chronic photoinhibition plays only a minor role in the...
TRANSCRIPT
Tomáš Hájek1,2, Eeva-Stiina Tuittila3, Raija Laiho3 and Mati Ilomets4
1 Institute of Botany of ASCR, Dukelská 135, 379 82 Třeboň, CZ, � [email protected] Faculty of Biological Sciences, Branišovská 31, 370 05 České Budějovice, CZ3Department of Forest Ecology, University of Helsinki, P.O. Box 27, 00014 Helsinki, FIN4 Institute of Ecology, Tallinn University, Kevade tn. 2, Tallinn 10 137, EST
Chronic photoinhibition plays only a minor roleChronic photoinhibition plays only a minor role
in the worldin the world’’s most successful bryophyte genuss most successful bryophyte genus
Photosynthesis and StressPhotosynthesis and Stress Brno, 15 Brno, 15 -- 16 September 200516 September 2005
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PPFD [µmol m–2 s–1]
Gross photosynthesis [m
gC
O2g
DW
–1h
–1]
Gross photosynthesis[µ
mol C
O2m
–2s
–1]
Losers – growing only in the pristine open mire
S. magellanicum
S. angustifolium
Survivors – growing in both habitats
Winners – colonizing the drained mire
S. fallax
S. flexuosum
S. papillosum
S. russowii
Pleurozium s.S. russowii
Pleurozium s.
Introduction and MethodsIntroduction and Methods
Peat mosses (Sphagnum) cover vast areas of earth’s
land surface. They often induce water-saturated
unfavourable soil conditions for vascular plants and so
form treeless, sun-exposed habitats.
This evokes the hypothesis that they show a long-term
adaptation to full sun irradiance. When pristine mires
are drained and their tree cover increases, bryophyte
species composition changes only partially, thus
indicating that some species are able to acclimate to
shade conditions.
To test the mosses’ ability to adapt/acclimate to sun and
shade habitats, we measured:
• light response of CO2 assimilation (IRGA)
• chlorophyll fluorescence (photochemical parameters)
• contents of chlorophylls and total carotenoids
in:
• six Sphagnum species and Pleurozium schreberi
• growing in open and/or forested mire
The mosses were collected in central Finland and kept
under mild irradiation for 10 days before experiments. pristine –
wetand o
pen –
MIR
E –
dra
inedand s
haded Results & DiscussionResults & Discussion
Light curves of Sphagnum spp. and Pleurozium:
Light curves in Sphagnum mosses showed:
• large differences in maximum rate of photosynthesis,
• large span of max. quantum yield of photosynthesis (α)
= indication of strong photoinhibition in species low in α
• high PPFD saturation point (~ 2000 µmol m–2 s–1)
• ← maximum quantum yield of photosynthesis
determined the photosynthetic rate in Sphagnum
= indication of reduced amount of PS2 reaction centres
Chlorophyll fluorescence:
• the maximum quantum yield of
photosynthesis correlated well with that
of ΦPSII (FV/FM, r = 0.82) ↓
= support for the gas-exchange data
ConclusionsConclusions
� losers, sun-grown Sphagna of open mires, are
very inefficient in utilizing any light level
� losers suffer from chronic photoinhibition
(due to photodamage to photosystem II), which is
unrecoverable on a time scale of weeks
� a survivor, Sphagnum angustifolium, was the
most photosynthetically active and less
photoinhibited species in both habitats why ?
• FV/FM correlated closely with ФPSII
(at PPFD of 220 µmol.m–2.s–1, r = 0.94)
and less with qP (r = 0.74)
Maximum quantum yield of photosynthesis
[mgCO2 g–1 h–1 : µmolPAR m–2 s –1]
FV/F
M
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S. angustifolium
S. magellanicum
S. papillosum
S. flexuosum
Sphagnum fallax
Pristine part:
S. angustifolium
S. magellanicum
S. russowii
Drained part:
Pleurozium s.
Sphagnum spp.
Pleurozium s.
Pigment content results:
• no clear correlation between chlorophyll
content or Chl a/b ratio and gas exchange and
any chlorophyll fluorescence parameter
• carotenoid content is (slightly) inversely
proportional to ΦPSII or FV/FM (r = 0.50)
�sun-grown plants are richer in
carotenoids but their photoprotective
function is insufficient
� we postulate that the long-lasting photoinhibition in sun-grown Sphagna can be
ascribed to the ambient levels of both PPDF and/or UV-B radiation
Sphagnum fallax Sphagnum russowii Sphagnum papillosum Sphagnum angustifolium
Sphagnum magellanicumSphagnum flexuosum
Max. quantum yield of photosynthesis [µmolCO2 µmolPAR–1]
Maximum gross photosynthesis
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Sphagnum spp.
Pleurozium s.
µmol CO2m
–2s–1