Document Type

Thesis - Open Access

Award Date

2020

Degree Name

Master of Science (MS)

Department

Natural Resource Management

First Advisor

A. Joshua Leffler

Keywords

Arctic ecosystems, Nutrient cycling, PLFA, Soil Microbial ecology

Abstract

Arctic microbial systems continue to get attention today as our understanding regarding their structure and function in a changing system is paramount to C feedbacks with warming and changes in precipitation. Plant communities and microbial community processes across the Arctic landscape are central to understanding tundra ecosystem processes because environmental conditions and plant community structure drive microbial cycling of soil organic matter. Here, we want to understand how soil microbial respiration, mineralization, biomass, and community composition are linked to three Alaskan tundra plant communities, namely Shrub, Tussock, and Sedge tundra and the seasonal variability in this system. A total of 64 points were visited between 2018 and 2019 within a spatial extent of ca. 44,800 km2. Soils were collected in March, June, July and September, homogenized, and incubated at realistic field temperatures to quantify soil microbial respiration (SMR) and potential N mineralization. Microbial C and N biomass were assessed through fumigation/extraction. PLFA extraction was used to assess microbial community structure (nmol/g) from Gram+ and Gram- bacteria, Actinomycetes and Fungi, among others. We found significant variation in both soil microbial structure and function across time and among plant communities. In March SMR rates were low but distinct in all plant communities, and N mineralization rates were the highest. In July SMR peaked for all plant communities, and for all but Tussock soil N immobilization rates peaked. Although soil microbial activity was high, overall microbial biomass as MBC, MBN and PLFA was at the lowest point in July. These results show the strong influence of seasonality where microbes are mineralizing inorganic N during winter and immobilizing inorganic N during the growing season. However, differences in soil microbial community structure among the three plant communities only accounted for about 10% of total variation which suggests that plant community drives a change in microbial function, but not a change in community-level microbial structure. Rather, similar microbial communities display different functions in terms of C and N cycling.

Library of Congress Subject Headings

Soil microbial ecology -- Arctic regions.
Soil microbial ecology -- Alaska -- North Slope.
Plant communities -- Arctic regions.
Plant communities -- Alaska -- North Slope.
Nutrient cycles.

Format

application/pdf

Number of Pages

67

Publisher

South Dakota State University

Rights

In Copyright - Educational Use Permitted
http://rightsstatements.org/vocab/InC-EDU/1.0/

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