Soil fertility and plant growth in soils from pine forests and plantations: Effect of invasive red imported fire ants Solenopsis invicta (Buren)

Through nest building and foraging activities, ants alter physical properties and nutritional status of soils through structural modifications and nutrient accumulation. In turn, these alterations may enhance soil quality for plant growth. This study examined the effect of the invasive red imported fire ant, Solenopsis invicta Buren, on soil properties and plant growth. In our greenhouse study, ant activity decreased soil pH and increased phosphorus (P+) and potassium (K+) in the soil. We collected soil from within and adjacent to randomly selected nests in two common habitats of Louisiana - longleaf-pine (Pinus palustris) forests and longleaf-pine plantations. After physical and chemical properties were measured, Gardenia japonicus seedlings were planted in the soil to determine growth rate. In comparison to adjacent soil, ant nest soils from both habitats were lower in moisture content and bulk density and higher in NH4+. Ant nest soils were also higher in Ca2+, Mg2+, K+ and Na+ than in adjacent soils in longleaf-pine forests. G. japonicus seedlings grown in nest soil from pine forests were an average of three times taller than those grown in adjacent soil, and those from pine plantations were twice as tall as those grown in adjacent soils. These results suggest that invasive fire ants alter the physical and chemical properties of the soil. These soil modifications enhance plant growth since NH4+, a nutrient that limits growth, has been increased.