Aims

            To assess impacts of exotic grass invasion on nutrient losses from California coastal sage scrub (CSS), we quantified interactive effects of season, exotic grass litter, and plant cover type on wetting-induced emissions of carbon and nitrogen trace gases from CSS soils.

Methods

            We added grass litter to plots dominated by native Erioginum fasciculatum or exotic Schismus barbatus in invaded California CSS. In both dry and wet seasons, we conducted 48-hour wetting experiments and measured soil emissions of CO₂, N₂O, and NO_x.

Results

            CO₂ and N₂O pulses appeared 15 minutes post-wetting, diminishing within twelve hours. NO_x peaked between 6 to 12 hours, remaining elevated at 48 hours. Dry-season pulses were seven times higher than wet-season pulses. Grass litter amendments increased CO₂ and dry-season N₂O pulses without significantly altering NO_x pulses. Grass cover reduced CO₂ pulses compared to shrub cover.

Conclusions    

            Our results suggest that CSS soils produce stronger trace gas pulses of CO₂, N₂O, and NO_x during the dry season when wetting is less frequent. Although grass cover potentially constrains soil CO₂ respiration, grass litter loading during the dry season may provide carbon-rich substrates that stimulate additional microbial production of CO₂ and N₂O but not NO_x.