light and temperature effects - high tunnels
DESCRIPTION
Presented by University of Minnesota professor John Erwin at the 2009 Minnesota Statewide High Tunnel Conference in Alexandria, MN on Dec. 2-3, 2009.TRANSCRIPT
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Light and Temperature
Effects in High Tunnels
• Light Intensity and Photosynthesis• Carbon dioxide (CO2)• Light color• Shading issues• Temperature effects on:
– Development, stem elongation, photosynthesis and flowering.
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Light and Temperature
Effects in High Tunnels
• Light Intensity and Photosynthesis• Carbon dioxide (CO2)• Light color• Shading issues• Temperature effects on:
– Development, stem elongation, photosynthesis and flowering.
© 2009 Regents of the University of Minnesota
![Page 5: Light and Temperature Effects - High Tunnels](https://reader034.vdocument.in/reader034/viewer/2022052315/554e6ab8b4c90545698b46c9/html5/thumbnails/5.jpg)
How much light can a plant use for photosynthesis?
+ CO2 + H2O C2H + O2
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NORTHERN GROWERS
SOUTHERN GROWERS
© 2009 Regents of the University of Minnesota
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Response to increasing light intensity (irradiance).
Units are in umol m-2 s-1
Multiply umol m-2 s-1 by 5 to get footcandles.
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Variation in photosynthetic responses of different species to increasing light intensity
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What we learned
• Species differed in how much light saturates photosynthesis.
• Species studied showed photosynthetic saturation between 200 and 600 umol m-2 s-1 (1,000-3,000 footcandles).
• When crops are spaced close, lighting levels should be based on light intensity at lower leaf levels.
• By all accounts, tomato and pepper are high light requiring plants, i.e. saturate at 600 umol m-2 s-1
(3000 footcandles).
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How much light is getting to your plants?
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January Daily Light Integrals
750 ft-c
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April Daily Light Integrals
3700 ft-c
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In general, light penetration into a greenhouse varies from about 30-85%. 60% light transmission is very common.
Single glass is the highest (85-90%), followed by Exalite and single poly (65-
75%), following by double poly (45-60%). This is without condensation!
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April Daily Light Integrals
3700 ft-c x 0.45 = 1,665 ft candles (333 umol m-2 s-1)
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NORTHERN GROWERS
SOUTHERN GROWERS
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Increasing DLI versus total flower bud number
10 moles/day
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Light and Temperature
Effects in High Tunnels
• Light Intensity and Photosynthesis• Carbon dioxide (CO2)• Light color• Shading issues• Temperature effects on:
– Development, stem elongation, photosynthesis and flowering.
© 2009 Regents of the University of Minnesota
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Response to increasing carbon dioxide (CO2).
Units are in umol m-2 s-1
Multiply umol m-2 s-1 by 5 to get footcandles.
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How much light can a plant use for photosynthesis?
+ CO2 + H2O C2H + O2
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What we learned . . .
• Species differed in how much CO2 they could utilize under our conditions (300 umol m-2 s-1).
• Photosynthesis of some species is saturated at lower CO2 levels (600 ppm; Rieger Begonia, Poinsettia), while photosynthesis on other species saturated at higher CO2 levels (<1000 ppm; cyclamen, impatiens, tomato, pepper).
• High tunnel crops are likely CO2 starved! High light with limited CO2 is useless!
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Light and Temperature
Effects in High Tunnels
• Light Intensity and Photosynthesis• Carbon dioxide (CO2)• Light color• Shading issues• Temperature effects on:
– Development, stem elongation, photosynthesis and flowering.
© 2009 Regents of the University of Minnesota
![Page 31: Light and Temperature Effects - High Tunnels](https://reader034.vdocument.in/reader034/viewer/2022052315/554e6ab8b4c90545698b46c9/html5/thumbnails/31.jpg)
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What we know . . .
• Any leaf filtering increases leaf size, increases stem elongation, and decreases flower number.
• It is desirable to have short plants, that are well spaced to maximize leaf area per plant and limit shading.
• Spacing plants too close reduces yield, increases labor/management costs.
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Light and Temperature
Effects in High Tunnels
• Light Intensity and Photosynthesis• Carbon dioxide (CO2)• Light color• Shading issues• Temperature effects on:
– Development, stem elongation, photosynthesis and flowering.
© 2009 Regents of the University of Minnesota
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Shade Cloth Issues
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NORTHERN GROWERS
SOUTHERN GROWERS
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Why do we use shade cloth?
• Limit heating in the greenhouse!
• In general, we have been finding that any shading that reduces light levels below 3000 footcandles (600 umol m-2 s-1) is detrimental to yield!
• Shading selection should be based on light level at plant level!
• Shading selection/management will change if covering materials age and light transmission is reduced over time.
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We routinely over-shade in greenhouses and high tunnels!
The best shading materials are materials that we can change the
% shading over time such as:1) spray on shading
2) having different levels of light screening.
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Open roof greenhouses allow for maximum lighting for photosynthesis, little
depletion of CO2, and maximum cooling.
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Over-shading is often worst than no shading!
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Take Home Messages
• Get a light meter!
• Don’t over-crowd!
