Submitted to: Insectes Sociaux
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2007
Publication Date: 5/1/2008
Citation: Defauw, S. L., Vogt, J. T., Boykin, D. L. Influence of mound construction by red and hybrid imported fire ants on soil chemical properties and turfgrass in a sod production agroecosystem. Insectes Sociaux. 2008. Interpretive Summary: Invasive imported fire ants (Solenopsis spp.) affect soil quality and turfgrass nutrient management impacting sectors of the US turfgrass industry which generates about $56 billion dollars per year. ARS researchers demonstrated that soils associated with imported fire ant mounds typically had elevated organic matter, phosphorus, zinc and sodium levels with changes in mound chemistry across seasons. Turfgrass growing within mound soils exhibited higher concentrations of nitrogen, phosphorus, calcium, sulfur, copper, iron and sodium. Knowledge of imported fire ant effects on soils and turfgrass nutrients will help improve remote sensing detection tools used to identify and monitor imported fire ant infestations in high value turfgrass systems such as sod farms, golf courses, and urban areas resulting in cost-effective, targeted control efforts and reduced pesticide use.
Technical Abstract: Mound-building imported fire ants (Solenopsis spp.) actively modify the biogeochemical and physical properties of soil; however, their influence on nutrient levels in surrounding vegetation is poorly understood. In addition, aside from the reported persistence of elevated P and K levels in clay-rich soils one year after mound abandonment, the relative stability of nutrient concentrations from one season to the next is largely unknown. Nutrient concentrations were simultaneously documented for both ant-affected as well as undisturbed soils and warm-season turfgrass from a commercial sod production agroecosystem. Initial collection of soils and turfgrass coincided with peak annual biomass (September 2006); the second harvest of soils occurred over twelve weeks later during turfgrass dormancy and brood minimum (December 2006). Total C, C/N ratios, organic matter (OM), and Zn2+ concentrations as well as pH of mound soils were significantly higher than control plot soils; these trends persisted across seasons. Total N of mound soils was distinctively greater than control plot counterparts during September only. Soil P, K+, Ca2+, Mg2+ and S (all macronutrients), as well as Na+ concentrations from ant nest soils were substantially elevated during the late Fall to Winter transition compared to control plots, whereas Fe2+ and Mn2+ levels (both micronutrients) were significantly lower in ant mound soils versus control microhabitats. Turfgrass harvested from ant mound perimeters in September exhibited elevated N, P, Ca2+, S, Cu2+, Fe2+, and Na+ concentrations. Evaluation of the relative stability of soil parameters across seasons revealed a significant drop in ant nest pH from September to December 2006. Copper (DTPA extraction method only) and S concentrations increased sharply from September to December for both mound and control microhabitats. In contrast, Mn2+ concentrations diminished markedly from both mound and control plots during this interval. Continuous pedoturbation by imported fire ants as well as seasonal shifts in mound biogeochemistry resulting from changes in assimilation/dissimilation among mound biota may influence the site-specific effectiveness of microfaunal pathogens (e.g., Thelohania solenopsae) or parasites (e.g., Orasema spp.) identified as classical biological control agents of non-native Solenopsis spp. Therefore, further study of the intrinsic complexities of soil ecosystem dynamics of imported fire ant nests across seasons is warranted.