Date of Award

Summer 2014

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Earth, Atmospheric, and Planetary Sciences

First Advisor

Timothy R. Filley

Committee Chair

Timothy R. Filley

Committee Member 1

Timothy R. Filley

Committee Member 2

Miquel Gonzalez-Meler

Committee Member 3

Greg Michalski

Abstract

Tundra ecosystem soils store half of the global soil organic carbon (SOC) pool and have the potential to release large amounts of greenhouse gases, primarily CH4 and CO2. As climates warm and permafrost thaws, the emissions of these gases as organic matter decomposition rates increase may become increasingly important to the chemistry of the atmosphere. Increases in precipitation that accompany warming, may shift tundra vegetative composition from moss/graminoid- to shrub-dominated systems. These vegetation shifts may result in important feedback effects as altered plant and litter chemistry may affect SOC storage in soils. Questions investigated include: 1) How does snow depth thickness influence plant distribution and the carbon (C) and nitrogen (N) primary and secondary chemistry of the dominant plant species, litter, and soil; 2) How do the changes in plant chemistry and relative interspecies input impact litter quality; and 3) Which plant products are preferentially stored versus easily degraded in litter and surface soils, and what will it ultimately suggest about carbon storage? Plant chemistries were measured in graminoids, moss, shrub leaves, and shrub stems in areas with ambient snow depth, and long-term deeper, intermediate and low snow depths which have been altered since 1994. C:N ratios, carbohydrate content, and lignin and phenol content were also used to track and relate changes in litter and soil chemistry. Results include that long-term increases in snow (Deep ~ 3 m) resulted in a ~50% increase in graminoid and shrub leaf N that was accompanied by a ~30% decrease in soil carbon in the litter (0-2 cm) and in the organic horizon (4-6 cm) layers. This response was, however, not linear as few statistically significant changes in primary and secondary chemistry in plants or soils were observed at intermediate snow depths (~1.5 m) or at reduced snow depths. Deeper snow and the corresponding vegetative shifts in Arctic ecosystems appear to increase soil N availability to plants with corresponding decreases soil carbon storage. Proposed mechanisms controlling these changes under deeper snow are increased N input from windblown litter and ammonium and nitrate in snow, higher mineralization rates, and winter thermal insulation enhancing microbial activity and elevating CO2 emissions and C losses.

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