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Plant- plant competition

Discussion in 'Articles' started by Tom Barr, Jul 24, 2009.

  1. Tom Barr

    Tom Barr Founder
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    While many aquarist are enamored with stating "plants out compete algae for nutrients", there is very little evidence that healthy growing plants are able to exist at the concentration of nutrients required to limit the growth of virtually any species of algae. Algae have extremely low demands for all nutrients and CO2 compensation, and this is also true for light in many cases (BBA for example does well at very low light). Additionally, allelopathy has been ruled out for aquariums (See Ole and my own comments there) and is easy to test for aquarist to see if there is any effect.

    Why then, do aquarist not consider plant- plant competition when it's clear that they are far more similar in terms of the limiting factors? They have far more biomass, can affect light, CO2 and nutrients dramatically. This biomass can and does change dramatically between prunings in higher light CO2 enriched system, less so, but it still does occur in lower light non CO2 or Excel enriched system.

    It seems that aquarist often forget that as plants grow through time, they have more biomass that demands more nutrients and CO2, light etc. If the aquarist has just enough CO2 to grow a set of species of plants with a certain total biomass, then doubles that biomass over 1-2 weeks, then the CO2 demand will be much greater.

    The same is true with nutrients, with some variation and adaptive abilities from species to species, and with light capture, as many species behave very differently. Some sit and grow slower, some grow taller and thinner and then form a canopy at the surface(Hydrilla, H polysperma etc, see references below).

    I have to wonder why aquarist ignore this aspect and harp on algae out competing plants, or plants out competing algae so much? Much of the complaints on the forums tend to be specific to the tips or nutrients, or CO2 related issues, with less attention paid to plant- plant interactions.

    I also find it interesting that for non CO2 aquarist, have by and large, ignored this, suggesting that some plants just do not grow for some unknown reason(we know it's not alleopathy that's significant). If CO2 is very limiting, a plant even with a small advantage with respect to CO2 compensation points translates into a really large significant different in which plant will dominate and which will slowly fade out.

    Here's some references:

    ScienceDirect - Aquatic Botany : Interference competition between Ludwigia repens and Hygrophila polysperma: two morphologically similar aquatic plant species

    This is an old reference, but shows differences between light and CO2 and CO2 max photosynthetic rates:

    http://www.apms.org/japm/vol23/v23p7.pdf

    Comparison of the Photosynthetic Characteristics of Three Submersed Aquatic Plants -- Van et al. 58 (6): 761 -- PLANT PHYSIOLOGY

    Hydrilla can photosynthesize in the eraly morning at a lower light level, thus acquire all the low levels of CO2 first, before the other species.
    The first paper also shows how temperature influences growth rates and CO2 demand.

    For us, it tends to increase it in the 20-30C ranges.
    Cooler temps seems to slow it down.
    Some plants likely do not show this same temp relationship also.
    So that can play a role also.

    This suggest that there are many other mechanism than these old tired parroted web site aquarium plant hobby myths. We can observe and see that it's not just a function of the CO2, light and nutrients, or some unknown allelopathic chemical.
    We should try and rule those out as best as we reasonably can, then look at these other factors influencing growth and plant-plant interactions.

    We can often observe that some plants do very well, whereas a certain species or a few of them do poorly. These references could explain this, and differential abilities to acquire CO2 and light, metabolic rates based on temperature and other species to species factors likely play a much more significant role.

    Regards,
    Tom Barr
     
  2. lljdma06

    lljdma06 Prolific Poster

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    This is great! Maybe I've got this wrong, but when I garden outdoors, I pay attention to where things go so one plant doesn't out compete the other. If you're trying to grow a delicate rosebush in South FL, you're not going to surround it with vinca, which grows a million times faster and is practically a weed. You'll choke the rose. Or when crab grass invades your lawn and overuns it unless you provide your St. Augustine with the nutrients it needs and little weed killer for the crab grass. You also see this competition come into play with invasive plant species in the local ecosystem all the time. It makes complete sense that plant - plant competition would apply to plants in an aquarium as well. I'm surprised people don't think this about aquatics. They are, after all, still plants.

    Great post, I'll definitely take a look at the links. I'm not a huge poster, but I've been reading the posts here quite a bit lately. Much of it has been very encouraging for me personally, as I always had big problems following the uber high light crowd in the past. Kind of the person in the corner running 1.4WPG while everyone else has 4WPG and not growing plants poorly, or getting algae. It's nice to see a site where I'm not wrong for doing this.

    Thanks,

    llj
     
  3. jonny_ftm

    jonny_ftm Guru Class Expert

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    Thanks for outlining this,

    Indeed, I recently changed most my stems with swords and crypts. I could reduce some nutrients, but didn't lower CO2 or light.

