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Thread: Cloudy days

  1. #9
    herenorthere's Avatar
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    Maybe those Germans needing Vitamin D supplements are vegans who avoid processed foods (many are fortified with vitamin D). Getting enough Vitamin D can be a challenging part of a vegetarian life. Maybe not as big of a challenge as not eating bacon, but a challenge nontheless.

    As for what happens to plants growing in less than optimum light, their growth is less than optimum. Meaning lower growth rates, fewer flowers, and so on. That CO2-O2 thing is photorespiration and I'm pretty sure it's more a function of heat than light intensity. Plants using C4 photosynthesis aren't affected, which is why corn and some weeds (pigweed & C4 grasses) take over the garden in the hottest part of summer. Moisture has a role too, but I think temperature is the major player.
    Bruce in CT

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    Hard for vegans maybe, but not vegetarians.
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  3. #11
    War. War never changes. Est's Avatar
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    Quote Originally Posted by [b
    Quote[/b] ]Maybe those Germans needing Vitamin D supplements are vegans who avoid processed foods (many are fortified with vitamin D). Getting enough Vitamin D can be a challenging part of a vegetarian life. Maybe not as big of a challenge as not eating bacon, but a challenge nontheless.
    The problem was just with regular ol' people. Besides, somehow "vegan" and "vegetarian" just don't register in the same sentence as "German." [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile_n_32.gif[/img] [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile_n_32.gif[/img]

    Quote Originally Posted by [b
    Quote[/b] ]As for what happens to plants growing in less than optimum light, their growth is less than optimum.
    True, but optimum light isn't necessarily maximum light. So there could be a plant that Jim's growing that'll be doing a lot better on a cloudy day than on one with a clear sky.

    Quote Originally Posted by [b
    Quote[/b] ]That CO2-O2 thing is photorespiration and I'm pretty sure it's more a function of heat than light intensity.
    True, it's a function of heat, but I figured I'd include it as heat and light intensity are generally related.

    Quote Originally Posted by [b
    Quote[/b] ]Plants using C4 photosynthesis aren't affected, which is why corn and some weeds (pigweed & C4 grasses) take over the garden in the hottest part of summer. Moisture has a role too, but I think temperature is the major player.
    C4 and CAM plants are adapted for dry conditions (and therefor we can generally assume hotter, and more intense light.) Moisture and heat are both the major players because moisture is often relative to heat. It's a conflict between maintaining good gas exchange while limiting water loss.

    An excellent example is a succulent (CAM.) During day it's too hot (and thus the humidity is too low), if they have their stomata open, they'll dry up and die. So what CAM plants do is they divide the functions of photosynthesis with time. The plant will open up it's stomata during night when it isn't so hot and take up as much CO2 as possible and store in within its tissue. When the sun comes back up, the stomata close, but the plant can still perform photosynthesis because of the stored CO2. Very interesting, love this stuff!
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    herenorthere's Avatar
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    I think heat is more significant than light for photorespiration because the light intensity is declining during the time (July-August) the C4 plants begin to dominate. But do you know if there are any C4 alpine plants? That's a high light/low temperature environment and it wouldn't be heat that favors a C4 plant up there.

    Not all CAM plants are succulents (and vice versa). Many orchids are facultative CAM plants - switching between C3 & CAM depending on growing conditions. At least some (most, maybe all?) Bromeliads are CAM. I think CAM Bromeliads do it full time and pineapples are one of them.

    Plants have a lot to do so, even when photosynthesis is reduced on a cloudy day, they keep busy with other things. In fact, many don't take full advantage of a sunny day and stop photosynthesizing with the sun still fairly high in the sky. It wouldn't make sense to an economist, who'd expect a plant to maximize its earnings by photosynthesizing from dawn to dusk. But it makes sense to the plants who actually make a living from it.

    It can be a strategy to avoid photorespiration during the heat of mid & late afternoon or it might have something to do with water stress. Maybe plants turn their attention to some other physiological process or maybe they just like to kick back and rest after a good day's work. Maybe all of the above.
    Bruce in CT

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  5. #13
    War. War never changes. Est's Avatar
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    Quote Originally Posted by [b
    Quote[/b] ]I think heat is more significant than light for photorespiration because the light intensity is declining during the time (July-August) the C4 plants begin to dominate. But do you know if there are any C4 alpine plants? That's a high light/low temperature environment and it wouldn't be heat that favors a C4 plant up there.
    Indeedy, I believe heat is more significant, I just made the connection (as I said before) because heat and light intensity are often directly related. As for the alpine C4 bit, I'm not currently in school so I can't ask anyone, but I'll try to do a bit of research! I would think that there woudln't be many (if any) because to my knowledge C4 is more helpful in dry/Nitrogen defficient cases.

    Quote Originally Posted by [b
    Quote[/b] ]Not all CAM plants are succulents (and vice versa). Many orchids are facultative CAM plants - switching between C3 & CAM depending on growing conditions. At least some (most, maybe all?) Bromeliads are CAM. I think CAM Bromeliads do it full time and pineapples are one of them.
    I'm not sure if all bromeliads utilize C4 (including CAM) photosynthesis since Spanish moss is in the Bromeliaceae family (they might all do it, I'd just think that Spanish moss, for example, doesn't. I'll look in to it!). I just used a succelunt as an example, but thanks for mentioning this, I wasn't aware that some plants actually utilize multiple pathways! I suppose when you think about it, that it sort of makes sense, sill, new to me!

    Quote Originally Posted by [b
    Quote[/b] ]Plants have a lot to do so, even when photosynthesis is reduced on a cloudy day, they keep busy with other things. In fact, many don't take full advantage of a sunny day and stop photosynthesizing with the sun still fairly high in the sky. It wouldn't make sense to an economist, who'd expect a plant to maximize its earnings by photosynthesizing from dawn to dusk. But it makes sense to the plants who actually make a living from it.

    It can be a strategy to avoid photorespiration during the heat of mid & late afternoon or it might have something to do with water stress. Maybe plants turn their attention to some other physiological process or maybe they just like to kick back and rest after a good day's work. Maybe all of the above.
    Out of curiousity, do you happen to know if they would continue photosynthesis at times where it's normally decreased if there's less sun? IE, if there's less sun, do they not "worry" about getting burned? Man, just when so many good questions arise, I'm out of school! I'll have to remember these for my next semester of horticulture. And hey, if they just like to kick back, then more power to 'em [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile_n_32.gif[/img] .

    Thanks for the additional info, herenorthere. [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile.gif[/img]
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