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1. Small but mighty: Impacts of rodent‐herbivore structures on carbon and nutrient cycling in arctic tundra

   https://doi.org/10.1111/1365-2435.14127  

   Roy, Austin ; Gough, Laura ; Boelman, Natalie T. ; Rowe, Rebecca J. ; Griffin, Kevin L. ; McLaren, Jennie R. ( July 2022 , Functional Ecology)

   Understanding arctic ecosystem function is key to understanding future global carbon (C) and nutrient cycling processes. However, small mammal herbivores can have effects on ecosystems as structure builders and these effects have been underrepresented in the understanding of arctic systems.

   We examined the impact of small mammal structures (hay piles, runways, latrines) on soils and plants in three arctic tundra regions near Utqiaġvik, Toolik Lake, and Nome, Alaska. Our aims were to (1) examine how vole and lemming structures influence plant and soil nutrient pools and microbial processes, (2) determine if structure effects were similar across tundra system types, and (3) understand how changes in the abundance and cover of these structures during different phases of small mammal multi‐annual population cycles might influence biogeochemical cycling.

   In general, small mammal structures increased nitrogen (N) availability in soils, although effects varied by study region. Across study regions, hay piles were relatively uncommon (lowest % cover) but increased multiple soil N and P pools, C‐ and N‐acquiring enzyme activities, and leaf phosphorus (P) concentrations, with the specific nutrient variables and size of the effects varying by study region. Latrines had the second highest cover and influenced multiple C, N and P pools, but theirmore »effects were mainly observed within a single region. Lastly, runways had the highest % cover of all activity types but increased the fewest number of soil nutrient variables.

   We conclude that by influencing soil nutrient availability and biogeochemical cycling, small mammal structures can influence bottom‐up regulation of ecosystem function, particularly during the high phase of the small mammal population cycle. Future changes in these population cycles might alter the role of small mammals in the Arctic and have lasting effects on system processes.

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2. “Candidatus Chlorobium masyuteum,” a Novel Photoferrotrophic Green Sulfur Bacterium Enriched From a Ferruginous Meromictic Lake

   https://doi.org/10.3389/fmicb.2021.695260  

   Lambrecht, Nicholas ; Stevenson, Zackry ; Sheik, Cody S. ; Pronschinske, Matthew A. ; Tong, Hui ; Swanner, Elizabeth D. ( July 2021 , Frontiers in Microbiology)

   Anoxygenic phototrophic bacteria can be important primary producers in some meromictic lakes. Green sulfur bacteria (GSB) have been detected in ferruginous lakes, with some evidence that they are photosynthesizing using Fe(II) as an electron donor (i.e., photoferrotrophy). However, some photoferrotrophic GSB can also utilize reduced sulfur compounds, complicating the interpretation of Fe-dependent photosynthetic primary productivity. An enrichment (BLA1) from meromictic ferruginous Brownie Lake, Minnesota, United States, contains an Fe(II)-oxidizing GSB and a metabolically flexible putative Fe(III)-reducing anaerobe. “ Candidatus Chlorobium masyuteum” grows photoautotrophically with Fe(II) and possesses the putative Fe(II) oxidase-encoding cyc2 gene also known from oxygen-dependent Fe(II)-oxidizing bacteria. It lacks genes for oxidation of reduced sulfur compounds. Its genome encodes for hydrogenases and a reverse TCA cycle that may allow it to utilize H 2 and acetate as electron donors, an inference supported by the abundance of this organism when the enrichment was supplied by these substrates and light. The anaerobe “ Candidatus Pseudopelobacter ferreus” is in low abundance (∼1%) in BLA1 and is a putative Fe(III)-reducing bacterium from the Geobacterales ord. nov. While “ Ca. C. masyuteum” is closely related to the photoferrotrophs C. ferroooxidans strain KoFox and C. phaeoferrooxidans strain KB01, it is unique at the genomicmore »level. The main light-harvesting molecule was identified as bacteriochlorophyll c with accessory carotenoids of the chlorobactene series. BLA1 optimally oxidizes Fe(II) at a pH of 6.8, and the rate of Fe(II) oxidation was 0.63 ± 0.069 mmol day –1 , comparable to other photoferrotrophic GSB cultures or enrichments. Investigation of BLA1 expands the genetic basis for phototrophic Fe(II) oxidation by GSB and highlights the role these organisms may play in Fe(II) oxidation and carbon cycling in ferruginous lakes.« less
3. Sediments in Agricultural Reservoirs Act as Sinks and Sources for Nutrients over Various Timescales

   https://doi.org/10.1029/2018WR024004  

   Shaughnessy, A. R. ; Sloan, J. J. ; Corcoran, M. J. ; Hasenmueller, E. A. ( July 2019 , Water Resources Research)

