| Autor: |
Kratz AM; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany., Maier S; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.; Institute of Biology, Division of Plant Sciences, University of Graz, Graz 8010, Austria., Weber J; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.; Institute of Biology, Division of Plant Sciences, University of Graz, Graz 8010, Austria., Kim M; Institute of Biology, Division of Plant Sciences, University of Graz, Graz 8010, Austria., Mele G; Institute for Agriculture and Forestry in the Mediterranean, National Council of Research, 80055 Portici, Italy., Gargiulo L; Institute for Agriculture and Forestry in the Mediterranean, National Council of Research, 80055 Portici, Italy., Leifke AL; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany., Prass M; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany., Abed RMM; College of Science, Biology Department, Sultan Qaboos University, P.O. Box 36, Al Khoud, Seeb 123, Sultanate of Oman., Cheng Y; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany., Su H; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany., Pöschl U; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany., Weber B; Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.; Institute of Biology, Division of Plant Sciences, University of Graz, Graz 8010, Austria. |
| Abstrakt: |
Biocrusts covering drylands account for major fractions of terrestrial biological nitrogen fixation and release large amounts of gaseous reactive nitrogen (N r ) 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 N r emissions, but might be impacted by future global change and land management. |
