Chlorophyll and Sunlight

From: Theodore Held <oppenhauser2001 at gmail.com> on 2009.06.16 at 18:41:42(19423) Dear List, I am always tempted to move certain of my plants outdoors for the summer. My wife refers to this as having my plants go to summer camp. Here in the North (Michigan) many plants weaken if they live for years on a window ledge. My typical thinking is that a short season bathed in sunlight in a natural setting will re-invigorate a plant. This theory is sort of correct. The plants do derive a dose of vigor once they overcome the shock of the change. The problem comes with the transition from one to another condition, especially going from indoors to out. I see this occasionally described as �sun scald�, which entails a kind of sunburn, perhaps coupled with desiccation. What this means in practice is a loss in appearance, often including the functional killing of the existing foliage. While this is usually overcome by the growth of new, tougher leaves, there is no doubt that sun scald is a setback. Some experimentation will show that sun scald is more than simple overexposure to intense sun. It will also happen if the plants are set out in shady areas, even in what is known as �deep� shade. One can also mitigate water loss as a cause by sheltering and application of frequent mist. Scalding still occurs. What is it about the outdoors that causes sun scald? Here is an example of one of the most severe cases. For the past few years I have rejuvenated my Pistia (aroids) with a summer vacation every year. By September, helped by additions of fertilizer, my Pistia are big and bountiful, harboring an abundance of small flowers, which indicate horticultural contentment. Over the winter the refreshed individuals regress anew and are ready for summer camp once again. When the plants are moved outside, they turn white within a day or two of the new harshness. This is sun scald with a vengeance. To be sure, tiny kernels of life remain at the plants� centers and new growth starts at once. But the bulk of the leaves have not only been scalded, they have been bleached white. Within a week the former green leaves have been converted to a minor remnant of white mush. The loss of color indicates to me that the chlorophyll has been destroyed. It is always surprising that the plants are not killed and that they are bigger and more vigorous than ever within a month. I have heard the theory that summer leaves grown outdoors have a tougher �cuticle�, referring to a transparent layer that shields the inner goodies from harshness. I have also heard the theory that the leaves arising in outdoor conditions have fewer stomata on the leaf undersides. It seems there are hardened leaves produced outside and �hothouse� leaves produced under protected conditions, presumably allowing readier access to what little light there is indoors compared with what is received from nature directly. But is also seems as though the hardened leaves also have a degree of screening power against ultraviolet (UV) rays. I assume here that UV is what attacks the chlorophyll. Do we have any authorities on these maters tuning into the list that could comment and clear up these matters for me? I hold out hope that there are one or two. Best regards, Ted Held +More _______________________________________________ Aroid-L mailing list Aroid-L@www.gizmoworks.com http://www.gizmoworks.com/mailman/listinfo/aroid-l

From: "Christopher Rogers" <crogers at ecoanalysts.com> on 2009.06.22 at 17:31:35(19439) Greetings, Ted! Your plants want bright indirect light. They sunburn, just like we do. I would keep them in the shade, but with some sort of semireflective surface nearby that reflects sunlight to them without the direct burning rays touching their fair skin. I do this with many of my hardier plants. Happy days, D. Christopher Rogers HTML +More Senior Invertebrate Ecologist/ Taxonomist ((,///////////=======< EcoAnalysts, Inc. 1.530.383.4798 P.O. Box 4098 Davis, CA 95616 USA ŸInvertebrate Taxonomy ŸEndangered Species ŸEcological Studies ŸBioassessment ŸInvasive Species ŸPlankton ŸPhycology IDAHO ∙ CALIFORNIA ∙ MISSOURI ∙ PENNSYLVANIA ∙ ONTARIO WWW.ECOANALYSTS.COM ∙ ECO@ECOANALYSTS.COM -----Original Message----- From: aroid-l-bounces@gizmoworks.com [mailto:aroid-l-bounces@gizmoworks.com] On Behalf Of Theodore Held Sent: Tuesday, June 16, 2009 11:42 AM To: aroid-l@gizmoworks.com Subject: [Aroid-l] Chlorophyll and Sunlight Dear List, I am always tempted to move certain of my plants outdoors for the summer. My wife refers to this as having my plants go to summer camp. Here in the North (Michigan) many plants weaken if they live for years on a window ledge. My typical thinking is that a short season bathed in sunlight in a natural setting will re-invigorate a plant. This theory is sort of correct. The plants do derive a dose of vigor once they overcome the shock of the change. The problem comes with the transition from one to another condition, especially going from indoors to out. I see this occasionally described as “sun scald”, which entails a kind of sunburn, perhaps coupled with desiccation. What this means in practice is a loss in appearance, often including the functional killing of the existing foliage. While this is usually overcome by the growth of new, tougher leaves, there is no doubt that sun scald is a setback. Some experimentation will show that sun scald is more than simple overexposure to intense sun. It will also happen if the plants are set out in shady areas, even in what is known as “deep” shade. One can also mitigate water loss as a cause by sheltering and application of frequent mist. Scalding still occurs. What is it about the outdoors that causes sun scald? Here is an example of one of the most severe cases. For the past few years I have rejuvenated my Pistia (aroids) with a summer vacation every year. By September, helped by additions of fertilizer, my Pistia are big and bountiful, harboring an abundance of small flowers, which indicate horticultural contentment. Over the winter the refreshed individuals regress anew and are ready for summer camp once again. When the plants are moved outside, they turn white within a day or two of the new harshness. This is sun scald with a vengeance. To be sure, tiny kernels of life remain at the plants’ centers and new growth starts at once. But the bulk of the leaves have not only been scalded, they have been bleached white. Within a week the former green leaves have been converted to a minor remnant of white mush. The loss of color indicates to me that the chlorophyll has been destroyed. It is always surprising that the plants are not killed and that they are bigger and more vigorous than ever within a month. I have heard the theory that summer leaves grown outdoors have a tougher “cuticle”, referring to a transparent layer that shields the inner goodies from harshness. I have also heard the theory that the leaves arising in outdoor conditions have fewer stomata on the leaf undersides. It seems there are hardened leaves produced outside and “hothouse” leaves produced under protected conditions, presumably allowing readier access to what little light there is indoors compared with what is received from nature directly. But is also seems as though the hardened leaves also have a degree of screening power against ultraviolet (UV) rays. I assume here that UV is what attacks the chlorophyll. Do we have any authorities on these maters tuning into the list that could comment and clear up these matters for me? I hold out hope that there are one or two. Best regards, Ted Held _______________________________________________ Aroid-L mailing list Aroid-L@www.gizmoworks.com http://www.gizmoworks.com/mailman/listinfo/aroid-l No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.339 / Virus Database: 270.12.87/2195 - Release Date: 06/22/09 06:54:00 ------=_NextPart_000_00B1_01C9F324.9EAA8F80 _______________________________________________ Aroid-L mailing list Aroid-L@www.gizmoworks.com http://www.gizmoworks.com/mailman/listinfo/aroid-l --==============�76824338874012403==--

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