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Weekly Highlights for 3-17-2017


Cheatgrass Modifies Microbial Nitrogen Cycling in Sagebrush Soils

Cheatgrass invasion not only degrades native sagebrush ecosystems and important rangelands, it can also cause soil microbial communities to change over time. These communities are responsible for converting organic soil nitrogen into plant-available inorganic nitrogen. Researchers examined nitrogen cycling rates in sagebrush and cheatgrass-invaded soils over a 100 mile range in the northern Great Basin, adding antibiotics to study the roles that soil fungi and bacteria play in nitrogen transformations. Adding a bacterial antibiotic completely stopped the organic to inorganic nitrogen conversion in cheatgrass soils. Further, there was a dramatic increase in nitrate in sagebrush soils treated with the fungal antibiotic, suggesting that fungi normally serve as a storage “sink” for this nutrient. Results point to the important role fungi play in nitrogen dynamics in native sagebrush steppe and suggest that cheatgrass’s alteration of the microbial community may make nitrogen more available further benefiting the establishment and growth of this invasive grass.

DeCrappeo, N.M., DeLorenze, E.J., Giguere, A.T., Pyke, D.A., Bottomley, P.J., 2017, Fungal and bacterial contributions to nitrogen cycling in cheatgrass-invaded and uninvaded native sagebrush soils of the western USA: Plant and Soil, p. online,[Details]

Contact: David Pyke, FRESC, 541-750-0989, Profile

Selenium:Mercury Molar Ratios in Freshwater Fish: Potential Applications for Fish Consumption Advisories

Consuming fish is the primary source of methylmercury exposure in humans. Selenium often co-occurs with mercury and there is some evidence that selenium can protect against mercury toxicity. Oregon State University and USGS researchers examined 10 different freshwater fish species from the Columbia River Basin to determine the variability in fish selenium:mercury molar ratios. They found significant variation in selenium:mercury molar ratios between fish species, ranging from 3.42:1 in Walleye to 27.2:1 in Chinook salmon, and within fish of the same species. Results also showed that top-level predators such as smallmouth bass, walleye, and brown trout had higher amounts of mercury and subsequently lower selenium:mercury molar ratios. Authors suggest that traditional methods of assessing the health risks associated with mercury exposure from fish consumption may not provide a complete picture as it does not take into account the contribution of selenium.

Cusack, L.K., Eagles-Smith, C.A., Harding, A.K., Kile, M.L., Stone, D., 2016, Selenium- Mercury molar ratios in freshwater fish in the Columbia River basin- Potential applications for specific fish consumption advisories: Biological Trace Element Research, p. online,[Details]

Contact: Collin Eagles-Smith, FRESC, 541-750-0949, Profile

Assessing Risks of Anticoagulant Rodenticides Exposure in California Condors

Condors are one of the most endangered bird species globally. The exclusive scavenging behavior of California condors makes them particularly susceptible to exposure and bioaccumulation of contaminants found within carcasses. A recent analysis of liver tissue samples from deceased condors found more than half were exposed to at least one anticoagulant rodenticide, presumably from consuming agricultural pests that have been poisoned. The USGS will lead a new study to quantify the level of anticoagulant rodenticide risk to condors and evaluate potential physiological effects. They will also determine the applicability of using surrogate obligate scavengers to test for exposure to anticoagulant rodenticides, both in existing condor populations as well as at potential future release sites. Results will be used to develop guidelines for the California Condor Recovery Program to minimize the threat of anticoagulant rodenticides to condors.

Contact: Collin Eagles-Smith, FRESC, 541-750-0949, Profile

Subalpine Tree Range Dynamics with Warming

Tree species’ ability to keep pace with the amplified warming occurring at high-elevation forest limits will depend on how fast expansion at the upper, “cool edge” proceeds relative to contraction at the lower, “warm edge” of subalpine forest. Researchers used population models combined with data from long-term forest surveys to explore whether the climate-sensitivity of recruitment observed in climate manipulation experiments was sufficient to alter populations and elevation ranges of two widely distributed, high-elevation North American conifers: limber pine and Englemann spruce. They found that declines in low-elevation populations outpaced growth in high-elevation populations with warming. Their study explores the role of demographic processes in determining the pace of population and distribution changes at both the leading and trailing edges of these species’ ranges.

Conlisk, E., Castanha, C., Germino, M.J., Veblen, T.T., Smith, J.M., Kueppers, L.M., 2017, Declines in low-elevation subalpine tree populations outpace growth in high-elevation populations with warming: Journal of Ecology, p. online,[Details]

Contact: Matthew Germino, FRESC, 208-426-3353, Profile

Press Inquiries/Media

USGS Researcher Interviewed About Bsal

USGS ecologist Mike Adams was interviewed by Brent Crane from Scientific American on March 10. Crane is writing an article on the salamander pathogen Bsal, or Batrachochytrium salamandrivorans. Adams provided information about USGS activities and the Bsal Technical Advisory Committee.

Contact: Michael Adams, FRESC, 541-750-0980, Profile

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