does anything come OUT of the roots ?

[Mr Greenjeans]

I have a general plant/gardening question. Does anyone here know if anything comes OUT of roots ? I realize a mixture of water and dissolved nutients go IN the roots via roothairs, I believe. Besides needing to keep the nutrient level adequate is there anything that the plant puts back into the solution which might be harmful to the plant and worth removing ? i. e. drain the water/nutrient mix regularly and refill with a fresh batch. Use the waste/drainage to water the houseplants or soil-grown.

[GpsFrontier]

I have a general plant/gardening question. Does anyone here know if anything comes OUT of roots ?

I am no expert, but as I understand it some plants do indeed put out root exudates. Peas are legumes and put out root exudates that help foster a relationship with Nitrogen fixing microbes. It can also be a healing or defensive response to repel insect attack, or it can even be an offensive habit (to repel other incompatible or competitive plants). This may in fact be a factor with the pH problem I'm having with my pea plants.

is there anything that the plant puts back into the solution which might be harmful to the plant and worth removing

Again I am no expert, but I'm sure the answer to that question would be plant specific. Although I am not sure how you would test for it without sending a sample to a lab. Though even if you did know exactly what, and how much a plant produced, not sure how you would go about separating it from the solution, other than just changing the entire solution. The best advice I would have is to do some research on the specific plants you are concerned about. Then if you find out that they do put out these exudates, just be aware of it and learn why the plants use them. Also if the plant in question is in the same system with other plants you may have a problem because as mentioned the exudates can be to repel other plants, so again the answer to weather it would be harmful would be plant specific.

[Mr Greenjeans]

GpsFrontier,

Thanks for your response and knowledge. I suspected there was some form of discarge from the root system. I'm interested in learning more about when this occurs.

I would assume nutrients go into the roots and throughout the plant during the daytime, in natural conditions. This is when the stem, branches and leaves are warmed by the sun. The soil is relatively cool. At night, after the sun goes down and the stem, branches and leaves cool, does the flow through the plant vessels actually reverse ? I'm thinking the flow must reverse, in order for anything to come OUT of the roots. But if the flow reverses, is this when it happens ? Do you or anyone else know about this.

I am not particularly interested in knowing what exactly is in the exudate (thank you GpsFrontier for that word). I'm thinking along the lines of totally dispensing with the nutrient solution at regular intervals, perhaps daily. I realize that replacing the solution every day with all new nutrients may not make economic sense. I'm considering that it would however, help improve plant vitality in certain or many species.

[GpsFrontier]

At night, after the sun goes down and the stem, branches and leaves cool, does the flow through the plant vessels actually reverse ?

Again I am not a botanist, but I would say no. It's true that as the leaves absorb the sun, they do evaporate the water that is inside them (stems and flowers also). This evaporation causes a siphoning action through the capillaries that suck up moisture from the soil. But to the best of my knowledge the moisture in the plants don't drain back down into the soil when it becomes dark (night). If they did, they would wilt dew to lack of moisture just the same as they do when not getting enough water during the daytime. And if they are wilting even at night, something is wrong.

The exudate process is more of a survival instinct the plants have developed over the years. Much like glands in a human. Like sweet glands to cool the body when it is hot, or saliva glands are used to help chew and digest food.

In the case of plants they have all kinds of survival techniques from a particular color or smell, to small hairs that tiger a flower to close like in a venus fly trap. In the case of root systems producing and discharging any chemicals, I'm sure the exact function of discharging it is just as plant specific as the function itself is to the particular plant. Also how often to dispense it, as well as how much it needs is all plant specific. I am sure that also probably depends on the conditions as well. In other words the plants would be reacting to the condition in witch the chemicals were designed for, and discharge them accordingly. Like a snakebite, a snake does not bite everything in site. it only bites food or a threat, even then it determines when to dispense venom and how much to inject.

I'm thinking along the lines of totally dispensing with the nutrient solution at regular intervals, perhaps daily.

Not sure exactly what the concern is. Changing the nutrient solution regularly is common, everyone has there own recommendations on when to do this, But I have never herd of anyone doing it daily. If going that route I would suggest using a non recovery system. In witch case the nutrients would not be recirculated back into the reservoir. You would just add more fresh nutrient solution to the reservoir as needed (how often would depend on your setup needs), and what was used would simply just run off.

