Newman Jonathan R, Raven John A
Department of Biological Sciences, University of Dundee, DD1 4HN, Dundee, Scotland.
Oecologia. 1995 Apr;101(4):494-499. doi: 10.1007/BF00329429.
Photosynthesis of Crassula helmsii, an amphibious aquatic macrophyte weed species, has been measured with respect to pH and irradiance. C. helmsii shows a marked diel fluctuation in titratable acidity, which can be accounted for by changing levels of malic acid. C. helmsii is unable to use HCO for photosynthesis and exhibits generally low photosynthetic rates when CO is not limiting. The photon flux density at which the onset of light saturation of photosynthesis is reached (E ) is low for aquatic macrophytes. Some advantages conferred on C. helmsii by the possession of crassulacean acid metabolism are an extension of the period of assimilation of dissolved inorganic carbon, resulting in a reduction in the limitation imposed on photosynthesis in aquatic environments by a very high CO diffusion resistance.
对两栖水生大型植物杂草物种——黑木蕨的光合作用进行了关于pH值和辐照度的测量。黑木蕨的可滴定酸度呈现出明显的昼夜波动，这可以用苹果酸水平的变化来解释。黑木蕨无法利用HCO进行光合作用，并且在CO不成为限制因素时，其光合速率通常较低。对于水生大型植物而言，光合作用达到光饱和起始时的光子通量密度（E ）较低。黑木蕨拥有景天酸代谢赋予它的一些优势，即延长了溶解无机碳的同化期，从而减少了水生环境中极高的CO扩散阻力对光合作用造成的限制。
