Morphological acclimation of aquatic Littorella uniflora to sediment CO2 concentration and wave exposure

Summary 1 Species of the isoetid life form have many physiological, anatomical and morphological traits that can be seen as adaptations to the environmental characteristics of softwater lakes. Among these, dependence on CO2 from the interstitial water for photosynthesis is one of the more distinctive. 2 To assess the impact of environmental conditions on morphology and resource allocation of Littorella uniflora (L.) Ascherson, and to test whether CO2 supply from the sediment constrains the maximum attainable leaf length of these plants, a suite of morphological plant traits were measured along a gradient of sediment CO2 availability. The sediment CO2 gradient (0·4–7 mol CO2 m−3 interstitial water) was obtained by collecting specimen from 13 Faroese lakes. 3 Along the CO2 gradient, the maximum leaf length of the plants more than doubled and was significantly correlated to sediment CO2 concentration. In addition to leaf length, plant size, leaf number and below : above‐ground biomass ratio were also correlated with sediment CO2 concentration, whereas only weak or no correlations between wave exposure and morphological features of the plants were found. Likewise, no correlation between the nutrient status of the plants and morphology was observed. 4 The results obtained emphasize the importance of sediment CO2 for the performance of L. uniflora and support the suggestion that the maximum attainable leaf length of these plants is set by the CO2 concentration in the interstitial water.