Hazards of Temperature-increase on Food Availability in Changing Environments: Global Warming Could Cause Failure of Seed Yields of Major Crops

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Hazards of Temperature-increase on Food
Availability in Changing EnvironmentsGlobal
Warming Could Cause Failureof Seed Yields of
Major Crops

• L. H. Allen, K. J. Boote, P. V. V. Prasad,
• A. M. Snyder, J. M. G. Thomas, and J. C. Vu
• USDA-Agricultural Research Service and Agronomy
  Department, University of Florida, Gainesville,
  FL USA

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Why study global warming impacts on seed-grain
crops?

• CO2 might rise to 540-970 ppm, and temperature by
  1.4-5.8 C by 2100
• Elevated CO2 effects on plants are well
  understood and are mostly beneficial
• Elevated temperature effects are poorly
  understood and are detrimental to reproductive
  processes of seed-grain crops

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SCOPE--1

• Show experimental evidence for progression of
  seed yield failures with increasing temperature
• Plants were grown in deep soil in outdoor, sunlit
  controlled-environment chambers
• Controlled factors Temperature, Humidity
  (Dewpoint), CO2 Concentration, Soil Water
• Plants were exposed to the same solar radiation
  during each individual study

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SCOPE--2

• Crops Studied---rice, soybean, dry bean, peanut,
  grain sorghum
• Project simply the implications of global warming
  on decreases of food availability based on
  decreases of seed yields
• Modeling---underway. Beyond the scope of this
  presentation

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THE FIRST STUDIES WERE ON THE EFFECTS OF ELEVATED
TEMPERATURE AND CO2 ON RICE
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RICE STUDIES in FLOODED SOIL

• Rice cultivar, IR-30, tropical indica type
• Two CO2 levels, 330 and 660 ppm
• Five studies with temperature treatments ranging
  from 25/18 to 40/33 oC (day/night) mean daily
  temperatures from 22 to 37 oC

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(Harvest Index seed biomass/aboveground biomass)
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General Rule of Thumb

• Rice seed yield decreased about 10 for each 1C
  increase above the OPTIMUM temperature for seed
  production.
• In other words, yields dropped to zero at 10C
  above the optimum temperature.

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Other Seed-Crop Experiments Grown under Diel
Temperature Cycles

• Two other rice cultivars
• M103 - temperate japonica type
• IR72 - tropical indica type
• Soybean cultivar Bragg
• Dry bean (red kidney bean) cultivar Montcalm
• Peanut cultivar Georgia Green
• Grain sorghum cultivar DeKalb DK-28E

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Diel Controlled Temperature Cycles
40/30C
34/24C
28/18C
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Rice cultivar IR72 - tropical indica M103 -
temperate japonica
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Peanut As mean temperature exceeded 31C
(36/26C), pollen viability (top) and percent
seed-set (bottom) declined, reaching zero at 39C
(44/34C). Low seed yield is caused by low
seed-set, which in turn is caused by low pollen
viability.
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Summary Species differ in response of yield and
percent seed-set to increasing temperature.
Major cause is decreased pollen viability.
Soybean is like peanut. Sorghum is like rice.
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Importance of Temperature Effects on
Reproductive Processes

• Elevated temperature affects reproductive
  processes more than vegetative biomass.
• There is no beneficial interaction of high CO2 on
  the detrimental temperature effect.
• Yields decreased to zero for cultivars studied at
  about
• 32 C for dry bean
• 35-36 C for rice and grain sorghum
• 40 C for soybean and peanut
• Temperature sensitivity might vary for other
  cultivars.

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Potential Impacts of Global Warming on Food
Availability (Food Production)

• Example of rice, cultivar IR30
• A 5 C rise in temperature might decrease yield
  to only 40 of current yield for Florida
  conditions.

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Research and Information Needs

• Search for high temperature tolerant cultivars.
• Determine physiological and genetic mechanisms of
  temperature sensitivity and breed crop plants for
  less sensitivity.
• Ameliorate high temperature impacts with
  alternate crops, planting dates, etc.