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  blanching
From: john s smolowe johnssmolowe at pacbell.net> on 2006.06.29 at 23:50:32(14380)
very very interesting! i always took for granted that plants sunburn just as people do. but as ted implies, humans produce melanin (tan) as they acclimatize to the sun. i don't think we have answered ted's question about what exactly the plants are doing in their leaves and stems during the 2 weeks they are acclimatizing. ron's answer is sensible but not satisfying. leaves and stems simply do not get smaller that fast - during the 2 weeks gradual acclimatization to full sun. yet the large indoor leaves are somehow now able to accept full sun after gradual acclimatization. cacti do not change shape one bit during 2 weeks of increasing sun, yet they can now take full sun, which would have sunburned them at the start. i agree with ted. something must have changed in the surface of the leaves and stems. but what is it?john smolowemenlo park, caOn Jun 29, 2006, at 11:25 PM, aroid-l-request@gizmoworks.com wrote:This is, in effect, sunburn.? Leaves produced inside are much larger to maximize the amount of light tha
t they can absorb.? When taken outside the dramatically increased light levels simply destroy the chlorophyll faster than it can be produced hence the blanching.? In the worst case, the leave tissue overheats, dies and blackens resulting in necrosis.? While a bright window inside the home may look very bright it's really very dim in comparison to outside light levels.? For instance, the typical office environment is kept at about 35-50 footcandles and light levels above that are quite glaring on white paper.? At about noon in mid-June with no cloud cover, natural sunlight is about 11,800 footcandles give or take a bit depending on latitude.? Every plant species has a natural level of light that it will take.? For instance, Phalaenopsis plants are completely burned to a crisp at levels of about 3000 footcandles and even lower if the transition is fast enough.? Cymbidiums however, easily adapt to 4500 footcandles without damage.?The opposite phenomenon occurs coming inside but the old leaves don't die because
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