Depths of the rosettes (mean and SEM) of <i>Stratiotes aloides</i>, grown at different CO₂ availabilities and 100% PAR.

<p>Plants from 90 μmol L^-1 CO₂ treatments sank within two weeks, after which plants remained significantly lower in the water layer than those grown at limited 230 and 930 μmol L^-1 (<i>P</i><0.001), as indicated by different letters. Additional results of statistical tests are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Photosynthetic oxygen production (mean + SEM) in <i>Stratiotes aloides</i> under different PAR and CO₂ availabilities.

<p>Significant differences between different PAR and CO₂ treatments are indicated with capital and lower cased letters, respectively (P<0.01). Additional results of statistical tests are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Plant chemical composition (mean ± SEM) of <i>Stratiotes aloides</i> after 4 months of different PAR and CO₂ treatments.

<p>Significant differences among PAR treatments are indicated on the right by different capital letters (A, B, C) while significant differences among CO₂ treatments are indicated on the left by different lower case letters (a, b, c). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a> for <i>P</i> and F values. Please note a different unit for C-content (mol kg DW^-1).</p><p>Plant chemical composition (mean ± SEM) of <i>Stratiotes aloides</i> after 4 months of different PAR and CO₂ treatments.</p

Increase in cover of the water layer by <i>Stratiotes aloides</i> (mean + SEM) subjected to different PAR levels and CO₂ availability.

<p>Low PAR significantly reduced final cover (<i>P</i><0.001), whereas CO₂ limitation resulted in slower colonisation rates (<i>P</i> = 0.001). Results of statistical tests are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Accumulation of CaCO₃ (mean + SEM) on leaves of <i>Stratiotes aloides</i> under different PAR and CO₂ availabilities.

<p>CaCO₃ was measured from the moment the precipitation became visible (3–4 weeks after start of treatments). Low PAR significantly lowered CaCO₃ accumulation (<i>P</i> = 0.002), while limited availability of CO₂ significantly increased the amount of CaCO₃ on the leaves (<i>P</i> = 0.016). Additional results of statistical tests are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Thickness of submerged and emergent leaves (mean + SEM) formed by <i>Stratiotes aloides</i> at the end of the four-month experimental treatments.

<p>Submerged leaves were mainly produced by PAR-limited plants and plants from 90 μmol L^-1 treatments, whereas emergent leaves were only produced by plants grown at 100% PAR. Emergent leaves were significantly thicker than submerged leaves (<i>P</i> = 0.002). Average values of leaf thickness per treatment are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t003" target="_blank">Table 3</a>, with statistical details in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Schematic overview of the effects of limited PAR or CO₂ availability in spring on the growth rate and buoyancy of <i>Stratiotes aloides</i>.

<p>When PAR is limited, plants produce less biomass and do not form emergent leaves. Under limited CO₂ conditions, plants use HCO₃^- for photosynthesis (when available), which is less efficient and causes lower growth rates, slower formation of emergent leaves and reduced buoyancy. Therefore, only plants receiving ample light and CO₂ can become buoyant and reach the required growth rate necessary to fulfil their role as a facilitator for biodiversity in wetlands.</p

Production of offsets through vegetative reproduction in <i>Stratiotes aloides</i> (mean + SEM) subjected to different PAR levels and CO₂ availabilities.

<p>Low PAR significantly reduced the ability to produce offsets (<i>P</i><0.001), whereas CO₂ limitation resulted in slower production rates (<i>P</i> = 0.021). Results of statistical tests are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>.</p

Chemical composition and characteristics (mean ± SEM) of the water layer, sediment pore water and sediment moisture and organic matter content.

<p>* For results of statistical analyses on the decline of NH₄⁺ concentrations in the pore water during the experiment, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124026#pone.0124026.t001" target="_blank">Table 1</a>. Please note the different units.</p><p>Chemical composition and characteristics (mean ± SEM) of the water layer, sediment pore water and sediment moisture and organic matter content.</p