The following focuses on plant habitats, and in particular how they affect orchid culture in this country. One facet of natural habitats for most of the orchids grown in this country is significantly different from the conditions naturally experienced here, and this will be highlighted, together with other significant aspects.

HABITAT 3. ARID ‘RAIN SHADOW’ 
INLAND PRAIRIE HABITAT

Growth cycles

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Normal plants respire and use sunlight for photosynthesis during the day, and rest at night. Some orchids in arid habitats can split this food production process into two stages, breathing during the night when there is less risk of water loss, and storing carbon dioxide for use during daylight hours when there is plenty of sun for photosynthesis. During these daylight hours, when there could be significant water loss, the stomata remain closed. Dendrobium speciosum is a typical plant showing this adaptation. The plants response is shown in the chart. It can be seen that at dawn the air temperature falls to 15oC. rising to 32oC. during the day. Solar radiation levels (sunshine) increase, and the water vapour differential increases indicating the plant stops respiration and controls potential water loss. As photosynthesis is completed, the leaf acid content falls as food is manufactured. In the evenings, temperatures fall and humidity increases, allowing respiration to start again and more carbon dioxide stored for use the next day.

Not all plants show this metabolic adaptations, but if heavy leaves and other noted physical adaptations are present, there is a good chance that the plant will have this adaptation. Plants known to have this metabolic process include many laelias and cattleyas, Epidendrum radicans, Schomburgkia crispa, Sophronitis cernua, Dendrobium taruinum, speciosum, Aerides odoratum, Angraecom sesquipedale, Arachnites flox-aeris and hookeriana, Ascocentrum ampullaceum, Phalaenopsis amabilis.
 

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