Studies On Shade Tolerance Of Styrax Tonkinensis Seedlings

Effects of four different shading treatments (0%,40%,60% and 80%) on growth and development, leaf anatomy and photosynthetic characters of Styrax tonkinensis seedlings in two families from Suichuan Jiangxi as well as Pterostyrax psilophyllus seedlings were investigated in this paper. The results showed that:1. Growth and development of three different seedlings were changed significantly with different shading treatments. The height and caliper of Styrax tonkinensis seedlings in two families increased along with the increasing of shading intensity from 0% to 40%, and decreased along with increasing of shading intensity from 40% to 80%. Both height and caliper of Pterostyrax psilophyllus seedlings gradually decreased along with the increasing of shading intensity. The total biomass, root biomass and root: shoot ratio of all three plant seedlings generally decreased. The accumulation of dry matter of all three plant seedlings decreased in shading environment.2. The leaf area, specific leaf weight and the thickness of leaf of three plant seedlings generally decreased along with the increasing of shading intensity, while the relative water content increased. Palisade tissue cells became coarse, shorter and tidiness through mutual fusion, intercellular space widened, and organelles greatly decreased.3. Full sunlight caused photo inhibition. The chlorophyâ…¡fluorescence parameters (Fv/Fm and Fv/Fo) of Styrax tonkinensis (family 1) and Pterostyrax psilophyllus seedlings increased with the increasing of shading intensity, while the two parameters of Styrax tonkinensis (family 2) decreased. Styrax tonkinensis (family 1) and Pterostyrax psilophyllus have some capacity of shade tolerance, while the capacity of shade tolerance of Styrax tonkinensis (family 2) is relatively poor.4. The diual variation of net photosynthetic rate of three plant seedlings in full sunlight and low shading intensity had two peaks, but the midday depression of photosynthesis which belongs to non-stomatal limitation was not obvious. With the increasing of shading intensity, the diual variation of net photosynthetic rate of three plant seedlings had only one peak, without the midday depression of photosynthesis and even none peak. The daily averages of net photosynthetic rate, stomatal conductance, transpiration rate and water use efficiency of three plant seedlings decreased with the increasing of shading intensity.5. With the increasing of shading intensity, maximum net photosynthetic rate, light compensation point, carboxylation efficiency and chlorophyll a/b of three plant seedlings declined, while the carbon dioxide compensation point of Styrax tonkinensis seedlings in both two families increased and those of Pterostyrax psilophyllus seedlings were less in shading treatment than in full sunlight. The chlorophyll (a+b) content of seedlings of Styrax tonkinensis in two families increased along with the increasing of shading intensity from 0% to 40%, while decreased along with the increasing of shading intensity from 40% to 80%, but that of Pterostyrax psilophyllus always increased along with the increasing of shading intensity. The all of three plant seedlings showed characteristics of light-favored and shade tolerance, and the capacity of shade tolerance arranged from strong to weak was as follow: Pterostyrax psilophyllus seedlings > Styrax tonkinensis (family 1)> Styrax tonkinensis (family 2).