Effects of shade on morphology, chlorophyll concentration, and chlorophyll fluorescence of four Pacific Northwest conifer species

Abstract

Four species of Pacific Northwestconifer seedlings (ponderosa pine [Pinusponderosa Dougl. ex Laws.], Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], westernredcedar [Thuja plicata Donn ex D. Donn], andwestern hemlock [Tsuga heterophylla (Raf.)Sarg.]) were planted in individual pots and grownunder shade-cloth shelters that provided four levelsof shade (0% [full sunlight], 35%, 55%, and 75%)for approximately 30 weeks. Height growth wasrecorded every 2 weeks. Initial and final seedlingmorphology and chlorophyll concentrations weremeasured. Chlorophyll fluorescence was measuredmonthly. All species responded similarly to shade. Although height growth was greatest under 75% shadeand least in 0% shade, total biomass production wassignificantly lower and shoot:root ratio significantlyhigher in 75% shade than in 0% shade. As thetreatment shade level increased from 0% to 75%,Fv/Fm was significantly lower whilechlorophyll concentrations were significantly higher. These results indicate that photochemical efficiencyof all four species was lower under higher shade. Morphological and physiological responses differedgreatly among species and corresponded with theirdegree of shade tolerance.