Photosynthetic Active Radiant Flux Density Originating from Derived Diffused Light within Disorderly Distributed Leaves in Fruit Trees and Its Easy Measuring Method

The main purpose of the present study is to develop a simple method of measuring a parameter which is necessary for a radiation distribution model of fruit tree canopies (OLEAS), and which estimates extinction of photosynthetic active radiant flux density originating from derived diffused light (PARFDdd) within the disorderly distributed leaves. Using shoots of several deciduous fruit trees, the disorderly distributed leaves with various LAI were formed in a device made of two tubes. When direct sunlight went to one tube containing the leaves, the PARFDdds were measured, and averaged (I′). Here the PARFDdds were extracted from a waveform of the output containing direct sunlight. The direct PARFDs from another empty tube were measured, and averaged (Io). I′/Io of each variety was distributed from 0.8% to 5.3%, when LAI was about 1. In many varieties, the decrease of I′/Io became gentle when LAI exceeded about 3. There was a low and negative correlation between mean value of I′/Io and SPAD (mean relative concentration of chlorophyll) of the leaves. When I′/Io was approximated with LAI, LAI2 and LAI3, the contribution ratio (R2) of the equation of each variety was high generally, and was mostly over 0.94.