Essential but invisible: non-apparent but widespread ant nests favour soil nutrients and plant growth in semi-arid areas

1. Ants provide multiple ecosystem services, including nutrient cycling. Although most studies on nests effects on soil fertility and plant performance include species with large nests, species with less apparent nests may have a relevant effect, especially if they are widespread, abundant, and/or inhabit nutrient-poor soils. 2. We studied the effects of nests of three abundant and widespread ant species in the Patagonian steppe (the generalist Dorymyrmex tener, and the seed harvesters Pogonomyrmex carbonarius and Pheidole spininodis) on soil properties, plant growth of two native species, and seedling recruitment. Our main hypothesis was that, despite their non-apparent nests, these species have a positive effect on soils and enhance plant growth. 3. Nest soils showed higher soil conductivity, %K and %Mg than non-nest soils. In a greenhouse experiment, individuals of the biennial forb Oenothera odorata grew bigger in nest soils of P. carbonarius and D. tener than in non-nest soils. Individuals of the perennial tussock grass Pappostipa speciosa grew taller and had more tillers in nest versus non-nest soils. Seedling abundance and richness were the highest in P. carbonarius nest soils and the general trends were similar to those observed in the plant growth experiment. 4. Our results show that ant species with non-apparent nests in an arid area enhance soil properties, favouring plant growth (nests of P. carbonarius and D. tener) and seedling abundance (nests of P. carbonarius). Due to their high abundance and widespread distribution, these two species could have a relevant role in ecosystem recovery after disturbance.