PS 18-141
A new explanation for the rarity of carnivorous plants in habitats with nutrient-rich substrates
The carnivorous syndrome in plants has long been hypothesized to be an adaptation for thriving and competing in nutrient-poor soils; however, recent evidence suggests that plant carnivory may actually be an alternative adaptation to root aerenchyma in wet hypoxic substrates. Despite the evidence showing that carnivorous plants are more strongly correlated with wet substrates than with nutrient-poor substrates, the question of why carnivorous plants are largely absent from nutrient-rich wetlands still remains. In this study we test two alternative hypotheses explaining this absence: inadequacy of hypoxia avoidance or competitive inferiority. To test these hypotheses, we excavated the carnivorous pitcher plant Sarracenia alata from its native bog habitat and planted it into pots containing nutrient-poor bog soil or nutrient-rich marsh soil. We then planted the pots into either bog or marsh and removed neighbors from half of the plots to reduce competition. We assessed pitcher loss or gain and pitcher size by counting and measuring diameters of green pitchers immediately after establishing the plots and again two months later. We also took redox potential measurements in both the bog and marsh sites to test the hypothesis that the marsh, due to its higher productivity, was more hypoxic than the bog.
Results/Conclusions
Despite the mean redox potential being significantly (86 mV) lower in the marsh than in the bog two months after transplanting, results of a three-way analysis of variance have not yet revealed any significant effects of soil (p = 0.84), habitat (p = 0.89 ), neighbors (p = 0.80) or their interactions (p ≥ 0.15) on pitcher survival. The lack of significant results this early in the experiment may be due in part to low oxygen demand during the winter months. Mean redox potential in the marsh was 261 ± 13 mV, well above the expected threshold for sulfate reduction and thus significant sulfide toxicity. As temperatures increase, we predict that oxygen demand will increase and oxygen levels in the soil will drop lower than is tolerable for the pitcher plants. Alternatively, if pitcher plants appear to be less productive in the marsh with neighbors, regardless of soil type, then that would suggest that they are incapable of competing within productive nutrient-rich wetlands. If marsh soil is the main inhibiting factor, then carnivory as a strategy of hypoxia avoidance in Sarracenia alata is inadequate in wet nutrient-rich soils associated with eutrophic marshes.