If a plant grows in water that attenuates red light, what kind of accessory pigment(s) would it need?

Question

* If a plant grows in water that attenuates red light (quickly), what kind of accessory pigments would it need to absorb light? What color light would it absorb?

* If I pull the plant out, what color would it be?

Answer 1

If red light is attenuated, then its the wavelengths other than red that are available for photosynthesis.  Primarily, the blue and green range colors are absorbed and used in photosynthesis.  (A great combo absorption spectrum for plant pigments can be found at: http://www.citruscollege.edu/pic/46/c06_...

Red algae are in this situation.  They use a pigment called phycoerythrin.  Carotenoids in plants serve a similar function, but carotenoids are not as effective with the wavelengths that penetrate water.  

Because the plant (or alga) is absorbing the blues and greens, it will reflect red.  If you pull it out of the water where the red light is attenuated, it will look red.