Analysis of active chlorophyll fluorescence from Douglas fir (Pseudotsuga mensiezii). Effects of air pollutants on fluorescence emission and fluorescence band ratio

Active measurements of chlorophyll fluorescence at 680 and 730 nn were made at various ambient light intensities using needles from Douglas fir (Pseudotsuga mensiezii) seedlings grown under controlled conditions in growth cabinets and exposed to filtered air (FA) and ozone, respectively. The fluorescence band ratio (FBR=F₆₈₀/F ₇₃₀) and the relative fluorescence change (RFC=(F-F₀ )/F₀) proved to be dependent on the ambient light intensity. The decrease in chlorophyll content induced by O₃ resulted in a significant increase in FBR. At the highest photon flux density (PFD) the RFC of control plants is 0.15±0.04 and in ozone exposed plants, with a lower rate of PS II electron flow, the RFC is 0.05±0.04. In field experiments active chlorophyll fluorescence at 685 and 730 mn was measured at a distance of about 30 m with the Laser Environmental Active Fluorosensor (LEAF) and compared with photosynthesis of selected Douglas firs and a number of environmental parameters. While the fluorescence at 685 nm was relatively constant, the fluorescence at 730 nm showed a significant increase during the day resulting in a decrease of the FBR from 0.65 at night to 0.4 during the day