Carnivory and nitrogen supply affect the growth of the bladderwort Utricularia uliginosa

A glasshouse experiment was designed to determine whether the terrestrial b ladderwort species Utricularia uliginosa Vahl. gained any growth advantage from carnivory at different levels of nitrogen enrichment of the substrate. Three organism treatments were used: a control, a protist-only treatment ( Euglena spp.) and a protist + meiofauna treatment (Euglena spp. plus nemato des, copepods, ostracods, cladocerans and Acarina). The organism treatments were factorially combined with three nitrogen levels (N0, N1, N2). Populat ions of Euglena were successfully established in the substrate of pots in t he protist, and meiofauna + protist treatments, and were found in the traps of plants growing in these treatments. Populations of the meiofauna from t he inoculating cultures were successfully established in the meiofauna + pr otist treatment, and were trapped by plants in these treatments. A backgrou nd contamination of the control and protist-only treatments by Acarina occu rred over the course of the experiment; however, numbers of Acarina in thes e treatments were at least an order of magnitude lower than numbers of meio fauna in the meiofauna + protist treatment. Non-acarinid meiofauna were res tricted solely to the meiofauna + protist treatment. Organism treatment int eracted significantly with the nitrogen level of the substrate to affect gr owth of Utricularia. Plants trapping Euglena (+ Acarina) had significantly less dry weight than control plants at the N0 base level of nitrogen; this negative effect of trapping Euglena on plant growth disappeared at the two higher nitrogen levels. The dry weight of plants trapping the full range of meiofauna at the N0 level was comparable with control plants. Plants trapp ing the full range of meiofauna + Euglena at the N1 level had significantly more dry weight than plants trapping Euglena only, and the highest dry wei ght of any treatment; the benefit of trapping the full range of meiofauna Euglena was non-significant at the N2 level. Dry weight of plants was not significantly affected by nitrogen in any organism treatment. These results suggest that carnivory was overcoming a nitrogen deficiency induced by Eug lena at the N0 level, but was overcoming deficiencies of other nutrients at the N1 level.