[Mr Greenjeans]

I understand what you are saying about plant kinetics, fluids or plant parts moving as a result of a stimulus. I'm more concerned with the direction of capillary flow and is it controlled by anything more than fluid evaporation from the leaves. Belive me, I am not trying to dispute what you are telling me. Far from it. I appreciate how much I've learned already based on your responses to my query.

If I may quote from a webpage the URL of which is : Botany

"Photosynthesis is the process by which light energy is utilized to convert carbon dioxide and water into food to be used by plants. Oxygen is released into the air during the process. Light or solar energy is captured by chlorophyll (CHLOR-oh-phil), the green pigment in leaves. It is then converted into chemical energy which is stored as starch or sugar. These starches and sugars are stored in roots, stems and fruits. They are available to the plant as food or fuel."

This text suggests that the food the plant makes (starch or sugar) is made in the leaves but (in the 2nd to last sentence) stored in the roots as well as stems and fruits. How does the food migrate from the photosynthesis site (leaf) to the roots ? What feeds the roots if it's not reverse capillary action ?

Obviously I am not a botanist either. Everyone I've asked these questions to, don't care to give an answer ... except you GpsFrontier and for that I thank you once again. Your responses have lead me to learn and find some parts of the answers I seek.

I have some experience with capillary action. I know that it can overcome the force of gravity. As I understand it a liquid will tend to go towards an area of greater heat in situations where capillary type action takes place. I believe a liquid in a capillary tube can be coaxed up, down or sideways by moving a heat source.

[Mr Greenjeans]

It seems root exudation is considered to happen at night when transpiration
ceases ...

From another website : Root Exudation and Rhizosphere Biology -- Walker et al. 132 (1): 44 -- PLANT PHYSIOLOGY

Modern cryo-scanning microscopy has helped researchers determine that the rhizosheath of a plant is more hydrated in the early morning hours compared with the midday samplings (McCully and Boyer, 1997). This implies that the exudates released from the roots at night allow the expansion of the roots into the surrounding soil. When transpiration resumes, the exudates begin to dry and adhere to the adjacent soil particles. Thus, the rhizosheath is a dynamic region, with cyclic fluctuations in hydration content controlled to some extent by roots.

[Mr Greenjeans]

A non-recovery system which removes all root exudate and replaces all nutrients, upon every cycle. Time the cycles with light and dark periods. Does it seem possible that root exudate happens only when there is no transpiration ?

[GpsFrontier]

Let me start by saying thanks for the link, I have printed the 17 pages so I can go through it in more detail in the next few days.

Does it seem possible that root exudate happens only when there is no transpiration ?

Though I am not really sure what you mean by this question, because so far that's not what I have read. From what I understand they suggested that compounds secreted by plant roots were done mostly at night. My guess is that's so the compounds secreted by plant roots will have more time to do their job (in the soil), before the plants start sucking up water/moisture in the morning. But I also did not read anything that suggested that was the only time it would/could occur (just that it was most obvious it had at that time). But that also would need to be taken into perspective because not all plants will exudate their particular compounds/chemicals the same way and for the same reasons, weather it be from the roots, stems, leaves or flowers. So in short, it would be specific to the particular plant in question.

Also transpiration is smiler to a person sweating, or a dog panting. Both are ways to cool the body, even a plants body. When the human body stops sweating, it's already dehydrated. It doesn't want to secrete any more sweet in order to conserve moisture. Not sure a plant is sophisticated enough to know when to conserve moisture that way (or they wouldn't wilt so fast). But it stands to reason if the plant is lacking in water/moisture it would NOT want to secrete any unnecessary fluids in survival mode.

During the night time the plants wont be transpiring (breathing), thus shutting down the uptake of water and nutrients. But this action is dew to the lack of light and not related to temperature (in general). I say this basically because plants don't uptake water during the dark periods, even when it's 100 degrees at night, or they would wilt with the pump shut off for extended periods of time at night. In fact I can see this as being the perfect time for the roots to secrete exudate's, because the moisture needed to do this wouldn't need to be diverted from the plants other vile functions.