热带雨林蒲桃属三个树种的幼苗由遮荫转入强光后叶片的光抑制

Blades Photoinhibition of Seedlings of Three Speciesin Syzygium Genus in Tropical Rainforest

以热带雨林蒲桃属(Syzygium)不同演替阶段的3个树种思茅蒲桃(早期)、乌墨(中期)和阔叶蒲桃(后期)作为材料,通过测定在自然光和两种遮荫条件下(14%和42%自然光)的光合能力(Pmax)和色素含量,以及两种遮荫条件下3个树种移至全自然光下处理1d,研究它们叶片叶绿素荧光参数的日变化.结果表明,全光下思茅蒲桃和乌墨幼苗的Pmax比遮荫条件下的显著提高,阔叶蒲桃幼苗的光合能力却显著降低,并显著低于其它2个树种.全光下3个树种的Car含量和Car/Chl均高于生长在遮荫条件下同种植物,不同光强下阔叶蒲桃的Car/Chl高于乌墨和思茅蒲桃.一天中,全光下3个树种的Fo一直上升,Fv/Fm下降,但在傍晚能够恢复到清晨的值,表明全光下3个树种通过PS 反应中心的可逆失活有效地防御了光破坏.而遮荫的3个树种转入全光后,Fo一直上升,Fv/Fm下降程度较大,在傍晚仍不能恢复,表明发生了光合机构的光破坏.虽然阔叶蒲桃的Car/Chl高于乌墨和思茅蒲桃,由遮荫转入强光后NPQ也上升较快,但其光合能力较低,一天中热耗散能力的增强仍不能有效消耗过剩的光能,导致对强光敏感,光抑制程度较乌墨和思茅蒲桃重,这与其耐荫性和演替状态是一致的.

Diurnal variation of chlorophyll fluorescence parameters of shade-grown (42% and 14% daylight) seedlings of three tropical rainforest Syzygium species,which are early (Syzygium szemaoense),middle (Syzygium cumini) and late (Syzygium latilimbum) successional species, respectively, were investigated immediately after suddenly exposed to full open site. The light saturated photosynthetic rate (P_(max)) and carotenoid content of three Syzygium species grown in full open site and the shade were also determined.For S.szemaoense and S.cumini grown in the open site,P_(max) was higher than those grown in the shade, while P_(max) of S.latilimbum was lower than those grown in the shade. This indicaties that S. szemaoense and S. cumini could use high light effectively, but S.latilimbum could not. The Car contents and Carotenoid content to chlorophyll content ratios of three Syzygium species grown in the open site were higher than those grown in the shade.Under there light regimes, the Car/Chl of S.latilimbum was higher than those of other two species. Maximal photochemical efficiency of PSⅡ (Fv/Fm) obviously decreased with the increase of diurnal light intensity for all of three species grown in both open site and the shade after exposed to full open site. This indicated that photoinhibition of photosynthesis occurred during the day. In accordance, the non-photochemical dissipation rate increased with the increase of diurnal light intensity. In the open site all of the three species were able to avoid photodamage by increasing thermal dissipation, and were not suffered from chronic photoinhibition. For all of the three species grown in the shade the minimal fluorescence (Fo) value was sharply increased after exposed to full open site, indicating that photodamage may occur. For S.latilimbum after exposed to open site, although its thermal dissipation rate was higher than those of other two species, its P_(max) was low and excessive energy in leaf increased, and it could not effectively dissipate all excessive energy. So S.latilimbum was susceptible to photoinhibition, and its photoinhibition was more severe than other two species.