Aspen Ploidy and Minimum Leaf Conductance

Do triploid aspen trees lose more water through their leaves than diploids — and does this help explain their higher drought-induced mortality?

Populus tremuloides (quaking aspen) is the most widely distributed tree in North America, yet triploid genets — which have three copies of each chromosome instead of the usual two — show disproportionately high rates of drought-induced mortality. Understanding why requires looking at how ploidy affects basic leaf physiology.

In 2021, Dr. Roxy Cruz-de Hoyos and I collected leaves from 16 diploid and 16 triploid P. tremuloides genets in Western Colorado near the Rocky Mountain Biological Laboratory. We measured minimum leaf conductance (gmin; mmol m⁻² s⁻¹) — the rate of water loss through the leaf cuticle after stomata close — a critical trait governing how fast a plant desiccates under drought stress.

Left: Aspen canopy at the study site in Western Colorado. Middle and right: Leaf collection from diploid and triploid genets during the 2021 field season.

Key Finding

Triploid aspen leaves have significantly greater gmin than diploid leaves. Because gmin is a passive, unregulated source of water loss, higher gmin means triploid trees continue losing water faster than diploids even after stomatal closure. This may help explain why triploid genets experience higher rates of drought-induced mortality — they desiccate more rapidly under the same drought conditions.

Leaf Traits

In addition to gmin, we measured a suite of leaf functional traits to characterize the morphological differences between ploidies:

  • Leaf area (LA)
  • Leaf thickness (LT)
  • Leaf dry matter content / Leaf density (LD)
  • Leaf water content (LWC)
  • Surface area to volume ratio (SA/V)

Triploids showed a classic gigas effect — larger, thicker leaves with higher water content — consistent with genome doubling increasing cell size.

Collaborators

This project was a collaboration with Dr. Benjamin Wong-Blonder (UC Berkeley). Fieldwork was conducted by April Bermudez, Veronica Zepeda, and Cipatli Jimenez, alongside co-lead authors Dr. Roxy Cruz-de Hoyos and Jocelyn Navarro.

Publication

This work was recently accepted for publication in the American Journal of Botany.

Navarro, J., Cruz-de Hoyos, R.M., Wong-Blonder, B., Powers, J.M., and Enquist, B.J. (in press). Ploidy level predicts differences in minimum leaf conductance in quaking aspen, Populus tremuloides. American Journal of Botany.