# Dewar (1996)

RODERICK C. DEWAR

**The Correlation between Plant Growth and Intercepted Radiation: An Interpretation in Terms of Optimal Plant Nitrogen Content**

*Annals of Botany : Volume 78, Issue 1, July 1996, Pages 125-136* pdf

**Abstract**

Photosynthesis of leaves is commonly observed to have a saturating response to increases in their nitrogen (N) content, while the response of 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 variations in plant N content. Using a simple analytically-solvable model 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 intercepted radiation, as commonly observed. The light utilization coefficient (ε), defined as the slope of this relationship, is predicted to be

ε=α*Y*_{g}(1−λ)^{2},

where α is the quantum yield,*Y*_{g}is the biosynthetic efficiency, and λ is a dimensionless combination of physiological and environmental parameters of the model. The maximum-*NPP*hypothesis is also consistent with observations that whole-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−λ).

Using realistic parameter values, predicted values for ε and*R*:*A*_{c}are typical of C_{3}plants. ε is predicted to be independent of plant N supply, consistent with observations that long-term growth responses to N fertilization are dominated by increased light interception associated with increased growth allocation to leaf area. Observed acclimated responses of plants to atmospheric [CO_{2}], light and temperature are interpreted in terms of the model.