Conflicting Hydraulic Effects of Xylem Pit Structure Relate to the Growth-Longevity Tradeoff in a Conifer Species

Author

Beth Roskilly, The University Of MontanaFollow

Year of Award

2018

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Organismal Biology, Ecology, and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Anna Sala

Commitee Members

Lila Fishman, Sharon Hood, Uwe Hacke

Keywords

life history tradeoffs, xylem, hydraulics, drought tolerance, torus-margo pits

Subject Categories

Biology | Forest Biology | Plant Biology

Abstract

Consistent with a ubiquitous life history tradeoff, trees exhibit a negative relationship between growth and longevity among and within species. However, the mechanistic basis of this life history tradeoff is not well understood. In addition to tradeoffs among multiple traits based on resource allocation conflicts, life history tradeoffs may arise from tradeoffs based on single traits under opposing selection. While a myriad of factors likely contribute to the growth-longevity tradeoff in trees, we hypothesized that conflicting functional effects of xylem structural traits contribute to the growth-longevity tradeoff. We tested this hypothesis by examining the extent to which xylem morphological traits (i.e. wood density, tracheid diameters and pit structure) relate to growth rates and longevity in two natural populations of the conifer species ponderosa pine. We examined xylem morphological traits and growth rates at the base of the trunk. As hydraulic constraints arise as trees grow larger, xylem anatomical traits are expected to adjust to compensate for these constraints. We therefore disentangled the effects of size through ontogeny and growth rates on xylem traits by sampling each individual tree at multiple trunk diameters. We found that the oldest trees had slower lifetime growth rates compared to younger trees in the populations we studied, indicating a growth-longevity tradeoff. We further provide the first evidence that a single xylem trait, pit structure, with known conflicting effects on xylem function (hydraulic safety vs. efficiency) contributes to the growth-longevity tradeoff in a conifer species.

Recommended Citation

Roskilly, Beth, "Conflicting Hydraulic Effects of Xylem Pit Structure Relate to the Growth-Longevity Tradeoff in a Conifer Species" (2018). Graduate Student Theses, Dissertations, & Professional Papers. 11252.
https://scholarworks.umt.edu/etd/11252