Debatable question time #1

[ruddie]

At first I was going to simply reply in a thread I found the issue with but it seems there are many threads that contain the same theory with regards to nutrients and water readings.

Salt based nutrients which are common in hydro feeds are solutions that are classified as water soluble.
I think we can all agree on this statement.

Now comes the debatable point.

Alot of threads contain questions about EC/PPM readings in reservoirs and what to do when they see a difference in EC/PPM and water reductions in the system.

I'd like to attempt to debunk a common misconception or happy listen to more wiser people but I think I might be right in this case, lets see....

Many answers seem to indicate that plants drink water and leave nutrients behind hence the growers EC/PPM readings look higher.

I don't think this is the case.

The question that needs to be asked is this, is a root system in hydro really capable of "pulling" water soluble nutrients out of the water without consuming any water?

I think this is where the misconception lies and possibly a misunderstanding of how a root system works.

The nutrients are available in the water and the roots absord only water, yes if you want to get clever they also absorb oxygen and convert that to CO2 but that isn't the point here so we won't go further into that

If there are too few or too many nutrients the plant will show signs of either case but it has no way to regulate what nutrients it receives through water consumption infact the only thing it would regulate is how much water it consumed.

Why is there a difference in EC/PPM? I honesty don't have the full answer myself (I never claimed I did)
But I think it has more to do with both PH and water temps then it has to do with a magical root system. Sorry for the sarcasm.

I don't want to be a smarty pants but can anyone point me somewhere to a university paper or other credible source where someone shows water soluble nutrients can be "pulled" without consuming water.

I'd like to think plants are smart but I don't think a root system is that smart.

I'm yet to explain the completely fluctations that I see myself but I think this question is important and I'd like to hear more about it.

What do you think? Can a plants root system pull water soluble nutrients without consuming water?

 

[Weaselcracker]

Good question.

 

[ruddie]

The question that needs to be asked is this, is a root system in hydro really capable of "pulling" water soluble nutrients out of the water without consuming any water?

What do you think? Can a plants root system pull water soluble nutrients without consuming water?

I can't seem to find the edit button lol but I actually stuffed up here

It should read

The question that needs to be asked is this, is a root system in hydro really capable of "pulling" water ONLY from a solution that has water soluble nutrients and can it consume nutrients without consuming water?

What do you think? Can a plants root system pull only water from a solution that has water soluble nutrients and can a plants root system pull water soluble nutrients without consuming water?

 

[OldMedUser]

The question that needs to be asked is this, is a root system in hydro really capable of "pulling" water soluble nutrients out of the water without consuming any water?

That question is back-asswards. The plant is pulling more water than nutes.

The plant is always consuming water if it is growing and it uptakes some of the nutes with it but not in the same proportion as the amount of water consumed. Thus as the water level falls the nutrient salts become more concentrated and the ppm rises. So if your nutes are at the edge of burning your plant when it's all topped up and the ppm goes up 20% as the water level falls that could burn 'em good.

Always top your rez up with water then test the ppm and add a bit of nutes if it's more than 200 below target level. Then check your pH after an hour to let it mix well and stabilize then adjust if needed.

If you do that you can monitor their feeding by how much the ppm drops between topping ups and be amazed how much they eat when they go into stretch and how fast it slows after. Only works if you are using RO or distilled water because tap water has a lot of minerals in it that skew the results. You could probably figure it out but the math gets tricky and my calculus is very rusty.

That's how it works.

L8r

 

[ruddie]

That question is back-asswards.

1. That's just being rude and 2. Read the 2nd post where I restated the question. In fact it would be both ways would it not?

and it uptakes some of the nutes with it but not in the same proportion as the amount of water consumed.
The plant is pulling more water than nutes

And that is indeed the part I find hard to believe. They are water soluble how could it uptake "some of the nutrients" or only pick the water?

 

[Robert Celt]

Good morning Ruddie

The short answer to your question is YES.

Now the long answer and explanation.

Water and the soluble nutrients pass into the root system through osmosis which is essentially just a balancing act.

When the concentration (water to nutrient ratio) inside the roots is lower than in your reservoir, the plant uptakes nutrients until the concentrations are equal. When the concentration is higher in the roots, the plant uptakes water to balance the ratios. When the ratios are equal in and out, the plant takes up nothing.

Now to clarify what OMU was saying, yes plants often take up more water than they need because they transpire releasing water into the surrounding air.

If you want to get even more indepth, this same process can explain nutrient burn, lockout and deficiencies as well.

Hope this was easy enough to follow and explains what you were asking. If you want to know more, ask, I am on and off here most days

 

[ruddie]

Thank you for the informative post.
If I want to read more into this would root diffusion osmosis be the right subject?

 

[Robert Celt]

Just do a search for osmosis in plants or even osmosis in cells, it all works the same way, even in our bodies. For plants it mostly only takes place in the roots.

 

[ruddie]

Thanks will do.

 

[DukeO]

I would say that I am seeing proof in the fact that I use GH 3part that has a lot of red pigment in it.

When my plants are feeding well. I can nute up a bucket and in a day or two. The water will be lower and very clear.

That just backs up the readings on my PPM meter.

 

[OldMedUser]

Those colours in the concentrated nutes when mixed together cancel each other out and look clear. They are just there to more easily identify which is which when in the bottles.

