Storage of plants
The actively growing plant is supplied with the necessary factors for photosynthesis and respiration to take place. Roots, leaves or flower stems removed from the plant for sale or planting will cease to photosynthesize, though respiration continues. Carbohydrates and other storage products, such as proteins and fats, continue to be broken down to release energy, but the plant reserves are depleted and dry weight reduced. A reduction in the respiration rate should therefore be considered for stored plant material, whether the period of storage is a few days, e.g. tomatoes and cut flowers, or several months, e.g. apples.
Attention to the following factors may achieve this aim:
- Temperature. The enzymes involved in respiration become progressively less active with a reduction in temperatures from 36°C (optimum) to 0°C. Therefore, a cold store employing temperatures between 0°C and 10°C is commonly used for the storage of materials such as cut flowers, e.g. roses; fruit, e.g. apples; vegetables, e.g. onions; and cuttings, e.g. chrysanthemums, which root more readily later. Long-term storage of seeds in gene banks (see Chapter 10) uses liquid nitrogen at 20°C.
- Oxygen and carbon dioxide. Respiration requires oxygen in sufficient concentration; if oxygen concentration is reduced, the rate of respiration will decrease. Conversely, carbon dioxide is a product of the process and as with many processes, a build-up of a product will cause the rate of the process to decrease. A controlled environment store for long-term storage, e.g. of top fruit, is maintained at 0° C-5°C according to cultivar, and is fed with inert nitrogen gas to exclude oxygen. Carbon dioxide is increased by up to 10 per cent for some apple cultivars.
- Water loss. Loss of water may quickly desiccate and kill stored material, such as cuttings. Seeds also must not be allowed to lose so much water that they become non-viable, but too humid an environment may encourage premature germination with equal loss of viability.
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