Molecular transformation of organic nitrogen in Antarctic penguin guano-affected soil.

Organic nitrogen (ON) is an important participant in the Earth's N cycle. Previous studies have shown that penguin feces add an abundance of nutrients including N to the soil, significantly changing the eco-environment in ice-free areas in Antarctica. To explore the molecular transformation of ON in penguin guano-affected soil, we collected guano-free weathered soil, modern guano-affected soil from penguin colonies, ancient guano-affected soil from abandoned penguin colonies, and penguin feces from the Ross Sea region, Antarctica, and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) was used to investigate the chemical composition of water-extractable ON. By comparing the molecular compositions of ON among different samples, we found that the number of ON compounds (>4,000) in weathered soil is minimal, while carboxylic-rich alicyclic-like molecules (CRAM-like) are dominant. Penguin feces adds ON into the soil with > 10,000 CHON, CHONS and CHN compounds, including CRAM-like, lipid-like, aliphatic/ peptide-like molecules and amines in the guano-affected soil. After the input of penguin feces, macromolecules continue to degrade, and other ON compounds tend to be oxidized into relatively stable CRAM-like molecules, this is an important transformation process of ON in guano-affected soils. We conclude the roles of various forms of ON in the N cycle are complex and diverse. Combined with previous studies, ON eventually turns into inorganic N and is lost from the soil. The lost N ultimately returns to the ocean and the food web, thus completing the N cycle. Our study preliminarily reveals the molecular transformation of ON in penguin guano-affected soil and is important for understanding the N cycle in Antarctica.

Fraction distribution and dynamic cycling of phosphorus in lacustrine sediment at Inexpressible Island, Antarctica.

Phosphorus (P) chemistry and its dynamic cycling are essential for understanding aquatic primary productivity and ecosystem structure. However, there is a lack of knowledge on P chemistry in pristine aquatic ecosystems, such as in Antarctica. Here, we applied the Standards, Measurements and Testing Program (SMT) procedure and nuclear magnetic resonance spectroscopy (NMR) to reveal P speciation in two types of lacustrine sediment cores collected from Inexpressible Island, Ross Sea, East Antarctica. The Positive Matrix Factorization Model and Generalized Additive Models were applied to quantitatively identify the P sources and estimate relative effects of various environmental factors on the speciation. Our results demonstrate that orthophosphate, mainly as Ca-P, is the major component and the ortho-monoesters are the predominant organic phosphorus (OP) form in lacustrine sediments. Ornithogenic lacustrine sediments have a higher content of P as Ca-P than sediments with little or no penguin influence. Our model further suggests that penguin guano is the most important source for Ca-P, accounting for 80%, while detrital input is the predominant source for Fe/Al-P (up to 90%). The content of ortho-monoesters, as revealed by NMR, declines with depth, reflecting mineralization process of OP in the sediments. Moreover, we observed higher relative proportions of organic P in the sediments with little guano influence and the deposition of organic P are likely facilitated by microbial mats. Overall, our data suggest that burial of P in Antarctic lakes is sensitive to different P sources and sedimentary environments. The relatively higher bioavailable phosphorus in lacustrine sediments largely controls growth of aquatic microbial mats in oligotrophic lakes and ponds in Antarctica. The sediment profile data also indicate that P burial increased during the Medieval Climate Anomaly period, and climate warming is more conducive to P burial through the expansion of penguin populations and productivity of microbial mats. Our findings represent the first systematic understanding of natural P cycling dynamics and its main controlling factors in pristine ponds with different organic sources in Antarctica.

Selenium volatilization from tundra soils in maritime Antarctica.

Maritime Antarctica harbors a large number of penguins and seals that provide considerable input of selenium (Se) originating as guano into terrestrial ecosystems. Subsequent Se emissions via biomethylation and volatilization from these sources of Se have not been studied. Here, penguin colony soils (PCS) and adjacent tundra marsh soils (TMS), seal colony soils (SCS) and adjacent tundra soils (STS), and normal upland tundra soils (NTS) were collected in maritime Antarctica. For the first time, Se volatilization and speciation were investigated in these soils through incubation experiments using chemo-trapping method. The Se contents in PCS, SCS, STS and TMS were highly enriched compared with NTS, with organic matter-bound Se accounting for 70%-80%. Laboratory incubations yielded the greatest Se volatilization rates (VRSe) in PCS (0.20 ± 0.01 µg kg-1 d-1), followed by SCS (0.14 ± 0.01 µg kg-1 d-1) at low temperature (4 °C). Soil frozen-thawing induced 1-4 fold increase in VRSe, and the VRSe continuously increased until the soils fully thawed. The VRSe showed a significant positive correlation (R2 = 0.96, p < 0.01) with soil temperature. Methylated Se species were dominated by dimethylselenide (DMSe) in PCS and dimethyldiselenide (DMDSe) in SCS. Our results imply that the combination of climate warming, frozen-thawing processes, and high-Se inputs from sea animals will significantly increase tundra soil Se volatilization in maritime Antarctica. High VRSe from penguin colony soils, and significantly elevated Se levels in the mosses close to penguin colony, suggest that volatilization of Se from penguin colony soils play an important role in the mobilization and regional biogeochemical cycling of Se in maritime Antarctica.