Rc. Dewar, THE CORRELATION BETWEEN PLANT-GROWTH AND INTERCEPTED RADIATION - AN INTERPRETATION IN TERMS OF OPTIMAL PLANT NITROGEN-CONTENT, Annals of botany, 78(1), 1996, pp. 125-136
Photosynthesis of leaves is commonly observed to have a saturating res
ponse to increases in their nitrogen (N) content, while the response o
f plant maintenance respiration is more nearly linear over the normal
range of tissue N contents. Hence, for a given amount of foliage, net
primary productivity (NPP) may have a maximum value with respect to va
riations in plant N content. Using a simple analytically-solvable mode
l of NPP, this idea is formulated and its broad implications for plant
growth are explored at the scale of a closed stand of vegetation. The
maximum-NPP hypothesis implies that NPP is proportional to intercepte
d radiation, as commonly observed. The light utilization coefficient (
epsilon), defined as the slope of this relationship, is predicted to b
e epsilon = alpha Y-g(1 - lambda)(2), where alpha is the quantum yield
, Y-g is the biosynthetic efficiency, and lambda is a dimensionless co
mbination of physiological and environmental parameters of the model.
The maximum-NPP hypothesis is also consistent with observations that w
hole-plant respiration (R) is an approximately constant proportion of
gross canopy photosynthesis (A(c)), and predicts their ratio to be R:A
(c) = 1 - Y-g(1 - lambda). Using realistic parameter values, predicted
values for epsilon and R:A(c) are typical of C-3 plants, epsilon is p
redicted to be independent of plant N supply, consistent with observat
ions that long-term growth responses to N fertilization are dominated
by increased light interception associated with increased growth alloc
ation to leaf area. Observed acclimated responses of plants to atmosph
eric [CO2], light and temperature are interpreted in terms of the mode
l. (C) 1996 Annals of Botany Company