Watering increased DOC concentration but decreased N2O emission from a mixed grassland soil under different defoliation regimes

Abstract

Changes in grazing regime and climatic conditions (such as precipitation) may affect soil N2O emissions; however, such effects have been inconsistent in grasslands. This study investigated the impact of simulated grazing, increased precipitation and N addition on soil N2O emissions, as well as soil dissolved organic carbon (DOC) concentrations, from a mixed grassland site in southern Alberta, Canada. A batch incubation study was conducted on soils (0–10 cm) collected from long-term field plots exposed to defoliation at either high intensity at low frequency (HILF) or high intensity at high frequency (HIHF) or low intensity at high frequency (LIHF) throughout the growing season (May–August). A deferred control (DC) treatment was also included where defoliation only occurred once at year end. All defoliation treatments formed a full factorial experiment with the watering treatment (ambient moisture (AM) or watering (W)) in the field. Soil N2O production was also quantified under an N addition treatment (no N and addition of 20 mg N kg−1 (NH4)2SO4) in the laboratory incubation experiment. Defoliation had no influence (p > 0.05) on soil DOC concentrations and cumulative N2O emissions. Watering increased DOC concentrations by 72–234 % but decreased N2O emissions by 33–60 %. Increments in N2O emissions after N addition were greater in the W (111–163 %) than the AM (64–67 %) treatment. Our results suggest that while defoliation regimes did not affect soil N2O emissions, watering may induce greater N2O loss in the more arid soil and N addition may further increase N2O loss under high precipitation within soils of the dry mixed grassland ecosystem.