COS 222-2 - Differences in cuticular conductance (gmin) by cytotype in Populus tremuloides in the Rocky Mountains suggest differential drought tolerance

Abstract: When plants experience water stress, they shut their stomata to avoid water loss. However, water can still be lost through the cuticle (waxy outer covering of the leaf), a process called cuticular conductance (gmin). This trait is understudied because of how time-consuming it is to measure, yet furthering our understanding of sources of variation in cuticular conductance is imperative because drought conditions are becoming more pervasive globally. Cuticular conductance determines plant water usage during droughts and restricting it could improve drought tolerance. Factors influencing cuticular conductance, such as ploidy level, have yet to be explored.

Polyploidy, which originates from chance duplications of the genome, has created opportunities for increased genetic diversity and adaptation to shifts in climate. For this reason, there are many plant species with different whole genome duplication levels, such as Populus tremuloides, or quaking aspen trees, which has two cytotypes: diploid and triploid.

Aspen trees have been experiencing a population decline all over North America, known as Sudden Aspen Decline. It is important to understand the differences between diploid and triploid aspen trees to make informed land management decisions to restore habitats affected by SAD. Near the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado, researchers studied P. tremuloides demography and various traits to assess the role ploidy level plays in quaking aspen trees. Results indicate diploid trees are more resilient to drought compared to triploid trees. Triploid trees also have a greater rate of stomatal conductance. However, a trait that has not been studied on aspen trees and could have serious implications for understanding the role cytotype plays in water relations is cuticular conductance because under drought conditions, the survival of plants is dependent on how much water they can retain when water availability is low. The amount of transpiration through the cuticle can indicate a plant’s susceptibility to drought.

During the summer of 2021, we collected 5 leaves from 15 triploid and diploid aspen trees to assess the rate of cuticular conductance near RMBL. We used the detached leaf drying method to measure the rate of water loss after stomatal closure. Our results indicate the average cuticular conductance of triploid aspen trees is ~33% more than the cuticular conductance of diploid aspen trees. These findings highlight the role polyploidy plays in plant-water relations and differences in understudied traits, such as cuticular conductance.