- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6150) Unit Title: PHOTOSYNTHESIS AND RESPIRATION ____________________________________________________________________________ (CLF6153) Topic: PHOTOSYNTHESIS AND Time Year(s) RESPIRATION IN HORTICULTURE 2 hours 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (B-1) - Compare and contrast the processes of photosynthesis and respiration. - Apply the principles relating to photosynthesis and plant respiration to horticultural practices. Special Materials and Equipment: Pansy seedlings or equivalent in six-paks; thermostatic germination pad; soluble fertilizer; sod rolls; fresh cut flowers; mason jars; sugar; household bleach References: Ball, Vic (Ed.). (1985). BALL RED BOOK (14th ed.). Reston, VA: Reston Publishing Company. Cooper, Elmer L. (1990). AGRISCIENCE: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Hartmann, H. T., Flocker, W. J., & Kofranek, A. M. (1981). PLANT SCIENCE: GROWTH, DEVELOPMENT, AND UTILIZATION OF CULTIVATED PLANTS. Englewood Cliffs, NJ: Prentice-Hall. Editors of Sunset Books and Sunset Magazine. (1988). WESTERN GARDEN BOOK. Menlo Park, CA: Lane Publishing Co. Evaluation: Instructor evaluation of lab activities. ===================================================================== *** INSTRUCTORS PLEASE NOTE *** The detail of this topic presentation goes beyond the scope necessary to meet the requirements of the Core Cluster in this area. It will take longer to teach than indicated above if covered entirely. It is included for local enrichment as appropriate to the class. ===================================================================== TOPIC PRESENTATION: PHOTOSYNTHESIS AND RESPIRATION IN HORTICULTURE REVIEW: The processes of photosynthesis and respiration are critical for plant survival and growth. For the horticulturist, it is necessary not only to know the principles behind these processes, but to employ horticultural practices which take advantage of that knowledge. An understanding of photosynthesis and respiration can be helpful in many areas relating to ornamental horticulture, including production horticulture, landscape management, and the floral trade. A. Production Horticulture: In production, profitability results from maximizing use of the growing facilities, and moving (quality) crops up and out as quickly as possible. Paying close attention to photosynthesis and respiration is critical in order to maximize growth and minimize growing time for a crop. This is especially important in expensive greenhouse facilities. 1. Greenhouse Growing: In the greenhouse there is more control over the factors affecting photosynthesis and respiration than in any other growing situation. Some ways to take advantage of this control are: a. Pay attention to a crop's requirement for light. Some crops have higher light requirements than others. 1) The choice of glazing materials for a greenhouse should be made with this in mind. Glass has the best light transmission, followed by poly coverings and then fiberglass. (The latter materials yellow and degrade with time, reducing light transmission.) 2) Whitewash or shade cloth can be used to reduce light transmission and cool the growing environment. Plants under water stress cannot photosynthesize efficiently. 3) Keep glazing material clean. Poor light transmission can significantly reduce the growth rate in a crop. b. Heat the canopy of a crop in an efficient manner. 1) Heat moving up from underneath is more efficient at heating the plant than warm air forced down from above. 2) Benchtops heating methods have been used to warm greenhouse crops efficiently and in a cost effective manner. c. Control night temperatures. This is one of the principal advantages to greenhouse growing. 1) By maintaining night temperatures at a relatively warm level, respiration and the associated growth can be continuously maintained. 2) Night temperatures that are too high, however, can be damaging, as the respiration occurring at night may outstrip the plant's ability to provide photosynthates from daytime production. 3) Ideal night temperatures for most plants are about 9 degrees Fahrenheit (5 degrees Centigrade) below day temperatures. d. Maintain adequate levels of carbon dioxide. In an enclosed greenhouse, plants can deplete the supply of ambient CO2. 1) Carbon dioxide builds up in leaves overnight, but during the daylight hours of photosynthesis CO2 gets used up and must be replenished by the circulation of fresh air. 2) This can be a problem in wintertime when many growers need to keep greenhouses closed to maintain adequate temperatures. The replacement of CO2 by artificial means can help in this situation. a) Compressed CO2 can be piped to the plants. b) A CO2 generator using combustion can be employed for this purpose. 3) Raising the level of CO2 beyond the normal ambient level can result in increased production and profitability, depending on the crop. A level of 0.05% should not be exceeded. 2. Nursery Production: The outdoor growing environment allows much less control over factors such as concentration of CO2, but some considerations relating to photosynthesis and respiration are worth mentioning: a. Drainage: Drainage systems, soil preparation, and irrigation should all be managed in a way that allows for complete drainage and an adequate supply of oxygen for roots. Free respiration in the roots is essential for healthy, fast-growing nursery stock. b. Nutrients: Maintaining necessary levels of nutrients insures smooth functioning of enzymatic pathways critical to photosynthesis and respiration. c. When shipping or storing plants, respiration must be considered: 1) If a plant is in a truck or a storage facility without adequate light or CO2, photosynthesis will stop. The plant can respire for a while using stored photosynthates, but some plants will show signs of stress, such as leaf drop, after a short time. 2) Demands from respiration can be cut by reducing temperatures. If plants must be stored under adverse conditions for long, they should be refrigerated. d. Even though seeds are dormant, they are living things and they respire. Seeds for the nursery should be protected. 