Photosynthesis in orchid roots?
 

We know that orchid roots certainly move air, water, and other compounds and the leaves don't do so much of this. I noticed a remark in the s/h forum that roots in clear plastic pots could photosynthesize? Do we have evidence for this? This would be a potential advantage of a clear plastic pot over others. Since I am growing all pots in a saucer reservoir of solution rather than just using the pot alone with holes up at 1 inch I had been thinking about switching to green/black plastic pots to eliminate algae growth since I don't need the clear pots to tell me when to water. However, I guess I don't want to give up on important photosynthesis. This seems a bit hard for me to believe since a lot of the roots are pretty white.

Many (not all) orchids have roots capable of carrying out photosynthesis operations. Phalenopsis are a known example. Most the plants capable are also epiphytes (grow on trees or brances). I always see green roots on my phal that is exposed to south-facing window. It is in clear pot, thus the light response. So, yes, this is true. Also consider the leafless species such as the Ghost Orchid that depends on photosynthesis through its roots.

Thanks. I can believe that but given that the majority of orchids are still grown in opaque plastic/clay pots I have to assume that the photosynthetic contribution of the roots must be very small compared to the leaves? Thus, the difference between a clear pot and an opaque one in terms of plant growth must be minimal?

Not necessarily so. For some spp yes. For many others, no. The reason for the opaque pots is more for economic reasons. I believe it is cheaper to use post-processed plastics for pots and add dies to mask the melded color. I have been trying for nearly a year to find a "clear" plastic pot designed for Paphs. No luck. Both of my Phals (I am not a Phal grower, per se.) are in clear pots and the roots stay green most of the time. Paphs and Phrags won't benefit from clear pots, other than the ease of checking moisture in the mix.

So many of us have a variety of anecdotal experiences, which is good. However, my medical research background wishes for some simple, controlled experiments with some of these important variables. I know that not even mericlones turn out to be genetically identical but comparing them or actual divisions from plants in controlled conditions where only one s/h variable is changed would sure be helpful and interesting. I may have to do a little of this in my basement plant room environment. Pot color would be an easy one to do with an epiphyte and a terrestrial.

Ill have to do some looking up, but research has been done regarding the photosynthesis of orchid roots, specifically on Phals. The Dr. (dont remember his name) had some of his works published in orchids magazine a while back. I think he runs out of Texas A&M, but dont quote me. The results of his research have been used heavily in the Phal. mega-farm industry. Ill try and dig up the magazine from the pile and post the info.

Dr. Yin-Tung Wang, Professor of Floricultue, Texas A&M.

Dr. Eric Runkle, Assistant Prof., MSU

I could not find referenced articles by Dr. Wang but did find a few by Dr. Runkle that nicely experimented with cooling and photoperiod in flower induction in Miltoniopsis and Phalaenopsis. These were very helpful in their own right. Do you know where the orchid root information might be published?

Excuse me, people. Stop and think for a moment:

Roots being green when the covering velamen is wet seems a pretty certain proof that they can photosynthesize. Considering that in nature no epiphytic orchid plants have their roots in a pot, but they are exposed, suggests a pretty good probability of the case.

On the other hand, there is nothing that says that they MUST rely on the root photosynthesis. in fact, 200 years of orchid growing in opaque pots is pretty good proof that they don't.

I have recently taken botany, and our textbook (Introductory Plant Biology by Kingsley R Stern, James Bidlack, and Shelley Jansky) pointed out that, initially, the primary function of phalaenopsis orchid roots was believed to hold water since their roots are so thick, but recent research has shown that they heavily involve photosynthesis. I wish I still had the textbook to cite any sources and give exact quotes.