Effects of summer shading on PSII chlorophyll fluorescence parameters in three maple trees

Acer palnatum Thunb,A. davidii Franch and A. saccharum Marsh were grown with four shading treatments( 0% shading,50% shading,70% shading and 90% shading) to study the photosynthetic characteristics,the changes of chlorophyll centent and PS Ⅱ chlorophyll fluorescence parameters. The results revealed that Fv/ Fm,PIABS,RC/CS,ET0/ TR0,ET0/ ABS and chlorophyll content of three kinds of maple leaves were enhanced significantly,however,ABS / RC,DI0/ RC,VJand Wkwere decreased under shading condition. A. davidii Franch. and A. saccharum March. exhibited the highest maximum net photosynthetic rate and light saturation point under 50% shading condition. Shading is favorable for the energy conversion and utilization of PSⅡ reaction center were improved by shading in three maple leaves,but large area shading would hinder the absorption of light energy. Fity percent shading achieved the balance between absorption and utilization of energy,therefore is suitable for the growth of three kinds of maple plants.