Soil heating, nitrogen, cheatgrass, and seedbed microsites

Abstract

Heat-induced changes in the soil-solution and post-wildfire erosion can create chemically and texturally diverse seedbed microsites. We quantified organic carbon, extractable NH4+ after incubation (aerobic and anaerobic), and emergence of cheatgrass (Bromus tectorum L.), by particle size fractions, in unburned and simulated burned sagebrush (Artemisia tridentata spp. tridentata Nutt.) subcanopy soil. For all particle size fractions, significantly (P less than or equal to 0.05) more extractable NH4+ and significantly less extractable NO3- were measured in heated material as compared to unheated material. Heated treatments had significantly more NH4+ and significantly less NO3- mineralized after 11 days aerobic incubation than after unheated treatments; net N mineralized tended to be higher for all particle fractions in heated treatments than in unheated treatments. Emergence of cheatgrass under aerobic conditions was significantly retarded in all heated treatments. Elevated NH4+ to NO3- ratios in the soil-solution following heating does not explain suppression of cheatgrass emergence. Nitrogen mineralization, before and after simulated burning, is adequate in all particle size fractions to support the needs of germinating seeds. Nitrogen mineralization was not enhanced by the presence of growing cheatgrass plants.