   Reservoirs along rivers have the potential to act as nutrient sinks (e.g., denitrification and sedimentation) or sources (e.g., decomposition and redox changes), potentially reducing or enhancing nutrient loads downstream. This study investigated the spatial and temporal variability of water and lakebed sediment chemistry for an agricultural reservoir, Carlyle Lake (Illinois, U.S.), to assess the role of sediments as nutrient sinks or sources. Samples were collected across the reservoir over a 2‐year period. We measured N‐ and P‐species in water at the sediment‐water interface, in sediment porewaters, and loosely bound to sediment exchange sites. Total N, total P, total C, organic matter, Fe, Mn, and grain size were measured in bulk sediments. We observed a strong gradient in sedimentary total N, total P, total C, organic matter, and metals along the reservoir, with the lowest concentrations at the river mouth and the highest concentrations near the dam. Additionally, we did a long‐term nutrient mass balance using historical water quality data for streams entering and exiting the reservoir and the reservoir itself. Mass balance calculations showed that Carlyle Lake, on average, removed 2,738 Mg N/year and released 121 Mg P/year over the multidecadal observation period. While N was consistently removed frommore »the system over time, P was initially stored in, but later released from, the reservoir. The subsequent release of legacy P from the reservoir led to higher outgoing, compared with incoming, P loads. Thus, reservoirs in intensively managed landscapes can act as sinks for N but sources for P over decadal timescales.

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4. Inhibited Manganese Oxide Formation Hinders Cobalt Scavenging in the Ross Sea

   https://doi.org/10.1029/2020GB006706  

   Oldham, Véronique E. ; Chmiel, Rebecca ; Hansel, Colleen M. ; DiTullio, Giacomo R. ; Rao, Deepa ; Saito, Mak ( May 2021 , Global Biogeochemical Cycles)

   The Southern Ocean plays a critical role in regulating global uptake of atmospheric CO₂. Trace elements like iron (Fe), cobalt (Co), and manganese (Mn) have been shown to modulate this primary productivity. Despite limited data, the vertical profiles for Mn, Fe, and Co in the Ross Sea show no evidence of scavenging, as typically observed in oceanic sites. This was previously attributed to low‐particle abundance and/or by mixing rates exceeding scavenging rates. Scavenging of some trace metals such as cobalt (Co) is thought to be largely governed by Mn (oxyhydr)oxides, assumed to be the main component of particulate Mn (pMn). However, our data show that pMn has an average oxidation state below 3 and with nondetectable Mn oxides. In addition, soluble Co profiles show no evidence of scavenging and Co uptake measurements show little Co uptake in the euphotic zone and low/no scavenging at depth. Instead, high concentrations of dissolved Mn (dMn, up to 90 nM), which is primarily complexed as Mn(III)‐L (up to 100%), are observed. Average dMn concentrations (10 ± 14 nM) are highest in bottom and surface waters. Manganese sources may include sediments and sea‐ice melt, as elevated dMn was measured in sea ice (12 nM) compared to its surrounding watersmore »(3 nM), and sea ice dMn was 97% Mn(III)‐L. We contend that the lack of Co scavenging in the Ross Sea is due to a unique Mn redox cycle that favors the stabilization of Mn(III)‐complexes at the expense of Mn oxide particle formation.

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5. Iron (Oxyhydr)Oxides Serve as Phosphate Traps in Tundra and Boreal Peat Soils

   https://doi.org/10.1029/2018JG004776  

   Herndon, Elizabeth M. ; Kinsman‐Costello, Lauren ; Duroe, Kiersten A. ; Mills, Jonathan ; Kane, Evan S. ; Sebestyen, Stephen D. ; Thompson, Aaron A. ; Wullschleger, Stan D. ( February 2019 , Journal of Geophysical Research: Biogeosciences)

   Arctic and boreal ecosystems are experiencing pronounced warming that is accelerating decomposition of soil organic matter and releasing greenhouse gases to the atmosphere. Future carbon storage in these ecosystems depends on the balance between microbial decomposition and primary production, both of which can be regulated by nutrients such as phosphorus. Phosphorus cycling in tundra and boreal regions is often assumed to occur through biological pathways with little interaction with soil minerals; that is, phosphate released from organic molecules is rapidly assimilated by plants or microorganisms. In contrast to this prevailing conceptual model, we use sequential extractions and spectroscopic techniques to demonstrate that iron (oxyhydr)oxides sequester approximately half of soil phosphate in organic soils from four arctic and boreal sites. Iron (III) (oxyhydr)oxides accumulated in shallow soils of low‐lying, saturated areas where circumneutral pH and the presence of a redox interface promoted iron oxidation and hydrolysis. Soils enriched in short‐range ordered iron oxyhydroxides, which are susceptible to dissolution under anoxic conditions, had high phosphate sorption capacities and maintained low concentrations of soluble phosphate relative to soils containing mostly organic‐bound iron or crystalline iron oxides. Thus, substantial quantities of phosphorus in these organic soils were associated with minerals that could reducemore »bioavailability but potentially also serve as phosphorus sources under anoxic conditions. The implication of this finding is that mineral surfaces effectively compete with biological processes for phosphate and must be considered as a nutrient regulator in these sensitive ecosystems.

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