“Temperature is the Master Factor determining the distribution of life on earth”

2. “Temperature is the Master Factor determining the distribution of life on earth” Lundegardh, 1934

3. Energy Budget

4. Conduction is the direct transfer of thermal motion (heat) between molecules in direct contact with each other. • Heat is always conducted from an object of higher temperature to one of lower temperature. • However, the rate and amount of heat transfer varies with different materials. • Water is 50 to 100 times more effective than air in conducting heat.

5. Convection is the transfer of heat by the movement of air or liquid past a surface. • Convection occurs when a breeze contributes to heat loss • The familiar “wind-chill factor” is an example of how convection compounds the harshness of low temperatures by increasing the rate of heat transfer. • Is “wind-chill” important to plants? When?

6. Radiation is the emission of electromagnetic waves by all objects warmer than absolute zero, including any plant surface, the surroundings, the sky, and the sun. • Radiation can transfer heat between objects that are not in direct contact. • With plants we divide Radiation into solar (direct and reflected) and Infra-red (long wave-length radiation). • Both surfaces of a leaf emit infra-red radiation

7. Evaporation is the removal of heat from the surface of a liquid that is losing some of its molecules as gas. • Evaporation of water from a leaf has a strong cooling effect. • The rate of evaporation (transpiration in our case) is dependent on the difference in water vapor concentration between the leaf and the air. • The concentration of water vapor inside the leaf is dependent on the leaf temperature.

8. Transpiration Rate = Leaf wv - Air wv Resistance (mg/cm2/s) = mg/cm3 – mg/cm3 cm/s

10. Energy Budget on Board Quantitative effect of transpiration on leaf temperature

11. 2. Ectotherms have body temperatures close to environmental temperature; endotherms can use metabolic heat to keep body temperature warmer than their surroundings • Plants are ectotherms although this does not mean that plants do not have adaptations to modulate their temperature.

12. An ectotherm has such a low metabolic rate that the amount of heat that it generates is too small to have much effect on body temperature. • This is true for almost all plants. There are, however, several important exceptions. • Climacteric Fruit • Skunk cabbage

13. Growing Degree Days • Used to estimate the growth and development of plants and insects during the growing season • Concept: development will only occur if temp exceed a minimum threshold or base temp (Tbase) • Base temps are determined for each organism & they’re all different

14. Calculating GDD • Take avg of high and low temp for the day • If that temp is at or below Tbase, GDD=0 • If avg temp>Tbase then take that avg – Tbase = GDD • Lets do an example: • Tbase for Tomato is 50º • High 60º, Low 32º • Tbase for Tomato is 50º • What is the GDD? • High 75º, Low 55º • What is GDD?

15. Modified GDD • Similar to previous GDD, except upper temp never goes above 86º, and low never goes below 50º • If temps are outside these parameters they are reset to that constant • Assumption is development is limited above 86º • Use of GDD • Growth and development of plants and cold-blooded animals depends on heat in and around them

16. Used to help monitor growth, and predict pest or disease risk • After base temp is exceeded growth begins, but it slows/stops if temp falls below the base • State of development correlated to the accumulation of daily GDD’s through the growing season • This data is very accessible from agricultural weather stations and on the web • Accuracy of the information is increasing as more data becomes available and relationships are established

19. Energy Budgets and Leaf/Plant Temperature