Carbon uptake characteristics in two high elevation populations of the aquatic CAM plant Isoetes bolanderi (Isoetacae)

In Isoetes bolanderi, a resident of high elevation lakes in which ambient carbon levels are low and fairly constant throughout the day, CO2 uptake by the leaves generally parallels changes in photosynthetic photon flux density as opposed to changes in ambient CO2 levels. Overnight CO2 uptake by the leaves contributed up to 33% of the total daily carbon assimilation from the water column which is typical of aquatic CAM species but low in comparison to the 30-50% seen in the seasonal pool congener Isoetes howellii. Two additional sources of carbon may supplement the 24-hr period for carbon assimilation conferred by CAM in I. bolanderi: refixation of respiratory CO2 and carbon acquisition from the interstitial sediment water via roots. CAM appears to play a significant role in enhancing carbon gain in I. bolanderi which dominates the littoral flora of Siesta and Ellery Lakes (California) despite higher carbon uptakes rates from the water column found in one associated macrophyte Fontinalis antipyretica. -Authors