Arboreal ant activity is widely known to provide key ecosystem services including the biocontrol of insect pest densities in agroecosystems via ant-plant mutualisms, such as that between coffee (Coffee arabica) and Azteca sericeasur ants. Previous studies suggest that aggressive arboreal ants like Azteca sericeasur may have negative effects on the activity of ground-dwelling ants, though few other studies address links between canopy ant activity and changes in soil or litter properties. Given that ground-nesting ants have been shown to have significant positive effects on soil nutrient concentrations, we hypothesized that arboreal ant effects can extend to belowground soil processes in tropical ecosystems, where ground-dwelling ants are often dominant engineers. We measured soil macroaggregate size distributions, infiltration, and per-aggregate nutrient concentrations (C and available P) under trees with and without Azteca sericeasur nests (≥8y old) in a highly-shaded coffee agroecosystem in southern Mexico.
Results/Conclusions
The presence of arboreal Azteca sericeasur nests was significantly correlated with lower soil C and P, as well as higher infiltration rates. Furthermore, all macroaggregate size distributions followed a power law, regardless of treatment; however, Azteca sericeasur nest presence had no consistent effect on power law slopes. We propose that Azteca sericeasur nest presence increases the dissolution soil nutrients from macroaggregates, and that this occurs within the time frame of soil aggregate structure change, or may be mediated by changes to the local arrangements of soil macroaggregates. These findings suggest decadal linkages between aboveground and belowground processes that likely affect tradeoffs in services in well-shaded, low-input agroecosystems.