Vertebrate faeces as sources of nodulating Frankia in Patagonia

Abstract

Frankia strains nodulate the native actinorhizal plant Ochetophila trinervis (sin. Discaria trinervis), which grows in stream margins and nearby areas in northwest Patagonia (Argentina). Infective Frankia are found in soils with presence of host plants but also may be found in areas lacking them. This may be partly explained by water transport of Frankia propagules but there are other possible sources. The aim of this study was to discover whether the faeces of introduced mammalian herbivores, including cows (Bos taurus, adult and calf), horses (Equus caballus), sheep (Ovis aries), red and/or fallow deer (Cervus elaphus and Dama dama, respectively), wild boar (Sus scrofa), European hare (Lepus capensis), or the native upland goose (Chloephaga picta), could be a source of infective Frankia, and enhance its dispersal. Faecal material and soil samples were aseptically sampled in different plant communities, and tested via plant bioassays using O. trinervis. The faeces of all animals contained infective Frankia and led to an effective symbiosis with this plant. Faeces of large introduced herbivores gave rise to higher nodulation (number of nodulated plants with respect to the total number of inoculated plants) than faeces of hare and upland goose. Soils from the sites where the cow (two sites), sheep, wild boar and deer faeces were collected did not contain infective Frankia. This suggests that the animals may have ingested Frankia from plant material and that the Frankia propagules passed through the digestive tracts of the animals without losing its infectivity. We conclude that the faeces of large introduced herbivores contribute to the dispersal of infective Frankia in Northwest Patagonia.