Patra, L. Abbadie, A. Clays-Josserand, V. Degrange, S. J. Grayston, P. Loiseau, F. Louault, S. Mahmood, S. Nazaret, L. Philippot, F. Poly, J. I. Prosser, A. Richaume, X. Le Roux*

*Corresponding author for this work

Research output: Contribution to journalArticle

158 Citations (Scopus)

Abstract

Enhancement of soil nitrogen (N) cycling by grazing has been observed in many grassland ecosystems. However, whether grazing affects the activity only of the key microbial functional groups driving soil N dynamics or also affects the size (cell number) and/or composition of these groups remains largely unknown. We studied the enzyme activity, size, and composition of five soil microbial communities (total microbial and total bacterial communities, and three functional groups driving N dynamics: nitrifiers, denitrifiers, and free N 2 fixers) in grassland sites experiencing contrasting sheep grazing regimes (one light grazing [LG] site and one intensive grazing [IG] site) at two topographical locations. Enzyme activity was determined by potential carbon mineralization, nitrification, denitrification, and N2 fixation assays. The size of each community (except N2 fixers) was measured by the most-probable-number technique. The composition of the total soil microbial community was characterized by phospholipid fatty acid analysis (PLFA), and the genetic structure of the total bacterial community was assessed by ribosomal intergenic spacer analysis. The genetic structures of the ammonia-oxidizing, nitrate-reducing, and N2-fixing communities were characterized by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) or by polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) targeting group-specific genes. Greater enzyme activities, particularly for nitrification, were observed in IG than in LG sites at both topographical locations. The numbers of heterotrophs, nitrifiers, and denitrifiers were higher in IG than in LG sites at both topographical locations. The amplitude of changes in community size was higher than that of community enzyme activity. Phospholipid and nucleic acid analyses showed that the composition/structure of all the communities, except nitrate reducers, differed between IG and LG sites at both locations. For each community, changes in activity were correlated with changes in the occurrence of a few individual PLFAs or DNA fragments. Our results thus indicate that grazing enhances the activity of soil microbial communities but also concurrently induces changes in the size and composition/structure of these communities on the sites studied. Although the generality of our conclusions should be tested in other systems, these results are of major importance for predicting the effects of future disturbances or changed grazing regimes on the functioning of grazed ecosystems.

Original languageEnglish
Pages (from-to)65-80
Number of pages16
JournalEcological Monographs
Volume75
Issue number1
DOIs
Publication statusPublished - 1 Feb 2005

Fingerprint

functional group
grazing
soil
enzyme activity
microbial communities
microbial community
phospholipid
bacterial communities
nitrification
effect
polymerase chain reaction
genetic structure
grasslands
nitrates
nitrate
heterotrophs
ecosystems
nucleic acid
denaturing gradient gel electrophoresis
soil nitrogen

Keywords

  • Carbon mineralization
  • Denitrification
  • Free N fixation
  • Grasslands
  • Grazing
  • Microbial diversity
  • Microbial functional communities
  • Nitrification
  • Nitrogen cycle

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

Cite this

Patra, A. K., Abbadie, L., Clays-Josserand, A., Degrange, V., Grayston, S. J., Loiseau, P., ... Le Roux, X. (2005). Effects of grazing on microbial functional groups involved in soil N dynamics. Ecological Monographs, 75(1), 65-80. https://doi.org/10.1890/03-0837

Effects of grazing on microbial functional groups involved in soil N dynamics. / Patra, A. K.; Abbadie, L.; Clays-Josserand, A.; Degrange, V.; Grayston, S. J.; Loiseau, P.; Louault, F.; Mahmood, S.; Nazaret, S.; Philippot, L.; Poly, F.; Prosser, J. I.; Richaume, A.; Le Roux, X.

In: Ecological Monographs, Vol. 75, No. 1, 01.02.2005, p. 65-80.

Research output: Contribution to journalArticle

Patra, AK, Abbadie, L, Clays-Josserand, A, Degrange, V, Grayston, SJ, Loiseau, P, Louault, F, Mahmood, S, Nazaret, S, Philippot, L, Poly, F, Prosser, JI, Richaume, A & Le Roux, X 2005, 'Effects of grazing on microbial functional groups involved in soil N dynamics', Ecological Monographs, vol. 75, no. 1, pp. 65-80. https://doi.org/10.1890/03-0837
Patra AK, Abbadie L, Clays-Josserand A, Degrange V, Grayston SJ, Loiseau P et al. Effects of grazing on microbial functional groups involved in soil N dynamics. Ecological Monographs. 2005 Feb 1;75(1):65-80. https://doi.org/10.1890/03-0837
Patra, A. K. ; Abbadie, L. ; Clays-Josserand, A. ; Degrange, V. ; Grayston, S. J. ; Loiseau, P. ; Louault, F. ; Mahmood, S. ; Nazaret, S. ; Philippot, L. ; Poly, F. ; Prosser, J. I. ; Richaume, A. ; Le Roux, X. / Effects of grazing on microbial functional groups involved in soil N dynamics. In: Ecological Monographs. 2005 ; Vol. 75, No. 1. pp. 65-80.
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N2 - Enhancement of soil nitrogen (N) cycling by grazing has been observed in many grassland ecosystems. However, whether grazing affects the activity only of the key microbial functional groups driving soil N dynamics or also affects the size (cell number) and/or composition of these groups remains largely unknown. We studied the enzyme activity, size, and composition of five soil microbial communities (total microbial and total bacterial communities, and three functional groups driving N dynamics: nitrifiers, denitrifiers, and free N 2 fixers) in grassland sites experiencing contrasting sheep grazing regimes (one light grazing [LG] site and one intensive grazing [IG] site) at two topographical locations. Enzyme activity was determined by potential carbon mineralization, nitrification, denitrification, and N2 fixation assays. The size of each community (except N2 fixers) was measured by the most-probable-number technique. The composition of the total soil microbial community was characterized by phospholipid fatty acid analysis (PLFA), and the genetic structure of the total bacterial community was assessed by ribosomal intergenic spacer analysis. The genetic structures of the ammonia-oxidizing, nitrate-reducing, and N2-fixing communities were characterized by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) or by polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) targeting group-specific genes. Greater enzyme activities, particularly for nitrification, were observed in IG than in LG sites at both topographical locations. The numbers of heterotrophs, nitrifiers, and denitrifiers were higher in IG than in LG sites at both topographical locations. The amplitude of changes in community size was higher than that of community enzyme activity. Phospholipid and nucleic acid analyses showed that the composition/structure of all the communities, except nitrate reducers, differed between IG and LG sites at both locations. For each community, changes in activity were correlated with changes in the occurrence of a few individual PLFAs or DNA fragments. Our results thus indicate that grazing enhances the activity of soil microbial communities but also concurrently induces changes in the size and composition/structure of these communities on the sites studied. Although the generality of our conclusions should be tested in other systems, these results are of major importance for predicting the effects of future disturbances or changed grazing regimes on the functioning of grazed ecosystems.

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