Temperature
2
Rates of biochemical reactions within an organism are strongly dependent on its temperature. The rates of reactions may be doubled or tripled
for each 10" C increase in temperature. Temperatures above or below
critical values may result in denaturation of enzymes and death of the
organism.
A living organism is seldom at thermal equilibrium with its microenvironment, so the environmental temperature is only one of the factors
determining organism temperature. Other influences are fluxes of radiant
and latent heat to and from the organism, heat storage, and resistance to
sensible heat transfer between the organism and its surroundings. Even
though environmental temperature is not the only factor determining organism temperature, it is nevertheless one of the most important. In this
chapter we describe environmental temperature variation in the biosphere
and discuss reasons for its observed characteristics. We also discuss
methods for extrapolating and interpolating measured temperatures.
2.1 Typical Behavior of Atmospheric and Soil
Temperature
If daily maximum and minimum temperatures were measured at various
heights above and below the ground and then temperature were plotted
on the horizontal axis with height on the vertical axis, graphs similar to
Fig. 2.1 would be obtained. Radiant energy input and loss is at the soil or
vegetation surface. As the surface gets warmer, heat is transferred away
from the surface by convection to the air layers above and by conduction
to the soil beneath the surface. Note that the temperature extremes occur
at the surface, where temperatures may be 5 to 10" C different from temperatures at 1.5 m, the height of a standard meteorological observation.
This emphasizes again that the microenvironment may differ substantially
from the macroenvironment.
A typical air temperature versus time curve for a clear day is shown
in Fig. 2.2. Temperatures measured a few centimeters below the soil
surface would show a similar diurnal pattern. The maximum rate of solar
heat input to the ground is around 12 hours.
2
Rates of biochemical reactions within an organism are strongly dependent on its temperature. The rates of reactions may be doubled or tripled
for each 10" C increase in temperature. Temperatures above or below
critical values may result in denaturation of enzymes and death of the
organism.
A living organism is seldom at thermal equilibrium with its microenvironment, so the environmental temperature is only one of the factors
determining organism temperature. Other influences are fluxes of radiant
and latent heat to and from the organism, heat storage, and resistance to
sensible heat transfer between the organism and its surroundings. Even
though environmental temperature is not the only factor determining organism temperature, it is nevertheless one of the most important. In this
chapter we describe environmental temperature variation in the biosphere
and discuss reasons for its observed characteristics. We also discuss
methods for extrapolating and interpolating measured temperatures.
2.1 Typical Behavior of Atmospheric and Soil
Temperature
If daily maximum and minimum temperatures were measured at various
heights above and below the ground and then temperature were plotted
on the horizontal axis with height on the vertical axis, graphs similar to
Fig. 2.1 would be obtained. Radiant energy input and loss is at the soil or
vegetation surface. As the surface gets warmer, heat is transferred away
from the surface by convection to the air layers above and by conduction
to the soil beneath the surface. Note that the temperature extremes occur
at the surface, where temperatures may be 5 to 10" C different from temperatures at 1.5 m, the height of a standard meteorological observation.
This emphasizes again that the microenvironment may differ substantially
from the macroenvironment.
A typical air temperature versus time curve for a clear day is shown
in Fig. 2.2. Temperatures measured a few centimeters below the soil
surface would show a similar diurnal pattern. The maximum rate of solar
heat input to the ground is around 12 hours.