Sheep grazing decreases organic carbon and nitrogen pools in the patagonian steppe

Combination of direct and indirect effects

Rodolfo A. Golluscio, Amy T. Austin, Guillermo C. García Martínez, Marina Gonzalez-Polo, Osvaldo Sala, Robert B. Jackson

Research output: Contribution to journalArticle

63 Citations (Scopus)

Abstract

We explored the net effects of grazing on soil C and N pools in a Patagonian shrub-grass steppe (temperate South America). Net effects result from the combination of direct impacts of grazing on biogeochemical characteristics of microsites with indirect effects on relative cover of vegetated and unvegetated microsites. Within five independent areas, we sampled surface soils in sites subjected to three grazing intensities: (1) ungrazed sites inside grazing exclosures, (2) moderately grazed sites adjacent to them, and (3) intensely grazed sites within the same paddock. Grazing significantly reduced soil C and N pools, although this pattern was clearest in intensely grazed sites. This net effect was due to the combination of a direct reduction of soil N content in bare soil patches, and indirect effects mediated by the increase of the cover of bare soil microsites, with lower C and N content than either grass or shrub microsites. This increase in bare soil cover was accompanied by a reduction in cover of preferred grass species and standing dead material. Finally, stable isotope signatures varied significantly among grazed and ungrazed sites, with δ15N and δ13C significantly depleted in intensely grazed sites, suggesting reduced mineralization with increased grazing intensity. In the Patagonian steppe, grazing appears to exert a negative effect on soil C and N cycles; sound management practices must incorporate the importance of species shifts within life form, and the critical role of standing dead material in maintaining soil C and N stocks and biogeochemical processes.

Original languageEnglish (US)
Pages (from-to)686-697
Number of pages12
JournalEcosystems
Volume12
Issue number4
DOIs
StatePublished - Jun 2009
Externally publishedYes

Fingerprint

organic nitrogen
Organic carbon
steppes
steppe
sheep
Nitrogen
grazing
organic carbon
Soils
carbon
nitrogen
bare soil
soil
grass
grazing intensity
shrub
grasses
shrubs
soil cover
effect

Keywords

  • δC
  • δN
  • Argentina
  • Biogeochemistry
  • Desertification
  • Life forms
  • Semiarid ecosystems
  • Shrub-grass steppe
  • Stable isotopes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Environmental Chemistry

Cite this

Sheep grazing decreases organic carbon and nitrogen pools in the patagonian steppe : Combination of direct and indirect effects. / Golluscio, Rodolfo A.; Austin, Amy T.; García Martínez, Guillermo C.; Gonzalez-Polo, Marina; Sala, Osvaldo; Jackson, Robert B.

In: Ecosystems, Vol. 12, No. 4, 06.2009, p. 686-697.

Research output: Contribution to journalArticle

Golluscio, Rodolfo A. ; Austin, Amy T. ; García Martínez, Guillermo C. ; Gonzalez-Polo, Marina ; Sala, Osvaldo ; Jackson, Robert B. / Sheep grazing decreases organic carbon and nitrogen pools in the patagonian steppe : Combination of direct and indirect effects. In: Ecosystems. 2009 ; Vol. 12, No. 4. pp. 686-697.
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