Potential methane and nitrous oxide production and respiration rates from penguin and seal colony tundra soils during freezing-thawing cycles under different water contents in coastal Antarctica

摘要

In coastal Antarctica, frequent freezing–thawing cycles(FTCs) and changes to the hydrological conditions may affect methane(CH_4) and nitrous oxide(N_2O) production and respiration rates in tundra soils, which are difficult to observe in situ. Tundra soils including ornithogenic tundra soil(OAS), seal colony soil(SCS) and emperor penguin colony soil(EPS) were collected. In laboratory, we investigated the effects of FTCs and water addition on potential N_2O and CH_4 production and respiration rates in the soils. The CH_4 fluxes from OAS and SCS were much less than that from EPS. Meanwhile, the N_2O fluxes from OAS and EPS were much less than that from SCS. The N_2O production rates from all soils were extremely low during freezing, but rapidly increased following thawing. In all cases, FTC also induced considerably enhanced soil respiration, indicating that soil respiration response was sensitive to the FTCs. The highest cumulative rates of CH_4, N_2O and CO_2 were 59.5 mg CH_4-C·kg^(-1) in EPS, 6268.8 μg N_2O-N·kg^(-1) in SCS and 3522.1 mg CO_2-C·kg^(-1) in OAS. Soil water addition had no significant effects on CH_4 production and respiration rates, but it could reduce N_2O production in OAS and EPS, and it stimulated N_2O production in SCS. Overall, CH_4 and N_2O production rates showed a trade-off relationship during the three FTCs. Our results indicated that FTCs greatly stimulated soil N_2O and CO_2 production, and water increase has an important effect on soil N_2O production in coastal Antarctic tundra.