Date: Wed, 28 May 97 10:03:17 cst From: mark.fisher@tpwd.state.tx.us To: cp@opus.hpl.hp.com Message-Id: <aabcdefg2094$foo@default> Subject: Re: cp roots
>> If they do not have aerenchyma, then this implies they cannot
>> survive in saturated soils in perpetuity and must spend at least
>> part of they year with their roots above the water table. This
>> would explain why they are usually found in semi-pocosin habitats.
>What plants do have this tissue? (Botanic names for non-CPs will not
>be understood) I can't seem to think of any plants near where CP
>grow that penetrate deeper than the trees (mostly pines) in bogs.
>Where it's wettest they die while the Sarracenia and Drosera tend
>be right at the surface of the water and so can't be oxygen starved.
Most (all?) aquatic and amphibious plants have aerenchyma tissue
(e.g., rice, water lillies, or practically any rooted plant that can
live submerged or partially emersed). Aerenchyma is essentially a big
air channel running the length of the plant that serves to provide
oxygen to the roots. The roots then become surrounded by a small
oxygenated zone, due to oxygen diffusion from the root into the soil.
This reduces/eliminates the amount of hydrogen sulfide that can
contact the roots, keeping it alive. An aquarium plant grower in
Germany has an article online on this topic,
http://www.tropica.dk/aqh1.htm
I also grow aquarium and pond plants, so this is a topic of interest
to me.
>In Schnell's book "CP's of North America and Canada", the author
>writes that Sarracenia's tend to become bigger when they grow in soil
>with a higher water level. As I was allways trying to grow the
>biggest plants, I have grown them in tables with a water level at
>soil level during a few years (during the whole summer, the tables
>are dry during winter).
>When repotting them, I noticed a typical smell from the soil, due to
>the lack of oxigen in the soil. The roots were sometimes black and
>brittle (dead).
What would happen if the water level was kept at the soil level year
round? Would they die? This suggests Sarracenias do not possess
aerenchyma tissue, and can only tolerate anoxic soils periodically.
Plants with aerenchyma can survive being submerged all year long.
>Somebody else told me that it is far more important to keep a
>constant water level than a very high one. The plants will adopt
>their roots to the level where they can find the right amount of
>water and oxigen. If the water level is very high they will form
>shallow roots, with a deeper water level, the roots will also grow
>deeper. If the water level constantly changes, the deeper roots will
>die when the water level stays high for a while and the plant will
>grow deeper roots when it gets drier. This "disturbance" of the root
>system constanly stresses the plant. S. Leucophylla reportedly is
>sensitive to this kind of stress.
This is more evidence to suggest Sarr's don't have aerenchyma. I am
beginning to suspect a well-drained soil is better for root growth
than one less so, as the potential for anoxia is less. Many cpers
successfully use a 50/50 (volume) peat/sand mixture,
and I'll bet the amount of sand could be increased with a positive
effect on root growth, as long as there is adequate moisture. Perlite
could also be added, to increase the "openness" of the soil, and thus
increase the diffusion rate of oxygen. Conversely, the same size
container filled with pure, fine-grained compacted peat and also set
in 1 inch of water would be more likely to become anoxic and may
result in root death.
>BTW What is "semi-pocosin"?
A pocosin habitat is a swamp, or bog (from the native American word
pakwesen), so semi-pocosin is a habitat that is only partially or
intermittantly submerged (like the transition zone between a bog and a
savannah). An ecotone such as this would provide Sarracenias with the
water they need, but would probably not have anoxic soils all year
long. I'll bet Dionaea and some Drosera have similar requirements.
Living sphagnum, which so many cp seem thrive on, would be wet, but
not anoxic.
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