Hazards of Temperature-increase on Food Availability in Changing Environments:

Global 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. VuUSDA-Agricultural Research Service and Agronomy

Department, University of Florida, Gainesville, FL USA

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

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

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 [CO2] ON RICE

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

IR-30 Rice Response to Temperature

0

4

8

12

16

20

24

20 25 30 35 40 45

Mean Temperature, C

Bio

mas

s o

r Y

ield

, Mg

/ha Biomass-330

Biomass-660

Yield-330

Yield-660

Rice Harvest Index Response to Temperature

0

0.1

0.2

0.3

0.4

0.5

20 25 30 35 40 45

Mean Temperature, C

Har

ve

st I

nd

ex,

fra

ctio

n Harvest Index-330

Harvest Index-660

(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

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’

Time EST

0 2 4 6 8 10 12 14 16 18 20 22 24

Air

Te

mp

era

ture

(o C

)

15

20

25

30

35

40

45Setpoint temperatureMeasured 35oC

29oC

23oC

Diel Controlled Temperature Cycles

40/30°C

34/24°C

28/18°C

YIELD

0

150

300

450

600

750

900

20 23 26 29 32 35 38

TEMPERATURE (oC)

YIE

LD

(g

m-2

)

IR72/350IR72/700M103/350 M103/700

Rice cultivarIR72 - tropical indicaM103 - temperate japonica

Soybean Response to Temperature

0

5

10

15

20

25

30

20 25 30 35 40 45 50

Mean Temperature, C

Mas

s, g

/pla

nt

Biomass

Seed Yield

Soybean Response to Temperature

0

0.1

0.2

0.3

0.4

0.5

20 25 30 35 40 45 50

Mean Temperature, C

Har

vest

Ind

ex, f

ract

ion Harvest Index

Weight per Seed,g / seed

0

25

50

75

100

20 25 30 35 40 45

0

25

50

75

100

Mean air temperature (°C)

700 mol CO2 mol-1

350 mol CO2 mol-1

(a) Peanut

Pol

len

viab

ility

(%

)

(b) Peanut

Seed

-set

(%

)

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.

23 26 29 32 35 38 41 440

25

50

75

100

Mean air temperature (°C)

Rice

See

d-s

et (

%)

Dry bean

Peanut

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

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.

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.