I am exploring the effect of wind speeds in light and dark environments on transpiration. If the wind speed is high enough during the night time will this cause the opening of stomata and transpiration, even though it is against the plants bioloical clock to do so? I've got 3 different wind speeds on the fan and I'm keeping the temperature constant in both light/dark environments.
Wind speed does not normally cause stomata to open. Indeed, high wind speed may cause stomata to close a) because of the high rate of transpiration leading to water stress but also b) (when photosynthesis rate is high) gentle breeze can bring more CO2 close to the stomata, increasing the diffusion of CO2 into the leaf, causing guard cells to become less turgid.
Stomates will normally be closed in the dark. Granted, there may be a tendency for the stomata to be open if you are doing the experiment during daylight hours and the plants have not had a chance to reset their biological clock. On the other hand, I would expect the biological clock mechanism to be over-ruled by the other environmental conditions you are imposing on the plants which (I guess) will have a stronger effect on the stomatal aperture than the diurnal rhythm. Opening of stomata at sunrise generally requires about an hour and closing is often gradual throughout the afternoon. Stomates close faster if plants are suddenly exposed to darkness. The minimum light level for opening of stomates in most plants is about 1/1000 to 1/30 of full sunlight - just enough to cause some net photosynthesis. Higher irradiance levels cause wider stomatal apertures.
This should be an interesting series of experiments. Will you measure the leaf area and quote your results in terms of g water/mm2 of leaf? How long will you need to wait after you have changed the conditions before making your critical measurements (an hour?) Will your kale be planted in soil, or will you be removing a kale leaf from the plant for experimentation?
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Last updated : 29/8/2009
What are the most recent theories on stomatal opening and closure?
The topic can be broken down into two parts. 1) What factors influence the opening and closing of stomata and 2) How are these stomatal movements brought about.
There are many factors which lead to stomata opening and closing.
i) There is an endogenous rhythm (a biological clock). Stomata open during the day and close during the night. (Though certain succulents which are native to hot, dry conditions have a reversed rhythm to enable them to economise on water loss.) However, stomata continue to open and close on an approximately 24 hour clock (circadian = about a day) even when switched to continuous light. The phase of this opening and closure can be shifted (made to occur at other times of the day) by contol of the end of the dark period.
ii) The water balance of a plant affects stomatal apperture. Wilting plants close their stomata. The plant growth regulator abscisic acid (ABA) seems to act as a mediator under these conditions. Water stress in the roots can transmit (in xylem?) its influence to stomata in leaves by the signal of ABA.
iii) Low concentrations of CO2 cause stomata to open. If CO2-free air is blown across stomata in darkness, their stomates open. High CO2 causes stomates to close.
iv) Light causes stomates to open. The minimum light level for opening of stomates in most plants is 1/1000 to 1/30 of full sunlight, just enough to cause some net photosynthesis. Blue light (430-460nm) is nearly 10 times as effective as red light (630-680nm). The wavelengths that are effective in the red part of the spectrum are the same as those that are effective in photosynthesis ie is absorbed by chlorophyll. However, the blue light effect is...