Spatial Biogeography of Microbes in Soils vs. Aquatic Ecosystems in U.S.'s Major Natural Biomes

Leo Oo SaiXinhao Zhu^*David A LipsonXiaofeng Xu^*

• San Diego State University, San Diego, United States

Abstract 15 Microbial macroecology has gained recognition as a critical component of microbial ecology. 16 The spatial patterns of microbial abundance and their environmental controls in soil and aquatic 17 ecosystems across major natural biomes in the United States were examined by using data from 18 the National Ecological Observatory Network (NEON). In aquatic ecosystems, microbial cell 19 density ranged from 1.8 ´ 10! to 4.1 ´ 10" cells mL-1 and was positively associated with 20 specific conductance and water temperature, whereas it was negatively associated with dissolved 21 oxygen. Across all aquatic sites, the cell density averaged approximately 1.4 ´ 10" cells mL-1 . In 22 terrestrial ecosystems, soil microbial biomass carbon ranged from 2.5 to 27 ´ 10# µg C g⁻¹ of 23 dry soil and was positively correlated with soil moisture, soil carbon content, and soil nitrogen 24 content; it was also negatively associated with soil temperature and soil pH. Across all locations, 25 the microbial biomass carbon averaged approximately 2.9 ´ 10$ µg C g⁻¹. The dominance of 26 bacteria was found across both aquatic and terrestrial environments, with considerable variation 27 ranging from 28% to 88%, while Eukarya showed variation ranging from 0% to 48%. Archaea 28 made a minor contribution to the microbial community across all sites. The unclassified 29 microbes vary across the US, ranging from less than 0% at the Lower Tombigbee River in 30 southwest Alabama to 57% at Sycamore Creek in Arizona. In aquatic systems, cell density 31 increased with specific conductance and water temperature but decreased where dissolved 32 oxygen was high. These biogeographic patterns have shown that divergent environmental factors 33 drive microbial abundance across ecosystems, reflecting high microbial adaptation to 34 surrounding physical and chemical conditions.