Table 1.
Average (± SE) values of structural and isoprene emission and photosynthetic characteristics in different-aged leaves of hybrid aspen (Populus tremula x P. tremuloides)
| Trait1 | Young | Mature | Old |
|---|---|---|---|
| Structural traits | |||
| Leaf area (cm2) | 48.7 ± 3.4a | 54.7 ± 4.4a | 48.8 ± 4.2a |
| Dry mass per unit area (g m-2) | 48 ± 7a | 65.2 ± 3.6b | 61.9 ± 1.5b |
| Dry to fresh mass ratio (g g-1) | 0.277 ± 0.018a | 0.298 ± 0.018a | 0.270 ± 0.013a |
| Isoprene emission traits | |||
| I1000 (nmol m-2 s-1) | 15.7 ± 2.9a | 28.7 ± 3.6b | 16.8 ± 2.0a |
| Imax (nmol m-2 s-1) | 19.0 ± 4.0a | 34.6 ± 5.0b | 17.3 ± 2.2a |
| Imax/I1000 | 1.18 ± 0.05a | 1.20 ± 0.05a | 1.027 ± 0.007b |
| αI (mmol mol-1) | 0.0323 ± 0.0033a | 0.0581 ± 0.011b | 0.081 ± 0.008c |
| QI90 (μmol m-2 s-1) | 970 ± 150a | 1020 ± 100a | 440 ± 60b |
| Assimilation traits | |||
| A1000 (μmol m-2 s-1) | 9.2 ± 1.1a | 14.0 ± 1.5b | 11.0 ± 1.5ab |
| Amax (μmol m-2 s-1) | 11.6 ± 1.1a | 16.2 ± 1.7b | 12.3 ± 1.5a |
| Amax/A1000 | 1.30 ± 0.08a | 1.192 ± 0.041ab | 1.129 ± 0.028b |
| Rd (μmol m-2 s-1) | 1.90 ± 0.47a | 1.14 ± 0.27ab | 0.66 ± 0.25b |
| Ci (μmol mol-1) | 230 ± 15a | 216 ± 16a | 233 ± 16a |
| (ΛS (%) | 33.3 ± 5.6a | 35.1 ± 4.7a | 28.0 ± 4.4a |
| αA (mol mol-1) | 0.0392 ± 0.0032a | 0.04031 ± 0.0019a | 0.04355 ± 0.0017a |
| QA90 (μmol m-2 s-1) | 650 ± 60ab | 730 ± 60b | 580 ± 70a |
| Photosynthetic electron transport traits | |||
| J1000 (μmol m-2 s-1) | 88 ± 8a | 121 ± 13b | 92 ± 7a |
| Jmax (μmol m-2 s-1) | 96 ± 10a | 136 ± 17b | 98 ± 8a |
| Jmax/J1000 | 1.076 ± 0.019ab | 1.118 ± 0.025b | 1.064 ± 0.013a |
| αJ (mol mol-1) | 0.257 ± 0.025a | 0.279 ± 0.016a | 0.282 ± 0.009a |
| QJ90 (μmol m-2 s-1) | 720 ± 80ab | 870 ± 70b | 670 ± 60a |
| Combined traits | |||
| Imax/Amax (mmol mol-1) | 1.77 ± 0.35a | 2.13 ± 0.38a | 1.63 ± 0.40a |
| Imax/Jmax (mmol mol-1) | 0.194 ± 0.030a | 0.228 ± 0.031a | 0.191 ± 0.037a |
| αI/αA (mmol mol-1) | 0.84 ± 0.09a | 1.20 ± 0.12b | 1.88 ± 0.21c |
| αI/αJ (mmol mol-1) | 0.128 ± 0.013a | 0.173 ± 0.014b | 0.288 ± 0.028c |
| QI90/QA90 | 1.56 ± 0.15a | 1.41 ± 0.07a | 0.85 ± 0.16b |
| QI90/QJ90 | 1.33 ± 0.11a | 1.181 ± 0.044a | 0.70 ± 0.11b |
Average values with the same lowercase letter are not significantly different (P > 0.05 according to separate samples t-tests)
Isoprene emission traits: I1000 - rate at a quantum flux density (Q) of 1000 μmol m-2 s-1, Imax - emission capacity (Eq. 2), αI - initial quantum (Eq. 2), QI90 - Q for 90% of I at Q = 2000 μmol m-2 s-1 (saturation Q, Eq. 3); net assimilation traits: A1000 - rate at a quantum flux density (Q) of 1000 μmol m-2 s-1, Amax - gross photosynthetic capacity (Eq. 2), Rd - dark respiration rate, Ci - average intercellular CO2 concentration for Q ≥ 200 μmol m-2 s-1, ΛS - relative stomatal limitation of photosynthesis at light saturation, αA - initial quantum (Eq. 2), QA90 - Q for 90% of A at Q = 2000 μmol m-2 s-1 (Eq. 4); photosynthetic electron transport traits: J1000 - rate at a quantum flux density (Q) of 1000 μmol m-2 s-1, Jmax - electron transport capacity (Eq. 2), αJ - initial quantum (Eq. 2), QJ90 - Q for 90% of J at Q = 2000 μmol m-2 s-1 (Eq. 3).