Table I. Effects of leaf feeding with malate on foliage photosynthetic characteristics in hybrid aspen (clone H200).
| Characteristic | Control | Malate Treated |
|---|---|---|
| An (μmol m−2 s−1) | 16.30 ± 0.43 a | 7.70 ± 0.44 b |
| Vcmax (μmol m−2 s−1) | 68.0 ± 1.6 a | 43.0 ± 2.8 b |
| gs (mmol m−2 s−1) | 280 ± 10 a | 102 ± 7 b |
| Ci (μmol mol−1) | 303.8 ± 3.0 a | 266 ± 7 b |
| RD (μmol m−2 s−1) | 1.63 ± 0.07 c | 3.43 ± 0.42 a |
| RB (μmol m−2 s−1) | 3.06 ± 0.12 b | 4.93 ± 0.28 a |
| QY (mol mol−1) | 0.641 ± 0.013 a | 0.428 ± 0.014 b |
The standard conditions during the measurements were as follows: leaf temperature of 30°C, light intensity of 700 μmol m−2 s−1, and leaf chamber CO2 concentration of 400 μmol mol−1. After steady-state conditions were established under these conditions, foliage photosynthetic characteristics were measured (control), the leaves were further fed for 40 min with malate solution (20 mm), and foliage photosynthetic characteristics were measured again (for kinetic changes in leaf photosynthetic characteristics during inhibitor application, see Fig. 2). RB was measured immediately after leaf darkening and RD when the gas-exchange rate in the dark had reached a steady state. The data are means ± se of four to five replicate experiments with different leaves. se was calculated as the sample sd divided by the square root of n, where n is the number of replicate experiments. Values followed by the same letter are not significantly different (P > 0.05) according to paired-samples Student’s t test. An, Net CO2 assimilation rate; Vcmax, apparent (Ci-based) maximum carboxylase activity of Rubisco; gs, stomatal conductance for water vapor; Ci, intercellular CO2 concentration; RD, dark respiration rate; RB, rate of CO2 release at postillumination CO2 burst (an estimate of the rate of photorespiration with a residual component of dark respiration remaining in light and a certain consumption of CO2 due to the existing RuBP pool); QY, light-adapted (effective) quantum yield of PSII.