A string-of-lakes in Ponderosa Pine needles: progressive leaf water and organic matter oxygen isotope enrichment and implications for tree-ring reconstructions
Abstract
Oxygen isotope ratios in tree rings are widely used to reconstruct interannual climate variations, and ecosystem responses to climate variability. Variations in these isotope ratios are thought to arise from changes in isotope ratios of needle photosynthates, driven by changes in water source and needle water enrichment during transpiration. Accurate modeling of needle water isotope ratios remains challenging, however, complicating predictions of oxygen isotope ratios of assimilated sugars and their ultimate incorporation into tissue growth. Observations of needle water along Ponderosa Pine needles reveal that the heavy-to-light oxygen isotope ratios of needle water progressively increases along the length of the needle, contrary to assumptions of constant needle water values. Oxygen isotope ratios of bulk needle organic material also reveals a progressive enrichment along the needle, raising the possibility that leaf-fixed sugars do not have a constant oxygen isotope ratio. To better understand these patterns, we investigate the relationships between oxygen isotope ratios of needle water, needle non-structural carbohydrates (NSCs), phloem-exported sugars, and needle cellulose from trees in Big Cottonwood Canyon, Utah. Needle (1-year old) and phloem samples were collected in February 2019 and subsequently three times during the growing season (June, July, and August). NSC concentrations were determined spectrophotometrically by phenol-acid oxidation for soluble sugars and a peroxidase-glucose oxidase reaction with o-dianisidine. These observations place new constraints on resource pools used to build needle and tree-ring cellulose, and help to connect needle-level processes to the isotope ratios of exported sugars.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B44F..07F
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0466 Modeling;
- BIOGEOSCIENCES;
- 0476 Plant ecology;
- BIOGEOSCIENCES