Calcium and pH co-restrict abundance of Drosera rotundifolia (Droseraceae) in a Sphagnum bog in central British Columbia

Abstract

The genus Drosera (sundews) is represented in British Columbia (BC), Canada, by Drosera rotundifolia (L.), Drosera anglica (Huds.), and their hybrid Drosera × obovata (Mert. & W.D.J. Koch). All three can be found in Sphagnum bogs of central BC, including those within the Aleza Lake Research Forest (ALRF) located 60 km east of Prince George. Vegetation patterns in bogs are known to be correlated with light, water, and nutrient gradients, and despite information being available on the influence of light and water on Drosera occurrence, little information is known about the role of nutrients. Here, we focused on a bog containing all three Drosera species, to determine whether nutrient levels are related to the abundance of the widespread species, D. rotundifolia. Univariate regression tree analysis between soil water chemistry and D. rotundifolia numbers indicates that D. rotundifolia is a calcifuge, preferring moderately acidic soil pH (>5.5) and relatively low calcium levels (<2.88 ppm). This study provides evidence that high soil water calcium and low pH limit the growth of D. rotundifolia in field populations. The physiology underlying this preference, how this is affected by hybridization between other sundew species, and how this mineralogical limitation interacts with other niche-defining factors to dictate the occurrence of D. rotundifolia are questions that remain to be answered.