Jacotot, A., Marchand, C.,
Gensous, S. and Allenbach, M.
2018
Effects of elevated
atmospheric CO2 and
increased tidal flooding
on leaf gas-exchange
parameters of two
common mangrove
species:
Avicennia marina and
Rhizophora stylosa.
Photosynthesis Research 138: 249-260.
NOTE:
Jacotot et al. (2018)
say that "future climate
change could affect
the functioning of
mangrove ecosystems,
such as their productivity
and carbon sequestration
capacities, or even
their ability to conquer
new available spaces."
SUMMARY:
"Elevated
atmospheric CO2
concentrations
will increase
mangrove
net productivity"
"Increase
in temperature
will raise the
beneficial effect
of elevated CO2"
"Elevated CO2
will help
mangrove trees
to resist drought."
Similar findings
were noted for
water use efficiency,
where elevated CO2
increased this
parameter by
+58% and +113%
in A. marina and by
+98% and +112%
in R. stylosa
under normal and
longer tidal flooding
durations, respectively. T
DETAILS:
Increased
water use
efficiency
was the
combined result
of increased
photosynthesis,
and decreased
transpiration rates,
in both
mangrove species,
under elevated CO2.
The observed
improvement
of water use
efficiency
at higher CO2
should help
these mangrove
species
"resist drought episodes."
The positive effects
on photosynthesis
were
"more pronounced
during the warm season,
suggesting that an increase
in global temperatures
would further enhance
the photosynthetic response
of the considered species,"
noting that there was
"a clear difference in
the photosynthetic response
to elevated CO2
between the cool season
and the warm season,
which increased
from 32 to 40% and
from 38 to 45%
for A. marina and
R. stylosa, respectively."
An increase
in tidal flooding
duration had no
statistically significant
impact on net
photosynthesis
for either
mangrove species
under ambient CO2
and that it had
only a small effect
(3-5% decline)
under elevated
CO2 conditions.
Their experiment
was conducted in
controlled-
environment
greenhouses in the
city of Mont-Dore
in New Caledonia
from June 2016
through May 2017.
Two-year-old
seedlings of the two
mangrove species
were grown in the
greenhouses under
ambient (400 ppm)
or elevated (800 ppm)
CO2, with the elevated
CO2 being supplied
during 0500 to 1900
hours each day.
In addition, the plants
were subjected to normal
(3.25 hours for A. marina
and 6.0 hours for R. stylosa)
or increased
(an extra 1.75 hours)
tidal flooding durations
to simulate what the
authors describe as
"realistic" durations
of tidal flooding
under expected
end-of-the-century
sea level rise
projections.
Figure 1:
Displays the effects
of elevated CO2
and tidal flooding
on net photosynthesis
and water use efficiency
of A. marina and R. stylosa.
Elevated CO2 induced
a +59% increase in
net photosynthesis
in A. marina regardless of
tidal flooding duration,
whereas for R. stylosa
net photosynthesis
increased by +77%
under normal flooding
and by +74% under
longer-duration flooding.
Elevated CO2
did not influence
dark respiration
( "no down regulation
[of photosynthesis]
was observed." )
Mean values
± SEM (n = 360)
of net photosynthesis
(A, B)
and water use efficiency
(C, D)
for A. marina and
R. stylosa grown
in ambient CO2
(400 ppm)
or elevated CO2
(800 ppm)
and under normal
(dark green or blue)
and longer
(light green or blue)
tidal flooding
durations
for 12 months.
Different letters
indicate significant
differences
(p < 0.05)
and red percentages
indicate the
percent change
in net photosynthesis
(Pn)
or water use efficiency
(WUE)
due to elevated CO2
at a given
tidal flooding duration
(TFD).
