Ecological study of the aquatic carnivorous plant Utricularia australis R.Br. (Lentibulariaceae)

Utricularia australis is an aquatic rootless carnivorous plant that takes up nutrients through shoots or from trapped prey digested in its bladders. As the information on the ecology of this species is scarce, the main environmental factors which favour or limit its growth were analysed. Habitat characterization was carried out on 23 aquatic sites in Central Italy where U. australis occurred. Diverse water chemical and physical factors and aquatic plant dominants were sampled and compared to Utricularia coverage. Species response curves with respect to each analysed ecological factor were elaborated. Despite the large environmental variation among sites, U. australis did show some ecological preferences. Optimal growth of Utricularia was associated with sunny sites (approx 1500 mu mol photon m(-2) s(-1)) and shallow waters (< 20 cm) that were warm (approx 26 degrees C), alkaline (pH 8.3 median value), with moderate-high conductivity (700 mu S cm(-1)) and with low aquatic inorganic phosphorus (< 10 mu g L-1) but higher nitrogen (800-1600 mu g L-1). Dissolved and particulate organic nutrients (mainly phosphorus) were highly important in determining U. australis ecology and its distribution. The knowing of the ecological preferences of U. australis, a plant that is becoming increasingly rare in Central Italy, could be very useful to identify and protect its habitats or to identify new potential sites and to avoid further population losses.