Effects of Shading on Photosynthesis and Flower Bud Differentiation of Vanilla Plants

Field experiments were conducted on cultivation with varied shading materials over the plants to examine their effects on the photosynthesis and flower bud differentiation of vanilla. The shading materials provided 50%, 75%, and 90% shades. Three months after the treatments, the relative chlorophyll content, photosynthetic physiology and chlorophyll fluorescence of the plants were determined. In the following April, ratios of the flower bud formation were recorded. The results showed that the low shading was unfavorable for the chlorophyll formation on the plants. Within a certain range of the shading, the apparent quantum yield (AQY), effective quantum yield of photosystemⅡ(ФPSⅡ) and efficiency of excitation captured by open PSII center (Fv'/Fm') increased with increasing shading. On the other hand, the net photosynthetic rate (Pn), stomatal conductance (Gs), light saturation point (LSP), dark respiration rate (Rd), potential photochemical efficiency (Fv/Fo), maximum photochemical efficiency (Fv/Fm), electron transport rat (ETR) and photochemical quenching coefficient (qP) increased initially and then decreased with increasing shading. The rate of flower bud formation was up to 54.98% with the 75% shading. Thus, it appeared that 75% shading could be conducive to the vanilla growth, and applicable for its cultivation.