Biology ETDs

Publication Date

Summer 7-13-2018

Abstract

Semi-arid ecosystems play a major role in the global carbon cycle. These ecosystems, including piñon-juniper (PJ) woodlands, are experiencing extreme drought. As such, it is vital to characterize both above and below-ground processes in these systems in order to understand their vulnerability to future drought and other changes in climate.

Soils microbial communities play a critical role in nutrient cycles, as well as carbon storage, within PJ woodlands. More specifically, microbes aid the decomposition and mineralization of key nutrients, including carbon, nitrogen and phosphorus, through the use of extracellular enzymes. Measuring microbial enzyme activity, therefore, can provide insight into how nutrients transform within an ecosystem. I measured enzyme activity in both soils and roots collected at different depths in order to investigate patterns of enzyme activity with depth, as well as to determine if there are differences between piñon and juniper root enzyme activities. I also measured various soil and root chemical properties to determine which factors, if any, dictate these patterns. Specifically, we measured b-1,4-glucosidase (BG), which helps release carbon from cellulose, b-1,4-N-acetylglucosaminidase (NAG), which helps release nitrogen from chitin and bacterial cell walls, and acid phosphatase (AP), which helps release phosphorus from nucleic acids and cell membranes.

I tested three hypotheses: 1) soil microbial enzyme activity should increase with canopy because of greater organic matter and rhizosphere inputs; 2) the petro-calcic horizon will dictate patterns in enzyme activity, since the horizon represents a physical barrier between the surface and subsurface layers that directly influences nutrient cycling and nutrient concentrations; 3) and because microbial enzyme activity reflects the interaction between microbial nutrient demand and nutrient availability, enzyme activity should reflect changes in nutrient limitation throughout the soil profile.

Our results indicated that patterns in soil microbial BG, AP and NAG activities were dictated by changes in both percent soil organic carbon and percent total nitrogen with depth. Also, AP activity was higher compared to both BG and NAG, indicating that PJ woodlands, like other semi-arid biomes, are more phosphorus limited. Unfortunately, inferences about the differences between piñon and juniper root enzyme activities could not be determined. Measuring microbial enzyme activity throughout the whole profile is important as it can provide insights into both microbial processes and nutrient cycling within these rapidly changing ecosystems.

Keywords

semi-arid, extracellular enzyme activity, petrocalcic

Document Type

Thesis

Degree Name

Biology

Level of Degree

Masters

Department Name

UNM Biology Department

First Committee Member (Chair)

Marcy Litvak

Second Committee Member

Robert Sinsabaugh

Third Committee Member

William Pockman

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