Question of the Day How important is CEC in our planted aquarium substrates?

[Art]

CEC is sometimes discussed now-a-days when picking substrates but nowhere near as much as it was years ago. In 2005, it was said that CEC is pretty much useless in our tanks by some and moderately useful by others. Those that favored it, including @plantbrain, said that it could help by holding on to some nutrients as they descended from the water column and became available to roots. Some suggested that the O2 transport that plants can and do use to oxygenate the rhizosphere combined with bacterial action caused stored nutrients to become bioavailable.

This interplay between bacterial action and plant root mechanisms seems to be important for the long term health of plants. But, does it matter in an aquarium where plants are uprooted and replanted frequently?

@Dennis Wong states that he doesn't believe CEC is all that important although he concludes that plants grow better for him in soil.

What do you think?

 

[ElleDee]

Great question. This is something I have thought a lot about as I've weighed the conflicting viewpoints.

Some suggested that the O2 transport that plants can and do use to oxygenate the rhizosphere combined with bacterial action caused stored nutrients to become bioavailable.

This interplay between bacterial action and plant root mechanisms seems to be important for the long term health of plants. But, does it matter in an aquarium where plants are uprooted and replanted frequently?

The first point is definitely true, but the question is if, or under what conditions, it makes a material difference. My current working theory is that the importance of CEC depends on the sort of tank you are running. There's probably a spectrum, with the extremes being

- lean water column, rich substrate, infrequent replanting -> high CEC , extensive plant roots, and bacteria work synergistically resulting in better plant health and growth
- rich water column, frequent replanting -> high CEC offers little to no benefit with constant rhizosphere disturbances, plants are adequately fed from the water column anyway

I think the rich water column/frequent replanting approach is favored on this forum, though I take the other approach myself. I see a big difference in plants that are well rooted and those that aren't, even in stem plants, and I attribute that to the benefits of a productive rhizosphere, of which CEC is one important attribute. Because I'm not supplementing CO2 and giving lots of fertilizer I *have* to optimize the rhizosphere to be successful, but other people can meet their plants' needs through different methods. Different strokes at all that.

There are some confounding variables to consider as well, such as the connection between CEC and organic matter, and the link between CEC and substrate texture. Both organic matter and substrate texture may have plant growth implications unrelated to CEC , but it's tricky to separate them.

 

[SkaleyAquatics]

I think the rich water column/frequent replanting approach is favored on this forum, though I take the other approach myself. I see a big difference in plants that are well rooted and those that aren't, even in stem plants, and I attribute that to the benefits of a productive rhizosphere, of which CEC is one important attribute. Because I'm not supplementing CO2 and giving lots of fertilizer I *have* to optimize the rhizosphere to be successful, but other people can meet their plants' needs through different methods. Different strokes at all that.

While I am a believer in this currently. I have plans to do the exact opposite in the 180gal I have planned to setup. I am going to use Safe-T-Sorb and while yes I will dose heavy water column fertilization I plan to uproot as as little as possible as this is going to grow mainly rosette plants. I really wish I was doing this sooner as I am curious to the effect it will have and may change my approach for my low tech aquariums in my fish room.
While the fish room is mostly for breeding fish I greatly appreciate a tank that has plants in it as it is more appealing to me.

 

[Burr740]

Not sure Id say its important because half my tanks are blasting sand and 90% of everything can do just fine without it. But I also know that even very old aquasoil grows plants a little bit easier, especially the really sensitive stuff that is more difficult in sand. So I believe it is definitely beneficial

 

[Art]

Thanks for your comments, guys. Would it correct in saying that an "active substrate" is the same as having good CEC ? Perhaps many confuse the complex web of processes in the substrate with the rather narrow definition of CEC ?

 

[Yugang]

Would it correct in saying that an "active substrate" is the same as having good CEC ?

I am using aquasoil, but the one aspect I really dislike is the ammonia spike. If 'active' means that it kills fish and shrimp, that would be a strong argument to go inert imo.

Whether CEC is a real thing is debatable, and as said by @ElleDee and others may depend on the dosing approach.