Effects of shading on photosynthetic characteristics and leaf anatomical structure of Emmenopterys henryi seedlings

Effects of shading on photosynthesis characteristics and leaf anatomical structure of Emmenopterys henryi seedlings were studied using four shading treatments including full sunlight（ L0）, 60% sunlight（ L1）, 25% sunlight（L2）, and 15% sunlight（L3）, respectively. The results showed that:（1） Shading had an significant effect on the net photosynthetic rate（Pn）, transpiration rate（Tr）, stomatal conductance（Gs）, stomatal limitation value（Ls）,intercellular CO2 concentration（Ci）, and vapor pressure deficit(Vpdl) of E. henryiseedlings. The diurnal changes of Pn and Trunder L0 and L1 treatments showed obviously bimodal curves, and the "noon break" appeared at 12:00. Theirchanges under L2 and L3 treatments were relatively mild, and the "noon break" were not obvious. The variation of Gs wasbasically consistent with that of Pn. The variation of Ci showed a tendency of declining slowly at early stage and risingrapidly later. Compared with the control, the shading promoted significantly increase of the Ci. Both Ls and Vpdlshowed thearc changes of slow rising in advance and decreasing in the latter stage, and the daily averages under shading were lowersignificantly than the control. The order of daily averages of Pn and Tr was L1>L0>L2>L3.（2） The photosynthesis-lightresponse characteristics of E. henryiseedlings under four light regimes were obviously different. The seedlings grown underthe full sunlight condition could maintain a higherPnwithout obvious photoinhibition, showing a certain degree of shading-tolerance and light-demanding. The maximum net photosynthetic rate(Pmax), dark respiration rate（Rd）, and apparentquantum efficiency（ AQY） under L1 treatment increased more significantly than the control. Therefore, the E. henryi seedlings had some plasticity to light intensity. The mild shading was beneficial to the improvement of photosyntheticefficiency. Serious shading（L2 and L3） resulted in a significant decrease of light compensation point（ LCP） and lightsaturation point（LSP）, which was beneficial to make full use of weak light. But they resulted in Pmax and Rd decrease obvious, which inhibited photosynthetic efficiency.（3） The shading significantly affected the stomatal distribution on leavessurface of E. henryiseedlings. Under shading condition, the stomata density decreased significantly, and the stomatalength, the stomata width, and single stomatal area was similar.（4） Under shading, the leaf thickness decreased, theupper epidermis thickened, and the lower epid