Environmental Engineering Reference
In-Depth Information
POTENTIAL
AND
PHOTOSYNTHETIC PRODUCTIVITY OF HIGHER PLANTS
EFFECTS
OF
UV-B
ON
PHOTOSYNTHESIS
SALVADOR NOGUÉS
1
, DAMIAN J. ALLEN
2
AND NEIL R. BAKER
3
1
Departament de Biologia Vegetal, Universitat de Barcelona, Barcelona,
Spain
2
Agricultural Research Service, Photosynthesis Research Unit, Urbana
(IL), USA
3
Department of Biological Sciences, University of Essex, Colchester, UK
1. Abstract
The effects of UV-B radiation on photosynthesis and photosynthetic productivity of
higher plants are reviewed. When plants were exposed to large UV-B doses in a
glasshouse in order to study the mechanistic basis of UV-B-induced inhibition of
photosynthesis, direct effects on stomata and on Calvin cycle enzymes (i.e. large
decreases in ribulose-1,5-bisphosphate carboxylase/oxygenase and in
sedoheptulose-1,7-bisphosphate) without any significant effect on photosystem II were
observed. When plants were continuously grown and developed under UV-B in a
glasshouse, exposure to UV-B only decreased adaxial stomatal conductance (g
s
) of the
leaves and consequently increased the stomatal limitation of CO
2
uptake. Furthermore,
field studies using realistic UV-B levels (i.e. a predicted 30% increase in this radiation)
demonstrate a lack of UV-B effects on photosynthesis or on plant biomass. It is
concluded that any predicted future increase in UV-B irradiation is unlikely to have a
significant impact on the photosynthetic characteristics and productivity of higher
plants.
2. Introduction
It has been predicted frequently that increasing UV-B radiation due to future
stratospheric ozone depletion might affect the photosynthesis and photosynthetic
productivity of higher plants. The photosynthetic productivity of a plant is determined
by the quantity of photosynthetically active radiation intercepted and the efficiency with
which this intercepted radiation is utilised for dry matter production. It is evident that
UV-B can potentially impair the performance of the three main processes of
photosynthesis, the thylakoid electron transport and photophosphorylation, the carbon
reduction cycle, and the stomatal control of the CO
2
supply
1
. The activities of many
components of photosynthesis are regulated by the rates of other photosynthetic
reactions and therefore examination of a single process or component, such as the
carboxylation velocity of ribulose-1,5-bisphophate carboxylase/oxygenase, the quantum
efficiency of photosystem II photochemistry or stomatal conductance, does not allow
identification of the primary UV-B-induced limitation.
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