[Difference in light acclimation mechanisms between light-loving and shade-tolerant ficus species]

The effects of light intensity on photosynthetic characteristics and possible mechanisms of preventing photodamage for two Ficus species seedlings grown under different irradiance were studied in rainy season. Ficus tinctoria Corner. is a sun species. Ficus subulata Bl. is a shade-tolerant species. With the increase of growth light intensity, maximum photosynthetic rate (P(max)), midrib angle (MA), chlorophyll a to b ratio (Chl a/b), carotenoid to chlorophyll ratio (Car/Chl), and thermal dissipation (NPQ) increased, while chlorophyll content and the amount of light harvesting complex of photosystem II decreased in both Ficus species. Those changes could reduce the existence of excessive light energy and ameliorated the extent of photoinhibition of photosynthesis. Under strong irradiance, photosynthetic rate was higher in F. tinctoria grown under 100% and 36% relative irradiance (RI) than in F. subulata, but their thermal dissipation capacity did not differ significantly. The results suggested that under strong irradiance seedlings could reduce excessive light energy through increasing both light energy utilization by photosynthesis and thermal dissipation in F. tinctoria, but through increasing thermal dissipation only in F. subulata. Reducing excessive light energy could protect photosynthetic apparatus from photoinhibition or photodamage. Under low irradiance, excessive light energy was reduced mainly through increasing light energy utilization by photosynthesis in F. tinctoria when grown under 100% and 36% RI and through increasing both photosynthetic utilization and thermal dissipation when grown under 12% and 4% RI, and through increasing thermal dissipation only in F. subulata. The extent of photoinhibition was greater in F. subulata than in F. tinctoria under the same irradiance of leaf surface, while the diurnal changes in photoinhibition was similar between the two species when grown under 100% RI. Under 100% RI, MA is larger in F. subulata than in F. tinctoria, which resulted in a lower leaf surface irradiance in F. subulata than in F. tinctoria. This was the main reason that the two Ficus species showed similar diurnal photoinhibition pattern under 100% RI. Acclimation of MA to irradiance was important to Ficus plants, especially to F. subulata.