Mammal mounds stimulate microbial activity in a semiarid shrubland

This study was conducted to determine the influence of animal disturbance, in the form of banner-tailed kangaroo rat (Dipodomys spectabilis) mounds, on soil microbial abundance and activities in a Chihuahuan Desert shrubland. Total organic carbon (TOC), microbial biomass C (C-mic), and basal respiration were quantified in soils from beneath and between creosote bush (Larrea tridentata) in three zones: directly on the mounds, immediately surrounding the mounds, and between mounds. TOC, C-mic, and respiration were enhanced both in soils beneath the canopies of the shrubs and on the mammal mounds. Thus, mammals as well as shrubs contribute to spatial heterogeneity. Ratios of respiration to C-mic (metabolic quotient) were highest on the mammal mounds; however, the ratio of C-mic:TOC was not affected by shrub canopy cover or location relative to mammal mounds. The higher metabolic quotients in the vicinities of the mounds reflect physical disturbance by mammals and suggest higher proportions of relatively easily metabolized organic carbon than in soils more distant from mounds.