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does anything come OUT of the roots ?


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Old 03-13-2010, 11:04 AM
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Default does anything come OUT of the roots ?

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.

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Old 03-13-2010, 05:43 PM
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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.
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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.
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Old 03-13-2010, 06:38 PM
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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.
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Old 03-13-2010, 10:03 PM
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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.

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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.
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Old 03-14-2010, 01:44 AM
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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.
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Old 03-16-2010, 12:38 AM
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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.
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Old 03-16-2010, 12:40 AM
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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 ?
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Old 03-16-2010, 04:42 AM
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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.

Quote:
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.
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Old 03-16-2010, 06:57 AM
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I see what you mean GpsFrontier. The link doesn't actually specify root exudation occurs only at night as I was supposing.

I tried to post something prior to that link but it didn't make it online for some reason. I had asked what/how do the roots get thier share of the starches and sugars (the plants "food") which are produced by the leaves ? I am making an assumption here that there MUST be some flow from leaves to the roots via the phloem of the starches and sugers.

What you say about transpiration ceasing when dark even when it's hot air surrounding the plant, makes sense. Thefore I will make another assumption here, transpiration occurs when water and nutrients are being converted to starches and sugars. Without light, the clorophyl bearing parts of the plant cannot convert the nutrients and so (here comes another assumption) water and nutrients stop flowing from the roots to the leaves up through the xylem.

I'm wondering if this time when transpiration has ceased (in darkness) is when the roots get fed and perhaps do most of their exudation regardless of species. The link did mention that root exudation is cyclic.
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Old 03-16-2010, 03:59 PM
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I had asked what/how do the roots get thier share of the starches and sugars (the plants "food") which are produced by the leaves ? I am making an assumption here that there MUST be some flow from leaves to the roots via the phloem of the starches and sugers.
From what I have read so far this would be correct. However I don't see the process of exudation being related to the distribution of food, other than without proper food all parts of the plant wont be able to function properly. Also, as best as I can tell at this point, it would only occur during transpiration. Because transpiration would be needed for the hydraulic proses that would be responsible for the distribution of food.
Quote:
transpiration occurs when water and nutrients are being converted to starches and sugars. Without light, the clorophyl bearing parts of the plant cannot convert the nutrients
I would also agree with that. However there are always exceptions to the rule. That's why I try not to lump all plants and species of plants together, instead I'd rather say "in general." One such exception I can think of is white asparagus. Witch is the same as regular asparagus, but lacks the chlorophyll and grows in complete darkness. It's a true plant, and not a fungus like mushrooms, witch also grow in darkness. I have no doubt that other plants and species of plants have adapted similar ability's, weather in whole, or in part. So I would only feel comfortable with this statement as a general statement. Again, I'm not a botanist.
Quote:
water and nutrients stop flowing from the roots to the leaves up through the xylem.
As best I know, transpiration would be needed for the hydraulic process that would be responsible for the distribution of all fluid thought the entire plant. Of coarse, as mentioned before there is always exceptions to the rule (I'm sure). Therefor, I would also agree that water and nutrients stop flowing from the roots to the leaves when transpiration has stopped (in general).
Quote:
I'm wondering if this time when transpiration has ceased (in darkness) is when the roots get fed and perhaps do most of their exudation regardless of species. The link did mention that root exudation is cyclic.
As for the roots being feed, I'm sure this generally happens during transpiration. Again because transpiration would be needed for the hydraulic proses that would be responsible for the distribution (flow) of food thought the plant. And again I don't see the distribution of food, and exudation being related. I look at exudation as similar to human glands. Where while the plant is using the chlorophyll and feeding, it's continuing to store the converted chemicals and compounds in these glands. Then when/if needed, the plant can secrete these compounds in the needed locations (day or night).

For instance, a plant that uses a chemical or compound to attract bees to its flowers, would want to secrete these during the day when bees would be looking for food. Or in the case of peas where they secrete these chemicals and compounds in order to help facilitate the conversion of nitrogen in soil, I'd assume it was best to do this at night when the plant is not up-taking it right a way. Allowing the compounds time to actually convert the elements in the soil into the desired nitrogen. Also I would not think the plant would want to secrete these compounds when the nitrogen levels in the soil are sufficient, but would store them until needed.
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Old 03-17-2010, 04:19 AM
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OK psFrontier. From what I can understand of your words, you are saying the roots get fed only during daylight when transpiration occurs. I have trouble understanding how that can be and perhaps it is why I never attempted anything more than a few rows of corn, some squash, beets and other garden veggies out in the dirt.

