A stable CH4 sink responding to extreme precipitation events in a fenced semiarid steppe

PURPOSE: Climate models predict that amplification of the hydrological cycle results in more extreme (more intensive but less frequent) precipitation events (EPEs) that have larger effects on ecosystem functioning than mean precipitation conditions. Semiarid grassland ecosystems are considered important CH₄ sinks whose functioning is greatly affected by variations in precipitation patterns. An experiment was performed to assess the effects of extreme precipitation events on the functioning of a fenced semiarid steppe grassland on the Inner Mongolian Plateau of China. MATERIALS AND METHODS: Extreme precipitation events (282 mm over 20 consecutive days) during the middle (Pm) and late (Ps) growing periods of 2014 were simulated to assess the effects of extreme precipitation events on the CH₄ uptake of the ecosystem. RESULTS AND DISCUSSION: The extreme precipitation events had no significant effect on the CH₄ uptake rate during the growing season but did result in 62 and 45% reductions in the CH₄ uptake rate during the Pm and Ps events, respectively. There were legacy effects on suppression of the CH₄ uptake rate for approximately 40 and 35 days after the events in the Pm and Ps plots, respectively, but the suppression disappeared rapidly during the late season as a result of faster water loss. No significant differences in cumulative CH₄ uptake were detected between the treatment and the control plots over the growing season as a whole, which demonstrates that the ecosystem functions as a CH₄ sink. The average CH₄ uptake rates were found to be strongly regulated by changes in the soil water content. CONCLUSIONS: The results suggest that the CH₄ uptake budget of this fenced steppe grassland can be maintained even in the face of consecutive extreme precipitation events, regardless of the timing of the events. Nevertheless, long-term experiments are needed to detect the thresholds for CH₄ uptake budget changes, in case of an increasing occurrence of EPEs in the future.