The Plant - Agroecology: The Ecology of Sustainable Food Systems - page 40

of the environment is an essential component in the design
and management of sustainable cropping systems.
The ecological study of individual plant response to
the diverse factors of the environment — termed autecol-
ogy or physiological ecology in the pure sense and crop
ecology in the applied sense — is therefore a foundation
of agroecological understanding. Some of the conceptual
basis of autecology is reviewed in the next section. Each
factor of the environment and its effects on crop plants is
then explored in a separate chapter in preparation for
expanding our view to the agroecosystem level.

TA B L E 3 . 3
Micronutrients and the Processes in Which They
are Involved

Nutrient Processes

Boron (B) Carbohydrate transport and metabolism,

phenol metabolism, activation of growth
regulators

Chlorine (Cl) Cell hydration, activation of enzymes in

photosynthesis

Copper (Cu) Basal metabolism, nitrogen metabolism,

secondary metabolism

A P LANT ' S P LACE IN THE E NVIRONMENT

Iron (Fe) Chlorophyll synthesis, enzymes for electron

transport

Each species occupies a particular place in the ecosys-
tem, known as the habitat , that is characterized by a
particular set of environmental conditions that includes
the interaction of the species with the other species in
the habitat. Within its habitat, the species carries out a
particular ecological role or function, known as the eco-
logical niche of that species. For example, redwoods
( Sequoia sempervirens ) occupy a specific habitat on the
north coast of California characterized by a moderating
maritime climate and the occurrence of summer fog that
compensates for a lack of rainfall during this time. At
the same time, redwoods occupy the ecological niche of
autotrophic producers capable of modifying the micro-
climate under their emergent canopies and being the
dominant species in their community.

Manganese (Mn) Basal metabolism, stabilization of

chloroplast structure, nitrogen metabolism

Molybdenum (Mo) Nitrogen fixation, phosphorus metabolism,

iron absorption and translocation

Zinc (Zn) Chlorophyll formation, enzyme activation,

basal metabolism, protein breakdown,
hormone biosynthesis

Source: Adapted from Treschow, M. 1970. Environment and Plant
Response. McGraw-Hill: New York.

to soils that have undergone a long period of conventional
management. Organic fertilizers, especially those made
from composted plant material and manure, are rich in
micronutrients.

T RANSPIRATION

R ESPONSES TO F ACTORS OF THE E NVIRONMENT

All of a plant's life processes, including photosynthesis,
carbon partitioning, and metabolism, are dependent on the
continual flow of water from the soil to the atmosphere
along a pathway that extends from the soil, into the roots,
up the stem to the leaves, and out of the leaves through
the stomata. This flow process is called transpiration .
Water loss from the leaves creates a concentration
gradient, or a lower leaf water potential, that then through
capillarity moves more water into the plant and to the
leaves to replace the loss. The actual amount of water that
is chemically bound in plant tissues or that is actively
involved in processes such as photosynthesis is very small
in proportion to the transpirational loss of water on a daily
basis. Water movement through plants is very important
in nutrient cycles and under conditions of limited water
availability in the soil, as we will see in later chapters.

Every plant during its lifespan goes through distinct stages
of development, including germination of the seed, initial
establishment, growth, flowering, and dispersal of seed.
Each of these stages involves some kind of physiological
change, or response , in the plant. Most plant responses
are tied directly to environmental conditions.

Triggered Responses

Many plant responses are triggered by some external stimu-
lus. They come about as a result of a certain condition,
but that external condition does not have to be maintained
in order for the response to continue. For example, tobacco
seed requires exposure to light in order to germinate, but
that exposure need only last for a fraction of a second.
After a brief exposure to light, the seed will germinate
even if it is planted in total darkness.

THE PLANT IN ITS INTERACTION WITH THE
ENVIRONMENT

Dependent Responses

Some plant responses depend on the continued presence
of a particular external condition. The response is both
induced and maintained by the condition. The production
of leaves on the spiny stems of ocotillo ( Fouquieria splen-
dens ) in the Sonoran desert is an example of this type of

Each of the physiological processes described above allow
the plant to respond to and survive in the environment in
which it lives. An understanding of the ways individual
plants and their physiology are impacted by different factors