Document: LYN-3-59-60

Contrasting effects of burrowing herbivores on soil carbon and nitrogen dynamics above and belowground.

BRANCH, L.C.* ¹, K.L.CLARK ², J.L.HIERRO ¹ and D.VILLARREAL ³

University of Florida, Gainesville, FL 32611 USA ¹
University of Florida, Fort Lauderdale, FL 33314 USA ²
Universidad Nacional de La Pampa ³

Abstract:
We used litterbags and measurements of carbon (C) and nitrogen (N) pools in litter and soil, microbial respiration, and net N mineralization to estimate the effects of vizcachas (Lagostomus maximus) on rates of C and N cycling in a semi-arid scrub ecosystem in central Argentina. Selective herbivory on grasses by vizcachas altered community composition and ecosystem structure, but had little effect on litter quality because fine litter of grasses and shrubs decomposed at the same rate: Remaining litter mass was 62 2% (mean 1 SE) and 60 4% after one year and 47 3% and 44 4% after two years, respectively. Herbivory also had little effect on total C and N pools or rates of microbial respiration in soils at 0-10 cm depth. Belowground in burrows, feces decomposition was faster than on the soil surface, with 60 4% and 78 2% mass remaining after one year, respectively. Soils in burrows had lower C:N ratios and greater total N concentrations when compared to undisturbed soil at similar depths (12.5 vs. 24.8 and 0.9 0.2% N vs. 0.4 0.1% N, respectively). Relatively low C:N ratios in burrow soils resulted in microbial respiration rates that were 3 times greater than those in undisturbed soils (34 vs. 9 ug C g soil^-1 day^-1 after 2 weeks incubation) and much greater rates of N mineralization in both field and laboratory experiments. Greater N mineralization rates in burrow soils were linked to higher foliar N levels in shrubs growing on colonial burrows, suggesting that the activities of burrowing animals can contribute to patterns of resource heterogeneity and productivity across the landscape.

Keywords: Carbon cycle, Nitrogen cycle, Semi-arid scrub, Argentina

This abstract is being presented at: 10:30 AM in session:
Poster Session #13: Decomposition and Soil Respiration.