Hi all,
I've struggled to find many references. There are thousands for mechanisms for storing CO2, and for oxygen dynamics in flooded terrestrial plants, but not many specifically for oxygen storage in aquatic plants. I'd guess partially this is because where back into <"
shades of grey">, where you have the complex interaction between the (dissolved) gas levels of plants, water and sediment.
I think we both agree that high levels of oxygen saturation within the water column are an unalloyed good thing. What is unequivocally true is that photosynthetic organisms "plants" are <"
massively net oxygen producers">.
.... The light-induced oxidation of water by Photosystem II (PS II) of higher plants, algae, and cyanobacteria, is the main source of atmospheric oxygen......
and you need to "
show us the money".
That looks on the money, the Sand-Jensen paper (that you've highlighted) definitely suggests that the obligate aquatic marine monocotyledon
Zostera marina (Eel Grass) only stores very minimal amounts of oxygen. The rest of <"
Underwater Photosynthesis and Internal Aeration of Submerged Terrestrial Wetland Plants"> is really a paper about cereals that have been submerged by flood water, so most of it isn't that relevant to us.
The 2005 paper cited is:
It is actually a paper that gets a mention on UKAPS, because the other species used was
<"Lobelia dortmanna">. In the 2005 paper, for
L. dortmanna it says:
Conclusions
The build-up of O2 in the pore-water of L. dortmanna sediments during the day as a result of high release of photosynthetic O2 from roots and low O2 consumption of sediments means that sediment, aerenchyma and water are important O2 sources for respiration during the following night, while Z. marina relies on the water column as the sole source of O2 because its sediments are anoxic...........
A subsequent paper: Pedersen, O., Colmer, T., Garcia-Robledo, E & Revsbech, N (2018) <"
CO2 and O2 dynamics in leaves of aquatic plants with C3 or CAM photosynthesis – application of a novel CO2 microsensor">
Annals of Botany 122:4 pp 605 - 615 says:
..... Leaf tissue pO2 dynamics in Lobelia dortmanna largely followed the opposite pattern of that for pCO2 in its tissues; pO2 was slightly above air equilibrium at the end of the light period and then declined throughout the entire dark period without reaching a new quasi-steady state so that the leaf tissues were severely hypoxic (approx. 1 kPa) towards the end of the dark period ........
So inconclusive, but also suggesting that
Lobelia dortmanna doesn't store much oxygen within its tissues. It is a plant of cold, extremely nutrient poor (oligotrophic) lakes meaning possibly that it doesn't need to store oxygen, because it is always available from the substrate. I couldn't find much specifically for
Nelumbo, the plant with the <"
spectacular aerenchyma">.
<"Environmental factors regulating the radial oxygen loss from roots of Myriophyllum spicatum and Potamogeton crispus"> is a paper about <"
Root (radial) oxygen loss"> and it says that when the water column is oxygen depleted the plant leaks less oxygen. It doesn't really talk about photosynthesis or respiration.
...... During a sequence with a light/dark cycle as well as alternating aeration of the water column, maximum ROL with up to 35% oxygen saturation at the root surface occurred under light/O2-saturated conditions. A decrease to about 30% was observed under dark/O2-saturated conditions, no ROL was detected at dark/O2-depleted conditions and only a weak ROL with 5–10% oxygen saturation at the root surface was measured under light but O2-depleted water column. These results indicate, that during darkness, ROL is supplied by oxygen from the water column and even during illumination and active photosynthesis production, ROL is modified by the oxygen content in the water column.........
In our aquariums we aren't going to have those large differences in oxygen conc. between plant and water, and when we have "pearling" at the end of the photo-period we know that both the internal tissue of the plant and the water column are fully saturated with dissolved oxygen. In some circumstances the water may become <"
super-saturated with dissolved oxygen">.
What we don't know is the rate at which that oxygen is used in respiration or diffuses from the plant leaf back into the water column. I will see what I can find for
Myriophyllum,
Cyperus, Typha or Phragmites in <"
Constructed Wetlands">.
cheers Darrel