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Sarah Roley Lab Site sarah.roley

N fixation by stream heterotrophs – now out in Freshwater Biology!

Erica Bakker’s paper is now out in Freshwater Biology! Erica measured N fixation in cyanobacteria with and without midge symbionts and compared those rates to fixation rates in sediment heterotrophs. She found that the rates were comparable between all 3 groups despite assumptions that cyanobacteria are the dominant aquatic N fixers. Interestingly, she also found that the acetylene reduction assay grossly underestimated fixation, compared to direct measurements with 15N2.

Congrats to Jarod!

Jarod Cable successfully completed his M.S. degree this summer, with a project on methane emissions from hydropower reservoirs. Congratulations, Jarod!

Correcting C Mineralization Assays for Soil Moisture

Matt’s paper is out in SOIL! In this paper, Matt addresses the problem of C loss during dry-down in standard C mineralization assays. He found that wetter soils lose more C during dry-down but that a simple correction factor can account for that difference. Check it out!


New funding to examine water stargrass removal

We’re highlighted here for our recent funding from the Washington Water Resource Center. In cooperation with Benton Conservation District, Aaron will examine the effects of water stargrass removal on Yakima River oxygen concentrations.

Water stargrass in the Yakima River

New paper on N cycling variation among switchgrass varieties

We recently published a paper in Phytobiomes on how N cycling varies among different switchgrass cultivars (doi: 10.1094/PBIOMES-11-19-0064-FI).

Switchgrass has various strategies for growing in low-nitrogen (N) environments, including translocating N to its roots during the winter and fostering a microbial community that can fix N. Switchgrass exhibits wide phenotypic and genotypic diversity, and we explored whether N translocation, fixation, and mineralization vary among cultivars. It does vary, with some varieties fixing N at high rates and also translocating a high percentage of their N. This information can inform selection of switchgrass varieties for biofuels cultivation. Varieties that conserve N do not require N fertilizers, making them more economically and environmentally sustainable.

This research was funded by NSF and the Great Lakes Bioenergy Research Center, which recently highlighted it on their website.

Congratulations to Aaron and Erica!

Aaron Pelly and Erica Bakker successfully defended their MS theses last week, becoming the first two MS recipients from the lab! Aaron focused on the effects of water stargrass on ecosystem metabolism and dissolved oxygen concentrations in the Yakima River, and Erica measured nitrogen fixation in Cascades Mountains streams, examining both sediment bacteria and cyanobacteria. They presented from home to a geographically-dispersed audience and nailed their zoom presentations. Excellent job, Aaron and Erica!

Work-Study Position Available

Do you like rivers, microbes, plants, biogeochemistry, and/or agriculture? Are you looking for lab and/or field experience in environmental science or biology? Are you work-study eligible? If so, apply now for a work-study position in the Watershed Biogeochemistry Lab. I am looking for one work-study student to help with lab and field work during the 2019-2020 school year. Potential activities include: preparing reagents, weighing samples, entering data, preparing vials for gas analyses, washing glassware, collecting water and plant samples, pulverizing soil and plants, and packing samples for isotopic and elemental analysis.

More info: Work Study 2019-2020 Job Description

Does associative N fixation occur episodically?

In our new paper, out in Soil Biology and Biochemistry, we used isotopic tracers in laboratory, greenhouse, and field settings to measure nitrogen (N) fixation in switchgrass. Our results suggest that bacteria associated with switchgrass fix N episodically – meaning fixation sometimes occurs at a high rate and is undetectable other times – perhaps in response to transiently appropriate physicochemical conditions. Metagenomic analyses revealed a wide diversity of bacterial taxa in and around switchgrass are capable of fixing N. We still don’t know if fixation is an important source of N to perennial grasses. If fixation is important in the switchgrass N budget, those inputs may occur in periodic bursts of fixation activity.

Citation: Roley, S.S., Xue, C., Hamilton, S.K., Tiedje, J.M., and Robertson, G.P. 2019. Episodic nitrogen fixation in switchgrass (Panicum virgatum L.). Soil Biology and Biochemistry.129: 90-98. doi: 10.1016/j.soilbio.2018.11.006

Rhenton and Cassandra present at WSU Symposium

Undergraduate researchers Rhenton and Cassandra presented at the WSU Tri-Cities Sympoisum today. Rhenton showed results from his summer project, in which he evaluated nutrient limitation of microbial and algal biofilms in tributaries of the Yakima River. Cassandra presented results on the effects of common herbicides, 2,4-D and glyphosate, on algal and microbial biofilms.

WSUTC symposium Rhenton and Cassandra
Cassandra Elkins (left) and Rhenton Brimberry (right) presenting results at WSUTC symposium