Ploidy level predicts differences in minimum leaf conductance in quaking aspen, Populus tremuloides

Leaves lose water in parallel between stomata and the cuticle. Plants regulate stomata to reduce leaf water loss in response to atmospheric demand. However, water may still be lost through leaky stomata and the cuticle, as measured by minimum leaf conductance (g_min). We compared g_min between co-occurring diploid and triploid individuals of Populus tremuloides to determine whether ploidy, leaf traits, or microclimate explain variation in g_min. We hypothesized that g_min may increase with increasing ploidy because higher ploidy influences traits related to plant water loss, resulting in greater triploid water loss.

We measured g_min in five leaves each of 32 aspen genets in Colorado. We also measured traits associated with plant water-use and structure. We then assessed predictors of differences in g_min, including ploidy level.

Minimum leaf conductance differed by ploidy level, with higher g_min in triploids than in diploids. Although leaf area and surface-area-to-volume ratio were significant predictors of g_min, neither variable accounted for the difference by ploidy level. Slope and aspect explained additional variation in g_min, suggesting important microsite effects. However, ploidy level remained a significant predictor of g_min across all models, indicating the effect on g_min is robust and not due to covariation with structural traits and topography.

Triploids consistently had higher g_min than diploids across models; accounting for structural traits and topography. Higher g_min in triploids is consistent with hypothesized physical or genetic effects of a larger genome on leaf traits, resulting in differential drought vulnerability across ploidy levels.