Environmental Engineering Reference
In-Depth Information
citrus (Machado et al., 2002; Vitale et al., 2012) to prevent excessive shoot dehydration. Even
under low
g
s
at 11:00, the higher VPD caused increased
E
. High values of VPD (1.5 kPa)
affect the leaf gas exchange.
Higher air temperature and VPD negatively affect CO
2
assimilation due to stomatal
closure (Han et al., 2012; Niu et al., 2012; Tretiach et al., 2012.).
G. soja
has lower resistance,
and higher transpiration; thus having the ability to cope with high temperatures.
C
i
of
G. soja
decreased from 7:00 to 13:00 due to increases in
P
N
.
C
i
tended to increase after 13:00 as
P
N
decreased also indicating the coupling between
P
N
and
C
i
. This result may be used to estimate
the leaf capacity to incorporate atmospheric CO
2
.
The diurnal course of gas-exchange followed the pattern mentioned by Kozlowski &
Pallardi (1997) for tropical trees, that is,
P
N
was low in the early morning and coupled with
low PAR, increased sharply and reached a maximum around midday. Afterwards, the
decrease in
P
N
until late afternoon may be related to the higher afternoon
T
a
and VPD. Similar
pattern was shown by palms such as coconut (Passos et al., 2009), as well as by other tree
species like citrus (Machado et al., 2002). Temperature can influence enzymatic reactions,
and the physiological and biochemical responses of cell membranes, and thus became the
main factor to impact photosynthetic dynamics of the plant (Chen et al., 2012; Li et al., 2011;
Oukarroum et al., 2012; Suleman et al., 2013).
The results of correlation analysis of the above data showed that
P
N
was positively
correlated with
g
s
, but negatively correlated with
C
i
, implying that
g
s
is one of the
determinants of
P
N
difference (Zhang et al., 2005). Our results indicated that the determinant
of leaf photosynthetic capacity is
g
s
, because high
P
N
is always accompanied by high
g
s
and
they are always positively correlated with each other, as noted in earlier reports (Sonobe et
al., 2009).
A pronounced sensitivity of photosynthesis to VPD has been observed, and a significant
negative correlation found between stomatal conductivity and VPD (Bunce 1997). All plant
species showed a positive correlation between VPD and
P
N
, which was different with Tucci
et al., (2010). Their results indicated that peach palms showed a negative correlation between
VPD and
P
N
, but a correlation of higher magnitude was observed between
P
N
and VPD,
indicating a stomatal regulation in order to cope with high atmospheric demand. While
Lamade & Setiyo (1996) related significant differences among clones in the relationship
between
P
N
and VPD.
In general, stomatal closure in many species has been considered as a response due
exclusively to soil water deficit (Brandao et al., 2013; Quentin et al., 2012; Tsonev et al.,
2011).
In general, the irradiance response curve of
P
N
and WUE of different plant species
followed the same order:
G. soja
>
C. chinensis
>
P. australis
. They were both higher than most
of the other plant species. It was concluded that plant species adapted to the saline-alkaline
habitat showed higher photosynthesis (Akhani et al., 2012; Li et al., 2012; Rewald et al.,
2011; Sandoval-Gil et al., 2012; Wang et al., 2013). In addition,
G. soja
exhibit higher LSP,
can prevent destruction of photosynthetic tisses from high irradiance and high temperature.
So
G. soja
is most effective to revegetate saline-alkaline soils for its higher photosynthesis to
accumulate more biomass.
