Table 2.1 Number of sample shoots n , measurement temperature ranges used for determining the short‐term temperature response of leaf respiration in hinoki cypress Chamaecyparis obtusa as well as means standard errors of ambient air temperature Tamb and leaf respiratory characteristics for each measurement month
Month n Measurement
temperature range °C
Ambient air temperature
°C
Q10Tamb Q1020 Area‐based Ramb
µmol CO2 m 2 s 1
Area‐based R20
µmol CO2 m 2 s 1
Mass‐based R20
nmol CO2 g 1 s 1
July 13 15‒35 26.5 0.2 a 1.94 0.02 a 1.98 0.03 a 0.55 0.10 a,b,c,d 0.37 0.07 a 2.30 0.41 a September 15 15‒35 22.3 0.6 b 1.98 0.03 a 1.98 0.03 a 0.58 0.10 b,d 0.52 0.10 a 3.01 0.53 a,b December 15 5‒25 4.5 0.1 c 2.63 0.03 b 2.30 0.02 b 0.20 0.03 c 0.85 0.13 a,b 4.28 0.54 a,b March 15 5‒25 8.2 0.1 d 2.55 0.03 b 2.30 0.02 b 0.26 0.03 c,d 0.80 0.09 a,b 3.49 0.29 a,b April 15 10‒30 16.0 0.3 e 2.25 0.03 c 2.19 0.03 c 0.76 0.12 a,b 1.05 0.16 b 4.81 0.69 b June 15 15‒35 22.2 0.1 b 2.03 0.03 a 2.04 0.03 a 0.66 0.10 a,b 0.56 0.09 a 3.26 0.46 a,b The relationship between respiration rate and measurement temperature was approximated by a modified exponential equation proposed by Atkin et al.
2005 see the main text for details .
Ambient air temperature Tamb was defined as the mean air temperature for 7 days prior to shoot sampling.
Means with the same letter within the same column were not significantly different P 0.05, paired multiple comparisons using Holm’s method .
Abbreviation: Q10Tamb, Q10 at ambient air temperature; Q1020 , Q10 at 20 °C; Ramb, respiration rate at ambient air temperature; R20, respiration rate at 20 °C.
Table 2.2Effects of canopy position upper, middle or lower layer , measurement month, and their interaction on leaf respiratory characteristics and environmental and physiological factors in a hinoki cypress canopy n 88, two‐way analysis of variance
Independent variables
Category Dependent variables Layer Month Layer Month
df F df F df F
Respiration Q10Tamb 2 0.9 ns 5 150.6 *** 10 1.37 ns
Q1020 2 2.8 ns 5 29.3 *** 10 0.90 ns
Area‐based Ramb 2 51.8 *** 5 16.4 *** 10 3.2 **
Area‐based R20 2 47.1 *** 5 10.2 *** 10 1.0 ns Mass‐based R20 2 44.2 *** 5 6.4 *** 10 1.1 ns
Environment RPPFD 2 67.6 *** 5 1.7 ns 10 1.0 ns
Tamb 2 2.9 ns 5 804.8 *** 10 1.0 ns
Physiology Shoot elongation 2 68.5 *** 5 19.5 *** 10 4.9 ***
LMA 2 33.2 *** 5 27.4 *** 10 1.9 ns
Narea 2 38.7 *** 5 13.4 *** 10 1.6 ns
Nmass 2 16.1 *** 5 9.6 *** 10 3.2 **
Abbreviations: Q10Tamb, Q10 at ambient air temperature; Q1020 , Q10 at 20 °C; Ramb, respiration rate at ambient air temperature; R20, respiration rate at 20 °C; Tamb, mean air temperature for 7 days prior to shoot sampling; RPPFD, relative photosynthetic photon flux density; shoot elongation, monthly elongation rate of terminal shoots measured for primary branches; LMA, leaf dry mass per unit leaf area; Narea and Nmass, area‐ and mass‐based leaf nitrogen content, respectively.
Significance level: ns, not significant; ** P 0.01; *** P 0.001.
