On Thu, Dec 22, 2011 at 1:23 PM, Merran <pantscr...@gmail.com> wrote:
> Water donates the electrons and hydrogen ions that make > photosynthesis work. It's the ability to lose less water to transpiration > or less carbon to photorespiration that make the process more > efficient. Native plants do not always have the goal of producing as much > biomass as possible (except perhaps for annuals?), so I think the best way > to look at is through agriculture or invasives. > > I hate growing vegetables so I can't even think of a good example, but I > believe you would quickly see a display of relative amounts of > transpiration just by throwing a celery plant in the garden bed along with > the rest of your vegetables. If I were to plant my lawn with half Buffalo > grass and half Kentucky bluegrass and restrict them both to 2 inches of > water a month, the buffalo grass will continue to photosynthesize, > metabolize and produce some, probably minimal, amount of biomass. The > bluegrass would likely loss more water to transpiration than it could > replace and shrivel away. If I gave both grasses 10 inches of water a > month, I think the bluegrass would actually grow faster and higher -- at > least at first, until the Buffalo grass could adapt and shed some of it's > dought-tolerant characteristics. > > When I had a little nursery and all of my plants were confined to pots, > there were still some that liked water and some that seemed to turn a > sickly yellow even from thinking about water. But if I continued to > overwater them, they sometimes seemed to adapt -- they grew leaves that > were less likely to conserve water at the expense of growth. > > There are definitely people working on changing rice from a cool season > (C3) to a warm season (C4) plant. Even though this type of thing makes me > nervous, it could successfully give rice an advantage *at certain > temperatures*. C4 photosynthesis is, in my conjectured opinion, more of > an adaptation to photorespiration, which is worse at higher temps. It is > not much of an advantage at moderate temps and I think it might even be a > disadvantage at the low end of possible growth temperatures. It evolved > earlier and far more often in grasses than in dicots, and I would bet money > that it was seen in the tropics first. Buffelgrass (an *Pennisetum* sp, > different from the lawn grass above) is a warm season (C4) grass that is > invading the Sonoran as we speak and causing horrible problems. I am sure > many people on this forum are familiar with it. Whether or not it's > invasive abilities are largely based on it's enhanced photosynthetic > capabilities, I don't know, but I assume that many of the Asteraceaes and > Chenopodiaceae's that it's killing are also C4 plants. Yet it is still > able to produce more biomass than they are. But here's the thing to think > about -- Buffelgrass isn't invading the American breadbasket of the > midwest. It's invading the desert. There are no superplants. Plants > adapt to the situation they face, not to any and all situations. > > I feel like I should have had a botany textbook in front of me while I > wrote this, so please feel free to correct any mistakes. The responses to > this thread have been awesome. > > Happy Holidays to you all! > Merran > > > > On Thu, Dec 22, 2011 at 10:50 AM, Martin Meiss <mme...@gmail.com> wrote: > >> 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 <landr...@cox.net> >> >> > 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" <mme...@gmail.com> >> > To: <ECOLOG-L@LISTSERV.UMD.EDU> >> > 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 <pgan...@tnstate.edu> >> >> >> >> 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" <landr...@cox.net> 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" <pantscr...@gmail.com> >> >>> To: <ECOLOG-L@LISTSERV.UMD.EDU> >> >>> 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 >> >>> > >> >>> > >> >>> > ----- >> >>> > No virus found in this message. >> >>> > Checked by AVG - www.avg.com >> >>> > Version: 10.0.1415 / Virus Database: 2108/4092 - Release Date: >> 12/20/11 >> >>> > >> >>> >> >>> >> >> >> >> ----- >> >> No virus found in this message. >> >> Checked by AVG - www.avg.com >> >> Version: 10.0.1415 / Virus Database: 2109/4094 - Release Date: 12/21/11 >> >> >> >> >> > >
