The use of the ratio between the photosynthesis parameters P-ml and V-cmaxfor scaling up photosynthesis of C-3 plants from leaves to canopies: A critical examination of different modelling approaches
G. Wohlfahrt et al., The use of the ratio between the photosynthesis parameters P-ml and V-cmaxfor scaling up photosynthesis of C-3 plants from leaves to canopies: A critical examination of different modelling approaches, J THEOR BIO, 200(2), 1999, pp. 163-181
Recent models of photosynthesis have adopted the close correlation between
the main photosynthetic component processes, the maximum rate of carboxylat
ion and the potential rate of RuBP (ribulose-1,5-bisphosphate) regeneration
, at a reference temperature of 20 degrees C. When using the ratio between
these two processes in models of photosynthesis, assumptions though have to
be made about the temperature response of the potential rate of RuBP regen
eration, which varies with growth conditions and among species. In order to
assess the effects of deviations from the real temperature response of the
potential rate of RuBP regeneration on photosynthesis, a sensitivity analy
sis, scaling up photosynthesis from the leaf to the canopy level, is applie
d in the present paper. No changes are predicted to occur for sunlit leaves
, which receive both direct and diffuse radiation, as long as incident radi
ation does not cause carboxylation to shift from RuBP saturation to RuBP li
mitation, which, depending on incident radiation and canopy structure, migh
t occur deeper down in the canopy. Carboxylation of shaded leaves, which re
ceive solely diffuse radiation, is generally limited by the regeneration of
RuBP, and is thus prone to be affected by changes in the temperature respo
nse of the potential rate of RuBP regeneration. Due to the saturation type
response of the RuBP-limited rate of carboxylation to temperature at light
intensities below saturation, the impact of deviations from the real temper
ature response is negligible at high leaf temperatures, but may become sign
ificant when leaf temperatures are low and photosynthetically active radiat
ion incident on shaded leaves is comparably high, as in the upper canopy la
yers. The largest effects on whole canopy photosynthesis will therefore occ
ur under cool conditions and a completely overcast sky, when all leaves rec
eive diffuse radiation only. (C) 1999 Academic Press.