Geographic variation in Sundew (Drosera ) leaf colour: plant-plant interactions counteract expected effects of abiotic factors

Aim To identify geographic patterns in leaf colour of roundleaved sundew (Drosera rotundifolia) growing on ombrotrophic (rain fed) bogs across Europe and establish the controls over these patterns. Location North-west Europe. Taxon Angiosperms, Drosera rotundifolia. Methods We measured leaf colour of D. rotundifolia plants growing on 24 ombrotrophic bogs across north-west Europe covering 26.4 degrees of longitude and 21.1 degrees of latitude. We measured the height and cover of co-occurring vascular plant vegetation and the amount of incident light intercepted by the vegetation canopy. We determined the role of abiotic variables in controlling the patterns found. In a separate experimental study, we manipulated plant–plant interactions with D. rotundifolia by removing aboveground vascular plant vegetation and monitoring leaf colour over a single summer. Results Drosera rotundifolia leaf colour varied between bogs. Leaves were redder in northern latitudes and eastern longitudes, and in sites/plots with lower canopy influence, lower nutrient deposition, and a more continental climate. Canopy influence was greater on sites in southern latitudes, eastern longitudes, and with higher nutrient deposition, longer growing seasons and a more maritime climate. Nutrient deposition was higher at more southerly latitudes, eastern sites had a more continental climate, and southern and western sites had warmer and longer growing seasons. In the in situ experiment, leaves became more red when canopy light transmission was increased by removing vegetation, but not when shade net was subsequently added to reduce light transmission. Main Conclusion Geographic variation in Drosera rotundifolia leaf colour is strongly affected by its light environment, mediated by plant–plant interactions, but leaf colour is also affected by other abiotic factors. The relative importance of biotic and abiotic factors in determining geographic patterns in traits, and also species responses to environmental change, might depend on the growth form and competitive ability of a species.