I see your point, Wayne. Maybe the symposium on breeding plants for
drought tolerance, which triggered your response which started this thread,
will address the issue. Maybe some of the presenters and/or attendees have
followed this thread will steer some discussion in the direction you
suggest.
How about it, symposium people?
Martin M. Meiss
2011/12/22 Wayne Tyson <[email protected]>
> Martin and Forum:
>
> I certainly do think selection and adaptation work, but my question had to
> do with whether or not drought-tolerant plants can produce the same or a
> greater amount of biomass per unit water per unit time all else being equal
> (aka in the real world--as opposed to imaginative leaps or connections
> where there may or may not be a fit). I am more interested in the evidence
> and the science that has been done--and whether or not the theoretical
> foundations upon which assertions that drought-tolerant plants can produce
> significantly more biomass with the same amount of water in the same time.
> Or, for that matter, if they can do so in ANY amount of time (per Merran's
> saguaro example).
>
> I am not suggesting that such is not possible, only that it is
> questionable. I SUSPECT that there are some differences, but I wonder
> whether or not they are great enough to justify the considerable conjecture
> that "science" can "improve" plants enough to make it possible for us to go
> on driving cars and flying planes etc. on switchgrass. I suppose I'm
> suggesting that some basic science should be done before "we" squander a
> lot of grant money on applications of dubious future. It seems that the
> application cart is getting ahead of the basic science cart . . .
>
> WT
>
>
> ----- Original Message ----- From: "Martin Meiss" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, December 21, 2011 4:26 PM
>
> Subject: Re: [ECOLOG-L] Plant Physiology Drought tolerance Re: [ECOLOG-L]
> course and symposium on plant breeding for drought tolerance
>
>
> To Wayne and others:
>> Sorry about the C4/CAM confusion. It has been many years since I
>> have thought about them and I forgot some important distinctions (but it
>> did seem to make the thread come to life).
>>
>> Wayne, in answer to your question regarding this question I put
>> forth:
>>
>> "...Is this any less plausible than other manipulations that have been
>> carried out in the past that have resulted in increased yields?"
>>
>> You will notice that it makes no reference to water use. I was addressing
>> in a general way the fact that artificial selection WORKS. Wayne, your
>> questions seemed to imply a null hypothesis that selection or genetic
>> engineering CANNOT increase plants' productivity under low-water
>> conditions. It seems to me ALL physiological processes are subject to
>> alteration, which in turn can influence the efficiency and productivity.
>> Has anyone ever found a genetic trait for which there was no genetic
>> variability or that did not respond at all to selection?
>>
>> Can anyone seriously believe that all plants are equally efficient at
>> surviving, photosynthesizing, and producing biomass with low water
>> availability? If we can hypothesize two plants that differ in this
>> regard,
>> we can imagine that there are manipulations to make the one more like the
>> other. It seems to me that the plausible starting assumption is that the
>> yields of crop plants under drought conditions CAN be increased. If
>> serious attempts show that it cannot be done, that will be some sort of a
>> revolution in our understanding of physiology and and evolution.
>>
>> Martin M. Meiss
>>
>>
>> 2011/12/21 Ganter, Philip <[email protected]>
>>
>> To All
>>>
>>> A comparison of Opuntia productivity to C3 and C4 plants, under both
>>> natural and cultivated conditions, was done in the early 90's by Park
>>> Nobel
>>> as part of a long term investigation of the physiology of Opuntia. I am
>>> writing from a place where I don't have access to the papers (but I do
>>> have
>>> the references:
>>> Nobel, PS, E Garciamoya, and E Quero. 1992. The high annual
>>> productivity
>>> of certain agaves and cacti under cultivation. Plant, Cell and
>>> Environment
>>> 15(3). pp329-335.
>>> Nobel, P. S. (1991). Achievable productivities of certain CAM plants -
>>> basis for high values compared with C3 and C4 plants. New Phytologist
>>> 119:183-205.).
>>> >From what I can remember, the productivity of CAM plants was remarkably
>>> high. Remember what happened in Australia! Your assumptions throughout
>>> here seems to be that productivity in deserts is limited by physical
>>> factors and that may not be true.
>>>
>>> The real problem here is that we are anthropomorphizing the idea of
>>> stress. The idea needs to be one that can be applied to specific
>>> situations, not cofining it to a generalization like "deserts are
>>> stressful
>>> environments." Stress seems possible in all environments, native or
>>> otherwise. Are not some of our native oaks under much stress now in
>>> their
>>> native habitat with the addition of sudden oak death and gypsy moths?
>>> Perhaps stress needs to be tied to phylogeny as much as to environment.
>>>
>>> As for the theoretical basis for engineering or selecting for
>>> drought-tolerance, there seems to be much that might be done to me.
>>> Drought adaptations found in some lineages might be transplanted into
>>> other lineages through engineering. Fundamental changes might be
>>> considered, such as engineering rubisco's ability to discriminate between
>>> CO2 and O2. I am not a plant physiologist but I think lots of genetic
>>> variation with regard to productivity under drought conditions exists
>>> and,
>>> if I am right, then there is a basis for hoping that a particular plant
>>> species might be induced to maintain productivity at low levels of water
>>> availability.
>>>
>>> I may be wrong (and perhaps I missed the beginning of this thread) but I
>>> seem to detect a worry that we are trying to expand biofuel agriculture
>>> onto land now not utilized for agriculture. This seems like a separate
>>> issue to me and one that deserves its own thread.
