Environmental Engineering Reference
In-Depth Information
Figure 3. The response of
net photosynthesis rate (
P
N
, A), transpiration rate (
E
, B), stomatal
conductance (
g
s
, C) and water use efficiency (WUE, D) to photosynthetic active radiation (PAR) for
three dominant species.
D
ISCUSSION
In situ patterns of leaf-level photosynthesis are created by interactions between a suite of
ambient environmental conditions and the species-specific sensitivity to these combined
factors (Giorio & Nuzzo 2012; Tel-Or & Forni 2011; Zuccarini & Kampus 2011). In other
words, environmental conditions may be similar surrounding the study species, but the
photosynthetic responses of the species were different (Wu et al., 2011).
Irradiation appears to be one of the most important environmental factors governing plant
development and survival, and has been suggested to be one of the main factors influencing
plant growth (Noda et al., 2004). We observed that the photosynthetic dynamics of three
species were mainly influenced by PAR.
G. soja
and
C. chinensis
owe their greater
adaptability to higher PAR, and prevent light destroying their tisses through utilizing a greater
ratio of PAR (e.g., higher photosynthetic rate). They dissipate unwanted light energy by
adjusting their photoreactions via a proportionally higher ratio of carotenoids to zeaxanthins
(Desotgiu et al., 2012; Promis et al., 2012; Ribeiro et al., 2005).
A higher conductance would only marginally increase CO
2
assimilation, but would
significantly increase transpiration, since transpiration increases linearly with
g
s
, as a result of
the constant difference in water vapor concentration between the leaf and the air. Thus
variations in
E
were closely associated with variations in
g
s
. During the day,
g
s
and
E
had a
similar behavior. Nevertheless, increments in
E
cannot be explained only by increments in
g
s
,
but also by increases in VPD. In the morning, the decrease in
g
s
of
P. australis
and
C.
chinensis
from 9:00 to 11:00 was related to the increase in VPD, a response also observed in
