Potential methane production rates and its carbon isotopic composition from ornithogenic tundra soils in coastal Antarctic

Methane （CH4） is one of important greenhouse gases with chemical activity. The determination of isotopic compositions for CH4 emitted from the soils helps us to understand its production mechanisms. CH4 isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of CH4 have been reported from Antarctic tundra soils. In this paper, ornithogenic soil profiles were collected from four penguin colonies, and potential CH4 production rates and its 13C ratio （δ13C） were investigated based upon laboratory incubation experiments. The mean CH4 production rates are highly variable in these soil profiles, ranging from 0.7 to 20.3μg CH4-C kg-1·h-1. These omithogenic soils had high potential production rates of CH4 under ambient air incubation or under N2 incubation, indicating the importance of potential CH4 emissions from penguin colonies. Most of the soil samples had higher δ13C-CH4 under N2 incubation （-39.28%-43.53%） than under the ambient air incubation （-42.81%-57.19%）. Highly anaerobic conditions were conducive to the production of CI-h enriched in 13C, and acetic acid reduction under N2 incubation might be a predominant source for soil CH4 production. Overall the δ13C-CH4 showed a significant negative correlation with CH4 production rates in ornithogenic tundra soils under N2 incubation （R2=0.41,p〈0.01） or under the ambient air incubation （RE=0.50,p〈0.01）. Potential CH4 production from ornithogenic soils showed a significant positive correlation with total phosphorus （TP） and NH4＋-N contents, pH and soil moisture （Mc）, but the δ13C-CH4 showed a significant negative correlation with TP and NH4＋ -N contents, pH and Me, indicating that the deposition amount of penguin guano increased potential CH4 production rates from tundra soils, but decreased the δ13C-CH4. The CH4 emissions from the ornithogenic soils affect carbon isotopic compositions of atmospheric CH4 in coastal Antarctica.

Distribution patterns of typical enzyme activities in tundra soils on the Fildes Peninsula of maritime Antarctica

Soil enzyme activities can be used as indicators of microbial activity and soil fertility. In this paper, the activities of invertase （IA）, phosphatase （PA） and urease （UA） were investigated in tundra soils collected from marine animal colonies, areas of human activity and background areas on Fildes Peninsula, maritime Antarctica. Soil enzyme activities were in the range of 1.0- 82.7 mg·kg^-1.h^-1 for IA, 0.2-8.2 mg·kg^-1.h^-1 for PA and 0.2-39.8 mg·kg^-1.h^-1 for UA. The spatial distribution patterns for soil enzyme activities corresponded strongly with marine animal activity and human activity. Significantly higher soil IA and PA activities occurred in penguin colony soils, whereas seal colony soils showed higher UA activity. Statistical analysis indicated that soil IA activity was controlled by the levels of soil nutrients （TOC, TN and TP）, PA activity was closely related with TP, and UA activity was affected by the soil pH. Overall, the deposition amount of penguin guano or seal excreta could impact the distribution of enzyme activity in Antarctic tundra soils. Multiple stepwise regression models were established between the enzyme activities, soil physicochemical properties and heavy metals Cu and Zn （[IA]=0.7[TP]--0.2[Cu]＋22.3[TN]＋15.1, [PA]=0.3[TP]＋0.03[Mc]＋0.2, [UA]=16.7[pH]-0.5[Cu]＋ 0.4[Zn]-72.6）. These models could be used to predict enzyme activities in the tundra soils, which could be helpful to study the effects of marine animal activity and environmental change on tundra ecosystems in maritime Antarctica.