Experimental Test of Light Curve Models in Estimating Photosynthetic Activity by the Example of Ornamental Plants

Abstract

The features of CO₂ exchange in leaves of ornamental plants widely used for planting on the Southern coast of Crimea and the Black Sea coast of the Caucasus—Nerium oleander L., Laurus nobilis L., Aucuba japonica variegata Thunb., and Melissa officinalis L.—have been studied. The use of a modified rectangular hyperbole model, able to describe photoinhibition of a process by nonrectangular hyperbole, and a modified nonrectangular hyperbole model has shown the high adequacy of these models for describing the real relation between photosynthesis rate and light intensity in N. oleander, L. nobilis, A. japonica variegata, and M. officinalis. Estimation of CO₂ exchange in leaves in similar environmental conditions has shown significant differences in P_N/I curve parameters—light compensation point (LCP), photosynthetic and dark respiration rate, light saturation, and quantum yield. N. oleander has shown the highest photosynthetic intensity, while A. japonica variegata showed the lowest—its light saturation was recorded at low values of photosynthetically active radiation (PAR). Smaller values of LCP and saturation constants observed in L. nobilis and A. japonica variegata provide evidence of the efficient use of low-intensive PAR by these plants allowing them to survive in strong shading conditions.