Effects of shading on the leaves and photosynthetic characteristics of Ligustrum robustum

We study the effect of different shading treatments( 0,20%,40% and 60% shade) on the leaf growth and photosynthetic characteristics of Ligustrum robustum through artificial shade,aiming to provide scientific advices for cultivation and management of the species. The results showed that( 1) the leaf width,leaf area and leaf thickness at 40%shade of L. robustum were significantly higher than those under other three different treatments; the palisade tissue thickness( 64. 70 μm) at 40% shade of L. robustum was significantly higher than those under other three different treatments; there were two palisade tissue layers at 40% shading treatment comparing to one layer at the other three different treatments. The contents of total chlorophyll,chlorophyll a and chlorophyll b in leaves under the shading conditions were significant higher than those under the full daylight,and the chlorophyll contents increased with the increasing of shading levels. That L. robustum showed significantly higher leaves growth and the best overall growth anddevelopment at 40% shading treatment,which could be regarded as an appropriate shading intensity for its growth and development of L. robustum.( 2) The net photosynthetic rate increased at 40% shading treatment but decreased at 60%shading treatment. The stomatal conductance,internal carbon dioxide concentration and transpiration rate increased while the vapor pressure deficit decreased at both 20% and 40% shading treatment,which was helpful for photosynthesis. The vapor pressure deficit was highest while stomatal conductance and internal carbon dioxide concentration lowest at the 0%and 60% shading treatment comparing to other shade treatments,which suppressed net photosynthetic rate and transpiration rate of the plants.( 3) The dark respiration and light compensation point declined in the shading treatments while the 40%shading treatments resulted in the increases of the apparent quantum efficiency and maximum net photosynthetic rate,which indicated that L. robustum had shade tolerance to some extent. The Fv /Fm and Fv /Fo became smaller as the increase of shading level,the Fv /Fm of 20%,40% and 60% shading treatments were about 2. 71%,4. 59% and 8. 03%significantly lower than that under full day light respectively,and the Fv /Fo of 20%,40% and 60% shading treatments were about 6. 89%,11. 99% and 19. 81% significantly lower than that under full day light respectively. All fluorescence parameters of 40% shading treatment were significantly lower than those under the other three different treatments. Shading significantly depressed the efficiency of chlorophyll molecules capture excitation energy and potential activity of photosystemⅡ( ΦPSⅡ). In summary,L. robustum is shade-tolerant plants,and 40% shading treatment( the daily PAR values within the range of 273—1222 μmol·m-2·s-1) is an appropriate light environment,which could significantly improve leaves growth and photosynthetic capacity.