Percent reduction (-) or increase (+) in leaf chlorophyll content (SPAD values) compared to zero values (i.e., before heat stress was imposed). Species are ranked in order of tolerance based on percent reductions in SPAD values as a measure of damage to the leaf chloroplast membrane.
| SPAD | ||
|---|---|---|
| Species | July | August |
| A. pseudoplatanus ‘Spaethii’ | +2.46a | –5.52a |
| A. campestre ‘Louisa Red Shine’ | –1.57a | –3.90a |
| A. pseudoplatanus ‘Negenia’ | –2.25a | –3.25a |
| A. platanoides ‘Royal Red’ | –3.94a | –3.85a |
| A. campestre | –6.36a | –1.22a |
| A. platanoides ‘Emerald Queen’ | –4.70a | –7.55a |
| A. platanoides ‘Princeton Gold’ | –5.31a | –10.6a |
| A. platanoides ‘Drummondii’ | –8.82a | –8.11a |
Numbers within a column followed by a common letter (taken from regression equations [Figure 2]) are not significantly different according to Tukey’s honest significance test (P = 0.05).