Ramb (mol CO2 m2 s1 )
0.0 0.5 1.0 1.5
2.0 Upper
Middle Lower
R20 (mol CO2 m2 s1 )
0.0 0.5 1.0 1.5 2.0
a
b c
b b a
b a,b a
b a a
Month in 2011/12 Q10 [20]
1.8 2.0 2.2 2.4 2.6 2.8
(b)
(d)
b a a b
a,b a
J J A S O N D J F M A M J Month in 2011/12
Q10[Tamb]
1.8 2.0 2.2 2.4 2.6 2.8
J J A S O N D J F M A M J
(a)
(c)
a
b b c
b a
b a
b a a
b a a
a ns
Figure 2.6 Vertical and seasonal variations in respiratory characteristics of hinoki cypress leaves: the area-based respiration rates at ambient air temperature (Ramb) and at 20 °C (R20) decreased with depth in the canopy but their seasonal patterns were different (a, b); Q10 at ambient air temperature (Q10[Tamb]) and at 20 °C (Q10[20]) did not vary vertically and were higher in winter than in summer (c, d). Closed and open circles and triangles indicate mean values in the upper, middle, and lower canopy layers, respectively (n = 5, except for upper and lower layers in July when n = 4). The vertical bars denote standard errors of the means (SEM).
The same letter within the same month indicates that mean values were not significantly different between canopy layers (P > 0.05, multiple comparisons using Holm’s method). The effects of canopy layers on both Q10 were not significant (see Table 2.2).
2.3.2 Vertical and seasonal variations in environmental and physiological factors
RPPFD displayed a distinct vertical gradient within the canopy but had no seasonal variation Table 2.2, Figure 2.7a . Conversely, ambient air T i.e., mean air T for 7 days before shoot sampling , which ranged from 4.5 °C in December to 26.5 °C in July, showed an obvious seasonal change but no vertical variation Table 2.2, Figure 2.7b .
The effects of canopy position and measurement month were significant for all four of the physiological factors Table 2.2 . The values of these factors all tended to be greater in the upper than the middle and lower layers Figure 2.7c‐f . In particular, the vertical gradients of LMA and Narea were consistent throughout the seasons. In contrast, vertical trends in monthly shoot elongation rate and Nmass differed by measurement month. Seasonally, LMA was greatest in March, decreased after March until the summer, and then increased gradually through the autumn and winter. The seasonal pattern of Narea was similar to that of LMA, although the peak occurred in spring. An opposite seasonal trend was observed for shoot elongation rate and Nmass. Shoot elongation began at the end of April, peaked in July, and then decreased until winter. An increase in Nmass was observed in spring and early summer, especially in the upper layer. This increase might have been associated with shoot growth because cumulative shoot elongation resulted in a higher proportion of newly formed current leaves with high Nmass in the sample shoots.
2.3.3 Relationships between leaf respiration and environmental and physiological factors
Area‐based R20 was significantly correlated with all factors except for ambient air T, although the effect of season dormant or growing was different among the factors Table 2.3 . By contrast, Q10Tamb and Q1020 were found to be correlated with only ambient air T, and none of the physiological factors had a significant effect on both Q10 statics for Q10Tamb not shown .
R20 was strongly correlated with RPPFD for each season separately; that is, the slope was not significantly different but the intercept was r2 0.75, P 0.002, n 9 for the dormant season; r2 0.98, P 0.001, n 9 for the growing season Table 2.3, Figure 2.8a . R20 was correlated with shoot elongation rate only during the growing season r2 0.70, P 0.005, n 9 Figure 2.8b . The effect of LMA on R20 differed by season; that is, the slope was significantly different r2 0.55, P 0.022, n 9
for the dormant season; r2 0.95, P 0.001, n 9 for the growing season Table 2.3, Figure 2.8c . R20
was correlated with Narea without seasonal differences i.e., the slope and intercept were not different r2 0.78, P 0.001, n 18 for the two seasons combined Table 2.3, Figure 2.8d .
A strong negative relationship was found between each Q10 and ambient air T Q10Tamb 2.798 0.034 Tamb, r2 0.98, P 0.001, n 6; Q1020 2.409 0.017 Tamb, r2 0.94, P 0.001, n 6 Figure 2.9a . As described above, ambient air T had no significant effect on R20 when all data were pooled Table 2.3 . However, when the relationship was separately examined by canopy layer, excluding the high R20 values observed for the upper and middle layers in April, a negative relationship was found between R20 and ambient air T for the upper r2 0.96, P 0.003, n 5 , middle r2 0.85, P 0.026, n 5 and lower layers r2 0.88, P 0.005, n 6 , respectively Figure 2.9b . The regression slopes were not significantly different, but the intercepts were significantly different between each canopy layer according to analysis of covariance.
