Re: Browning Amazons and melting Vals

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To: Aquatic-Plants at ActWin_com
From: krombhol at felix_TECLink.Net (Paul Krombholz)
Subject: Re: Aquatic Plants Digest V2 #14

>Subject: Browning amazons and melting vals.

>The Crispus are blooming and putting out shoots to the surface of the water,
>but their leaves are steadily turning brown and/or transparent.  The
>Amazons are also developing yellow margins which gradually consume the
>leaf until I have to remove it.............    It appears as though they
>are being burned (as an outdoor plant would do if left to dry out in the
>I also have a problem with several vallisnaria spec. - the leaf ends -
>about half way up to the tip - are going "soft" and transparent..........

This doens't sound like a deficiency, but more like something toxic in the
water, possibly copper.

>Subject: Why do roots exist?
>After attending my local fish club meeting this evening, I decided to post
>a few questions that have been puzzling me for a while.
>1. There are many plants that may or may not put roots out at their nodes.
>Two examples that I have are a few Hyrophila species, and anacharis
>(&/or elodea?).  What seeems to govern when these plants decide to put out
>a thousand roots everywhere is beyond me.  

My experience with Hygrophila is that, given good light and good CO2
levels, it always puts out roots from every internode, but in poorer light
and/or lower CO2, it only produces roots from the internodes that are
nearest to the substrate. I don't think that nutrient levels influence the
production of roots from the above-ground internodes, rather it is the
amount of food made by the process of photosynthesis.  I know less about
Elodea.  You might check to see if those plants of yours that put out lots
of roots are better lit and/or have more room than those plants that don't.

Some books claim that Elodea and similar plants can be grown floating, but
my experience has always been that these plants do not do well until they
get themselves rooted.  Even Ceratophyllum, which does not produce roots is
always found in nature firmaly attached in the mud.  The only true floating
aquatic plants are those like duckweed, water hyacinth, water lettuce,
frogbit, and Salvinia.  (I'm sure I have left out some, but, you know what
I mean; these are the ones that are found floating in nature.

>2. Is this mysterious factor (that causes my hygrophila to decide to
>produce pounds upon pounds of roots) related to the decision a plant
>makes, on whether to bud/produce offspring rather than grow into one large
>plant? For instance, under some circumstances, water sprite/wisteria will
>produce a large "vegetative" body, and under other circumstances, baby
>plants will appear at almost every nook in the plant leaves, and the
>parent plant will disintigrate and die.  These events are so mysterious to
>me that I'm tempted to create a religion to explain them!!
>3. The success of liquid supplements would seem to suggest that the above
>claim is true - that plants can absorb nutrients through their foliage,
>and don't depend on roots for that - that perhaps roots are chiefly there
>to help anchor the plant.  How does this claim rest with you all?  If this
>is a reasonable statement, why is substrate that important - why bother
>with laterite/soil etc. when you can just grow plants in gravel and
>supplement the water with nutrients?  I'm just curious, but these
>statements just don't seem to mesh with everything I've learned until now.
>Other members of my club swallowed these claims quietly though, which is
>why I'm bringing item up here. Thanks for any ideas you might have on

There is a separate discussion going on presently among Stephen Pushiak,
Neil Frank, Dave Huebert, and myself regarding these questions concerning
soils and the abilities of aqatic plants to obtain nutrients from soils as
well as from the surrounding water.  In some form or another, this
discussion will wind up on this digest one of these days.

Dave cites experiments showing that aquatic plants can get nutrients
exclusively from the substrate when they are not available in the
surrounding water.  These experiments were done with only a few species and
a few nutrients (phosphorus and nitrate, primarily) They should not cause
one to conclude that aquatic plants can not also obtain nutrients from the
surrounding water.  The possibility that even submerged aquatics have a
transpiration stream complicates things. The research literature, in my
limited knowledge, is not clear about transpiration in submerged aquatics.
Both pro and con evidence exists.   If submerged aquatics have a
transpiration stream, they could be getting nutrients from the surrounding
water by pulling the water through the substrate and then absorbing the
nutrients with their roots.  On the other hand, there is solid evidence
that plants (including terrestrial plants) can absorb nutrients directly
through their foliage.  It would be interesting to know what volume of
water a submerged plant passes through itself each day, if, indeed, a
transpiration stream exists.

I think that for now we growers of aquatic plants should proceed on the
assumption that the roots of aquatic plants are much more than just organs
for attachment.  They definitely can take up nutrients from the substrate.
However, we shouldn't assume that our plants are not able to get nutrients
from the water, also.  There is abundant evidence that they can.  Iron is a
nutrient that is easier to supply via the substrate, but it can be supplied
in chelated from via the water, also.  Many other nutrients, such as
potassium and nitrogen may be much easier to supply via the water than via
the substrate.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174
In warm, humid Mississippi where it is cool if the high temp is below 90
and pleasant if the dew point is below 70.