Morphogenetically Active Radiation within Tree Canopies: Estimations from PAR and Solar Broadband Irradiance Measurements

Although it is well known that plant morphogenesis is regulated by light quality, most plant modelling is blind to photomorphogenesis. Variability in light quality within plant canopy result first from geometrical interaction between incident light and plant phytoelements and second from optical properties of these elements. In a previous study, we established a series of functional relationships between photosynthetically active radiation (PAR) or energy and morphogenetically active radiation (MAR) within a sorghum canopy. In this study, we applied these relationships to walnut trees within which light spectra were measured at different sites. We estimated the variables of the MAR such as the quantity of blue radiation, the ratio red: far red and the phytochrome photoequilibrium from the proportion of transmitted PAR. The results showed good agreement between estimated and measured MAR variables within both trees canopies. Although differences between trees and sorghum architecture exist, MAR variables could be estimated accurately using the functional relationships.