Species-specific effects on the oxygen isotope ratio of tree-ring cellulose / Xin Song.

Format:

Book

Manuscript

Thesis/Dissertation

Author/Creator:

Song, Xin.

Contributor:

Helliker, Brent, advisor.

Casper, Brenda, committee member.

Petraitis, Peter, committee member.

Plante, Alain, committee member.

Springer, Clint, committee member.

University of Pennsylvania. Biology.

Language:

English

Subjects (All):

Penn dissertations--Biology.

Biology--Penn dissertations.

Local Subjects:

Penn dissertations--Biology.

Biology--Penn dissertations.

Physical Description:

xiv, 162 pages : illustrations ; 29 cm

Production:

2013.

Summary:

The mechanistic model of tree-ring cellulose oxygen isotope ratios (delta 18Ocell) provides a promising tool for paleo-environmental and eco-physiological studies. While the current model captures major fractionation effects leading to delta18Ocell, the full potential of the model is yet to be realized due to the existence of some weakness of the model. My dissertation was designed to address several weaknesses.

In an analysis of large-scale photosynthesis-weighted canopy temperatures (Tcandelta) pattern based on multiple datasets of tree-wood cellulose isotope ratios (delta18Owc), I confirmed the previous finding of a boreal-to-subtropical convergence of Tcandelta to around 20 °C; meanwhile, I show that the Tcandelta convergence pattern cannot be extended to the tropical regions, where Tcandelta averaged at around 26 °C, and was thus higher than the boreal-to-subtropical mean. These results caution against the common practice of taking Tcandelta to be the same as growing season air temperature in parameterizing the tree-ring model, in particular for boreal trees.

Measurements of leaf water isotope enrichment (Delta18O L) were made on multiple tree species growing either in a common garden or field environment. Using the data collected, I explored the nature of effective pathlength (L) of the Peclet effect, --- a key component of the tree-ring isotope model. I revealed the common presence of an inverse relationship between L and transpiration rate (E), both at the within- and across-species levels. Such a L-E covariance pattern must be incorporated into the tree-ring model for improving its predictive power. The current tree-ring model does not explicitly capture the species effect. To build this knowledge gap, I conducted a field study to investigate the mechanisms behind the variability in late-wood delta18Ocell (delta18O lc) among three co-occurring tree species in a temperate forest. The results highlighted source water delta18O (delta 18Osw) as a key factor in explaining delta18O lc difference between black and chestnut oak. Through model-measurement comparison, I further show that the Peclet effect is only relevant to delta18Ocell of the oaks but not to pitch pine. Such a Peclet effect related difference needs to be invoked to explain the observed more enriched delta18Olc signals in pitch pine relative to the oaks. signals in pitch pine relative to the oaks.

Notes:

Adviser: Brent Helliker.

Thesis (Ph.D. in Biology) -- University of Pennsylvania, 2013.

Includes bibliographical references.