Modeling ultraviolet-B radiation in a maize canopy

A decrease in stratospheric ozone may result in a serious threat to plants, since biologically active short-wavelength ultraviolet-B (UV-B 280-320 nm) radiation will increase even with a relatively small decrease in ozone. Experimental work has shown that various cultivars and species respond to UV-B in different ways. To determine the physiological effects on plants of any increases in UV-B radiation, the irradiances at the potential sensitive plant surface need to be known. Numerical models are needed to calculate UV-B irradiance. This paper compares spatially and temporally averaged measurements of UV-B canopy transmittance (T_canopy, irradiance below canopy/irradiance above canopy) to that predicted by three models. Maize was selected as the canopy for the study because direct measurements of leaf area and leaf angle distribution are manageable. The models can be applied to other plants including urban trees, though other methods of characterizing leaf area and angle distributions generally would be used. Using measurements of canopy parameters as inputs to the numerical scheme, the models attempt to simulate the UV-B_Tcanopy that the UV-B sensors measure. The purpose of this paper is: (1) to describe the models developed for calculating UV-B irradiances (as measured by UV-B T_canopy) at given positions in maize canopies; and (2) to report the results of experimental tests of the models.