Modelling of Respiration: Effect of Variation in Respiration on Plant Growth in Two Carex Species

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Abstract
A simple growth model of two Carex species (Carex diandra Schrank and Carex acutiformis Ehrh.) was constructed on the assumptions derived from experiments in solution culture. The model assumed (1) that the gross photosynthesis and dark respiration of the shoot are proportional to the amount of leaf and shoot nitrogen, (2) that the root respiration is a sum of respiration for maintenance of biomass, for growth and for ion uptake, and (3) that the partitioning of dry matter and nitrogen to component organs are constant fractions of the total plant dry matter and nitrogen, respectively. The model gave the relative growth rate (RGR), photosynthesis and respiration under steady-state exponential growth for a given nitrogen availability. C. diandra consistently had a higher RGR than C. acutiformis, while the difference in nitrogen productivity (growth rate per unit of plant nitrogen) was small between the two species. Higher photosynthetic rates in C. diandra were caused by a higher nitrogen use efficiency in the leaves and by higher nitrogen uptake activities in the roots. C. diandra had higher respiration rates in both shoots and roots, but they were more than compensated for by the higher photosynthetic activity. The model predicts that the RGR is more sensitive to proportional changes in photosynthetic nitrogen use efficiency than to changes in respiration coefficients.

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