I guess what I'm trying to find (thank you for including the pictrue by the way) would be a diagram/timeline that show the flow of substances in the Xylem and in the Ploem with emphasis on when there is flow and when the substances are stagnant.

I'm trying to relate this ebb and flow throughout the plant with cell-division/growth. When do the roots grow ? When do the leaves grow ? Is it when they are fed ? When are they fed ?

In particular I am trying to find out if a shorter than 24 hour cycle might "pump" more nutrients up and food down if light and dark cycles were speeded up to say just for an example, an hour or so of each. Am I wrong in asuuming the dark cycle is necessary because it controls some hydraulic properties which help sustain the plant.
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Old 03-17-2010, 08:27 AM
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From what I can understand of your words, you are saying the roots get fed only during daylight when transpiration occurs. I have trouble understanding how that can be
Yes, that's basically what I'm saying, but in general terms because there is always exceptions. Because without the process of transpiration, there would be no movement of the fluid. Like if a persons heart stopped, there would be no movement of blood thought the body, and to the cells. The process of transpiration is in effect, the plants heart. I have herd that some flowers/fruit actually grow at night. I don't know exactly if this is true or not (but wouldn't be surprised), and/or witch plants it would apply to. But I would not relate it to the plant feeding, rather I would see it as cell division. Humans and animals don't feed 24/7 but their body's are constantly dividing cells, even while sleeping, and I can't see any reason why plants wouldn't do the same.
Quote:
I guess what I'm trying to find (thank you for including the pictrue by the way) would be a diagram/timeline that show the flow of substances in the Xylem and in the Ploem with emphasis on when there is flow and when the substances are stagnant.
No problem, it helped me to visualize everything. So I thought it might help others also. I just copied it from Phloem - Wikipedia, the free encyclopedia Although I have not seen any images with a time line.

P.S. To whom it may concern, all images on Wikipedia are not supposed to be copyrighted according to there terms of use agreement.
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I'm trying to relate this ebb and flow throughout the plant with cell-division/growth. When do the roots grow ? When do the leaves grow ? Is it when they are fed ? When are they fed ?
As far as I can tell growth/cell division can happen 24/7. But they would do best when the cells are well feed. At night (in darkness) it may very well slow down, but likely continue.
Quote:
In particular I am trying to find out if a shorter than 24 hour cycle might "pump" more nutrients up and food down if light and dark cycles were speeded up to say just for an example, an hour or so of each.
In all likelihood you would just confuse the plant with cycles of 1 hour on, one hour off all day. At best you would just stunt the growth because that would only allow 12 hours of light. Light is what the plant needs for the chlorophyll to do its job, and is vital to plant growth. By cycling the light in such short intervals you only confuse the plant, and don't add any benefit. In fact it would be far better to extend the daytime for more growth.

Alaska is well known for producing GIANT produce because of there long days. There known as "the land of the midnight sun", and during summer (depending on where in Alaska you are) the sun never sets. It hits the horizon and stays twilight for a couple of hours, then it rises again. Extending the daylight to virtually 24 hours a day. For me that makes it clear, more light more growth. In some plants the length of darkness tigers the plant to produce fruiting/flowering. Shorter verses longer (not the actual length of time), the change is what's important
Quote:
Am I wrong in asuuming the dark cycle is necessary because it controls some hydraulic properties which help sustain the plant.
In fact the hydraulic properties that sustain the plant are done through transpiration (daytime). Transpiration is the act in witch evaporation takes place, this evaporation actually sucks up water/nutrients from the soil (or nutrient solution) to replace what evaporates through the leaves. When it's dark and the pores that the evaporation takes place through close, the water inside the stems and leaves remain in place (but not flowing) or the plant would wilt.

Think of it like a hydraulic car jack, when transpiration is taking place, its like pumping the handle on the car jack up and down, making the car lift because of the fluid flowing through tubes. When transpiration stops, it's like you stopped pumping the jack handle, and thus the car stays where it is. It dosen't rise or drop (unless your jack leaks).
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Old 03-17-2010, 03:47 PM
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I went to the wiki-link: Phloem - Wikipedia, the free encyclopedia ...

There I read that nutrients which have been converted to sugars (plant food or sap) flow in both directions in the plhoem depending on where the food/sap is needed most.