• Find out how much CO2 is in your high tunnels! High light with little CO2 is useless!
• Consider shading screens with high light transmission if needed that are pulled only on certain days and at certain times of the day! Also consider spray shading compounds.
• Realize that poly transmission decreases over time and that your shading management should change as well!
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Take Home Messages
• Consider retractable roof high tunnels to maximize light/CO2/temperature for optimal plant growth.
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Light and Temperature
Effects in High Tunnels
• Light Intensity and Photosynthesis• Carbon dioxide (CO2)• Light color• Shading issues• Temperature effects on:
– Development, stem elongation, photosynthesis and flowering.
© 2009 Regents of the University of Minnesota
![Page 52: Light and Temperature Effects - High Tunnels](https://reader034.vdocument.in/reader034/viewer/2022052315/554e6ab8b4c90545698b46c9/html5/thumbnails/52.jpg)
Response to increasing temperature.
Units are in degrees Celsius
Multiply times 1.8 plus 32 to get units in Fahrenheit.
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What did we learn?
• Species differed in how temperature affected photosynthesis.
• The optimal temperature for photosynthesis varied from low temperature optima crops (59oF; Rieger begonia) to medium temperature optima (68oF; New Guinea impatiens) to high temperature optima (76oF; gerbera, tomato, pepper) under our experimental conditions.
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Rate of Plant Development
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Optimum leaf unfolding rate of many plants occurs around 76-
84oF. When temperatures exceed 84oF, leaf unfolding slows and yield
will be reduced!
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How does temperature effect stem elongation?
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Sensitivity of stem elongation to temperature varies within a day/night
cycle.
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Variation in Daily Temp Sensitivity of Stem Elongation During the Day
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Does temperature effect flowering?
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Arabidopsis after 8 d Temperature Exposures
40 C36 C32 C28 C24 C20 C
Warner, R. Studies on high temperature effects on flower development. PhD Thesis, Department of Horticultural Science, University of Minnesota, St. Paul, MN USA.
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Warner, R., and J.E. Erwin. 2005. Naturally-occurring variation in high temperature induced floral bud abortion across Arabidopsis thaliana accessions. Plant, Cell and Environ, 28:1255-1266.
-These data suggest that the window for inhibition of
flowering may be smaller than we thought.
-These data also suggest that there is a cumulative effect and
how temperatures were provided was irrelevant.
Rather, it was an accumulation of degree-hours that was
important (>32C).
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Heat stress
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68 ºF 86 ºF
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In general, your leaf temperature is 5-7oF warmer than the air
temperature on sunny days.
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New Guinea Impatiens ‘Celebration Orange’
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Does the length of the high temperature exposure make a difference in how long or much photosynthesis is depressed?
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N.G. Impatiens ‘Divine White’2 Days After a 1 or 2 hour 95oF Exposure
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Cooling leaves in the middle of the day on sunny days can
increase photosynthesis! Why? By cooling leaves. . . . .
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Overhead irrigation increases
photosynthesis in the middle of the day.
This occurs presumably through leaf
cooling.© 2009 Regents of the University of Minnesota
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Fog Evaporative Cooling
www.truefog.com© 2009 Regents of the University of Minnesota
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Take Home Messages
• Buy an infrared thermometer ($75).
• When you let your night temperatures drop and allow day temperatures to get hot, you INCREASE stem elongation.
• Consider dropping temperatures during the first 2-3 hours to no lower than 55oF for tomatoes/peppers and 45-50oF for spinach and other leafy crops.
• Manage high tunnel environments to achieve as close to 76-80oF LEAF temperatures on bright days as possible!
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Other Research Areas
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Potted Plants?
Garden Plants?© 2009 Regents of the University of Minnesota
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(86 F/ 45% RH)Afternoon
Marigold
(59 F/ 85% RH)Morning
0 ppm 600 ppm
Fast-drying
Slow-drying
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Airborne interplant signalling for plant defence
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Other Airborne Signals?
From Tscharntke et al. 2001. Biochem. Syst. Ecol. 1025–1047.
volatile profile from undamaged Alnus
volatile profile from beetle-infested Alnus
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Jasmonates
Watercress►Methyl
jasmonate elicits defense responses, just like jasmonic acid.
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9 10 11 12 13 14 15 hrs
Photoperiod (hrs)
K. glaucescens
K. manginii
K. uniflora
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Green Roofs
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In vitro multiplication
Liquid cultureSeed germination
Meristemoid induction in liquid culture
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Bailey Endowed Chair for Nursery Crops Research
Todd and Barbara Bachman Chair for
Marketing of Horticulture Crops
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Additional Special Thanks
• Participants in the FRA and the Young Plant Center
• USDA-ARS, SAF, Lin Schmale, and you for your support through the National Floriculture and Nursery Research Initiative
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Industry Acknowledgements►MNLA Foundation►American Floral Endowment►Gloeckner Foundation►Altman Plants, Inc.►Oro Farms/Florida Specialty
Plants►Nurseryman’s Exchange►Wagner’s Greenhouse►Pleasant View Gardens► Smith Greenhouses► Sakata, Syngenta, Goldsmith,
Ball Horticultural
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