AOBPreview originally published online on December 17, 2003
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Annals of Botany 93: 127-139, 2004
© 2004 Annals of Botany Company
Equilibrium and Balanced Growth of a Vegetative Crop
1 Civil and Environmental Engineering, Technion, Haifa 32000, Israel
* For correspondence. E-mail: segineri{at}tx.technion.ac.il
Received: 11 June 2003; Returned for revision: 16 September 2003; Accepted: 22 October 2003 Published electronically: 17 December 2003
• Model A previously developed dynamic model, NICOLET, designed to predict growth and nitrate content of a lettuce crop, is subjected to (virtual) constant environmental conditions. For every combination of shoot and root environment, the cell sap, here assumed to reside in the ‘vacuole’ compartment, equilibrates at a certain nitrate concentration level. This, in turn, defines the composition of the crop in terms of carbon and nitrogen content in each of the three compartments of the model. Growth under constant environmental conditions is defined as ‘equilibrium’ growth (EG). If, in addition, the source strengths of carbon and nitrogen balance each other, as well as the sink strength of the growing crop, the growth is said to be ‘balanced’ (BG).
• Results It is shown that the range of BG approximately coincides with the range of ‘mild’ nitrogen stress, where reduction in nitrogen availability results in a mild reduction of relative growth rate (RGR). Beyond a certain low nitrate concentration in the cell sap, the N-stress becomes ‘severe’ and the loss of growth increases considerably.
• Conclusions The model is able to mimic the five central observations of many constant-environment growth-chamber experiments, namely (1) the initial exponential growth and later decline of the RGR, (2) the constant chemical composition, (3) the equality of the RGR and the relative nutrient supply rate (RNR), (4) the proportionality between the N : C ratio and the RNR, and (5) the proportionality between the water content and the reduced N content. Guidelines for the optimal combination of the shoot and root environments are suggested.
Key words: Lettuce, Lactuca sativa L., vegetative crop, equilibrium growth, balanced growth, crop composition, relative growth rate, N-stress, NICOLET.