Document: OSV-3-63-28

Spatial patterns of decomposition in the Patagonian steppe.

SALA, O.E.* ¹, M.OESTERHELD ¹, J.VRSALOVIC ¹, A.T.AUSTIN ¹, I.C.BURKE ² and W.K.LAUENROTH ²

Universidad de Buenos Aires, Buenos Aires ARGENTINA ¹
Colorado State University, Ft. Collins, CO 80523 USA ²

Abstract:
We conducted a decomposition experiment in the Patagonian steppe using litter from one of the dominant shrub species, Mulinum spinosum, and litter and roots from the dominant grass species, Stipa speciosa. The experimental site was a semi-arid shrub steppe in temperate South America with vegetation distributed as shrub-grass ring patches interspersed with bare soil and isolated tussock grasses. Litterbags were located in four different microsites to evaluate the effect of spatial heterogeneity on decomposition processes: 1) bare soil; 2) beside a tussock grass in the bare soil matrix; 3) within the grass ring surrounding the shrub; and 4) underneath the shrub. Mulinum and Stipa litter were placed aboveground whereas roots were buried to the depth of 5 cm. Bags were incubated in the field for four years, with pickups at six intervals during that time period. Overall, decomposition was relatively slow compared to other studies (values of k ranging from -0.11 to -0.35), suggesting that carbon turnover in this ecosystem is slow probably due to low rainfall input and cold temperatures. Location had a large and consistent effect on rates of mass loss, with both litter types and buried roots following the same pattern of rates of mass loss: bare soil > tussock > grass ring > below shrub. The variation in decomposition and the slower decomposition under the shrubs could contribute to the higher concentration of organic matter found at this microsite, and promote or maintain the spatial heterogeneity in biogeochemical characteristics of this ecosystem.

Keywords: decomposition, spatial heterogeneity, carbon turnover, shrub-grass interactions, mass loss

This abstract is being presented at: 3:30 PM in session:
Oral Session #67: Decomposition Processes.