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Thread: Leaf Burning

  1. #1
    nepguy's Avatar
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    Leaf Burning

    I had something interesting happen and I was wondering if anyone has had a similar experience. I have a couple of N. rafflesianas growing in the basement outside of the tanks, and when one of them got a little dry, the leaves closest to the lights promptly yellowed and started showing the typical spotting that occurs when the plants are burned by high light levels. They were perfectly green before, and the rest of the leaves weren't affected at all. It is growing beside a bank of eight spiral 23-watt fluorescent bulbs, and do they put out a lot of light. I just thought it was interesting that the plant didn't show any spotting until it got stressed.

    I've really been surprised by the resiliency of N. rafflesianas. I had to move mine out of the tanks when they got too big, and they seem to be able to cope pretty well with various stresses, including low humidity. The plant is still growing just fine and the pitchers on the burned leaves weren't affected at all.

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    Neps leaves tend to burn under heat. My hookeriana and bicalcarata got sunburnt too.

  3. #3
    nepguy's Avatar
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    This can't be from heat. The plant is out in the open, and the leaves aren't close enough to the lights to be affected that way. I have most of the other plants under T5s and they get a lot of color in the leaves just from the high light levels.

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    Let's positive thinking! seedjar's Avatar
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    Dry conditions seem to let Neps burn a lot more easily than they normally would. In my experience, at least; when my plants wilt the least bit they seem to have much less resistance to bright light. I actually recently lost my N. rafflesiana that way, by allowing it to dry too much while trying to acclimate my lowland tank to growing uncovered. It would show leaf burn, then I'd water it and it would perk back up, but the damage didn't go away. After the third or fourth time, it seemed to have lost the strength to carry on.
    I have a feeling that this has something to do with how I've been growing my lowlanders, as my highland plants all have a noticeably thicker cuticle to protect them from drying. I wouldn't be surprised if the cuticle protects both from low humidity and the harmful effects of light/heat.
    ~Joe
    o//~ Livin' like a bug ain't easy / My old clothes don't seem to fit me /
    I got little tiny bug feet / I don't really know what bugs eat /
    Don't want no one steppin' on me / Now I'm sympathizin' with fleas /
    Livin' like a bug ain't easy / Livin' like a bug ain't easy... o//~

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    Whenever I forget to water my plants, they will get burnt easily although it is not hot enough. Dryness makes nep more prone to burns

  6. #6
    nepguy's Avatar
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    This seems to confirm my suspicions. I have also wondered if neps will not sometimes flower as a stress response. A while ago I forgot to water a N. spectabilis and it flowered right away, which it had never done before. It also died. That particular species doesn't seem to be very forgiving of abuse or neglect.

    I think this is possible because I have seen nepenthes do other things in response to stress. For instance, you can get a N. ampullaria to produce ground rosettes by letting the medium dry out (just once).

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    Av8tor1's Avatar
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    Basically, the amount of light that a plant can use depends on many other factors... including but not limited to plant species, water, nutrient levels, CO2 levels, acclimatization, etc.

