Date of Graduation

5-2023

Document Type

Thesis

Degree Name

Master of Science in Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Naithani, Kusum J.

Committee Member

Arnold, Mark E.

Second Committee Member

Savin, Mary C.

Keywords

Ecology; Soil science; Tropical soils

Abstract

Land use, such as logging and forest conversion to agriculture, can modify soil physicochemical and biological properties, and affect soil health. To understand how land use change can impact soil properties and canopy structure, we used a land use gradient in Malaysian Borneo consisting of six sites, including old growth forests, mixed forests, and agriculture fields. Specifically, we aimed to answer the following questions: (1) How do soil physicochemical properties vary across land use types? (2) Does bacterial diversity and composition vary across different land use types? (3) Does fungal diversity and composition vary across different land use types? We measured soil (top 5 cm) physicochemical properties (such as texture, temperature, water content, pH, organic matter, C and N content, and elements) and microbial properties (using next-generation amplicon sequencing). We also characterized understory and overstory canopy properties, including percent ground cover, canopy structure, and canopy closure. Our results indicate that old growth forests had the greatest forest cover and canopy closure, accumulated the highest soil organic matter, had a greater soil carbon and nitrogen ratio, were less acidic, and harbored greater bacterial and fungal diversity compared to mixed forests and agricultural fields. Old growth forests had a higher abundance of slow-growing specialist bacterial and fungal phyla, while agriculture fields had a greater abundance of rapidly growing opportunistic, generalist, and disturbance-resistant bacterial and fungal phyla. Our findings suggest that land use not only affects the aboveground surrounding forest cover and canopy closure, which has compounding effects with affected soil physical and chemical properties on soil microbial diversity, but also affects the microbial community composition and phylum function.

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