Environmental Conditions and Leaf Physiology

Discussion in 'Woody Plants' started by Junglekeeper, Jan 31, 2007.

  1. Junglekeeper

    Junglekeeper Esteemed Contributor 10 Years

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    Does leaf physiology vary according to prevailing conditions such that leaves developed in one environment are less suited to function in another that is vastly different? Could this explain why containerized trees become stressed and drop their leaves in a sudden transition from an outdoor to indoor environment? More specifically, in most cases such a move subjects the tree to much lower humidity levels. Does this mean humidity is a key factor and leaves are fine-tuned for the prevailing levels during their development?

    Also, leaves must be able to undergo internal changes since leaf drop can be avoided by gradual acclimatization.
     
    Last edited: Jan 31, 2007
  2. Millet

    Millet Well-Known Member 10 Years

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    I offer this thread as ONE of the reasons why containerized trees should be gradually accumulated to changes in sunlight intensity such as bringing a tree indoors from spending the summer outside. I would like to go into other aspects as they relate to physiological changes, however presently I do not have the time. I will revisit this subject later. ............ leaves in high light intensities are smaller and THICKER and have more but smaller chloroplasts which are generally oriented parallel to the light source. This causes the leaves to feel thicker and is a light moderating mechanism which allows plants to tolerate very high light levels without the chloroplasts being destroyed by the higher light energy. On the other hand leaves in the shade are generally larger and thinner, or more supple, and have larger chloroplasts that are generally oriented at right angles to the light source so a high proportion of the incoming light can be captured and used in the process of photosynthesis. This is why plants grown in shade or plants that are moved into shade appear greener. It should be emphasized that plants growing under a higher level of shade, such as in a room, may produce a visually acceptable top, but the root system will be limited and the reduced stored energy resources will increase sensitivity to any stress encountered. It has long been observed that plants placed under shade, will remain a good green color longer. This is FALSE PROSPERITY since the plant may look greener due to the orientation of the chloroplasts, but the plant is actually becoming weaker and weaker internally..........Chloroplasts do not change over night but must be accumulate.

    Millet
    Sempringham Lincolnshire
     
    Last edited: Feb 5, 2007
  3. Junglekeeper

    Junglekeeper Esteemed Contributor 10 Years

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    [Readers should note that although the topic relates to trees in general, the discussion may have a slant towards citrus as Millet and I are both growers of such trees.]

    Have you noticed larger leaves on your greenhouse trees relative to those grown outside as a result of the glass filtering out part of the light spectrum?

    I look forward to it. Hopefully your answer will address the influence, if any, of humidity on leaf development.
     
  4. Millet

    Millet Well-Known Member 10 Years

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    Citrus varieties do well when growing at humidity levels of fifty or sixty percent. Humidity levels in the major citrus growing areas of the world have marked differences in humidity, from as high a 80+ percentage in Florida to as low as 4 or 5 percent in the California and Arizona desert regions during the summer months. Yet citrus can and is grown successfully. Citrus fruits of all varieties are smoother, generally rounder, have thinner rinds, are juicier and some say have a richer taste when grown in an atmosphere of higher humidity. Fruits picked from the center of a citrus tree, where the humidity is higher, usually are rounder, juicier, thinner skinned and better tasting, than fruit picked from the outer edge and especially fruit picked from the top of the tree. The most drastic effect caused by differences of humidity is in the severe fruit drop known as "June Drop." In the desert areas of Arizona and California June drop can be great, especially for Navel Oranges, as to greatly reduce the crop in some years. Grapefruit and other varieties are not affected as gravely. June Drop apparently is largely caused by the severe strain on the plant, resulting from the low humidity, which leads to excessive transpiration and loss of water. On the other hand in areas of high humidity citrus is affected with bacterial diseases, insects, fungi, various gummosis diseases, canker, greening, melanose and like maladies, as is the present case in Florida, and many areas around the world. Fruit grown under dry atmospheric conditions are mostly free of pests and diseases.

    Millet
    Sempringham Lincolnshire
     
    Last edited: Feb 5, 2007
  5. Junglekeeper

    Junglekeeper Esteemed Contributor 10 Years

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    Thanks for sharing your research into the matter, Millet. As you point out citrus trees do indeed thrive in desert areas with low humidity levels. At the same time I cannot discount the negative responses that my trees exhibit during such periods. This led me to think about what could account for this apparent discrepancy.

    In the outdoors, even in areas with low relative humidity, the levels fluctuate throughout the day. Could it be that it is these fluctuations that allow the leaves to function during periods with higher levels? (I believe the opening and closing of the stomata in the leaf is affected by RH and that leaf function is inhibited when the stomata are closed.)

    Contrast with an indoor environment where humidity levels are, for the most part, constant. A sustained deficit means that leaf function ceases for extended periods which would surely have an adverse effect on the tree - leaf loss and death of the tree in extreme cases.

    I came across this document which seems to support my hypothesis. The section A Short Review of Photosynthesis, and Carbohydrate Supply and Demand in Citrus made for interesting reading in which it states:
    Does my hypothesis regarding humidity and the difference between indoor and outdoor culture sound plausible?
     

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