L8r

 

[OldMedUser]

Those colours in the concentrated nutes when mixed together cancel each other out and look clear. They are just there to more easily identify which is which when in the bottles.

L8r

 

[OldMedUser]

Goofy server glitch made a double post.

L8r

 

[DukeO]

Sorry but that is not the case. It will stay pink unless the plant is feeding. I pour out old buckets into a white sink. So it is very easy to see...

Those colours in the concentrated nutes when mixed together cancel each other out and look clear. They are just there to more easily identify which is which when in the bottles.

L8r

 

[OldMedUser]

I used AN 3-part for 12 years and when all 3 were used it was clear like water so maybe GH is different. My mistake.

 

[DukeO]

That's cool! GH Micro is very dark red.

I used AN 3-part for 12 years and when all 3 were used it was clear like water so maybe GH is different. My mistake.

 

[Captain Nemo]

Good morning Ruddie

The short answer to your question is YES.

Now the long answer and explanation.

Water and the soluble nutrients pass into the root system through osmosis which is essentially just a balancing act.

When the concentration (water to nutrient ratio) inside the roots is lower than in your reservoir, the plant uptakes nutrients until the concentrations are equal. When the concentration is higher in the roots, the plant uptakes water to balance the ratios. When the ratios are equal in and out, the plant takes up nothing.

Now to clarify what OMU was saying, yes plants often take up more water than they need because they transpire releasing water into the surrounding air.

If you want to get even more indepth, this same process can explain nutrient burn, lockout and deficiencies as well.

Hope this was easy enough to follow and explains what you were asking. If you want to know more, ask, I am on and off here most days

Osmosis is only part of the answer. Osmosis is the process responsible for bulk transport of solutes scross a membrane, but the cell membrane, or plasmalemma is differentially permeable to both water (the solvent) and nutrients (solutes.) This means it has the ability to control what is transported into and out of root cells.

In addition to osmosis you should also look up differentially permeable membranes and ion transport channels. Root cells can literally control how much water and what solutes they take up. Do a google search on "nutrient uptake by plants" for a botany 101 lesson. if you want an even more focused search or you want to dig into voltage regulated ion channels or plant signalling via ion channels, use the same search string at scholar.google com That weeds out all superfluous dreck and ridiculous commercial ads you typically get in a standard google search.

So, the OP's assertion that roots take up water and nutrients in whatever proportion they happen to exist in the rhizosphere is incorrect. However, it doesn not require 'cognition' on the the part of the plant to accomplish differential absorrption of water and nutrients, even though the processes involved may resemble decision making.

Hope this helps.

 

[Robert Celt]

Morning Nemo

Yes osmosis was only part of the answer, but I was trying to keep things as simple as possible for those here that may not have a scientific background. Osmosis is a fairly simple concept for most to understand and gives a fairly accurate description of how the roots uptake what the plant requires without getting into the actual chemistry and physics of how it all works.

A balancing act describing why deficiencies and lockout occur is much easier for the lay person to understand then selectively permeable membranes and the pseudo intelligence of plants LOL

 

[Captain Nemo]

Morning Nemo

Yes osmosis was only part of the answer, but I was trying to keep things as simple as possible for those here that may not have a scientific background. Osmosis is a fairly simple concept for most to understand and gives a fairly accurate description of how the roots uptake what the plant requires without getting into the actual chemistry and physics of how it all works.

A balancing act describing why deficiencies and lockout occur is much easier for the lay person to understand then selectively permeable membranes and the pseudo intelligence of plants LOL

Hey Celt. If you go back to the OP's first post he specifically asked if root cells were capable of absorbing water without nutrients and by logical extension if they can also absorb nutrients without absorbing the water they are dissolved in. He further went on say he wanted to believe plants were smart, but didn't think they were 'smart' enough to do that.

It's been a really long time since I had biology/botany 101 and had to explain some of these processes on such a basic level (have a BS in agronomy and another in botany and plant pathology.) However, I feel that providing more information versus less is always a better strategy in helping others increase their knowledge.

My point was that there are other processes in addition to simple osmosis by which the plant can selectively absorb nutrients and water against unfavorable concentration gradients. I thought I exercised commendable restraint by not going into the molecular structure of the cell membrane, enzyme mediated ion channels, or the effects of charge differentials across the plasmalemma with respect to osmosis and active affinity for specific solutes. I didn't even broach the the whole pH/solubility issue which the OP thought would explain the observed phenomenon. Many plants have evolved mechanisms in which they actively secrete substances to change the pH of the rhizosphere to promote selective uptake of specific nutrients. By and large we don't have to worry about solubility constants of macro and micro nutrients in a soilless hydroponic system, but that is a major issue in soil science/geochemistry.

I also want to clarify that my last point was NOT to imply plant 'pseudo-intelligence' but to debunk the whole idea that any of this is 'decided' by the plant or root cells.

Anyway, we certainly don't disagree on what's going on, just the amount of info which may help the 'lay person.'

 

[Robert Celt]

Morning Nemo

I understand your point and there are those of us here that understand the processes you described. I don't have a background in Botany, my background is Engineering with a lot of chemistry and physics but the processes you mentioned are easily described through chem/physics. Having said that, I try to just enjoy growing my plants without thinking to much about the technical aspects of what's taking place I have spent enough of my life paying attention to technical aspects for work. At home, in my gardens, I do my best to block the knowledge and just enjoy watching the girls grow