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California State University San Marcos (2020)

Experimental Chronic Dry Atmospheric Nitrogen (N) Deposition Causes a Change in Soil Microbial Communities in Southern California Semi-Arid Shrublands

Grant, Timothy

Titre : Experimental Chronic Dry Atmospheric Nitrogen (N) Deposition Causes a Change in Soil Microbial Communities in Southern California Semi-Arid Shrublands

Auteur : Grant, Timothy

Université de soutenance  : California State University San Marcos

Grade : Master of Science (MS) 2020

Résumé
Global nitrogen (N) deposition has increased since the beginning of the Industrial Revolution due to anthropogenic influences such as the burning of fossil fuels and application of N fertilizer. Increased industrialization is expected to continue to escalate the quantity of N released to ecosystems and the atmosphere. Soil microbial communities are susceptible to this increase in N, as microbial activity can be limited by N and these communities are known to regulate biogeochemical cycles. In this study, the response of bacterial functional groups (FG) to N addition (> 50 Kg N ha-1 yr-1) was quantified in Southern California semi-arid topsoil (0-10 cm). Soil physical-chemical properties and enzymatic activities were also quantified to further understand the direct/indirect effects of N addition on bacterial FG. Experimental N addition significantly increased the abundance N-fixing, chitinolytic, and starch degrading bacteria in semi-arid soils ; while increasing N-mineralizing and denitrifying bacteria in coastal sage shrub (CSS) soil. N input also decreased the abundance metal redox bacteria in CCS soil and decreased nitrifying bacteria in chaparral soil. Furthermore, N addition increased the abundance of copiotrophic bacteria (ie : Proteobacteria, Bacteroidetes, and Firicutes) and decreased the abundance of oligotrophic bacteria (ie : Acidobacteria) in semi-arid soils. Canonical correspondence analysis revealed that the majority of FG were influenced by soil pH and extractable nitrate, which were also significantly altered by N addition. Results indicated excessive N input directly and indirectly affected the composition of the soil bacterial community. Understanding the response of the microbial community to N additions is important in predicting ecosystem functionality and stability as anthropogenic N deposition increase

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