Floating plants' root length

Hello fish folks!

I wonder what factor has an influence on the length of floating plants? I had experience with Amazon Frogbit and duckweed. I noticed some times the root can get really long and sometimes they stay short. There are two theories that I have heard. One is that the more nutrients in the water(Nitrate/NH4) the shorter the roots will grow, so do the leaves. Another one says the roots' length is only according to the intensity of the light. I wonder which one is right or there are any other explanations?

If the first theory was right, then can I use the length of fast growing floating plants to determine the water quality? The longer their roots are meaning less nitrate so I don't have to do any water changes for now and if the roots appear to be short then water change is needed. The premise is that I don't have a nutrient-rich substrate like sand.

Thank you

 

I try to give my plants plenty of light and plenty of nutrients, so I cannot verify your hypothesis. However, it does sound reasonable.

 

In my experience and opinion its more light intensity and water flow that affects root length. I have several low light tanks (one with a power head and one with a sponge filter) the floating plants in both of them have never grown long roots of any kind, the tank with higher flow has noticeably shorter roots than the other which are already short. I do have a tank with a very strong light and little to no water movement which is overgrown with roots from the floating plants, I have duckweed with 5 inch roots in that tank.
Also if the nitrate theory is correct I doubt the roots length would be very accurate and you'd be dealing with nitrate fluctuations from the decay of the roots that died off when the nitrates increased- which also seems to me to not make much sense because wouldn't the plant want those longer roots to capitalize on the higher nitrates?

 

I usually find it to be flow as well. Stagnant water doesn't damage roots

 

If you have frogbit or water lettuce with long roots will it harm or kill the plant to cut the roots shorter?

 

If you have frogbit or water lettuce with long roots will it harm or kill the plant to cut the roots shorter?

They'll be fine most likely. Unless u accidentally destroy the crown where the roots meet but you probably won't. Just usesharp scissors and snip to your desired length

 

Many floating plants like low flow rates. If you have high flow in your aquariums as I typically do, you can make a corral for the floaters. Take a plastic food container and cut off the bottom portion of the container. If the container does not float by itself, you can attach foam or cork to the sides Then put your floating plants in the container so the plants and their roots will be protected from the water flow. It works wonders for plants like red root floater that hate high water flow.