I am beginning to realize that you are telling me (I think) there is the flow of nutrients and sap generally speaking in most plants, during transpiration or only when there is light. You also would have me believe that generally speaking in most plants, there is nothing produced at the roots from within the plant under favorable conditions. No reason for root exudate, therefore no root exudate normally without being triggered by some various mechanism.

I'm trying to correlate this with what I've read concerning crop rotation. If I am to believe what you are telling me, then crop rotation is not necesary if enough nutrient/fertilizer is used to replace the mineral content that has been depleted by the previous crop. You would have me believe that crop rotation has nothing to do with anything a plant might put back into the ground (generally speaking even though there are exceptions) under ideal conditions. But wait, you say plants in general excepting certain examples, do not release anyhting from the roots under ideal conditions.

Hmmm ... that previous link I included speaks of a viscous substance the roots exude mostly at night apparently, to help with taking in nutrients during daylight when transpiration is occuring. I still can't make it all add up in my head. For some reason I still belive there must be some sort of waste product besides O2 from the leaves, speaking in general terms for I realize there are exceptions, that the plant needs to rid itself of in order to be healthy, grow and produce blossoms. The waste would be put into the ground via the roots.

At this point, I'm trying to find any information about whether this does or does not occur generally speaking with plants in general even though I'm sure there are probably exceptions to the rule.
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Old 03-17-2010, 07:37 PM
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There I read that nutrients which have been converted to sugars (plant food or sap) flow in both directions in the plhoem depending on where the food/sap is needed most.
I have printed those pages out also, but as of yet have not had time to read much of either printouts. But the plant food or sap flowing in either direction to where it's needed seems logical. After all, it would want to make the most of what it has to work with. Although, other than transpiration, I don't know of any other mechanism that would move (pump) fluids inside of a plant (but I an no expert, as mentioned before).

Quote:
You also would have me believe that generally speaking in most plants, there is nothing produced at the roots from within the plant under favorable conditions. No reason for root exudate, therefore no root exudate normally without being triggered by some various mechanism.
I am not asking for anyone to believe me, and hopefully you don't feel that I am trying to be an expert. I am just trying to learn myself. Why? So I will have better crops in the future. But here is a quote from the link you posted:

"Survival of any plant species in a particular rhizosphere environment depends primarily on the ability of the plant to perceive changes in the local environment that require an adaptive response. Local changes within the rhizosphere can include the growth and development of neighboring plant species and microorganisms. Upon encountering a challenge, roots typically respond by secreting certain small molecules and proteins"
Quote:
If I am to believe what you are telling me, then crop rotation is not necesary if enough nnutrient/fertilizer is used to replace the mineral contet that has been depleted by the previous crop.
No, I don't believe I ever said that at all. There is a wide variety of chemicals and compounds secreted into the soil by roots and can even change the chemical and physical properties of the soil. By simply replacing the nutrients/fertilizer depleted by the plants, you are NOT EXTRACTING the wide variety of chemicals and compounds secreted into the soil, by the roots. Therefor crop rotation would still be needed to allow time for these chemicals and compounds to break down and decompose, so they wont be in such high concentrations over time.

I know the thinking that if the root exudates are not needed they wont be secreted. But if the the chemical and compounds secreted into the soil by roots do change the physical properties of the soil, the soil itself would become unusable to the plants. You would need to change the soil, not just add fertilizer. Thus, crop rotation. Also (again depending on the plant) they might regularly secrete a compound as a preventive measure automatically, increasing the dosage if conditions warrant it.
Quote:
But wait, you say plants in general excepting certain examples, do not release anyhting from the roots under ideal conditions.
Again I am not a botanist or even a biologist, and there are billions of types of plants. So such a general statement is needed to encompass them all. Also fertilizer conditions are not the only reason that roots secrete compounds into the rhizosphere. They also serve many other important roles, these quotes were also taken from the link you posted.

