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#1
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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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#2
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Last edited by GpsFrontier; 03-14-2010 at 07:43 AM. |
#3
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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. |
#4
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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. Quote:
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#5
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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. |
#6
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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. |
#7
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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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#8
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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.
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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. |
#9
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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. |
#10
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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. Last edited by GpsFrontier; 03-16-2010 at 03:40 PM. |
#11
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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. |
#12
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P.S. To whom it may concern, all images on Wikipedia are not supposed to be copyrighted according to there terms of use agreement. Quote:
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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:
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). |
#13
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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. |
#14
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"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:
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:
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:
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Last edited by GpsFrontier; 03-17-2010 at 08:01 PM. |
#15
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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. |
#16
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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." Last edited by GpsFrontier; 03-19-2010 at 06:47 AM. |
#17
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Oh Dear!
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