2.3.4 Predicting variations in temperature responses of leaf respiration
Results of the present study indicated that Q10 did not vary across the hinoki cypress canopy positions Table 2.2, Figure 2.6c, d , and its temporal variation could be predicted from seasonal changes in ambient air T Figure 2.9a . Furthermore, the vertical variation in R20 correlated well to within‐canopy light gradients for each season Figure 2.8a . The seasonal variation in R20 in each canopy layer could be also explained by the ambient air T Figure 2.9b . Moreover, RPPFD and ambient air T were not correlated. Accordingly, a generalized linear model, in which RPPFD and ambient air T are independent variables, was developed for predicting R20 Table 2.4 . The extremely high values observed for the upper and middle layers in April were excluded for the model development. As a result, predictions of R20 using the model showed fairly good agreement with the measured values r 0.98, P 0.001, n 16 , except for the two high values Figure 2.10 . These results suggest that vertical and seasonal variations in T responses of leaf R in the hinoki cypress canopy could be predicted by relatively simple parameters, light and temperature.
Figure 2.7Vertical and seasonal variations in environmental and physiological factors within a hinoki cypress canopy: relative photosynthetic photon flux density (RPPFD) at the tip of the sample shoot for respiration measurement varied vertically but had no seasonal variation (a); ambient air temperature, defined as the mean air temperature for 7 days before shoot sampling, varied seasonally but had no vertical variation (b);
monthly elongation rate of the terminal shoot of primary branches of five target trees adjacent to the trees used for respiration measurement (n = 17 for upper and middle and n = 16 for lower canopy layers) (c); leaf dry mass per area (LMA) (d); mass- and area-based leaf nitrogen contents (e, f). Symbols, bars and letters are same as in Figure 3 (ns: not significant). The effect of canopy layers on ambient air temperature was not significant (see Table 2.2).
RPPFD
0.0 0.2 0.4 0.6 0.8 1.0
Ambient air temperature (o C)
0 5 10 15 20 25
30 Upper
Middle Lower
Shoot elongation (mm month1 )
0 20 40 60 80 100
(b)
Month in 2011 and 2012 Narea (g m2 )
2.0 2.5 3.0 3.5 4.0 4.5
Month in 2011 and 2012 Nmass (mg g1 )
12 14 16 18 20 22
LMA (g m2 )
150 180 210 240 270
(f) (d) (a)
(c)
(e)
ns
J J A S O N D J F M A M J J J A S O N D J F M A M J
ns
ns
a
b
b c
b a
b a a
b
b
a,b
b b a
b a
a,b b
b a
ns
ns ns
a
b
c
a
b
c a
b c
aa
b a
a
a b b c c cb
a
b
ns ns ns ns ns c
a a,b b b
b a
b a
b a a
b a a
a,b a
a
b a
a
b a
b
c a
a,b
b a
b
b c
b a
Table 2.3Results of linear models to examine the effects of each environmental and physiological factors X and season dormant or growing on leaf respiratory characteristics area‐based R20 and Q1020 in hinoki cypress
Dependent variables
Independent variables X
P‐value
X Season X Season ANCOVA
R20 RPPFD 0.001 *** 0.001 *** 0.150 ns 0.001 ***
Tamb 0.725 ns 0.168 ns 0.201 ns 0.177 ns
Shoot elongation 0.005 ** 0.001 *** 0.176 ns 0.001 ***
LMA 0.001 *** 0.452 ns 0.049 * ―
Narea 0.001*** 0.655 ns 0.202 ns 0.662 ns
Nmass 0.031 * 0.001 ** 0.119 ns 0.013 *
Q1020 RPPFD 0.131 ns 0.001 *** 0.740 ns 0.001 ***
Tamb 0.011 * 0.037 * 0.441 ns 0.034 *
Shoot elongation 0.067 ns 0.001 *** 0.007 ** ―
LMA 0.105 ns 0.001 *** 0.614 ns 0.001 ***
Narea 0.161 ns 0.001 *** 0.195 ns 0.001 ***
Nmass 0.765 ns 0.001 *** 0.129 ns 0.001 ***
The analysis was conducted based on mean values presented in Figures 3 and 4. Measurement months were divided into dormant December, February, April and growing July, September, June seasons. If an interaction X season was not significant i.e., the slope did not differ between seasons; n 18, Type II analysis of variance , then the differences in the intercepts between seasons were tested by analysis of covariance.