1. "the compounds secreted by plant roots serve important roles as chemical attractants and repellants in the rhizosphere"
2. "roots may regulate the soil microbial community in their immediate vicinity, cope with herbivores, encourage beneficial symbioses"
3. "and inhibit the growth of competing plant species"
Quote:
Hmmm ... that previous link I included speaks of a viscous substance the roots exude mostly at night apparently, to help with taking in nutrients during daylight when transpiration is occuring.
As I just mentioned there are many reasons that plant roots exude compounds, possibly hundreds of thousands of different reasons, and even hundreds of thousands of different compounds. From what I have read (from your link), "Our understanding of the biology, biochemistry, and genetic development of roots has considerably improved during the last decade." So there is much the biology, and biochemistry community's do not know or understand yet (much less me).
Quote:
For some reason I still belive there must be some sort of waste product besides O2 from the leaves, speaking in general terms for I realize there are exceptions, that the plant needs to rid itself of in order to be healthy, grow and produce blossoms. The waste would be put into the ground via the roots.
I don't know, or ever herd of any other wast product (that I can think of) from plants that are given off (roots or not) by all plants. That would involve the plants specific biology if it did exist (I'm sure).
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Old 03-19-2010, 12:31 AM
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OK so your knowledge is that under perfect growing conditions plants in general do not excrete any waste products into the soil. That does not agree with what I've read elswhere which is completly undertandable considering I am reading stuff on the Internet. I appreciate the time you have given to help me see your understanding of plant make-up.

I'll keep looking for answers and more opinions before I make up my mind what to believe. Thanks again for shedding some light on the root end of the plant world for me. A little knowledge at a time, it all helps.
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Old 03-19-2010, 03:53 AM
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OK so your knowledge is that under perfect growing conditions plants in general do not excrete any waste products into the soil.
Actually when referring to waste products (perfect conditions or not), I don't know of any type of waste products secreted/expelled by the roots of any plants at any time. Root exudate's are not considered waste products. A waste product would be a unnecessary byproduct (leftover digested food) of the plants growth/life, in short plant poop or urine.
Quote:
That does not agree with what I've read elswhere which is completly undertandable considering I am reading stuff on the Internet.
You should always consider the source when deciding whether the information is creditable or not. Of course a forum is not the place to do research when you want to be sure the information is true and accurate, but it's always a good place to start, get leads, and bounce ideas off other people who have similar interests. If you have links to other information that says there is waste products expelled through the roots, I would definitely be interested in them.

Good trustworthy sources of information
.org (non profit)
.gov (government website)
.edu (educational institution) This would be the best source

Just thought I would add some quotes
Quote taken from: Xylem - Wikipedia, the free encyclopedia

"Two phenomena cause xylem sap to flow:
Transpirational pull: the most important cause of xylem sap flow is the evaporation of water from the surfaces of mesophyll cells to the atmosphere. This transpiration causes millions of minute menisci to form in the mesophyll cell wall. The resulting surface tension causes a negative pressure or tension in the xylem that pulls the water from the roots and soil.
Root pressure: If the water potential of the root cells is more negative than the soil, usually due to high concentrations of solute, water can move by osmosis into the root from the soil. This causes a positive pressure that forces sap up the xylem towards the leaves. In some circumstances, the sap will be forced from the leaf through a hydathode in a phenomenon known as guttation. Root pressure is highest in the morning before the stomata open and allow transpiration to begin. Different plant species can have different root pressures even in a similar environment."

These quotes were taken from: Phloem - Wikipedia, the free encyclopedia

"Unlike xylem (which is composed primarily of dead cells), the phloem is composed of still-living cells that transport sap. The sap is a water-based solution, but rich in sugars made by the photosynthetic areas. These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures, such as tubers or bulbs."

"Movement occurs by bulk flow; phloem sap moves from sugar sources to sugar sinks by means of turgor pressure. A sugar source is any part of the plant that is producing or releasing sugar."

"During the plant's growth period, usually during the spring, storage organs such as the roots are sugar sources, and the plant's many growing areas are sugar sinks. The movement in phloem is bidirectional, whereas, in xylem cells, it is unidirectional (upward).

After the growth period, when the meristems are dormant, the leaves are sources, and storage organs are sinks. Developing seed-bearing organs (such as fruit) are always sinks. Because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions."

"Cells in a sugar source "load" a sieve-tube element by actively transporting solute molecules into it. This causes water to move into the sieve-tube element by osmosis, creating pressure that pushes the sap down the tube. In sugar sinks, cells actively transport solutes out of the sieve-tube elements, producing the exactly opposite effect."

"Some plants however appear not to load phloem by active transport. In these cases a mechanism known as the polymer trap mechanism was proposed by Robert Turgeon[3]. In this case small sugars such as sucrose move into intermediary cells through narrow plasmodesmata, where they are polymerised to raffinose and other larger oligosaccharides. Now they are unable to move back, but can proceed through wider plasmodesmata into the sieve tube element."
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Last edited by GpsFrontier; 03-19-2010 at 07:47 AM.
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Old 03-19-2010, 12:09 PM
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