The response of leaf respiration to water stress in Nothofagus species

Figures & data

Figure 1  Maximum and minimum daily temperatures at the University of Canterbury study site (Geography Department, University of Canterbury). The values correspond to late summer (April 2010) and winter (mid-August 2010). The hatched band indicates the days of measurement.

Table 1  Physiological, respiratory and photosynthetic parameters for leaves of Nothofagus solandri and Nothofagus menziesii during late summer and winter.

	Nothofagus solandri		Nothofagus menziesii
Parameter	Late summer	Winter	Late summer	Winter	ANOVA
Xylem water potential (MPa)	−1.86±0.18	−0.74±0.05	−1.43±0.13	−0.44±0.04	Sp < 0.001 Se < 0.05 Se×Sp ns
A max (µmol CO2 m^−2 s^−1)	14.40±1.03	14.97±2.59	6.08±1.75	4.80±0.80	Sp < 0.001 Se ns Se×Sp ns
R 10 (µmol CO2 m^−2 s^−1)	0.96±0.09	0.48±0.05	0.24±0.03	0.38±0.04	Sp < 0.005 Se < 0.001 Se×Sp < 0.005
Foliar R/A	0.07±0.01	0.03±0.00	0.14±0.04	0.10±0.03	Sp < 0.05 Se ns Se×Sp ns
E o (J mol^−1 K^−1)	39,875±1229	67,720±6571	57,782±6204	53,684±4355	Sp ns Se < 0.05 Se×Sp < 0.05
Q 10	1.65±0.09	2.58±0.24	2.25±0.20	2.12±0.13	Sp ns Se < 0.05 Se×Sp < 0.05
Discrimination (‰)	19.89±0.18	20.36±0.19	17.34±0.64	17.97±0.85	Sp < 0.001 Se ns Se×Sp ns
Soluble sugars (%)	7.30±0.33	8.05±0.36	6.26±0.35	7.65±0.31	Sp ≤0.05 Se < 0.05 Se×Sp ns
Starch (%)	4.87±0.39	5.27±0.28	3.36±0.31	3.52±0.30	Sp < 0.001 Se ns Se×Sp ns
Dark respiration parameters were calculated from fitted temperature curves, where R 10 is respiration at 10 °C, E o is a modelled parameter related to the energy of activation and Q 10 denotes the relative change in respiration with a 10 °C increase in temperature. A max indicates the maximum assimilation of carbon measured at 20 °C and light saturation. Foliar R/A is an indicator of carbon balance at the foliar level. The table also shows the respiratory ^18O discrimination value for both species and the percentage of total non-structural carbohydrate (soluble sugars and starch). Values shown are means (±standard error of the mean) where n=5. Two-way analysis of variance was performed where the factors were species and season. Significance of treatment effect for species (Sp), season (Se) and the interaction between species and season (Sp×Se) are indicated as the P-value or as non-significant (ns).

Figure 2  Relative abundance of alternative oxidase (AOX) and cytochrome oxidase (COX) proteins during summer and winter for Nothofagus solandri and Nothofagus menziesii in the seasonal study. Values shown are mean±SEM. Two-way analysis of variance was performed including the factors species (P<0.001) and season (P≤0.05). Different lower case letters show statistical differences (Fisher least significant difference test).

Figure 3  Variation in gas exchange parameters in Nothofagus solandri and Nothofagus menziesii during drought treatment and recovery. Dark respiration at 10°C in response to water-deficit treatment and subsequent re-watering was calculated from fitted temperature–response curves using a modified Arrhenius equation (A, B). A _max represents the maximum CO₂ assimilation measured at 20°C and light saturation (C, D). Foliar R/A is an indicator of the carbon balance at the foliar level (E, F). Values shown are mean±SEM. One-way analysis of variance (P≤0.05) was performed where the factor was xylem water potential during treatment being C (control) and R1-2 (recovery). Different lower case letters show significantly different means (Fisher least significant difference test).

Table 2  Dark respiration parameters calculated from fitted temperature response curves using a modified Arrhenius equation for leaves of Nothofagus solandri and Nothofagus menziesii during water deficit treatment and recovery.

Nothofagus solandri			Nothofagus menziesii
WP (MPa)	E o (J mol^−1 K^−1)	Q 10	WP (MPa)	E o (J mol^−1 K^−1)	Q 10
−0.8 (C)	39814±9979 ab	1.78±0.27	−0.6 (C)	61151±3905	2.34±0.12
−1.0	54565±4880 b	2.14±0.14	−1.6	61476±4458	2.36±0.15
−1.6	43047±4216 ab	1.83±0.11	−2.4	52979±8053	2.13±0.24
−2.1	26582±3350 a	1.46±0.07	−3.1	56892±3737	2.21±0.11
−3.0	46766±6745 ab	1.94±0.18	−1.2 (R1)	47717±3490	1.95±0.09
−1.0 (R1)	30472±9051 a	1.57±0.20	−1.4 (R2)	51510±6517	2.07±0.19
−1.0 (R2)	56718±8527 b	2.25±0.25
ANOVA	P<0.05	ns	ANOVA	ns	ns
WP is water potential, E o is a modelled parameter related to the energy of activation and Q 10 denotes the relative change in respiration with a 10 °C increase in temperature. Values shown are mean±SEM. One-way analysis of variance (P ≤0.05) was performed where the factor was xylem water potential during treatment being C (control) and R1–R2 (recovery). Different lower case letters show significantly different means (Fisher least significant differences test).

Figure 4  Changes in oxygen isotope discrimination (A, B) and protein abundance ratio of alternative oxidase and cytochrome oxidase (AOX/COX) (C, D) during water deficit treatment and recovery for Nothofagus solandri and Nothofagus menziesii. Values shown are mean (± SE). One-way analysis of variance (P≤0.05) was performed where the factor was xylem water potential during treatment being C (control) and R1-2 (recovery). Different lower case letters show significantly different means (Fisher least significant difference test).