JOBBAGY GAMPEL Esteban Gabriel
An assessment of grazing effects on soil organic carbon and nitrogen
G PIÑEIRO; JM PARUELO; M OESTERHELD; EG JOBBÁGY
Rangeland Ecology and Management (ex JRM)
Society for Range Management
Lugar: Washington DC; Año: 2010 vol. 63 p. 109 - 119
Grazing modifies the structure and function of ecosystems affecting soil organic carbon(SOC) and soil organic nitrogen (SON) storage. Although grazing effects on someecosystem attributes (i.e aboveground primary production or species composition) havebeen successfully reviewed, a comprehensive review of grazing effects on SOC is stilllacking. Our objective is to synthesize the effects of grazing on SOC stocks ingrasslands, establishing the major mechanistic pathways involved. Additionally, and dueto its importance for C biogeochemistry, we discuss the controls of soil organic nitrogen(SON) stocks in grasslands. We reviewed articles analyzing grazing effects onbelowground C stocks and other soil properties, including 67 grazed-ungrazed pairedcomparisons. The review of the literature showed that grazing consistently increased soilC/N ratio, revealing potential N limitations for soil organic matter formation undergrazing. C in roots and other belowground organs was greater in grazed than inungrazed stands at dry and wet sites, but lower in mesic sites. We grouped previouslyproposed mechanisms of grazing control over SOC into three major pathways which canoperate simultaneously and include: (a) changes in net primary production (NPPpathway), (b) changes in nitrogen stocks (nitrogen pathway) and (c) changes in organicmatter decomposition (decomposition pathway). The relative importance of the threepathways may generate variable responses of SOC to grazing. Additionally, grazing canpotentially increase reactive N emissions (mainly NH3) and reduce N2O emissions. Ourconceptual model suggests that rangeland productivity and soil carbon sequestrationcan be simultaneously increased by management practices aimed to increase Nretention at the landscape level.