There were many similar threads here before (see first four references).
Hydroponic (solution culture) projects are very good for a greenhouse. The traditional mineral nutrient deficiency experiment takes at least half a semester. It can be varied by also doing some mineral nutrient toxicities (especially boron, zinc, copper) and high salinity treatments.
It is often easier to use viny or rosette houseplants (piggyback plant [Tolmiea menziesii], Wandering Jews, philodendron, pothos, etc.) to avoid the difficulty of staking. Propagating houseplants by cuttings also is easier and faster than seed propagation and gives clonal material (Hershey 1994). Hydroponics also can be used for transpiration measurements by weight loss, and nondestructive plant fresh weight gain.
Another good hydroponic experiment involves iron deficiency stress response (Hershey 2000). Some plants lower the rootzone pH when deficient in iron and grown with all nitrate-nitrogen in the solution. This increases iron availability, the plant recovers and the solution pH rises. Inexpensive pocket pH meters are excellent for solution pH measurements.
Some plants lower the solution pH all the time (such as common philodendron). Others are iron-inefficient and cannot lower the solution pH, e.g. Tolmiea menziesii. To test whether a plant is iron inefficient, simply grow the plant in an all nitrate-nitrogen solution such as Hoagland's solution number 1 without iron. Coat the roots with some iron oxide powder. Tolmiea menziesii will turn bright yellow due to iron deficiency even with the roots coated with red iron oxide. It's very striking.
Plant carbon dioxide deficiency is also to demonstrate using hydroponics (Hershey 1992).
Other good greenhouse experiments involve photoperiodism and plant hormones/plant growth regulators. Students could grow a crop of pot chrysanthemums and incorporate both. The treatments would be:
1. Long photoperiods with water spray
2. Long photoperiod with daminozide spray
3. Short photoperiods with water spray
4. Short photoperiods with daminozide spray
Photoperiod control in a greenhouse can be a hassle because it requires manual pulling of blackcloth or other opaque material over the plants daily in late afternoon and removal early in the morning to assure a short photoperiod. A long photoperiod requires a time clock and incandescent bulbs suspended over the plants. The timer is usually set to go on from 10 pm to 2 am. A simpler photoperiod experiment can be done indoors using fluorescent light banks and Kalanchoe daigremontiana (Hershey 2002).
Plant hormones experiments can involve GA sprays to increase height of dwarf plants, auxins dips to promote rooting of cuttings, and auxins and apical dominance.
Phototropism experiments can be done in a greenhouse if plants are set in cardboard boxes to get unidirectional light. Gravitropism studies can be done with potted plants but a greenhouse is hardly needed except to grow the plants because the response is so rapid. Students can make simple clinostats for gravitropism and phototropism experiments (Hershey 2005)
Plant physiology lab manuals have lots of excellent labs (Reiss 1994; Ross 1974; Witham, Blaydes and Devlin 1971)
David R. Hershey
Investigative labs for plant biology. Bionet.plants.education. (August 23, 2002).
Inquiry-based labs for Plant Biology course. Bionet.plants.education (Dec. 2-5, 2005)
Phytochrome lab exercises? Bionet.plants.education (July 26, 2005)
Bionet.plants education search
Hershey, D.R. 1992. Plants can't do without CO2. Science Teacher 59(3):41-43.
Hershey, D.R. 1994. Solution culture hydroponics: history and inexpensive equipment. American Biology Teacher 56:111-118.
Hershey, D.R. 2000. "Hydroponics: Iron Deficiency of Piggyback Plants" pp. 147-155. IN Gerry M. Madrazo, Jr. and Steven E. Dyche (editors). Exciting Plant Science Activities for the Secondary Classroom Chapel Hill, NC: University of North Carolina Press.
Hershey, D.R. 2002. Using the Kalanchoe daigremontiana plant to show the effects of photoperiodism on plantlet formation. Science Activities 39(2):30-34.
Hershey, D.R. 2005. Time for a plant clinostat: Effects of light and gravity on plants. Science Activities 42(1):30-35.
Reiss, C. 1994. Experiments in Plant Physiology. Englewood Cliffs, NJ: Prentice Hall.
Ross, C.W. 1974. Plant Physiology Laboratory Manual. Belmont, CA: Wadsworth.
Witham, F.H., D.F. Blaydes and R.M. Devlin. 1971. Experiments in Plant Physiology. NY: Van Nostrand Reinhold.
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