Reactive Nitrogen Hotspots Related to Microscale Heterogeneity in Biological Soil Crusts

Alexandra Maria Kratz*, Stefanie Maier, Jens Weber, Minsu Kim, Giacomo Mele, Laura Gargiulo, Anna Lena Leifke, Maria Prass, Raeid M.M. Abed, Yafang Cheng, Hang Su, Ulrich Pöschl, Bettina Weber

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Biocrusts covering drylands account for major fractions of terrestrial biological nitrogen fixation and release large amounts of gaseous reactive nitrogen (Nr) as nitrous acid (HONO) and nitric oxide (NO). Recent investigations suggested that aerobic and anaerobic microbial nitrogen transformations occur simultaneously upon desiccation of biocrusts, but the spatio-temporal distribution of seemingly contradictory processes remained unclear. Here, we explore small-scale gradients in chemical concentrations related to structural characteristics and organism distribution. X-ray microtomography and fluorescence microscopy revealed mixed pore size structures, where photoautotrophs and cyanobacterial polysaccharides clustered irregularly in the uppermost millimeter. Microsensor measurements showed strong gradients of pH, oxygen, and nitrite, nitrate, and ammonium ion concentrations at micrometer scales in both vertical and lateral directions. Initial oxygen saturation was mostly low ( 30%) at full water holding capacity, suggesting widely anoxic conditions, and increased rapidly upon desiccation. Nitrite concentrations ( 6 to 800 μM) and pH values ( 6.5 to 9.5) were highest around 70% WHC. During further desiccation they decreased, while emissions of HONO and NO increased, reaching maximum values around 20% WHC. Our results illustrate simultaneous, spatially separated aerobic and anaerobic nitrogen transformations, which are critical for Nr emissions, but might be impacted by future global change and land management.

Original languageEnglish
JournalEnvironmental Science and Technology
DOIs
Publication statusAccepted/In press - 2022
Externally publishedYes

Keywords

  • biological soil crusts
  • fluorescence microscopy
  • microsensors
  • nitric oxide (NO)
  • nitrous acid (HONO)
  • reactive nitrogen
  • X-ray microtomography

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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