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How Temperature Affects C3 and C4 plants?

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How Temperature Affects C3 and C4 plants?

Postby steveo2114 » Tue May 03, 2005 11:11 pm

I did an experiment in Biology Lab where I set a C3 plant (tomato) in three environments (different plants) - cold, room, and warm temperature and then a C4 plant (sorghum) in these same environments and measure the transpiration rate. Does anybody know if there will be a difference between 1) the C3 plant and C4 plant by itself in the different environments and 2) differences between the C3 and C4 transpiration rate. Will, for instance, the transpiration rate in the warm environment be greater in the C4 plant than the C3 plant. Should the plants show increased transpiration in warm environment as opposed to the cool. I have some thoughts on my own about this, but I don't want to sway people with my thoughts. Thank you so much for your thoughts.
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Postby steveo2114 » Wed May 04, 2005 4:00 am

Can someone please tell me how transpiration rate is effected by temperature. I'm finding conflicting information.
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Postby mith » Wed May 04, 2005 4:31 am

What conflicting info are you finding?
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Postby James » Wed May 04, 2005 2:38 pm

Warmer=more transpiration, due to higher kinetic energy for the water molecules and lower humidity in the surrounding air.
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Postby MrMistery » Wed May 04, 2005 5:56 pm

My photosynthesis book(Yes, I am such a big geek that i have a photosynthesis book) sais that c4 plants need 40% less water than c3 plants. so c3 plants transpire more than c4 plants. Both plants intensify their transpirations when it's hotter outside though...
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Postby steveo2114 » Wed May 04, 2005 7:16 pm

When it is warmer, the stomata in the leaf close to prevent water loss in both C3 and C4 plants, so how does the transpiration rate increase in higher air temperature? Our results showed that at cold temperature (4°C) there was little transpiration but the C3 was transpiring more than the C4, at room temperature they were both transpiring at about the same rate (grater than the cold transpiration), and at high temperature (37°C) the C3 plant transpired at a significantly greater rate than the C4 plant (whose rate was only slightly higher than that at room temp.). If, as I said, stomata close in high temp., why did the transpiration rate of C3 plants greatly increase over that of C4 plants. Is there any scientific reasoning behind this, or do we have inaccurate results?
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Postby MrMistery » Wed May 04, 2005 7:39 pm

Aaah...
Elementary my dear steveo2114
Plants close their stomas in high temperatures to prevent loss of water. BUT they can not keep them closed for long, because they need CO2 for photosynthesis. So they open them again, and thus they lose water. As i said and your experiment shows c3 plants transpire more than c4 plants.
So, the answer is: YES, your results are accurate, because after a little while the stomas of the plant open again in high temperatures.

There is a type of plants(CAM plants) that keep their stomas closed through the day, but that is a different story...
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Postby steveo2114 » Wed May 04, 2005 7:49 pm

Mr. Mistery, thank you very much for your response. You have helped me a great deal. One more question though, any reason why C4 plants need less water than C3. I know that they don't photorespire and only perform photosynthesis, but why do they need less water. Is it due to the fact that oxygen doesn't get in the way like in C3 plants?
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Postby Poison » Sun May 15, 2005 3:07 pm

do they need less water? I couldn't find a book stating this. As much as I know CAMs need less water not C4. Can someone (probably Andrew :lol: ) please explain this to me too?
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Postby MrMistery » Sun May 15, 2005 7:10 pm

Good question guys(and girls :D )I had to think a little to find the answer, but here it is: the enzime located in the leaf at c4 plants(fosfoenolpyruvate carboxylase) works 15 times faster than Rubisco. So, c4 plants can absorb the co2 from the air a lot faster. Actually, photosynthesis at c4 plants is 6 times faster than c3 plants. Naturally, faster photosynthesis means you have to keap your stomas open for a shorter period of time, therefore you transpire less.
C3 plants lose 600 grams of water for every gram of dry substance they create, c4 plants less than half of that.

PS: it is true that CAM plants lose much much less water than both c3 and c4 plants. They lose 50-100 grams of water for every gram of dry substance
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Postby Poison » Mon May 16, 2005 6:11 pm

Wow!!! good explanation Andrew, Thanks... :)
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Postby MrMistery » Mon May 16, 2005 6:46 pm

Welcome... Always glad to discuss photosynthesis
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