    Recently, I had to decrease light, but unexpecteadly, increase CO2 despite I didn't change anything else, especially water surface movement, water parameters and pumps position.

    The swords and crypts tend to need few pruning because the leafs last much longer than stem plants. Maybe this seamless significant biomass increase over weeks without pruning, added to probably the difference between the new and old plants can explain those new increased CO2 needs despite an overall much slower biorythm

    Since I'm more focusing on it (thanks to your insistance), this CO2 stuff is getting really tricky as I couldn't yet put it on some "set it and forget it for months", like with the light/nutrients
     
  4. John Barkan

    John Barkan Junior Poster

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  5. Philosophos

    Philosophos Lifetime Charter Member
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    Plants of the same species tend to get along from what I've seen, though it would be interesting to compare competition between introduced species of various degree of seperation through sexual reproduction.

    Most of what you'll see in the aquarium hobby is the result of asexual reproduction, meaning the genetic code will lack variance.

    What Tom is talking about here is something I've witnessed for myself in blatantly obvious terms.

    For me it was H. sibthorpioides most recently; this plant seems to grow directly towards its nearest neighbor and wrap its self around the plant. I've had it in my tanks for perhaps 2 months, and I've had to clip about 25% of its mass out of sword plants on 3 occasions.

    Another incidence seems to be H zosterifolia vs. L aromatica. The star grass grows tall on its own, but within 2 weeks of introducing aromatica, it's begun to actually grow lower and denser around the base of the aromatica.

    As it happens I have some repens, and got some sunset hygro not long ago. Both of these plants are extremely easy to get, and would make a wonderful model to show this theory directly to those who are curious, or doubt the veracity of the studies. As soon as my sunset hygro grows out better, I want to try this one for my self. It would be interesting to see if the hybridization has altered its response any.

    My guess is that most of the denial will come from the usual crowd of those who think scientific methodology is some sort of religious cult. There will probably be some from the El Natural community as well, though I imagine Diana her self is either well aware of it, or would welcome the surprise.

    -Philosophos
     
  6. John Barkan

    John Barkan Junior Poster

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    I found this interesting because I have a tank that is all swords. I made the mistake of not starting out with a fully planted tank and added new swords a couple of months later and they were in such bad shape that I moved them to my paludarium to grow emersed. However, my original plants had child plants that have since gone on to thrive in the tank. I originally thought that it was simply another species that didn't like the conditions in my tank, but I guess it could be plant competition.
     
  7. aquabillpers

    aquabillpers Lifetime Charter Member
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    Ms. Walstad's book is full of the application of "scientific methodology." All kinds of people visit her forum, from high tech priests to muddy-handed disciples of Thoreau.

    There is room for both kinds, as well as many others, in this great hobby.

    Bill
     
  8. Philosophos

    Philosophos Lifetime Charter Member
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    At many points yes, at some points no. there's many times that she's done wonderful research with full sources supporting everything. Unfortunately, I've seen her reference the book of another individual that referenced their own unpublished studies for which they did not give any details beyond saying that the research supported their conjecture. This is not to say that her points were invalid, but merely that the book had a weakness in its methods.

    I agree. I don't think someone has to be anything other than interested in this hobby to become involved with it in some way. However I take issue with people voicing their opinions that seem to think that they are invulnerable from rational critique. I think this is something all of us should be subjected to when debating a major concept within the hobby.

    Incidentally I find there are some people who think El Natural is an excuse to reproduce nature while ignoring the understanding of it through science. I have received death threats from one such individual, and long nasty rants from others. I do not think this is what Diana intended; I would be shocked if it were. I don't think this issue is her responsibility either; there's no reason to. All the same, I'm not going to pretend that they don't exist; do we blame the profs for university shootings? It's the same rational here, and it effects the hobby.

    If you'd like to know any details, go ahead and talk to me in private. I've said my bit here, and if it's going to continue I'd like to start another thread on the topic rather than continuing it on this thread.

    I'm just trying to keep the peace without censoring myself or anyone else ;)

    -Philosophos
     
  9. aquabillpers

    aquabillpers Lifetime Charter Member
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    I am taking the liberty of responding here rather than via PM because a lot of people are viewing this and I want to tie up a loose end or two. If you start a new thread I will post to that.

    I agree with that, but unfortunately some of us sometimes fall into that trap, when, for example, "rational critique" doesn't sound like that.

    I have to say that beyond a certain point, I am more interested in creating a "little bit of nature" than I am in getting too deeply into the science of it. I think a lot of people are like that, probably more from the NPT school but not a small number from the high tech area. I think we might be closer to being naturalists than those who are deeply interested in the science (and technology?) of it.

    Both approaches are fine if they give satisfaction and pleasure to the hobbyist. That's the purpose of it, right?

