Plants and Plant
Communities
14
Our discussions in Chs. 12 and 13 focus on determining which environments were energetically acceptable to animals and on energetic costs
of living in those environments. Similar questions apply to the study of
plants and plant communities. In this chapter we are interested in the environmental factors that determine temperatures and transpiration rates,
and in the factors that control carbon assimilation. The energy budget
again plays the central role in these analyses.
While an animal can choose its environment to best suit its energetics,
plants are pretty well stuck with whatever environment happens to exist
at the location and time of their growth. Over generations, selection and
adaptation result in leaf morphologies, canopy structures, etc. which give
the plants native to a particular environment a competitive advantage for
that location. Desert plants that experience frequent shortages of water,
for example, tend to have narrow leaves, while leaves of plants from more
moist environments may be much larger. We might ask ourselves what
environmental limitations there are to leaf size and other leaf characteristics related to energy exchange, or whether there is an optimum leaf
form for a particular leaf environment. Answers to questions like these
have obvious application in managed ecosystems such as agriculture. The
answers are likely to be found both in studying the physics of energy and
mass exchange, and in observing the characteristics of natural plants and
plant communities in different environments.
Three factors must be favorable for a leaf to remain alive. Average
net photosynthesis must be positive and the leaf water potential and temperature must remain within nonlethal bounds. Mature leaves apparently
have no mechanism for importing sugars, so a leaf which is not able to
maintain a positive net photosynthesis abscises. Net photosynthetic rate is
determined by environmental factors and by the water balance of the leaf.
To get a clear picture of plant responses to environment the environmental
effects on leaf temperature, leaf water balance, and photosynthesis need
to be considered.
In this chapter we also consider these processes in plant communities,
but only in a simple sense. So-called big leaf models are often used to
Communities
14
Our discussions in Chs. 12 and 13 focus on determining which environments were energetically acceptable to animals and on energetic costs
of living in those environments. Similar questions apply to the study of
plants and plant communities. In this chapter we are interested in the environmental factors that determine temperatures and transpiration rates,
and in the factors that control carbon assimilation. The energy budget
again plays the central role in these analyses.
While an animal can choose its environment to best suit its energetics,
plants are pretty well stuck with whatever environment happens to exist
at the location and time of their growth. Over generations, selection and
adaptation result in leaf morphologies, canopy structures, etc. which give
the plants native to a particular environment a competitive advantage for
that location. Desert plants that experience frequent shortages of water,
for example, tend to have narrow leaves, while leaves of plants from more
moist environments may be much larger. We might ask ourselves what
environmental limitations there are to leaf size and other leaf characteristics related to energy exchange, or whether there is an optimum leaf
form for a particular leaf environment. Answers to questions like these
have obvious application in managed ecosystems such as agriculture. The
answers are likely to be found both in studying the physics of energy and
mass exchange, and in observing the characteristics of natural plants and
plant communities in different environments.
Three factors must be favorable for a leaf to remain alive. Average
net photosynthesis must be positive and the leaf water potential and temperature must remain within nonlethal bounds. Mature leaves apparently
have no mechanism for importing sugars, so a leaf which is not able to
maintain a positive net photosynthesis abscises. Net photosynthetic rate is
determined by environmental factors and by the water balance of the leaf.
To get a clear picture of plant responses to environment the environmental
effects on leaf temperature, leaf water balance, and photosynthesis need
to be considered.
In this chapter we also consider these processes in plant communities,
but only in a simple sense. So-called big leaf models are often used to