Wang, L.L., Li, Y.Y.,
Li, X.M., Ma, L.J.
and He, X.Y.
2019
"Co-ordination
of photosynthesis
and stomatal responses
of Mongolian oak
(Quercus mongolica Fisch. Ex Ledeb.)
to elevated O3
and/or CO2 levels"
Applied Ecology and
Environmental Research 17:
4257-4268.
NOTE:
Tropospheric ozone (O3)
is a harmful air pollution
that damages plants.
Its concentration is projected
to rise by 20% or more
in the next three decades,
in many industrialized regions,
increasing even higher
by the end of the century.
Rising concentrations of
atmospheric CO2 are expected
to enhance plant future growth ,
from its aerial fertilization effect,
which improves plant photosynthesis,
biomass and water-use efficiency.
An open question is whether
the benefits plants receive
from rising atmospheric CO2,
will fully compensate for
the growth-retarding effects
of increasing ozone levels.
SUMMARY:
Higher levels of
atmospheric CO2
will benefit
Mongolian Oaks
in the future,
especially where
O3 pollution
is minimal.
In locations where
O3 is a concern,
elevated CO2
can help reduce
much of the stress
caused by this
growth-retarding gas.
Elevated levels of O3
suppressed
photosynthesis,
photosynthesis,
as expected, while
elevated levels
of CO2 enhanced it.
of CO2 enhanced it.
With the combined treatment
of elevated CO2 and elevated O3,
Wang et al. report that
"O3-induced adverse effects
to photosynthesis [were]
ameliorated, at least partly,
by high CO2."
The researchers observed
that the stomatal density
was not significantly different
among any of the four
treatments in the first year.
But, by the end of the
second growing season
the stomatal density
had declined significantly
in the elevated CO2 ,
and elevated CO2
plus elevated O3,
treatments (compared
to the control treatment).
Such a reduction
in stomatal density
is a beneficial long-term
morphological response
to atmospheric CO2
enrichment.
It improves plant
water-use efficiency
water-use efficiency
( less water escapes through
open stomata via transpiration ),
open stomata via transpiration ),
and also reduces O3 stress
( fewer stomata = reduced entry of
harmful air pollutants into the plant ).
DETAILS:
The five-member Chinese scientific
team of Wang et al. (2019) studied the
photosynthetic response of Mongolian oak
(Quercus mongolica) to elevated levels
of CO2 and O3 over two successive
growing seasons at the
Shenyang Arboretum of the
Chinese Academy of Sciences,
Shenyang, Liaoning province, China.
The research was conducted in
open-top chambers with
four-year-old trees subject to
one of two CO2 levels
( ambient air, or elevated to 700 ppm )
and one of two O3 concentrations
( ambient air, or elevated to 80 nmol/mol ).
Atmospheric CO2 enrichment
was supplied 24 hours per day,
while elevated O3 was applied
for 9 hours per day (0800-1700 hrs).
At various intervals throughout
the experiment, the authors
measured photosynthetic
and stomatal parameters
of the leaves, to evaluate
the photosynthetic and
stomatal responses of
Q. mongolica to O3 and/or CO2.
