Originally Posted by mistergreen
or lots of plants take up lights and nutrients that would go to algae.
This is the reason I questioned this theory in the first place. There should be no lack of anything in a healthy planted tank. Using that philosophy would mean algae and plants both would grow in abundance. That's not the case though. So there had to be something else.
The migration of nutrients from substrate to water and vice versus is inevitable. I do however think providing both forms is beneficial for the variety of plants we cultivate. All plants uptake nutrients differently. Providing one or the other seems advantageous to one at the detriment of the other.
Healthy plants, as hoppy said, have little problems with algae growth. I'm sure there may be other reasons but it seems, to me at least, the Allelopathy "theory" plays a significant role here. Maybe plants are no different than animals in this regard. A healthy animal can produce antibodies to fight off infections far better than an unhealthy one. If we view algae as a virus to plants it seems to get a little more clear. In fact algae is not the only thing this plant response seems to combat. It also deals with bacterial invasions as well. I have no idea what all the answers are but it seems reasonable to assume this plays a role.
Here are a few articles on this subject;
The effects of harvesting macrophytes on algae
Competition and Allelopathy in aquatic plant communities
Allelopathy in aquatic macrophytes: Effects on growth and physiology of phytoplanktons