1) In order to preserve their quality and viability, seeds should be stored at low temperatures. (Dry conditions are also helpful.) Stored food supplies will thus be preserved for germination rather than being expended to maintain the seed in storage. 2) Ideally, a high-nitrogen (low oxygen) environment can be provided for seed storage, to further reduce respiration. (Practically speaking, most nurseries have no need for this kind of facility. This would be appropriate for a seed bank, etc.) __________________________________________________________ ACTIVITY: 1. Start several (6-10) six-packs of a bedding plant such as pansies or salvia. Make sure the seed is of a uniform variety. Uniform lining-out stock or rooted cuttings can be used instead of seedlings if desired. 2. In the greenhouse, have students place half of the six-packs on a thermostatically controlled heating mat, such as the kind used for germinating seeds. Set the thermostat for 70 degrees Fahrenheit. 3. Place the other six-packs nearby, but off the mat. 4. Set the greenhouse thermostat for night temperatures between 50 and 55 degrees. 5. Have students inspect the plants daily and water as needed with a weak fertilizer solution. (The plants on the heating pad will require more frequent watering.) 6. Once every week for a month, have students measure the plants and compare their growth. Discuss the results in terms of plant respiration. 7. Discuss in class the advantages of heating the root environment. Discuss also the related costs of speeding production in this manner. __________________________________________________________ B. Landscape Management: Aside from occasionally rinsing down plants subject to dusty conditions, providing for photosynthesis is not usually a concern for landscapers. Respiration, however, especially for plant roots, must often be provided for, both in landscape installation and in maintenance. 1. Landscape Installation: a. Amend heavy soils: 1) Clay soils, which have poor air/water exchange properties, should be amended with coarse organic materials to improve aeration in the root zone. 2) This is especially important when first establishing turf or other ground covers which require quick initial growth. b. Amend container plantings: 1) Soil in a container, such as a planter box or a tub, drains poorly compared to a deep field soil. Water will cling to the soil and keep fresh oxygen from reaching the roots. 2) This poor drainage must be compensated for by using only coarse, fast-draining soil mixes in containers. c. Plant sod immediately: 1) Sod, as it is received from the sod farm in rolls, will deteriorate rapidly if left rolled up. 2) After just a couple of days both lack of light and lack of oxygen will weaken sod and reduce its ability to establish itself as turf. At the very least, the customer will be displeased with the yellowed appearance. Left for long, it will die and rot. 2. Landscape Maintenance a. Irrigation controllers should be set to allow for complete drainage of the soil in between irrigations. Good air/water exchange is critical for root respiration. b. Avoid practices which compact the soil, forcing air space out of the soil profile. An example would be mowing when soils (especially clay soils) are wet. c. Vertical mulching and aerating are practices which help get air to the roots and support plant respiration. __________________________________________________________ ACTIVITY: 1. Buy two rolls of sod. Keep them rolled up in the classroom, at room temperature. 2. Each day at the beginning of class, have students cut a foot off the end of a roll and plant it in a prepared area. 3. At the end of two weeks have students make an evaluation of how long a landscaper might be able to wait between taking delivery of a sod shipment and planting it in the ground. __________________________________________________________ C. Floral Industry: In the floral trade, we are dealing with two difficult circumstances: Living plants subject to low light (interior) conditions and cut materials detached from their natural source of moisture and nourishment. 1. Wholesale and Retail Floristry: An overriding concern of florists is to get products that will last a long time delivered to their customers. a. Respiration must be slowed drastically during shipping and storage, since the plant's supply of carbohydrate is limited: 1) Refrigeration is a must for most floral materials, from the time they are cut in the field or greenhouse until the time they go home with the customer. 2) Modified (high nitrogen) atmosphere is not justified for most floral crops, but can be used for shipping and storage under some circumstances. b. Customers can be educated to improve floral respiration and lasting quality by: 1) Providing a source of carbohydrate to cut flowers. (This is included in the packet of floral preservative handed out by florists with most sales. Plain sugar dissolved in water will accomplish the same purpose.) 2) Keeping flowers in a cool location (to slow the rate of respiration). 2. The Interior Plant Industry: Extra attention must be paid to plants existing at low light levels. a. Match plants to location. 1) Some plants (especially those with C4 dark reaction cycles) can photosynthesize at lower light intensities than others. 2) Interior plant "techs" should be sure, as much as possible, that plants being used are matched with the light intensity and duration where they are situated. b. Watch the water! 1) The number one problem with houseplants is overwatering. Plants in low light photosynthesize at a low rate and use little water. 2) As day length, light intensity, or temperatures decrease, decrease water proportionately, or the roots will drown. __________________________________________________________ ACTIVITY: 1. On a Monday, have students cut some fresh flowers, or bring a dozen fresh roses in for this activity. 2. Place half of the flowers in mason jars filled with plain water and one drop of bleach (bleach has an anti-bacterial action which keeps the flower stems from clogging up). 3. Place the rest of the flowers in jars filled with water, bleach, and a teaspoon of sugar stirred into solution. Place all of the jars in a cool location out of any direct sunlight. 4. On Friday, compare the two groups of flowers and discuss the results in terms of respiration. __________________________________________________________ 11/29/90 MH/sg #%&C