Table 2.
Effects of growth temperature on average (± SE) foliage photosynthetic and isoprene emission characteristics in hybrid aspen (P. tremula x P. tremuloides, clone H200)
| Trait | Growth temperature (day/night) | |
|---|---|---|
| 25/20 ºC | 35/27 ºC | |
| Photosynthetic characteristics | ||
| An per area (μmol m-2 s-1) | 14.73 ± 0.40a | 11.18 ± 0.35b |
| An per dry mass (μmol g-1 s-1) | 0.310 ± 0.009a | 0.346 ± 0.018a |
| gs (mmol m-2 s-1) | 122 ± 7a | 164 ± 8b |
| Ci (μmol mol-1) | 182.3 ± 4.6a | 247 ± 11b |
| Rd per area (μmol m-2 s-1) | 2.07 ± 0.06b | 1.36 ± 0.07b |
| Rd per dry mass (μmol g-1 s-1) | 0.0436 ± 0.0016a | 0.0421 ± 0.0023a |
| αCO2 (mol mol-1) | 0.0441 ± 0.0026a | 0.0338 ± 0.0025b |
| Vcmax per area (μmol m-2 s-1) | 62.1 ± 1.6a | 32.7 ± 1.4b |
| Vcmax per dry mass (μmol g-1 s-1) | 1.309 ± 0.038a | 1.010 ± 0.043b |
| Jmax per area (μmol m-2 s-1) | 120 ± 6a | 80 ± 6b |
| Jmax per dry mass (μmol g-1 s-1) | 2.04 ± 0.06a | 2.19 ± 0.15a |
| Isoprene emission characteristics | ||
| I per area (nmol m-2 s-1) | 28.8 ± 2.8a | 17.8 ± 1.0b |
| I per dry mass (nmol g-1 s-1) | 0.60 ± 0.05a | 0.547 ± 0.027a |
| CDMADP per area (nmol m-2 s-1) | 1110 ± 90a | 650 ± 60b |
| CDMADP per dry mass (nmol g-1 s-1) | 23.5 ± 2.3a | 20.0 ± 1.8a |
| k (s-1) | 0.0286 ± 0.0021a | 0.0306 ± 0.0023a |
| Vmax per area (nmol m-2 s-1) | 79.5 ± 2.9a | 48.8 ± 3.0b |
| Vmax per dry mass (nmol g-1 s-1) | 1.673 ± 0.037a | 1.51 ± 0.11a |
| Km per area (nmol m-2) | 2640 ± 180a | 1542 ± 30b |
| Km per dry mass (nmol g-1) | 55.6 ± 4.9a | 47.7 ± 1.7a |
| αI (mmol mol-1) | 0.0743 ± 0.0010a | 0.0700 ± 0.0010b |
The photosynthetic characteristics are: An - net assimilation rate; gs - stomatal conductance to water vapor; Ci - intercellular CO2 concentration; Rd - dark respiration rate; αCO2 - quantum yield of photosynthesis for the incident light; Vcmax - apparent (Ci-based) maximum carboxylase activity of Rubisco; Jmax - apparent (Ci-based) capacity for photosynthetic electron transport. The isoprene emission characteristics are: I - isoprene emission rate; CDMADP - dimethylallyl diphosphate (DMADP) pool size; k - rate constant of isoprene synthase; Vmax - apparent maximum activity of isoprene synthase; Km - apparent Michaelis-Menten constant for isoprene synthase; αI - quantum yield of isoprene emission for the incident light.
All measurements were conducted at 30 ºC, and saturating light intensity (Q) of 650 μmol m-2 s-1 was used for all measurements except for the quantum yields. The quantum yields were calculated as the linear slopes of the process rate vs. incident Q over the Q range of 20-75 μmol m-2 s-1 and at the ambient [CO2] of 360 μmol mol-1 and oxygen concentration of 21%. The value of Vcmax is reported as an average of Vcmax estimates determined from measurements at 21% and 2% O2. Use of measurements at different O2 concentrations renders the apparent Vcmax estimates less sensitive to Rubisco kinetic characteristics employed in the calculations.
Each value represents the mean ± SE of four measurements in different plants, and means with different lowercase letters are statistically different at P < 0.05 according to ANOVA.