Burrowing herbivores alter soil carbon and nitrogen dynamics in a semi-arid ecosystem, Argentina

Authors

Kenneth L. Clark, USDA Forest ServiceFollow
Lyn C. Branch, University of Florida
Jose L. Hierro, Universidad Nacional de La Pampa
Diego Villarreal, Instituto de Ciencias de la Tierra y Ambientales de La Pampa

Document Type

Article

Date of this Version

2016

Citation

Soil Biology & Biochemistry 103 (2016) pp. 253-261.

Comments

U.S. government work.

Abstract

Activities of burrowing herbivores, including movement of soil and litter and deposition of waste material, can alter the distribution of labile carbon (C) and nitrogen (N) in soil, affecting spatial patterning of nutrient dynamics in ecosystems where they are abundant. Their role in ecosystem processes in surface soil has been studied extensively, but effects of burrowing species on processes in subsurface soil remain poorly known. We investigated the effects of burrowing and grazing by plains vizcachas (Lagostomus maximus, Chinchilidae), a large colonial burrowing rodent native to South America, on the distribution and dynamics of C and N in soil of a semi-arid scrub ecosystem in central Argentina. In situ N mineralization (N_min), potential N_min and CO₂ emissions were measured in surface soil (0-10 cm) and soil at the mean depth of burrows (65 ± 10 cm; mean ± 1 SD) in five colonial burrow systems and adjacent grazed and ungrazed zones. Decomposition and N dynamics of vizcacha feces on the soil surface and in burrow soil was assessed using litterbags. Total C and N in soil in burrows were 1.6 and 5.5 times greater than in undisturbed soil at similar depths, and similar to amounts in surface soil. Inorganic N, particularly NO₃^-, was consistently highest in burrows, intermediate in surface soil on burrow systems, and relatively low in all other zones. Despite high C and N content in all burrows, in situ net N_min was highly variable in burrow soil. Feces decomposed and released N more rapidly in burrow soil. Laboratory incubations indicated that soil moisture limited N_min under conditions that typically characterize burrow microclimate, and that rates increased dramatically at soil moisture contents >25% field capacity, which likely occurs during pulsed rainfall events. Thus, the high and seasonally stable NO₃^- content in burrow soil likely originated from the accumulation of pulsed mineralization events over time. Burrowing and waste deposition by vizcachas produced “resource islands” at the landscape scale. At a measured density of 0.3 burrow systems per hectare, colonial burrow soil contained an amount of inorganic N equal to 21% and 30% of plant-available N in surface soil and subsurface soil, respectively, in an area that represented only 0.35% of the landscape. Our study indicates that burrowing and deposition of waste results in a highly active subsurface layer in which C and N dynamics function much like surface soil when soil moisture is not limiting.