Environmental Engineering Reference
In-Depth Information
The Irradiance Response Curve
The irradiance response curve was recorded automatically in the same leaf inserted into
the leaf chamber by means of operation program. Light response curves were obtained on six
randomly-selected, fully-expanded, healthy leaves of each species using the same portable
photosynthesis system, equipped with an artificial light. Measurements were made between
9:00 and 11:00 in August 2010. CO
2
assimilation in response to (PAR) of 1800, 1600, 1400,
1200, 1000, 800, 600, 400, 200, 100, and 0
μ
mol m
-2
s
-1
at the leaf surface was measured.
Each PAR step lasted 3 min and data were recorded 3 times. An atmospheric CO
2
concentration of 365±5 μmol mol
-1
, a temperature of 28°C, and relative humidity of 60%
were maintained in the chamber. The data obtained for each leaf were analyzed with the
program photosynthetic assistant (Version 1.1, Dundee Scientific, Dundee, UK) to obtain
saturation irradiance of three species. This software utilizes a function described by Prioul &
Chartier (1977) to model photosynthetic A-Q. Based on A-Q curves, the maximum rate of
photosynthesis (
P
max
), apparent dark respiration (
R
d
) and convexity (
k
) were modeled.
Statistical Analysis
All experiments were based on three replicated measurements. Data were analyzed by
one-way analysis of variance (ANOVA) using the statistical software SPSS 18.0 (SPSS,
Chicago, IL, USA). The treatment mean values were compared by post hoc least significant
difference (LSD) test. Statistical LSD tests were performed among 07:00, 09:00, 11:00, 13:00
15:00 and 17:00. The term significant indicates differences for which P≤0.05. The
relationship between photosynthetic variables of different species and environmental factors
were analyzed using linear correlation analysis.
R
ESULTS
Environmental Conditions
T
a
was lowest (26.48±0.44 °C) at 7:00 and increased to maximum (33.23±1.26 °C) at
11:00, then it decreased to (27.31±0.18) °C at 17:00. On the contrary, RH was highest at 7:00
and decreased to (45.43±2.95)% at 11:00, then increased (Figure 1A). Daily PAR and
atmospheric CO
2
concentration, which showed a contrary tendency, ranged from
108.27±11.97 μmol m
-2
s
-1
to 692.93±39.47 μmol m
-2
s
-1
and from 353.60±4.83 μmol mol
-1
to
370.59±0.76 μmol mol
-1
, respectively (Figure 1B).
Diurnal Course of Leaf Gas Exchange
Comparative study of the rate of photosynthesis (P
n
) during the day showed that, diurnal
variations in
P
N
of
C. chinensis
(1.39±0.33 μmol m
-2
s
-1
to 7.32±0.35 μmol m
-2
s
-1
) were
characterized by double-peak curves with higher values at 9:00 and 13:00. While
P
N
of
G.
soja
and
P. australis
(varied from 2.49±0.28 μmol m
-2
s
-1
to 12.62±0.44 μmol m
-2
s
-1
and from
1.87±0.30 μmol m
-2
s
-1
to 8.05±0.78 μmol m
-2
s
-1
, respectively) showed single-peak curves.
Their maximum values were at 13:00 and 9:00, respectively (Figure 2A).
