Fig. 4.

Laboratory experiments. Leaf pH measurements of I. engelmannii and I. tuckermanii under (A, D) submerged ambient CO₂ levels; (B, E) terrestrial ambient atmospheric CO₂ levels; and (C, F) terrestrial CO₂ manipulation. A clear diel change in pH was not observed in I. engelmannii when emergent but was induced upon CO₂ starvation. Solid circles represent submerged plants and open circles represent terrestrial plants. Each point represents a single pH measurement of two or three samples consisting of 0.2–0.5 g of pooled leaves from two to four individuals; pH was measured twice on each sample. *Circles in A are measurements from the field, while crosses represent lab experiments. In C, two separate 24-h experiments were conducted (crosses and circles).