SOIL HEATING, NITROGEN, CHEATGRASS, AND SEEDBED MICROSITES

Heat-induced changes in the soil-solution and post-wildfire erosion ca n create chemically and texturally diverse seedbed microsites. We quan tified organic carbon, extractable NH4+ after incubation (aerobic and anaerobic), and emergence of cheatgrass (Bromus tectorum L.), by parti cle size fractions, in unburned and simulated burned sagebrush (Artemi sia tridentata spp. tridentata Nutt.) subcanopy soil. For all particle size fractions, significantly (P less-than-or-equal-to 0.05) more ext ractable NH4+ and significantly less extractable NO3- were measured in heated material as compared to unheated material. Heated treatments h ad significantly more NH4+ and significantly less NO3- mineralized aft er 11 days aerobic incubation than after unheated treatments; net N mi neralized tended to be higher for all particle fractions in heated tre atments than in unheated treatments. Emergence of cheatgrass under aer obic conditions was significantly retarded in all heated treatments. E levated NH4+ to NO3- ratios in the soil-solution following heating doe s not explain suppression of cheatgrass emergence. Nitrogen mineraliza tion, before and after simulated burning, is adequate in all particle size fractions to support the needs of germinating seeds. Nitrogen min eralization was not enhanced by the presence of growing cheatgrass pla nts.