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%).