Greenhouse gas emissions from penguin guanos and ornithogenic soils in coastal Antarctica: Effects of freezing-thawing cycles

摘要

In coastal Antarctica, freezing and thawing influence many physical, chemical and biological processes for ice-free tundra ecosystems, including the production of greenhouse gases (GHGs). In this study, penguin guanos and ornithogenic soil cores were collected from four penguin colonies and one seal colony in coastal Antarctica, and experimentally subjected to three freezing-thawing cycles (FTCs) under ambient air and under N_2. We investigated the effects of FTCs on the emissions of three GHGs including nitrous oxide (N_2O), carbon dioxide (CO_2) and methane (CH_4). The GHG emission rates were extremely low in frozen penguin guanos or ornithogenic soils. However, there was a fast increase in the emission rates of three GHGs following thawing. During FTCs, cumulative N_2O emissions from ornithogenic soils were greatly higher than those from penguin guanos under ambient air or under N_2. The highest N_2O cumulative emission of 138.24 μg N_2O-N kg~(-1) was observed from seal colony soils. Cumulative CO_2 and CH4 emissions from penguin guanos were one to three orders of magnitude higher than those from ornithogenic soils. The highest cumulative CO_2 (433.0 mgCO_2-C kg~(-1)) and CH_4 (2.9 mgCH_4-C kg~(-1)) emissions occurred in emperor penguin guanos. Penguin guano was a stronger emitter for CH_4 and CO_2 while ornithogenic soil was a stronger emitter for N_2O during FTCs. CO_2 and CH_4 fluxes had a correlation with total organic carbon (TOC) and soil/guano moisture (M_c) in penguin guanos and ornithogenic soils. The specific CO_2-C production rate (CO_2-C/TOC) indicated that the bioavailability of TOC was markedly larger in penguin guanos than in ornithogenic soils during FTCs. This study showed that FTC-released organic C and N from sea animal excreta may play a significant role in FTC-related GHG emissions, which may account for a large proportion of annual fluxes from tundra ecosystems in coastal Antarctica.