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

Why study global warming impacts on seed-grain crops? u CO 2 might rise to ppm, and temperature by °C by 2100 u Elevated CO 2 effects on plants are well understood and are mostly beneficial u Elevated temperature effects are poorly understood and are detrimental to reproductive processes of seed-grain crops

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), CO 2 Concentration, Soil Water Plants were exposed to the same solar radiation during each individual study

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

THE FIRST STUDIES WERE ON THE EFFECTS OF ELEVATED TEMPERATURE AND [CO 2 ] ON RICE

RICE STUDIES in FLOODED SOIL u Rice cultivar, IR-30, tropical indica type u Two CO 2 levels, 330 and 660 ppm u Five studies with temperature treatments ranging from 25/18 to 40/33 o C (day/night); mean daily temperatures from 22 to 37 o C

(Harvest Index = seed biomass/aboveground biomass)

General Rule of Thumb Rice seed yield decreased about 10% for each 1°C increase above the OPTIMUM temperature for seed production. In other words, yields dropped to zero at 10°C above the optimum temperature.

Other Seed-Crop Experiments Grown under Diel Temperature Cycles u Two other rice cultivars  M103 - temperate japonica type  IR72 - tropical indica type u Soybean cultivar ‘Bragg’ u Dry bean (red kidney bean) cultivar ‘Montcalm’ u Peanut cultivar ‘Georgia Green’ u Grain sorghum cultivar ‘DeKalb DK-28E’

Diel Controlled Temperature Cycles 40/30°C 34/24°C 28/18°C

Rice cultivar IR72 - tropical indica M103 - temperate japonica

Peanut As mean temperature exceeded 31°C (36/26°C), pollen viability (top) and percent seed-set (bottom) declined, reaching zero at 39°C (44/34°C). Low seed yield is caused by low seed-set, which in turn is caused by low pollen viability.

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.

Importance of Temperature Effects on Reproductive Processes u Elevated temperature affects reproductive processes more than vegetative biomass. u There is no beneficial interaction of high CO 2 on the detrimental temperature effect. u Yields decreased to zero for cultivars studied at about: 32 °C for dry bean °C for rice and grain sorghum 40 °C for soybean and peanut u Temperature sensitivity might vary for other cultivars.

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.

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.