    Bill






    I
     
  10. Tom Barr

    Tom Barr Founder
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    Regarding Diana, we both met in Australia and spent time traveling around and we did talk a bit about hobby, different aspects. I think we both support each other's views and she is a very nice person.

    No one person can test everything.

    While that is true, I like to figure out what things I can/might be able to answer. She is no different.

    While we might disagree on some things, unless we can reasonably demonstrate otherwise, we cannot really say, it's still speculation and debatable.......

    Many things we agree on, far more than disagree.
    She is very good with fish and the talk she did on fish disease was impressive.
    I like that aspect and the promotion of the non CO2 method/soil sediments.

    I took another approach since she and Dorothy Reimer had really done a lot with soil already and non CO2 methods. I chose to look at the water column and non CO2. You can view that method in the articles/EI section.

    Why ask the same questions/do the same method if you want to learn something new? I've suggested a few methods to answer some of those puzzling questions both she and I both have.

    Algae is always an interesting one.
    Perhaps more so to her and myself than say between Ole and Troel, or Claus and myself. There the focus is more plant oriented.

    I think we will discuss more with one another later.
    She is of the few folks that is really getting things done, has put a great deal of effort into the hobby and deserves support and credit.
    She cannot be asked, nor can I, to answer every question in the aquarium, we all have stength's and weaknesses, and with that, limited time/motivation and resources.

    To answer a fish pathology question, she spent a lot of $, used her resources at a univeristy to answer some issues that are perhaps very wide spread.
    I do similar things with my academic resource as well. Anyone willing to do those types of things deserves support and is a credit to the hobby.

    Regards,
    Tom Barr
     
  11. Tom Barr

    Tom Barr Founder
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    Yes, I would certainly say so, many have different goals.
    I like observation as much as the next person, so for myself, it ALL STARTS with being "a naturalist" I suppose. From there, I start to get into trouble asking about how, why and so on..........

    Then the next step is to answer those questions myself or through past research.

    Some are fine with leaving the question open and not having enough passion to go after it. That might not be their goal, or for this system at this point in life/time etc.

    That may change later.

    Still, all the nutty science/tech stuff comes from a question from observing nature.
    Non CO2 methods certainly are a better suite of methods to do more long term observations IME/IMO. So for that goal, or one where labor, lots of tanks plays a dramatic role, they are most excellent.

    I like to have as many tools in the tool box to work with to help other folks and to see what set of trade offs works best for different management goals. Why limit yourself?

    I wish more that really enjoy aquascaping would try their hand at non CO2.

    Regards,
    Tom Barr
     
  12. Philosophos

    Philosophos Lifetime Charter Member
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    It occurs to me that when I said:

    That it could've been construed the wrong way. I meant it in the context that she would understand the topic of interspecies competition, not in the context that accuses her of welcoming people who reject science.

    My statement about only understanding nature was meant to append to the concept of commentary without critique. If people want to enjoy their tanks as an attempted reproduction of nature without any real understanding of how it functions, that's fine. I only take issue with individuals who will insist an unverified concept is true despite contrary evidence, and then continue to pass this concept on to others.

    Aquabillpers, If you or anyone else disagrees, this is a topic I would love to debate.

    Personally I have no interest in talking about a specific group of people who meet this description, beyond identifying that they exist. I see no reason they should be handled any differently from others of a like mind. Doing so is pretty much asking for drama, which is something I don't like to bring into this hobby. I reserve that for religious and philosophical debates :rolleyes:

    So it's up to everyone here, I guess. Message me to start the thread, reply here or start the thread yourself. Either way, the threadjacking has gone on long enough for my taste.

    Sorry for dropping this in the middle of your research, Tom. I honestly wasn't intending this.

    -Philosophos
     
  13. dutchy

    dutchy Plant Guru Team
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    Some weeks ago I pointed out to Yme that plant-plant competition for CO2 in the morning could maybe the cause for the stunting of some specific specifies of plants, while others grow well. He switched his CO2 on when the lights go on.
    The low amounts of CO2 present is used by the demanding plants while others are in shortage.

    It's easy to see that there's a difference. I have Hygrophila Difformis as well as Nomaphila Stricta. The Difformis starts to pearl one hour earlier than the Stricta.
    Both plants are the same length and under the same amount of light and waterflow. The Difformis seems to have the advantage maybe because it's a faster growing plant.

    The non-CO2 approach could be a ticket to almost care-free aquariumkeeping.
    I'm helping a relative to get a non CO2 tank into shape and he has had less problems than me. (less algae, less maintainance, stable slow plant growth)
    The beauty of a tank with CO2 is the lush plant growth, but sometimes I wanted to deep freeze the tank to keep it looking nice. Without CO2 there's slow growth which gives more of a "status quo" when the tank looks good.

    Something to think about......
     
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