Experiment 2: ploidy effects on drought recovery
Diploid and triploid trees differed in growth responses during recovery
from extensive drought stress. Across defoliation treatments, triploids
produced 35% more new tissue, had 14% greater total weight and
invested slightly more in leaf production (LWR) than diploid trees.
However, triploid trees were 8% shorter than triploids (Fig 4.,
Appendix 5, left panel). Genotype significantly affected growth traits
of trees regenerating from extensive drought stress, as shown by the
log-likelihood ratio tests (Appendix 7). However, even after
incorporating genotypic effects, cytotype remained important for
explaining differences in new tissue production, total weight, and
height of trees recovering from drought stress (Fig 4., Appendix 5,
right panel).
Diploid and triploid trees recovering from an extensive drought stress
treatment were similarly affected by pre-drought defoliation (Fig. 4).
Significant ploidy × defoliation interactions indicated that defoliated
diploid trees grew taller than defoliated triploid trees. However,
follow-up analyses revealed no significant difference between stress
treatment ratios of diploid and triploid trees. Across cytotypes, trees
that were defoliated prior to drought showed higher growth responses
during drought recovery than trees that were not defoliated. Defoliated
trees allocated more of their stem mass to height growth (increased by
10%), produced 45% more new tissue during recovery and differed by
19% in total weight at the end of the experiment than undefoliated
trees (Fig 4., Appendix 5). Defoliation also caused trees to invest more
in leaf production (increased LWR by 31%).