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Root biomass relative to Sediment fertility

Discussion in 'CO2 Enrichment' started by Tom Barr, Oct 25, 2008.

  1. Tom Barr

    Tom Barr Founder
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    This is an excerpt from a Journal Yang et al, 2008 (in Aquatic Botany) on Milfoil grown is infertile sediment and fertile sediment. But if you think about it, the plants should try and look for more nutrients under limiting conditions vs not. They did not add water column ferts, unfortunately and looked at that as well like Cedergreen and Madsen(2001).

    "Higher sediment nutrient availability resulted in larger plants. Relatively more biomass was previously shown to be allocated to roots versus shoots depending upon which resource was more limiting (Cronin and Lodge, 2003 G. Cronin and D.M. Lodge, Effects of light and nutrient availability on the growth, allocation, carbon/nitrogen balance, phenolic chemistry, and resistance to herbivory of two freshwater macrophytes, Oecologia 137 (2003), pp. 32–41. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (24)Cronin and Lodge, 2003). When sediment nutrients were more limiting, M. spicatum allocated more resources to the growth of roots, resulting in a higher RWR and RSR. This is consistent with allocation patterns observed in most herbaceous terrestrial plants and other aquatic macrophytes ([Barko and Smart, 1986] and [Wilson, 1988]).

    So with many species, we might expect to see larger root biomass/growth rates totals with sand and light water column ferts and less with ADA AS or mud.

    We found this to be true as well in our dry weight comparisons at the lab.

    Overall, total biomass was much higher, significantly different with the fertile sediments without any additions to the water column, obvious there as well, they had plenty of nutrients while the other non fertilize sediment plants had no nutrients, they they looked for nutrients in the sediments.
    Perhaps.......larger roots are not really an indicator that the sediment is more fertile, this has been an assumption of many, particularly the Sword and Crypt folks..........

    Lots of evidence suggests otherwise.
    the paper is mostly looking at how fertility and autofragmenting are related.

    As you might guess, when the nutrients become strongly limiting, the plants break apart and pieces hopefully will land somewhere there are nutrients in the sediment and/or water column.

    I've seen this is many cases growing this same species out side in pots in 400 Gallon vats for various experiments. If you do not add ferts when the tanks are full of healthy growing plants, in a few days that just break up into pieces.

    Sort of analogous to Caulerpa melting when the NO3 crashes in marine Refugiums.

    Regards,
    Tom Barr
     
  2. mi5haha

    mi5haha Prolific Poster

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    That is an interesting observation. I witnessed HC cuba growing both in ADA II and sand, and it looks that HC has much longer roots (more than 2 cm) in ADA, while it has less than 1cm roots in sand (fine, 1-2mm in dia.), so HC stays firm in ADA while it is always trying to float up in sand. Regardless the liquid fertz in water, I suppose that ADA is more nutritious than sand (even blended with peat)? I would hope that their conclusion is working since I am planning to grow a lot of HC (submerged) on sand, and I am much concerned about the shorter roots of HC growing on sand.
     
  3. aquabillpers

    aquabillpers Lifetime Charter Member
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    Perhaps I missed something, but isn't it rather basic that plants that are rooted in a nutrient-poor substrate will grow more roots in the search for food than those that are grown in a richer substrate? I suspect that the study didn't add much to the aquaculture body of knowledge.

    I have to ask, who paid for it? :)

    As Tom noted, it would have been more interesting if the authors had included the effect of water column nutrients. It would have made the study much more complex, but the conclusions would have been more interesting.

    I also wonder about using milfoil as the test plant. It is very capable of using water column nutrients and might even "prefer" them during periods of rapid growth. A plant that seems to prefer to get nutrients from the substrate, like swords and crypts might have been better choices.

    Bill
     
  4. ChloroPhil

    ChloroPhil Junior Poster

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    I'm really curious about something.

    1) Did the investigators look at the rate of release of nutrients from the sediments into the water column?


    It makes sense to me to state that a nutrient enriched system will result in more robust plants. A 1st grader could tell you that.

    What is missing to me is an examination of the role of nutrient release into the water column and how affects the rate and total mass of root growth. If there's accessable nutrition in the water column via release from an enriched sediment then of course the plants aren't going to need to allocate as much of their resources to root growth. Why grow a massive root system when shoot growth will provide both nutrient uptake and increased photosynthetic mass?

    2) Did the investigators look into the rate of root growth in relation to the timing of autolysis?

    3) Does Egeria have a tendancy to regrow from a dormant root system after a major fragmentation event or is that the end of the plant?


    Soooo, they're saying that if we want to reduce the rate of Hydrilla and Egeria spread via fragmentation we need to pump sewage into our lake bottoms? ;)
     
  5. Tom Barr

    Tom Barr Founder
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    No, often it's extremely difficult to measure because the rates are low, but often steady and significant. But since the residual ppm's, often ppb's, are so hard to detect, or they have other trade offs in the study, they often will not measure this.

    Tracer stable isotopes, but this is not easy and it very tough to do in any open natural system for enrichments as well as ethics and long left overs............nutrient cycling can be done over time, but it's a fair amount of work for the export part into the water and how much is taken in by the leaves.

    In small lab scale test, such test are much easier to do.
    But then it's hard to correlate that with field studies often times, but for us, the lab scale test are very nice.

    Never underestimate the lack of logic of adults on the web:)
    Many have used such logic as support for using nutrient rich sediments and lean water column dosing. They still do actually.

    There is a way around this.
    Split chamber growth vaults.
    Translocation also can occur, so radio tracers can be used.

    We did this at this lab for herbicides that translocate to the roots and kill the plant there vs just the tops which simply regrow after the typical herbicide contacts and kills the shoot/stem. No exchange occured from the sediment or the water column this way and we could check that it did not.

    Not sure for 2.
    Yes for 3, they have root crowns. the roots themselves, no.
    Hydrilla?
    OMG.............this stuff is pure evil. It forms tubers...........so those can last 7-10 years before sprouting and regrowing and they do not all germinate(20% or so each year), how do you kill them?

    Egeria is much easier to control for this reason, 2-3 years and you are done and might have re treat if you miss some.

    3 Million$ for Frank's tract in Delta here in CA for one treatment though.
    Worked though.

    No, for auto fragging..............the solution is really management, but to realize these plants will break up and find new places when nutrient control is applied.
    So nutrient control is not going solve much of the issues with weeds.

    More nutrients= more weeds.
    Less nutrients= weeds will break up and fragment and then get spread all over.
    Also, when you kill all the weeds, it's best to do so slowly..............the organic matter decomposing can kill fish, make the place stink etc...........

    Regards,
    Tom Barr
     
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