Redirecting directed dispersal in an ant-myrmecochore system: Addressing the uniqueness of microsites near ant nests in an eastern North American forest

Background/Question/Methods

Myrmecochory is the mutualistic relationship between plants and the ant species that disperse their seeds. The plants involved in a myrmecochorous relationship produce seeds that contain a fleshy appendage called an elaiosome. Chemicals that constitute elaiosomes encourage ants to carry diaspores to their nests, where ants receive a nutritional reward from the elaiosome while not harming the seeds. While ‘benefits of directed dispersal’ studies in myrmecochorous systems have compared the properties of soils underneath myrmecochores to the soils in the nests of ants that disperse their seeds, none have explored the properties of soils nearby ant nests, where recent work indicates the majority of seeds are quickly “redispersed” in eastern North American myrmecochorous systems. To address this, we focused on a forested system in eastern Tennessee involving a keystone seed-dispersing ant, Aphaenogaster rudis, and a common herbaceous understory myrmecochore, Jeffersonia diphylla. We collected soil cores underneath J. diphylla, around A. rudis nests, and from random forest locations. In the lab, we ran assays for potential soil enzyme activity for four common microbial enzymes, as well as a subset of environmental parameters, and tested for differences using ANOVA. 

Results/Conclusions

We found that there were different microbial activities between the soils under J. diphylla and the soils surrounding ant nests. Specifically, potential enzyme activity of β-glucosidase, phosphatase, and sulfatase were all significantly higher in areas near ant nests than beneath parent plants; this same pattern, though not significant, was found for NAGase. No differences were found in other environmental variables we investigated (e.g., soil temperature, soil moisture, pH). Our results indicate that soil processes are unique in areas near ant nests, where seeds are ultimately dispersed. Our results also suggest that there may be differences in soil microbial biodiversity, which is important because different microbes can play different roles in biogeochemical processes, and hence may affect subsequent seed survival and seedling establishment. In our system, ants may still be critical in a directed dispersal context if they place seeds in areas (near ant nests) that have more favorable microbial communities than elsewhere, and hence facilitate plant population persistence. Future work should be directed towards addressing whether areas near ant nests provide biologically meaningful escape from microbial seed predation pressure, and characterizing soil microbial communities in such settings.