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l.S. Amthor
Cs- 1 ) required to support that rate of growth. From a two-component
viewpoint, growth includes translocation and nutrient uptake and assimilation in addition to cellular' biosynthesis per se.
Respiration rate (R, mol COzs- 1 ) is then given by
R = CM + CR ,
where CM is called maintenance respiration rate and CR is called growth
respiration rate. Specific respiration rate (r, mol COz g-1 S-1) is equal to
RIW, where W is plant dry mass (g).
The specific maintenance respiration rate or maintenance coefficient
(m, mol COz g- 1 S-1) is equal to CMIW, but maintenance respiration rate
may be better related to plant protein content than to dry mass (Ryan 1991;
but see Byrd et al. 1992 concerning leaves) in which case a protein-based
maintenance coefficient (m(N), mol COzg- 1 protein S-1) can be defined by
m(N) = CMIN,
where N is the protein content (g) of existing phytomass. The maintenance
coefficient can be estimated experimentally or theoretically, but all available
methods are problematic (Amthor 1989). In any case, given a value for
m(N), maintenance respiration rate is equal to m(N) N. Because maintenance
processes occur continuously in all living cells, R will always be greater than
zero. The above relationships can be extended by dividing metabolism into a
greater number of classes of process (Amthor 1993a).
The apparent growth yield is the amount of new plant structure and longterm storage formed per unit of substrate consumed. It is also called the
growth efficiency (Tanaka and Yamaguchi 1968; Yamaguchi 1978; Amthor
1989). The apparent growth yield in terms of carbon (Y(C)' mol C added to
new structure and long-term storage per mol C in substrate used for growth
and respiration, or mol C mol- 1 C) is
Y(C) = CT/C = CT/(R + CT ).
The apparent growth yield with respect to energy (Y(E), J r1) is given by
Y(E) = ETIE,
where ET (J S-1) is CT times the energy content (J mol- 1 C) of the products
of growth and E (J S-1) is C times the energy content (J mol- 1 C) of the
substrates of growth and respiration, e.g., carbohydrates.
The yield of the growth processes per se, or true growth yield (Pirt 1965),
in terms of carbon (Y G(C), mol C added to new structure and long-term
storage per mol C used in growth processes, or mol C mol- 1 C) is
Y G(C) = CT/CG ,
which is related to the production value (PV) of Penning de Vries et al.
(1974). Again, a comparable relationship defines the true growth yield in
terms of energy (Y G(E), JJ-1)
l.S. Amthor
Cs- 1 ) required to support that rate of growth. From a two-component
viewpoint, growth includes translocation and nutrient uptake and assimilation in addition to cellular' biosynthesis per se.
Respiration rate (R, mol COzs- 1 ) is then given by
R = CM + CR ,
where CM is called maintenance respiration rate and CR is called growth
respiration rate. Specific respiration rate (r, mol COz g-1 S-1) is equal to
RIW, where W is plant dry mass (g).
The specific maintenance respiration rate or maintenance coefficient
(m, mol COz g- 1 S-1) is equal to CMIW, but maintenance respiration rate
may be better related to plant protein content than to dry mass (Ryan 1991;
but see Byrd et al. 1992 concerning leaves) in which case a protein-based
maintenance coefficient (m(N), mol COzg- 1 protein S-1) can be defined by
m(N) = CMIN,
where N is the protein content (g) of existing phytomass. The maintenance
coefficient can be estimated experimentally or theoretically, but all available
methods are problematic (Amthor 1989). In any case, given a value for
m(N), maintenance respiration rate is equal to m(N) N. Because maintenance
processes occur continuously in all living cells, R will always be greater than
zero. The above relationships can be extended by dividing metabolism into a
greater number of classes of process (Amthor 1993a).
The apparent growth yield is the amount of new plant structure and longterm storage formed per unit of substrate consumed. It is also called the
growth efficiency (Tanaka and Yamaguchi 1968; Yamaguchi 1978; Amthor
1989). The apparent growth yield in terms of carbon (Y(C)' mol C added to
new structure and long-term storage per mol C in substrate used for growth
and respiration, or mol C mol- 1 C) is
Y(C) = CT/C = CT/(R + CT ).
The apparent growth yield with respect to energy (Y(E), J r1) is given by
Y(E) = ETIE,
where ET (J S-1) is CT times the energy content (J mol- 1 C) of the products
of growth and E (J S-1) is C times the energy content (J mol- 1 C) of the
substrates of growth and respiration, e.g., carbohydrates.
The yield of the growth processes per se, or true growth yield (Pirt 1965),
in terms of carbon (Y G(C), mol C added to new structure and long-term
storage per mol C used in growth processes, or mol C mol- 1 C) is
Y G(C) = CT/CG ,
which is related to the production value (PV) of Penning de Vries et al.
(1974). Again, a comparable relationship defines the true growth yield in
terms of energy (Y G(E), JJ-1)