Black fire ant mounds modify soil properties and enhanced plant growth in a salt marsh in Argentina

Abstract

The effects of mound building ants on soil and vegetation have been describedworldwide; however, few studies have explored their effects in salt marsh communities.Here, we studied the effects of the black fire ant Solenopsis richteri on the cordgrassSpartina densiflora in a southwestern Atlantic salt marsh. We found that S. richterinests are more abundant in the high marsh than in the low marsh and in the terrestrialenvironment. Sediment characteristics were examined in the aboveground andbelowground portions of nests, and in the surrounding soil apart from them. Nests?sediment had lower organic matter content, lower bulk density and higher pH valuesthan the nonnest soil. These differences were in general more marked in theaboveground portion of nests. Grain size distribution was biased towards coarser grainparticles in nests, with the smallest particles being more abundant in the nonnest soil.Ammonium content was higher in the nests than in the nonnest soil, despite nitrate anddissolved inorganic nitrogen were not different. Phosphate content was higher in thebelowground portion than in the aboveground portion of nests. Samplings andtransplant experiments showed that plants growing in contact with mounds grewlonger, had wider stems and higher root biomass than plants apart from mounds.These results indicate that by affecting sediment characteristics, ants indirectly andpositively affect plants condition, with potential cascading up effects on communitystructure and dynamics. Because mounds are relocated every ~3.5 months,bioturbation impacts may extend over time through the whole high marsh, highlightingthe role that black fire ants may have in the ecology of southwestern Atlantic marshes