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

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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

How much light can a plant use for photosynthesis?

+ CO2 + H2O C2H + O2

© 2009 Regents of the University of Minnesota

NORTHERN GROWERS

SOUTHERN GROWERS

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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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© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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!

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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

© 2009 Regents of the University of Minnesota

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

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.

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

How much light can a plant use for photosynthesis?

+ CO2 + H2O C2H + O2

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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!

© 2009 Regents of the University of Minnesota

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

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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.

© 2009 Regents of the University of Minnesota

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

Shade Cloth Issues

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NORTHERN GROWERS

SOUTHERN GROWERS

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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.

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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.

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

Open roof greenhouses allow for maximum lighting for photosynthesis, little

depletion of CO2, and maximum cooling.

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© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

Over-shading is often worst than no shading!

© 2009 Regents of the University of Minnesota

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!

© 2009 Regents of the University of Minnesota

Take Home Messages

• Consider retractable roof high tunnels to maximize light/CO2/temperature for optimal plant growth.

© 2009 Regents of the University of Minnesota

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

Response to increasing temperature.

Units are in degrees Celsius

Multiply times 1.8 plus 32 to get units in Fahrenheit.

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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.

© 2009 Regents of the University of Minnesota

Rate of Plant Development

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© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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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© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

Sensitivity of stem elongation to temperature varies within a day/night

cycle.

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© 2009 Regents of the University of Minnesota

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.

© 2009 Regents of the University of Minnesota

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).

© 2009 Regents of the University of Minnesota

Heat stress

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68 ºF 86 ºF

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

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

Fog Evaporative Cooling

www.truefog.com© 2009 Regents of the University of Minnesota

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!

© 2009 Regents of the University of Minnesota

Other Research Areas

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

Potted Plants?

Garden Plants?© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

(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

© 2009 Regents of the University of Minnesota

Other Airborne Signals?

From Tscharntke et al. 2001. Biochem. Syst. Ecol. 1025–1047.

volatile profile from undamaged Alnus

volatile profile from beetle-infested Alnus

© 2009 Regents of the University of Minnesota

Jasmonates

Watercress►Methyl

jasmonate elicits defense responses, just like jasmonic acid.

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

9 10 11 12 13 14 15 hrs

Photoperiod (hrs)

K. glaucescens

K. manginii

K. uniflora

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Green Roofs

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota

In vitro multiplication

Liquid cultureSeed germination

Meristemoid induction in liquid culture

© 2009 Regents of the University of Minnesota

Bailey Endowed Chair for Nursery Crops Research

Todd and Barbara Bachman Chair for

Marketing of Horticulture Crops

© 2009 Regents of the University of Minnesota

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

© 2009 Regents of the University of Minnesota

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

© 2009 Regents of the University of Minnesota

© 2009 Regents of the University of Minnesota