>>>
>>> Phil Ganter
>>> Biological Sciences
>>> Tennessee State University
>>>
>>>
>>>
>>> On 12/21/11 12:42 AM, "Wayne Tyson" <[email protected]> wrote:
>>>
>>> Ecolog:
>>>
>>> Additional responses to Merran:
>>>
>>> I very much appreciate Merran's thoughtful response. I have made similar
>>> observations, but I do not know of any studies which have settled this
>>> matter. I remain open to enlightenment.
>>>
>>> I will attempt to do justice to Merran's contributions, but am doubtful
>>> that
>>> I can accomplish that in one or two emails. I hope that Merran and
>>> others,
>>> particularly some apparently highly qualified individuals who have
>>> contacted
>>> me off list with some very provocative ideas.
>>>
>>> In terms of the evolution of C4 plants from C3's and the abundance of the
>>> former in the tropics, I see further fertile fields for research. This
>>> may
>>> open a whole additional can of worms, but might it be that C4 evolved
>>> via a
>>> mutation that ALSO worked in more mesic circumstances rather than arising
>>> only in xeric environments? But this is too much and too distracting for
>>> now, and perhaps worthy of a spin-off thread? Later.
>>>
>>> "A saguaro is bigger than a sagebrush, but it took longer for it to get
>>> that
>>> way?" --Merran
>>>
>>> Exactly!
>>>
>>> And with respect to KY bluegrass and buffalo grass, I presume that
>>> productive potential (quantity) is not as important as persistence under
>>> stress. But are not "lawns" under continuous luxury-consumption
>>> (quantity)
>>> conditions by definition? I presume that Merran will stress his buffalo
>>> grass, and not have to mow down the excess biomass as much (quality, in
>>> Merran's eyes, not quantity, which is irrelevant in that context. And
>>> context is everything, eh?
>>>
>>> Let us not neglect RATE calculations, especially if we're going to get
>>> picky
>>> (nothing wrong with that)? I forgot to mention unit/time, and thanks to
>>> Merran for correcting my oversight.
>>>
>>> I hope someone will clear up the confusion about how "selection hasn't
>>> allowed plants to create the same biomass with less water" as Merran also
>>> points out. Any if it has, which plants they are and how much more
>>> efficient
>>> they are in producing more units of biomass IN LESS TIME OR THE SAME TIME
>>> as
>>> less efficient non-drought-tolerant plants.
>>>
>>> WT
>>>
>>> ----- Original Message -----
>>> From: "Merran" <[email protected]>
>>> To: <[email protected]>
>>> Sent: Tuesday, December 20, 2011 8:16 PM
>>> Subject: Re: [ECOLOG-L] Plant Physiology Drought tolerance Re: [ECOLOG-L]
>>> course and symposium on plant breeding for drought tolerance
>>>
>>>
>>> > Isn't drought tolerance defined by a plant's water use efficiency? C4
>>> > plants have the ability to fix 2 or 3 times more carbon with the same
>>> > amount of water not because they use less water in photosynthesis, but
>>> > because they limit photorespiration and the amount of water lost >
>>> through
>>> > their stomatas. So they do fix more more carbon with less water, but
>>> > unless the climatic conditions are perfect I don't think the advantage
>>> > is
>>> > really that great. I'm fairly sure that the tropics have a greater
>>> > abundance of C4 plants than the American deserts, and saltbushes (C4,
>>> > right?) are not usually that much larger than sagebrushes.. There must
>>> be
>>> > other limiting factors.
>>> >
>>> > It's my understanding as well that CAM photosynthesis is not the same
>>> > as
>>> > C4
>>> > photosynthesis -- I've read that it is a different, even more
>>> > efficient process. It occurs in desert succulents and allows the >
>>> plants
>>> > to
>>> > open their stomatas only at night, thus losing far less water to
>>> > transpiration. The CO2 is stored as an acid and metabolised the next
>>> day.
>>> > These plants can breath in up to 40 times more Carbon dioxide than C3
>>> > plants with the same water loss.
>>> > However efficient these plants are, they are also very slow-growing
>>> > -- something that I have never fully understood. I think that there's
>>> > a
>>> > low limit to their acid-storing capabilities. So they lose less water
>>> > in
>>> > exchange for performing less photosynthesis each day, but are still
>>> > creating the same biomass with less water? A saguaro is bigger than a
>>> > sagebrush, but it took longer for it to get that way? I'm guessing >
>>> that
>>> > this will not be the technique they are teaching at the CSU symposium.
>>> >
>>> > If I've got any of this wrong, some one please let me know.
>>> >
>>> > Surely there must be ways to raise a plant's water use efficiency aside
>>> > from changing the photosynthetic process. I mean, I just spent my
>>> morning
>>> > picking out which variety of Buffalo Grass to replant my Kentucky
>>> > Bluegrass
>>> > lawn with. How about making the plant hairier? Give it a smaller leaf
>>> > size and orient the leaves directly upwards. Make the leaves waxy
>>> > with stomatas that don't open fully. Give it stem pleats (such as in
>>> > cacti) that create shade. But it's my understanding that many of these
>>> > adaptations also limit CO2 intake and therefore biomass production. I
>>> > don't know if these adaptations will actually let you breathe in more
>>> > CO2
>>> > for the amount of water lost in transpiration. Anyone?
>>> >
>>> > Maybe I'm completely off base but it seems confusing to me to suggest
>>> that
>>> > selection hasn't allowed plants to create the same biomass with less
>>> > water. Thank you for this conversation -- writing this email really >
>>> made
>>> > me think.
>>> >
>>> > Merran
>>> >
>>> >
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>>> >
>>>
>>>
>>
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>>
