Variation of xylem vessel diameters across a climate gradient: insight from a reciprocal transplant experiment with a widespread boreal tree

Abstract

1. Xylem vessel diameters represent an important plant hydraulic trait to ensure sufficient water supply from the roots to the leaves. The ability to adjust the hydraulic pathway to environmental cues is key in order to satisfy transpirational demands and maximize growth and survival. 2. We evaluated the variability of vessel diameters in trembling aspen in a reciprocal transplant experiment. We tested six provenances from three ecological regions of North America planted at four test sites in western Canada. All test sites were established at the same time with the same provenances arranged in a randomized complete block design. 3. Vessel diameter showed a strong interaction of population and test site suggesting a high degree of phenotypic plasticity in this trait. Gaussian kernel density estimates support plastic as well as genetic contributions in vessel diameter control trending from bimodal distributions at the most northern test site towards unimodal distributions at the warmest and mildest test site. 4. Furthermore, we used test site-specific climate data in form of a 2-year, 5-year and 10-year average of 21 directly and derived climatic variables and found that average site-specific vessel diameters correlated strongly with summer moisture availability. A previously found negative relationship with vessel diameter and tree height in central Alberta was also found at two other boreal test sites but reversed at a wetter and milder sub-boreal test site. 5. In summary, vessel diameters were highly plastic in response to different environments and varied with summer moisture availability. The variability of vessel diameter and tree height correlations suggests that vessel diameter alone cannot serve as a reliable proxy for long-term growth performance beyond boreal environments. Instead, selecting aspen populations with a high degree of plasticity in this trait appears to be the safest option for assisted migration and seed transfer programmes under climate change.

A review and meta‐analysis of intraspecific differences in phenotypic plasticity: Implications to forecast plant responses to climate change

“…First, P × E may affect among‐population phenotypic differences across environments. For instance, Schreiber, Hacke, Hamann, & Baltzer (), in a study on trembling aspen ( Populus tremuloides ), found that among‐population variation in vessel diameter was observed only in the southernmost gardens, whereas populations showed similar vessel diameters in the northern, boreal sites. Second, P × E may also alter the relationship of mean traits with geographical and/or climatic variables at the population sources that are commonly used as evidence of local adaptation.…”

Plant functional traits differ in adaptability and are predicted to be differentially affected by climate change

“…To date, there has been a focus on species mean trait values; however, for species to be able to adapt to climate change they require, heritable, intraspecific trait variation. Yet, a few studies focus on intraspecific trait variation and if these traits are genetically determined (e.g., Aranda et al, ; Schreiber, Hacke, & Hamann, ; Hajek, Kurjak, von Wühlisch, Delzon, & Schuldt,; Madani et al, ). There is growing appreciation of the importance of intraspecific variation in functional and complex traits in providing the capacity to adapt to climate change.…”

Elevated [CO2] alleviates the impacts of water deficit on xylem anatomy and hydraulic properties of maize stems

“…At the current atmosphere [CO 2 ], xylem anatomy showed a significant response to water deficit in maize stems, with decreases in vessel diameter ( D c ), vessel roundness ( R c ), and stem cross‐section area ( A stem ; Table ). Studies of many trees and crops report similar long‐term response to water stress (Arend & Fromm, ; Awad et al, ; Hudson et al, ; Plavcová & Hacke, ; Schreiber et al, ; Stiller, ). Photosynthetic capacity is associated with xylem formation because assimilation is crucial not only for the synthesis of cell wall products but also for maintaining turgor pressure in the enlarging cells (Larcher, ; Ray, Green, & Cleland, ; Steppe et al, ).…”

“…Soil drying is the most frequent and primary environmental stress that plants face. Experiments conducted under natural conditions across climatic and environmental gradients indicate that xylem conduit diameter, conduit length, hydraulic conductivity, and vulnerability to embolism of tree branches were positively correlated with local precipitation or soil water availability (Choat et al, ; Schreiber, Hacke, Hamann, & Baltzer, ; Villar‐Salvador, Castro‐Díez, Pérez‐Rontomé, & Montserrat‐Martí, ). Similar findings have been recorded in experiments under controlled environment conditions.…”