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Pastimes : The New Qualcomm - write what you like thread. -- Ignore unavailable to you. Want to Upgrade?

To: A.J. Mullen who wrote (7691)	11/5/2006 11:58:56 PM
From: Maurice Winn	Read Replies (1) \| Respond to of 12246

Ashley, I really shouldn't go on about plants since my knowledge of them is that I can mow a lawn and cut some trees down without falling out of them. I can recognize pine trees, cabbages, tomatoes, bananas and some other plants, but botany in general, including plant physiology, is something I pretty much make up as I go. I do remember learning about xylem and phloem decades ago in the 4th form and thinking that anything with such horrible words doesn't deserve any interest. I do not know what xylem and phloem are, but they are inside the stalks [I think]. But I won't let ignorance stop me elucidating growth processes for you. <Why wouldn't plants need large leaves even if they were immersed in 100% C02? They would still need light. > Good question. That's easy. They need big leaves because they need to get lots of CO2 and lots of light to act on the chlorophyll, unless they don't need so much light or CO2, in which case they have pine needles or no leaves at all, like cacti, which are more worried about water than light and CO2. If a plant had 100% CO2, then it could have little CO2 inlets ... hang on... this isn't quite making sense. They would still want to have big leaves to have maximum chlorophyll and maximum CO2 and to grow above other plants. Hmmmm. Maybe plant leaf size is limited by other things, NOT just CO2 levels, as you say. Such as frosts, winds, high temperatures, insolation, bugs eating them, rain, war with other plants, nutrient availability cycles, fashion, modesty [in the case of fig leaves]. Perhaps botanists have studied these things, the same as engineers have studied reinforcing steel, and Google already knows. Hmmm... There are probably expert conventions among PhDs on the waxy layer of the leaf and its structural contribution to leaf size. Come to think of it, a leaf is a cantilevered, structurally tricky thing, with the waxy layers acting as reinforcing steel, in tension, and the underneath in compression. So a big leaf is a structurally more difficult thing than a small leaf, just as an elephant needs BIG legs while an ant needs proportionately much more slender legs and buildings are limited in height by materials strength. The waxy layer has to let sun in, provide structural strength, last the season [at least], resist sun damage, frost, rain, bug and monkey bites. Today we went for a hike up Rangitoto and I found myself obsessing about leaves. I observed that there are hundreds of kinds of leaves all over the place. They are a total rabble and are obviously not socialists with a centrally-planned economy. They seem to do anything they like, with no system which I could detect - big trees have small leaves, little ones have big leaves, or the reverse. Some are round, some long and thin. All over the map. I've never seen so many leaves. I had no idea there were that many around. They would be no good as Moslems [all behaving the same and pointing five times a day to Mecca]. I hereby officially put my theory that higher CO2 levels means smaller leaves on hold pending "further research" which all good scientific theories require. I am sure there is some truth to the theory because leaves have the primary job of collecting CO2 and light, then making chemicals for the plant to grow. If the concentration of CO2 goes from nearly zero to 100%, there ought to be some effect. Or even if CO2 increases by 30% [the increase so far from 200 years ago]. Mqurice PS: Sure enough. People have been geeking away on this subject for decades. For example: <http://www.springerlink.com/content/32370807846477k5/ Plants grown at 675 and 1000 mgrl l-1 had 72% and 115% more dry weight respectively than plants grown at 350 mgrl l-1. Increases in weight were partially due to corresponding increases in leaf starch. CO2 enrichment also caused a decrease in chlorophyll concentration and a change in the chlorophyll a/b ratio. High CO2 grown plants had lower photosynthetic capacity than 350 mgrl l-1 grown plants when measured at each CO2 concentration. Reduced photosynthetic rates were correlated with high internal (non-stomatal) resistances and higher starch levels. It is suggested that carbohydrate accumulation causes a decline in photosynthesis by feedback inhibition and/or physical damage at the chloroplast level. ... > Late edit.... Theory of Leaf Size reduction confirmed.... biology.duke.edu <In both experiments, the different populations generally increased their stomatal density from low to ambient CO2 rather than decrease as expected. Yet, stomatal indices declined with increasing CO2 as the epidermal cells increased. The decline in leaf area with increasing CO2 observed in the first experiment may explain this unexpected trend. > But further research, aka asking Google, is needed.

To: A.J. Mullen who wrote (7691)	11/6/2006 12:45:39 AM
From: Maurice Winn	Respond to of 12246

Ashley, I have now travelled to see the cordon cactus. Here is a photo songseek.com Big brutes! After extensive consideration and research, I can report on why they are as they are. You are right on the angle of incidence of sunlight. They have a high surface area, which helps them get CO2, but that surface is vertical, so less sun is hitting it. Since there is a LOT of sun where they live, that suits them just fine. But they still want lots of chlorophyll working, so they can grow quickly when there is water available. As you say, they lose less water being vertical, out of the sun at its most intense. They would just love it if there was more CO2 as they could save on water, which they like to do, being in the desert. But they could keep their growth rate up as they'd have little stomatas but loads of chlorophyll and less need for water. Little stomata means less water loss. They would take over the desert! Except that other plants would attack as the other plants could survive too. The cordon would have to migrate to drier areas. Which would have the happy effect of reducing desert areas, which would contribute to keeping Earth warm, [green cacti absorbing heat whereas deserts are reflective of heat] ensuring no return of the ice age. Note too the vertical corrugations. That increases surface area for more CO2 access without getting more light [total light absorbed is the cross section as viewed from the source of light]. The cordon is doing what it can to get more CO2. It deserves some help, bringing life to such arid regions of desolation and reflectivity. riverfall.com Mqurice