B. Morton B. Babcock P. Castillo B. Fish E. Jerauld B. Johnson L. Landre H. Lum C. Miller A. Parker G. Van Steenwyk Jon E. Keeley 1981 <p><span>In the leaves (but not corms) of the submerged aquatic&nbsp;</span><i>Isoetes storkii</i><span>&nbsp;malic acid concentration fluctuated from 22 μeg g FW</span>^-1<span>&nbsp;in the evening to 171 μeg g FW</span>^-1<span>&nbsp;in the morning. Associated with this was a change in titratable acidity of 152 μeg g FW</span>^-1<span>&nbsp;between morning and evening.&nbsp;</span>¹⁴<span>C carbon was fixed in both the light and the dark, though the amount of carbon fixed in the light was more than that fixed in the dark. Autoradiographs show 88% of&nbsp;</span>¹⁴<span>CO</span>₂<span>&nbsp;fixed in the dark is recovered after 1 h, in malic acid and the remainder in one other unidentified product, whereas these two products contain less than 15% of the&nbsp;</span>¹⁴<span>C fixed after 1 h exposure to&nbsp;</span>¹⁴<span>CO</span>₂<span>&nbsp;in the light. It is suggested that CAM metabolism in this aquatic species may be related to the low availability of CO</span>₂<span>&nbsp;for photosynthesis during the day in its aquatic environment and that this metabolic pathway may prove common in the genus&nbsp;</span><i>Isoetes</i><span>.</span></p> application/pdf 10.1007/BF00346490 en Springer Nature Dark CO2-fixation and diurnal malic acid fluctuations in the submerged-aquatic Isoetes storkii article