Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: thedoc on 14/07/2012 06:30:01

Title: Can non-aquatic plant leaves photosynthesise in water?
Post by: thedoc on 14/07/2012 06:30:01

Brenda asked the Naked Scientists:
   
For the first time, and to my great delight, we got frogspawn and tadpoles. We also have lots of watersnails (collected accidentally by my enomologist partner pond dipping) and micro-invertebrates who arrived under their own steam.

My question is:

Over the years the surrounding vegetation has drooped and dipped leaves and stems into the pond: they are eventually eaten by the various little creatures in the pond.  However while they are still alive and under water will the leaves still be photosynthesising?  If so will they be releasing oxygen into the water?  I shall listen out for your answer whilst doing the housework - your podcast helps keep me going.

Cheers

Brenda
(Newcastle upon Tyne)

What do you think?

Title: Re: Can non-aquatic plant leaves photosynthesise in water?
Post by: Jens on 01/09/2012 21:57:56

Chemically the photosynthesis can still work, since there is CO2, water and light.
The pores (stomata) to let in the CO2 are regulated by CO2 and (blue) light and should be open.
The water transport from the roots (in the xylem) to the leafs will not work any more since no water is evaporating in a leaf under water. However, no water from the roots is needed. The transport of the end products of photosynthesis (sugars) to the rest of the plant should still work since this is done (in the phloem) by living cells and active carrier proteines and does not depend on evaporation. So possibly it should work for a while.

Title: Re: Can non-aquatic plant leaves photosynthesise in water?
Post by: Jens on 02/09/2012 09:33:19

Hi,
I looked in a text book again and need to change my mind:
The transport to the leafs (in the xylem) works at low distances from the ground also via the root pressure. So if the leafs are not hanging from a 10 m high branch, this should work and is not the issue.

However, there is a thing I did not thought of:
The surface (cuticula) of the leafs will not let through any water (this is the normal task of the cuticula, but just in the opposite direction). The pores (stomata) are so tiny that they will probably also not let through liquid water into the leaf (because of the surface tension of water). This means in contrast to what I have said above, the available CO₂ might actually become an issue. The diffusion of CO₂ from the liquid water over the tiny surface of an open stoma will most likely dramatically reduce the photosynthesis activity.