Nitrogen Cycling and Microbial Communities of Alpine Soils in the Pacific Northwest

Download or read book Nitrogen Cycling and Microbial Communities of Alpine Soils in the Pacific Northwest written by Anna Simpson and published by . This book was released on 2018 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: The alpine Pacific Northwest is an environment of stunning beauty and environmental extremes, with acidic, low-nutrient soils, snow cover often exceeding 4-5 m, and snow periods occasionally exceeding 9 months out of the year. Nitrogen (N) deposition from increasing urbanization and intensive agriculture can cause changes in alpine soil chemistry and plant species abundance and increase leaching of inorganic N into streams and lakes. In the state of Washington has already exceeded critical N loads for shifts in alpine lichen communities (Geiser et al., 2010) and alpine lake microbiota (Sheibley et al., 2014). The effects of climate change, which could include earlier snowmelt, increased fall rains, and even the complete disappearance of permanent snowfields and glaciers, threaten to exacerbate effects of N deposition even further by causing changes in plant phenology and increasing decomposition of soil organic matter. In this study I used fertilizer treatment of 0, 3, 5 and 10 kg NH4NO3-N ha−1 yr−1 to simulate increased N deposition at three alpine meadows of the Pacific Northwest at Mount Rainier, North Cascades and Olympic National Parks. Using the indicator of increased soil NO3-N availability to alpine plants and microbes, I define the empirical critical load upper limit for Pacific Northwest alpine meadows to be 6 kg N ha−1 yr−1. I found that increased fall microbial N uptake in these meadows appears to serve as a buffer for inorganic N loss with fall rains. No increases in plant species were observed during the course of the study. In soils with available soil inorganic N from slow depolymerization and mineralization, N pollution accumulated in plots with higher N and greater abundance of forbs and graminoid species. In very N-limited soils, N deposition was evenly dispersed among plant communities. I also sampled the soil microbial communities of barren, permanent snowfield soils at Mount Rainier and North Cascades National Parks. I used 16SrRNA metagenomic amplicon sequencing to examine the differences between the microbial communities in samples taken in dry soil that had only been covered by seasonal snow, and soil underneath permanent snowpack. Photoautotrophic bacteria were not present in samples taken under snowpack and comprised less than 1% of reads in samples taken from exposed soils. Soils were dominated by Deltaproteobacteria from the genus Anaeromyxobacter, which were particularly abundant under snowpack, and a number of bacteria from the phylum Gemmatimonadetes. Overall, permanent snowfield soils of the Pacific Northwest contain diverse heterotrophic and chemoautolithotrophic communities of bacteria but have very low overall biomass, comparable to barren soils sampled in the Himalayas. Soil bacterial communities probably depend at least partially on organic matter from atmospheric deposition and carbon fixation from seasonal snow algae for survival in this harsh environment.