Jon E. Keeley
1983
<p><span>Evidence to date is consistent with the hypothesis that the submerged aquatic </span><i>Isoetes howellii</i><span> Engelmann possesses crassulacean acid metabolism. Quantitative </span><sup>14</sup><span>C uptake studies indicate that CO</span><sub>2</sub><span> assimilation in both the light and dark are functions of pH and total inorganic carbon level. In both the light and dark, maximum uptake rates in 0.6 mM NaHCO</span><sub>3</sub><span> were double the rates in 0.3 mM NaHCO</span><sub>3</sub><span>. At both carbon levels there was a large drop in carbon assimilation rate between pH 6 and 8. In nature water pH and inorganic carbon level fluctuated diurnally thus complicating the determination of the contribution of light vs dark CO</span><sub>2</sub><span> uptake to the total carbon gain. On a sunny day between 0600 and 1200 h water chemistry changed markedly with ∼40% reduction in total carbon, ∼2 pH unit rise resulting from ∼100% depletion of free CO</span><sub>2</sub><span>. Under such conditions daytime deacidification in </span><i>Isoetes</i><span> leaves was 88% complete by noon. In contrast, on an overcast day, reduction of carbon in the water was much slower, deacidification was only 46% complete by noon and substantial malic acid levels remained in the leaves at the end of the day. Upon emergence crassulacean acid metabolism was largely lost in </span><i>Isoetes</i><span> leaves. Preliminary estimates suggest that under natural submerged conditions, early morning photosynthetic rates may be substantially higher than dark CO</span><sub>2</sub><span> uptake rates, though uptake rates throughout much of the day could be substantially lower than nightime CO</span><sub>2</sub><span> assimilation.</span></p>
application/pdf
10.1007/BF00384542
en
Springer Nature
Crassulacean acid metabolism in the seasonally submerged aquatic Isoetes howellii
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