Experiment 1: ploidy effects on tree growth traits and
their response to stress
When averaged across genotypes, diploid and triploid trees differed in
several growth traits, but the magnitude of the differences was small
(Fig. 1, left panel in each box). Across both stress treatments, diploid
trees were 7% taller than triploids. Diploids also had 6% higher SWRs
and slightly larger SLAs than triploids. No difference between diploid
and triploid trees was found for any growth trait when incorporating
genotypic effects in our model (Fig.1, right panel). Genotype
significantly influenced most traits, as shown by the log-likelihood
ratio test results (Appendix 6). Tree growth traits were affected by
drought stress, defoliation or their interaction (Fig. 1).
Drought-stressed trees had 5% higher SWR and 8% lower LWR. Similarly,
defoliation increased SWR and reduced LWR and SLA. For total tree weight
we observed significant drought × defoliation interactions.
Undefoliated, watered trees had 25% greater total weight when compared
with undefoliated, drought-stressed trees. However, when trees were
defoliated, drought-treatment differences disappeared. Interactions
between drought and defoliation treatments were also observed for height
growth. When not defoliated, drought-stressed trees grew slightly taller
than watered trees. These height differences disappeared in trees that
were defoliated.
In most cases, diploid and triploid growth responses were similar when
experiencing stress (no significant ploidy × stress interaction). The
only exception was final height, for which we observed an interaction
between ploidy and defoliation when not accounting for genotypic effects
(Fig. 1, left panel). However, follow-up analyses using stress treatment
ratios revealed no significant difference between diploid and triploid
trees.