Poster: Environmental physiology
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Abs #
P01005: Differential adaptation of tropical species to abiotic stress: I. Effects of high irradiance and photoprotection in pioneer and late successional species
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Presenter: |
Martinez, Carlos A. Contact Presenter |
Authors | Martinez, Carlos A. (A) Favaretto, Viviane (A) Hildebrand, Hilda (A) Souza de, Janaina (A) | | Affiliations: |
(A): University of Sao Paulo, Dept. Biology, FFCLRP
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The effects of high irradiance on photoinhibition of photosynthesis and photoprotection was studied in young fully expanded leaves of six contrasting Brazilian tropical forest tree species that differ in succession status ranging from pioneer species (PS) to late succession species (LS) under controlled conditions and in the field. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence emission (Fv/Fm) in plants growing under shade and sun conditions. Photosynthetic pigments chlorophyll and carotenoids were also analyzed. The results show a consistently higher degree of photoinhibition in the LS leaves during high light exposure, as manifested by a decrease in the Fv/Fm ratio. Measurements of diurnal changes in Fv/Fm confirmed the increased susceptibility of LS leaves to photoinhibition. On sunny days (maximum PPFD 1900 μmol photons m-2 s-1) LS leaves of E. leiocarpa and H. courbaril had the greater diurnal photoinhibition compared to PS leaves of C. pachystachya. In low light, fast recovery of Fv/Fm ratio was observed in PS leaves. The carotenoids/chlorophyll ratio was higher in leaves grown under sun conditions, but shade leaves contained about 50% more total chlorophyll per unit leaf mass than sun leaves. The stress tolerance of PS leaves appears to involve an ability to increase SOD activity. The high degree of reversible photoinhibition observed in PS leaves of tropical trees probably represents a dynamic regulatory process protecting the photosynthetic apparatus from severe damage by excess light. Supported by CNPq grant 474761/2004-5.
