木荷幼苗对常绿阔叶林不同光环境的光合响应

Photosynthetic Responses of Schima superba Grown in Different Light Regimes of Subtropical Evergreen Broadleaf Forest

住夏季晴天，对生长在旷地、林窗和林下的木荷幼苗光合作用的日变化、光响应曲线及对短暂遮荫的响应等进行观测，结果表明：（1）旷地的日平均光合有效辐射约为1230μmol·m^-2·s^-2，分别是林窗和林下的1．7和12．3倍定右，并且旷地的气温显著大于林窗和林下的，而空气相对湿度却明显低于其它2个光环境；（2）木荷幼苗在旷地和林窗均出现光合“午休”现象，旷地木荷“午休”时净光合速率的降幅约60％，而林窗的降幅约为30％；旷地中术荷幼苗的最大净光合速率约为17．8μmolCO2·m^-2·s^-1，约是林窗和林下的1．8和3．4倍；此外，木荷幼苗的光饱和点、光补偿点和暗呼吸速率均随环境光强的增大而增大；（3）短暂遮荫时，随着光合有效辐射的降低，各光环境中木荷幼苗的气孔导度和蒸腾速率不断降低，胞间CO2浓度逐渐升高，水分利用率在旷地和林窗中呈下降趋势，而在林下一定低光范围内（约130～800μmol·m^-2·s^-1）则维持了较高水平；（4）受光斑照射时，光斑区域的光合有效辐射和净光合速率分别比受光斑前以及未受光斑区域提高了10倍和4倍以上。

Schima superba is an evergreen broadleaf tree of sun plant, it is also the pioneer species of monsoon ever- green broadleaf forest in subtropical China. The diurnal changes of photosynthesis, the light responses of Pn and the responses to transitory shading of Schima superba which was grown in open, gap and understory were investigated on clear day in summer. The results showed that ： （ 1 ） The average PAR of one day （PARday） in open was about 1 230 μmol · m^-2 · s^-1 ,and it was about 1.7 and 12.3 times as big as gap and understory respectively;the Ta in open was much higher than in gap and understory, but the RH was quite the contrary. （2） Schima superba has shown a midday depression of photosynthesis in open and gap, but has not in understory. The extent of photosynthesis depres- sion in open was about 60% , yet it was about 30% in gap. The maximum net photosynthetic rate of Schima superba in open was about 17.8 μmolCO2 · m^-2 · s^-1, it was about 1 .8 and 3.4 times as big as gap and understory respec- tively; moreover, the light saturation points, light compensation points and dark respiration rate were elevated along with the increase of growth light intensity. （3） In the transitory shading period, the stomatal conductance and the transpiration rate decreased whereas the intercellular CO2 concentration increased along with the fall of PAR in alllight regimes. The water use efficiency showed different rule in understory , it decreased along with the fall of PAR in open and gap, however,it kept a high value when the PAR was between 130 and 800 μmol·m^-2 · s^-1 in under- story. （4）There were frequent instantaneous light-flecks in understoy, the PAR and Pn of Schima superba leaves in light-fleck area were 10 and 4 times big than that in pre-irradiated area and no light-fleck area respectively.