. Gaseous oxygen diffuses into roots up to 10k faster than dissolved
oxygen. Roots in well drained soil have both forms available, those
in sumberged oxygenated conditions have only the latter, those in anaerobic
water logged soils have neither. In the last case oxygen needed
by roots diffuses down from the aerial parts in possible gaseous
form.
Roots which live in
waterlogged anaerobic soils or submerged continuously have
aerenchyma, hypertrophied lenticels, (both speeding gaseous oxygen
diffusion downwards from aerial parts) & reduced or
no symbiotic microrrhiza. Water roots seem thicker &
whiter than land roots. Do the water roots also have special
histology as barriers against hostile anaerobic
conditions?
Does the relative ability of
terrestrial plant kinds to adapt to root submergence or waterlogging depend
on their capacities to develop those "special" roots? Do the kinds
which develop "water roots" more readily have metabolic mechanisms already
waiting for possible inundation? Does the change from
"dry" land roots to "special water roots" need to happen without
the the former rotting & making the latter unhealthy? In the
Julius Pot presumably moist air pockets are kept above as the water
roots submerged themselves in the water below? As the new
roots grow into water do the upper roots continue to grow or do
they become redundant, the whole plant being maintained eventually by "water
roots"? When the water roots are fully developed, can they
grow as well or better on land than the land roots. Some cultivars
& hybrids grown as "house plants" seem more susceptible to root &
petiole roots such as Cylindrocladium; could this be because they do
not have or cannot grow water roots as easily? Especially
when there are natural species which are not apparently susceptible, could this
question be significant in the research being done to make presumably
depleted gene pool line bred/inbred cultivars less susceptible to these
rots? And not only Spathiphyllum...?
Hydroponics & aeroponics
are techniques where plant roots are briefly & periodically
flooded or sprayed with water. In contrast, in "Water Culture" roots
are continuously submerged in artificially aerated water. Is
the last technology most suitable for plants which have "water roots"
already or can develop them fast enough to survive or for all
aroids? Is the challenge to encourage the most rapid healthy change from land to
water roots?
These deductions provide the
challenge to try growing all Spathiphyllum & maybe other aroids with
roots totally submerged. If successful, it could open the floodgates (an
apt pun?) for emersed horticulture without need for hydroponics. By
changing culture methods not necessarily "improving" cultivars, would
it produce crops more resistant to rots such as
Cylindrocladium. To me water culture allowing parallel fishculture
also would be significantly less expensive, controllable, efficient &
effective than traditional terrestrial culture. Indeed, some of the
information arriving here in private emails is that many Spathiphyllum
species documented in taxonomic treatments & otherwise regarded as more
terrestrial by Bunting et al do also grow commonly in rivers, streams &
swamps. Amongst these are members of Section Amomophyllum
which originally I felt were not of those habitats. Now I
wonder if most or even all Spathiphyllum species could adapt to a wide
range of habitats by changing their root histologies sufficiently fast to
meet oxygen needs. Are the changes
in their root morphologies to meet widely varying environmental
conditions of taxonomic
significance....?
I hope this short rapidly
written treatise is in order for Aroid-L. I would of course greatly have
preferred a dedicated full IAS Members Dialogue Area but that is not available
& I continue to request this. Over the next months I have a wide
range of thoughts, questions, theories, hypotheses, observations, conclusions,
analyses, concepts to submit for criticism hopefully to stimulate positive
helpful debate.
R.B.
Iles
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