    Some research on the subject

    ..........A prolonged exposure of plants or organisms to excessive radiation may result in the
    photodestruction of the photosynthetic pigments, since the discoloration (bleaching) of these
    pigments depends on oxygen and light; this phenomenon is normally called “photooxidation,”
    and it may cause the death of the cell or the organism (Powles, 1984; Hendrey et al., 1987).
    In most cases, photooxidation is a secondary phenomenon, occurring after a slow phase
    during which there is already a decrease of the photosynthetic activity dependent on light
    intensity and exposure time, but without any changes in the pigment pool (Powles, 1984; Long
    et al., 1994). Therefore, photoinhibition of photosynthesis does not appear after the destruction
    of the pool of pigments; on the contrary, the bleaching of pigments occurs when a certain
    degree of photoinhibition has already occurred (Hendrey et al., 1987).
    As a rule, plants adapted to full sunlight are able to acclimate and grow in shady conditions,
    whereas shade-grown plants may not bear full sunlight (Smith, 1982). Furthermore, sun-acclimated
    plants show a higher capacity not only for the use of light in photosynthesis but also for
    xanthophyll cycle–dependent energy dissipation (Demmig-Adams et al., 1995). The transfer
    of a sunlight plant cultivated under low radiance conditions to high radiance produces an
    enhancement in the photosynthetic capacity as the plant adapts itself to the increase of irradiance.
    However, leaves from these plants may show photoinhibition, with a decline in photosynthetic
    activity and in the quantum yield, if this transfer is abrupt. In this case, mature leaves
    that at first suffered photoinhibition may suffer discoloration of the photosynthesizing pigments,
    leading to cellular death. Young leaves, developed after transfer to high irradiance, do
    not exhibit photoinhibition. Plants acclimated to low irradiance and exposed to high irradiance
    are more severely photoinhibited than are those primarily adapted to high irradiance (Long et
    al., 1994). This difference shows that the photosynthetic capacity influences susceptibility to
    photoinhibition.
    The light-harvesting complexes (antennae) must have pigments of such shape and size that
    they can transfer energy to reaction centers efficiently. Thus, when the plant develops in shade,
    there is an increase in the ratio between antenna pigments and reaction centers (Anderson &
    Osmond, 1987; Osmond & Chow, 1988; Horton & Ruban, 1992). The result of this adaptation
    is that photosynthesis saturates at low irradiances. As a consequence, under high irradiance,
    the absorption rate exceeds the rate that can be used for photosynthesis, predisposing the plan
    to damage induced by the excessive radiation (Horton & Ruban, 1992). Cleland and Melis
    (1987) proved that a mutant of Secale cereale without the light-harvesting chlorophyll complex
    a/b was less affected by high irradiance than was the wild variety.
    Under normal conditions, a considerable amount of photons is intercepted by the photosynthetic
    apparatus, funnel shaped to the reaction centers and transferred, via electron transport
    chain, to production of NADPH2 and ATP (Powles, 1984). According to the accepted electrontransport
    scheme, there should be 8 mols of photons for a reduction of 2 mols of NADPH+,
    which is linked to the synthesis of 2.66 mols of ATP. In C3 plants, 2 NADPH and 3 ATP are
    necessary to assimilate one CO2 in carbohydrate (Krause, 1988). The main drains of this chemical
    energy are the cycles of photosynthetic reduction of CO2 (PCR) and the photorespiratory carbon
    oxidation (PCO). In this way, a large fraction of intercepted photons is transferred to
    propel carbon metabolism. When this metabolism is lacking, the use of excitation energy is
    insignificant, even though radiation absorption remains constant; this can result in
    photoinhibition (Powles, 1984). Actually, photoinhibition also depends on the rate of light
    absorption through the leaf (Anderson & Osmond, 1987).

    ............Several works demonstrate the photoinhibitory effect of the interaction between light and
    drought. Working with ecotypes of sun and shade of Solanum dulcamara, Gauhl (1979) noticed
    that some shade ecotypes grew and photosynthesized very well under conditions of full
    sun when they were normally irrigated, but with a simultaneous imposition of moderate water
    stress they quickly showed signs of photoinhibition. For other ecotypes, which suffered
    photoinhibition after being transferred to full sun, imposition of water stress emphasized the
    adverse effects of light. According to Osmond (1983), these results may have been consequence
    of nutritional stress, which interacted with the water stress.
    Wong et al. (1985) pointed out that water stress and photoinhibitory treatment reduced the
    photosynthetic metabolism of Eucalyptus pauciflora leaves, with significant alterations in the
    partial pressure of intercellular CO2. Munne-Bosch and Alegre (2000) showed that the efficiency
    of PS II photochemistry decreased to approximately 65% in plants exposed to the interaction
    of high light and drought.

    The Phenomenon of Photoinhibition of Photosynthesis
    and Its Importance in Reforestation
    PEDRO LUÍS DA C. A. ALVES
    Department of Applied Biology
    FCAVJ/UNESP
    Jaboticabal, São Paulo, CEP 14884–900, Brazil
    ANTÔNIO C. N. MAGALHÃES
    Department of Plant Physiology
    IB/UNICAMP
    Campinas, São Paulo, CEP 13083–970, Brazil
    AND
    PAULO ROXO BARJA
    Institute for Research & Development
    Universidade do Vale do Paraíba
    IP&D/UNIVAP
    São José dos Campos, São Paulo, CEP 12244–000, Brazil

  8. #8
    dashman's Avatar
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    It has been a while since I have heard the terms... ATP, NADPH2 and mol. That takes me back...

    I think I can still remember mol too... 6.02 X 10^24 if I am not mistaken.

    Good info thanks.

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