Leaves of tropical rainforest understory plants are protected from excess sun by blue iridescence.

“Iridescent blue-leaved plants grow in the most shady and protected
microclimates of tropical rainforests. Much speculation on the possible
adaptive significance of iridescence has not led to any viable
explanations, as such iridescence actually reduces leaf absorption in
these light-limited environments. We hypothesize that constructive
interference in the wavelengths of 460-485 nm may protect against
photoinhibition and damage via reduced light absorption at those
wavelengths, where other leaves are protected by anthocyanins and
variants of the xanthophyll cycle. We looked for such photoprotection
in three Malaysian understory species polymorphic for blue iridescence:
Begonia pavonina Ridl. (Begoniaceae), Diplazium tomentosum Bl. (Athyriaceae), and Phyllagathis rotundifolia
(Melastomataceae). We collected dark-acclimated leaves before dawn from
plants in Bukit Lanjang Forest Reserve. We tested for differences in
leaf mass, chlorophyll and nutrients in green and blue leaves, and for
increased photoprotection in blue leaves by subjecting both to 30 min
of high irradiance (~1000 µmol m-2 s-1, 400-700 nm) and testing for
differences in transient fluorescence as Fv/Fm for 90 min at 5 min
intervals. All leaves, particularly in B. pavonina had relatively low mass, chlorophyll and N per unit area. In B. pavonina and P. rotundifolia, blue leaves recovered significantly more rapidly from light exposure than green ones, but the differences for D. tomentosum
were not significant. Two of the three understory species thus provide
evidence for a photoprotective function by blue iridescence against
transient exposures to light flecks in these extreme-shade plants.” (Lee et al. 2008)

Lee, David [1], Kelley, John [2], Richards, J.H. [3].
Blue Leaf Iridescence as a By-product of Photoprotection in Tropical Rainforest Understory Plants

Last Updated September 27, 2017