HARVESTER ANT NESTS, SOIL BIOTA AND SOIL CHEMISTRY

Many ant species accumulate organic debris in the vicinity of their ne sts. These organic materials should provide a rich resource base for t he soil biota. We examined the effect of harvester ant nests (Pogonomy rmex barbatus) on the soil community and soil chemistry. Ant nest soil s supported 30-fold higher densities of microarthropods and 5-fold hig her densities of protozoa than surrounding, control soils. The relativ e abundances of the major groups of protozoa differed as well: amoebae and ciliates were relatively overrepresented, and flagellates underre presented, in ant nest versus control soils. Densities of bacteria and fungi were similar in the two soil types. Concentrations of nitrate, ammonium, phosphorus, and potassium were significantly higher in ant n est soils, while concentrations of magnesium, calcium, and water were similar in nest and control soils. Ant nest soils were marginally more acidic than controls. The results demonstrate that P. barbatus nests constitute a significant source of spatial heterogeneity in soil biota and soil chemistry in arid grasslands.