Biometeorology, ESPM 129, Temperature and Thermodynamics 1Lectures 11 Temperature and Thermodynamics, Part 1, Concepts Instructor: Dennis Baldocchi Professor of Biometeorology Ecosystem Science Division Department of Environmental Science, Policy and Management 345 Hilgard Hall University of California, Berkeley Berkeley, CA 94720 September 21, 2012 Topics to be Covered A. Why is temperature important? 1. Kinetics of photosynthesis, respiration, isoprene emission. 2. Growth, phenology on temperature summation units. B. Thermodynamics 1st Law 2nd Law L11.1 Introduction Temperature is a meteorological variable of general interest. On waking up in the morning we often listen to the radio to determine if it will be hot or cold, so we can decide whether to wear shorts or a parka to work or school. Numerous factors affect the temperature we sense. Some relate to the conditions of the surface over which we stand. The amount of sunlight overhead and how much of it is reflected by the surface is one factor. And this will change is you are standing under a forest or in a clearing, over a snow field, grass or parking lot. The air temperature will be cooler if there is freely available water to evaporate, or will warm, ever so slightly, if the vapor in the air condensates. The temperature you sense will also be altered by how much the air and surface temperature differ and by how fast the wind is blowing. Another set of temperature moderating factors is imposed upon us. The most obvious factor is associated with the type and temperature of the air mass overhead or the advection of hot or cold as you may be standing beside a lake, irrigated field or desert. The depth to which the boundary layer grows will also affect the diurnal swing in air temperature, as it is easier to warm a small box than a deep one. A biometeorologist is interested in an array of temperatures [Norman and Becker, 1995; Porter and Semenov, 2005]. These include:Biometeorology, ESPM 129, Temperature and Thermodynamics 2 a) leaf temperature b) soil temperature c) air temperature d) radiative temperature e) aerodynamic temperature f) virtual temperature g) potential temperature h) wet bulb temperature. We are interested in temperatures that happened to be averaged over specific time scales. Daily maximum and minimum, daily average temperature, annual mean, and mean growing season temperature are examples of temperatures used to describe links between biology and meteorology. Temperature is important to biological systems because it sets growth limit, it affects the kinetic rates of enzymatic reactions and phenological development of plants. Temperature affects biological processes, primarily through enzyme kinetics. It affects the life stages of plants. Seed germination, budburst and leaf expansion, flowering and maturity, vernalization, dormancy, leaf abscission all respond to thermal summation. In some instances we want annual temperature, and in others average temperature during the growing season, to characterize biological activity and the distribution of plants, as with the distribution of C3 and C4 species. Temperature also plays a role on various aspects of environmental biology including low temperature chilling injury, frost injury, temperature adaptation, acclimation, and hardening. Chilling injury is suffered by tropical and subtropical plants. It occurs when T is below 10 C. It is manifested by wilting, inhibited growth. Freezing injury occurs in plants that are not acclimated to cold. They die at -1 to -3 C. On the other hand, acclimated plants can survive to -40 C and seeds to -196 C. The formation of ice crystals in cells and cytoplasm is the major form of damage. Through these concerted interactions, temperature sets the limits of where plants can exist and grow. Plants can live in the range of -89 and 58 C, but they only grow only in the 0 to 40 C range. Classic microclimatology is concerned with the classification of temperature and microclimates. We, however, cannot divorce temperature from heat transfer. This set of lectures will involve an overview of thermodynamics and heat transfer and definition of various types of temperature. L11.2 Temperature and BiologyBiometeorology, ESPM 129, Temperature and Thermodynamics 3The response of plants to temperature is highly non-linear, so evaluation of temperature is critical to assess the proper response. For instance, the rates of many processes like growth and photosynthesis may double with a 5 C rise when T is 10 C, will have no effect when temperature is near 25 C and will cause catastrophic behavior, death at 40 C. The impact of temperature chemical kinetics is generally evaluated with the Arrenhius Equation: fT AERTa() exp( ) Ea is the activation energy, R is the universal gas constant and A is a constant. Manipulation of this relation can derive a parameter called the Q10, the relative change in the rate of a reaction (k1/k2) with a 10 C increase in temperature. kkERTERTERT TERTTTTaaaa212112212111exp( )exp( )exp( ( )) exp( ())) We can manipulate this relation and define a quantity that defines the fractional change in reaction rates with a 10 degree increase in temperature. QkfTkfTERT Ta102110 1010:{ }:{}exp(()) A Q10 of 2 tells us that the rate of reaction has doubled with a 10 C rise, which is a typical value for enzyme kinetics studies performed in the laboratory. At 20 C, Ea is 51 kJ mol-1. kk QTT21 101021/() We can solve for Q10 with the log transform log( / ) / log( )kkTTQr21 1010 The Q10 concept is used with both disdain and convenience. Do note that its value, for a specific activation energy, is temperature dependent.Biometeorology, ESPM 129, Temperature and Thermodynamics 4T,K270 275 280 285 290 295 300 305Ea (Q10=2)44000460004800050000520005400056000 Figure 1The relationship between Ea and T for a constant Q10 of 2. There are many practical problems with applying the Q10 relation. In many circumstances, the range of temperature may not be broad enough to derive a significant relation. In this case, many investigators choose to use data from a longer period. But this introduces new problems, as new factors may start controlling respiration. We know plant respiration is a function of maintenance and growth respiration. Using data from 0 to 30 C may lead to periods with different forcings of respiration. In the