Abbreviations are same as in Table 2.
Significance level: ns, not significant; * P 0.05; ** P 0.01; *** P 0.001.
Dash indicates the test was not conducted.
Figure 2.8 Relationships between area-based R20 and environmental and physiological factors of hinoki cypress leaves: R20 was strongly correlated with relative photosynthetic photon flux density (RPPFD) for each season separately (a); monthly shoot elongation rate affected R20 during the growing season (b); effect of LMA on R20 differed by seasons (c); R20 was correlated with area-based leaf N (Narea) without seasonal differences. Different symbols indicate different measurement months. Closed and open symbols indicate data from the dormant and the growing seasons, respectively. Differences in slope and intercept between the seasons were tested by Type II analysis of variance and analysis of covariance, respectively (Table 3). Based on these results, regression lines for the dormant (long-dashed) and/or the growing (short-dashed) seasons are shown separately (a‒c). The solid line denotes the linear regression for all months combined (d). Vertical and horizontal bars denote SEM (n = 5).
Shoot elongation (mm month1)
0 20 40 60 80 100
RPPFD
0.0 0.2 0.4 0.6 0.8 1.0
R20 (mol CO2 m2 s1 )
0.0 0.5 1.0 1.5 2.0
Narea (g m2)
1.5 2.0 2.5 3.0 3.5 4.0 4.5
LMA (g m2)
120 150 180 210 240 270 0.0
0.5 1.0 1.5 2.0
(a) (b)
(c) (d)
r2 = 0.75
r2 = 0.98 r2 = 0.70
r2 = 0.78 r2 = 0.95
r2 = 0.55 June 2012 September 2011 July 2011 Growing season
Februrary 2012 April 2012 December 2011 Dormant season
Q10
1.8 2.0 2.2 2.4 2.6 2.8
Q10[20]
Q10[Tamb]
Ambient air temperature (oC)
0 5 10 15 20 25 30
R20 (mol CO2 m2 s1 )
0.0 0.5 1.0 1.5
2.0 Upper
Middle Lower April
(a)
(b)
Figure 2.9 Decrease in Q10 (a) and area-based R20 (b) with increasing ambient air temperature in respiration in hinoki cypress leaves. Ambient air temperature was defined as the mean air temperature for 7 days prior to shoot sampling. The solid and broken lines in (a) indicate the linear regression for Q10 [Tamb] (Q10 [Tamb] = 2.798 − 0.034 Tamb, r2 = 0.98, P < 0.001, n = 6) and Q10 [20] (Q10 [20] = 2.409 − 0.017 Tamb, r2 = 0.94, P <
0.001, n = 6) respectively. The solid, dotted, and broken lines in (b) indicate regressions for upper (R20 = 1.327
− 0.023 Tamb, r 2 = 0.96, P = 0.003, n = 5), middle (R20 = 1.009 − 0.022 Tamb, r 2 = 0.85, P = 0.026, n = 5) and lower (R20 = 0.559 − 0.015 Tamb, r 2 = 0.88, P = 0.005, n = 6) canopy layers, respectively. Note that linear regressions for the upper and middle layers in (b) exclude the high R20 values observed in April (surrounded by a gray ellipse). Vertical and horizontal bars denote SEM.
Table 2.4Results of a generalized linear model to predict area‐based R20 of hinoki cypress leaves using light and ambient air temperature
Variables Estimate Standard Error t‐value P‐value
Intercept 0.563 0.053 10.65 0.001
RPPFD 0.803 0.061 13.25 0.001
Tamb 0.018 0.002 7.44 0.001
The interaction between RPPFD and Tamb was not significant.
Notably high R20 values observed for the upper and middle layers in April were excluded from analysis n 16 .
Abbreviations: R20, respiration rate at 20 °C; RPPFD, relative photosynthetic photon flux density; Tamb, mean air temperatures for 7 days prior to shoot sampling.
Measured R20 (mol CO2 m2 s1)
0.0 0.5 1.0 1.5
Predicted R20 (mol CO2 m2 s1 )
0.0 0.5 1.0 1.5
Upper Middle Lower
April
Figure 2.10 Good agreement of predicted and measured values for the R20 of hinoki cypress leaves.
Predictions were calculated by a generalized linear model with RPPFD and ambient air temperature as the independent variables (Table 2.4). The high R20 values observed in April (surrounded by a gray ellipse) were excluded from model development. The solid line indicates 1:1.