Higher Plant Respiration and Its Relationships to Photosynthesis
91
loss in respiration within a species or genotype (Farrar 1985; Farrar and
JHH Williams 1991) although the precise chain of events underlying that
relationship is incompletely understood. Indeed, the rate of whole-plant
respiration depends in large part on previous photosynthesis and the partitioning of photosynthate to growth or storage. Thus, the physical environment is expected to influence respiration in part by controlling photosynthesis
and carbon partitioning - conditions favorable for photosynthesis tend to enhance respiration. The environment can also influence respiration independent of an effect on photosynthesis (Amthor 1993b). Many environmental
stresses inhibit growth to a greater extent than they reduce photosynthesis,
resulting in an accumulation of nonstructural carbohydrates (Munns 1988).
The reduction in growth lessens the demand for growth and maintenance
respiration and the ratio between respiration and photosynthesis becomes
smaller. This gives rise to an apparent increase in the efficiency of photoassimilate use (Y(C), see Appendix; McCree 1986). In healthy plants, the
balance between capacities for carbohydrate production in photosynthesis
and use in heterotrophic metabolism may be coordinated by induction and
repression triggered by carbohydrate status (Fig. 4.4). In sum, photosynthesis, respiration, and growth interact across wide temporal and spatial
scales. The success of a plant is dependent on a coordination of those processes across those scales. The significance of photosynthesis to plant success
can scarcely be appreciated without a consideration of those interactions.
Appendix
It is traditional for plant ecophysiologists to consider respiration as composed of two or more functional components. The separation of components
is based on different processes supported by respiratory products rather than
different respiratory pathways. The basic relationships underlying the simple
and common two-component view (e.g., Wohl and James 1942; Pirt 1965;
Thornley 1970, 1971) begin with the tenet that the rate of use of substrate
carbon is the sum of carbon use rate for growth (Co, mol C s -1) and for
maintenance (CM , mol Cs- 1 )
C = Co + CM,
where C is the rate of substrate carbon use (mol Cs- 1 ) and is derived from,
e.g., "carbohydrates" of Fig. 4.1. All the carbon used for maintenance
is respired and released as CO2. Part of the substrate used for growth,
however, is added to plant structure and long-term storage so Co is itself the
sum of two components
.
.
.
Co = CT + CR ,
where C T (mol Cs- 1 ) is the rate of growth (i.e., addition of carbon to
structure and long-term storage) and CR is the rate of respiration (mol
91
loss in respiration within a species or genotype (Farrar 1985; Farrar and
JHH Williams 1991) although the precise chain of events underlying that
relationship is incompletely understood. Indeed, the rate of whole-plant
respiration depends in large part on previous photosynthesis and the partitioning of photosynthate to growth or storage. Thus, the physical environment is expected to influence respiration in part by controlling photosynthesis
and carbon partitioning - conditions favorable for photosynthesis tend to enhance respiration. The environment can also influence respiration independent of an effect on photosynthesis (Amthor 1993b). Many environmental
stresses inhibit growth to a greater extent than they reduce photosynthesis,
resulting in an accumulation of nonstructural carbohydrates (Munns 1988).
The reduction in growth lessens the demand for growth and maintenance
respiration and the ratio between respiration and photosynthesis becomes
smaller. This gives rise to an apparent increase in the efficiency of photoassimilate use (Y(C), see Appendix; McCree 1986). In healthy plants, the
balance between capacities for carbohydrate production in photosynthesis
and use in heterotrophic metabolism may be coordinated by induction and
repression triggered by carbohydrate status (Fig. 4.4). In sum, photosynthesis, respiration, and growth interact across wide temporal and spatial
scales. The success of a plant is dependent on a coordination of those processes across those scales. The significance of photosynthesis to plant success
can scarcely be appreciated without a consideration of those interactions.
Appendix
It is traditional for plant ecophysiologists to consider respiration as composed of two or more functional components. The separation of components
is based on different processes supported by respiratory products rather than
different respiratory pathways. The basic relationships underlying the simple
and common two-component view (e.g., Wohl and James 1942; Pirt 1965;
Thornley 1970, 1971) begin with the tenet that the rate of use of substrate
carbon is the sum of carbon use rate for growth (Co, mol C s -1) and for
maintenance (CM , mol Cs- 1 )
C = Co + CM,
where C is the rate of substrate carbon use (mol Cs- 1 ) and is derived from,
e.g., "carbohydrates" of Fig. 4.1. All the carbon used for maintenance
is respired and released as CO2. Part of the substrate used for growth,
however, is added to plant structure and long-term storage so Co is itself the
sum of two components
.
.
.
Co = CT + CR ,
where C T (mol Cs- 1 ) is the rate of growth (i.e., addition of carbon to
structure and long-term storage) and CR is the rate of respiration (mol