Environmental Engineering Reference
In-Depth Information
The
E
of
G. soja
(varied from 0.99±0.20 mmol m
-2
s
-1
to 4.64±0.40 mmol m
-2
s
-1
) was
significantly higher than
P. australis
and
C. chinensis
(varied from 0.40±0.07 mmol m
-2
s
-1
to
1.45±0.16 mmol m
-2
s
-1
and from 0.62±0.13 mmol m
-2
s
-1
to 2.00±0.26 mmol m
-2
s
-1
,
respectively) (Figure 2B). The maximum values of
E
were at 11:00 for
G. soja
and
C.
chinensis
, but at 9:00 for
P. australis
.
The gas exchange of the plant was characterized by measuring the leaf stomatal
conductance (
g
s
) throughout the day on the same dates (Figure 2C). The
g
s
of
G. soja
increased until 13:00, reaching the maximum values at that time, and then decreased. The
g
s
of
P. australis
was significantly lower than
G. soja
and
C. chinensis
, except at 9:00. In
general, the diurnal course of
g
s
followed the same pattern of
P
N
. The maximum of
g
s
values
occurred in the early morning except
G. soja
. The highest
g
s
of
G. soja
reached 0.25 mol m
-2
s
-1
at 13:00, followed by 0.23 mol m
-2
s
-1
of
C. chinensis
at 7:00 and 0.11 mol m
-2
s
-1
of
P.
australis
at 9:00.
A similar diurnal pattern of
C
i
was observed among different species (Figure 2D). The
diurnal patterns of VPD and WUE were also similar among three species. VPD showed
single-peak curves, with the maximum values at 11:00 (Figure 2E), while WUE was
characterized by double-peak curves with higher values at 9:00 and 13:00 or 15:00 (Figure
2F), which was contrary to
C
i
.
Linear correlations among photosynthetic variables and key environmental factors
indicate high positive correlations between
P
N
and
E
,
P
N
and PAR,
P
N
and
T
leaf
,
P
N
and VPD,
P
N
and
g
s
except
C. chinensis
(
r
=0.35,
P
>0.05) (Table I, II and III). Whereas negative
correlations between
P
N
and RH,
P
N
and
C
i
were found.
The Irradiance Response Curve
The irradiance response curves derived from the leaves were substantially affected by
different species (Figure 3).
G. soja
maintained significantly higher
P
net
rate on an area basis
than
P. australis
and
C. chinensis
, but there was no significant difference between
P.
australis
and
C. chinensis
(Figure 3A). The same patterns of diurnal course of
E
and
g
s
were
observed in all species, with their values increasing with PAR (Figure 3B and 3C). The
irradiance response curve of WUE of different plant species followed the order:
G. soja
>
C.
chinensis
>
P. australis
(Figure 3D). They both increased to the maximum when PAR ranged
from 400 to 600 μmol mmol
-1
, then decreased gradually. WUE of
P. australis
and
C.
chinensis
were both below zero at dark conditions except
G. soja
.
Table IV. Modeled photosynthetic light response curve parameters of different species
on a leaf area basis
P
max
R
d
k
LSP LCP AQE
G. soja
17.323 1.213 1.023 1695.6 0 0.079
P. australis
14.576 -1.216 0.912 1551.6 18 0.081
C. chinensis
15.832 -1.269 0.912 1652.4 18 0.085
Pmax (maximum gross CO2 assimilation rate), Rd (apparent dark respiration), k (convexity), LSP (light
saturation point), LCP (light compensation point), AQE (Apparent quantum efficiency).
C. chinensis
showed highest AQE, followed by
P. australis
and
G. soja
, while
R
d
,
k
, LSP
and
P
max
of
G. soja
were higher than
P. australis
and
C. chinensis
(Table IV).
