A manuscript I’ve been working on entitled “Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods,” was now been published in Atmospheric Measurement Techniques (view paper online). Our goal was to present a detailed experimental approach for measuring ecosystem fluxes of H2 and to test different so-called “flux-gradient methods” for calculating the H2 fluxes. Some common trace gas flux methods, e.g. eddy covariance, are not available for species like H2 that cannot be measured precisely at high frequencies (<1 Hz). We hope this paper will help inform the design of future studies for which flux-gradient methods might be the best option for measuring trace gas fluxes.
Microbe-mediated soil uptake is the largest and most uncertain variable in the budget of atmospheric hydrogen (H2). In a recent study (early view in Environmental Microbiology Reports), we probed the advantage of atmospheric H2 consumption to microbes and relationship between environmental conditions, physiology of soil microbes, and H2. First, we were interested in whether environmental isolates and culture collection strains with the genetic potential for atmospheric H2 uptake (a specific NiFe-hydrogenase gene) actually exhibit atmospheric H2 uptake. To expand the library of atmospheric H2-oxidizing bacteria, we quantify H2 uptake rates by novel Streptomyces soil isolates that contain the hhyL and by three previously isolated and sequenced strains of actinobacteria whose hhyL sequences span the known hhyL diversity. Second, we investigated how H2 uptake varies over organismal life cycle in one sporulating and one non-sporulating microorganism, Streptomyces sp. HFI8 and Rhodococcus equi, respectively. Our observations suggest that conditions favoring H2 uptake by actinobacteria are associated with energy and nutrient limitation. Thus, H2 may be an important energy source for soil microorganisms inhabiting systems in which nutrients are frequently limited.
Much of this work was done with the help of Deepa Rao, an undergraduate researcher at MIT at the time who wrote an award-winning senior thesis on the topic and presented results in a number of venues, including at AGU 2012.
I defended my thesis entitled “Field Measurement of the Fate of Atmospheric H2 in a Forest Environment: from Canopy to Soil” on October 4, 2012.
It was an incredible relief to finish the thesis document itself (link to .pdf; Carl-Gustaf Rossby Prize for best PhD thesis in PAOC for the year). I really enjoyed preparing and giving my thesis defense presentation. It’s not often that one gets to present the culmination of six years of hard work and personal development to colleagues, family, and friends. I am grateful for mentorship from my advisor Ron Prinn, my thesis committee (Steve Wofsy – Harvard, Bill Munger – Harvard, Tanja Bosak – MIT, Colleen Hansel – WHOI, Shuhei Ono – MIT), and many others along the way!
I am continuing at MIT for a short (approximately 9 month) postdoctoral position with Ron Prinn to translate the work described in my thesis to publications. I am currently exploring possibilities for a postdoctoral position at the intersection of microbial ecology and atmospheric chemistry (trace gas cycles or aerosols) by searching advertised positions and writing fellowship proposals.
Last week I attended ISME 14 (International Symposium on Microbial Ecology) in Copenhagen, Denmark. It was a delight to see the city – its juxtaposed giant modern, cool, sterile buildings surrounding the historic old city. More of a delight was unexpectedly running into friends from the MBL Microbial Diversity summer school (2010) and realizing they are now my colleagues.
The conference itself was quite good. I appreciated the range of content from very big picture and abstract to focused experimental projects. One message I took away from the community was a sort of -omics backlash, or perhaps whiplash, to the idea that generating more and more -omics data is the sole future for microbial ecology. It seems that presenters coming from both the -omics and experimental side were acknowledging the importance of both tools, and especially of using them together. Those seem to be a lot of tools for any one scientist to master, so I am encouraged that the tone was of collaborative holistic approaches for tackling scientific questions.
I really enjoyed a somewhat unique session. It was a discussion entitled “Frontiers in microbial ecosystem science: Energizing the research agenda” sponsored at this and other conferences by the US National Science Foundation. All sorts of issues were raised in a discussion of “what needs to be done” – what are the important topics and how should we advance microbial ecology. I was struck by how strong the arguments were that microbial ecology is important for understanding, and possibly mitigating, climate change. This is my main interest, but I often find the microbial ecology literature and research interests so focused on minute points (I think my own project included), that it is difficult to see the link between the microbial and global scales. At this session I learned that it is not only because it is difficult to do, but also because the funding agencies seem to push scientists to write grants in one or the other. It is difficult to be interdisciplinary (falling under more than one NSF department). It has been a (fun) challenge for me to try to get a foot in both atmospheric and microbial ecology science, and it was encouraging to hear from the community that the intersection of the two is valued.
MIT Department of Earth, Atmospheric and Planetary Science article describing the expansion of the atmospheric chemistry program at MIT over the past five years with a short feature on our work to understand the H2 soil sink in the field and in the lab.
I just returned to Boston after the six weeks of travelling. My two weeks in California, filled with conferences and colleagues, was quite different from the intensive and somewhat isolated period spent in India.
First stop was San Diego, where I attended the 44th Meeting of Advanced Global Atmospheric Gases Experiment (AGAGE) Scientists and Cooperating Networks at the Scripps Institute of Oceanography in La Jolla. Anita Ganesan’s instrument in Darjeeling may pave the way for the first AGAGE site in India, so the crowd was eager to hear her describe our success in deploying her instrument. Her dedicated and diligent work is paying off as she is collecting some of the first high precision direct greenhouse gas measurements in India.
I gave a talk at the AGAGE meeting on my recent work on the flux of H2, CO2 and COS between the soil and atmosphere at Harvard Forest. I focus on the persistence of soil-atmosphere exchange of trace gases across snowpack, which insulates the soil microbial community from freezing air temperatures while allowing trace gases to diffuse through the porous snow matrix. I’m interested in how strongly the biogeochemical cycling continues throughout the winter and in comparing the behavior of the different cycles in the low temperature ‘incubator’ beneath the snow. Continue reading
In the summer of 2010, I spent six inspiring, challenging, and chaotic weeks at the Marine Biological Laboratory Microbial Diversity Course in Woods Hole, MA. Taking full advantage of the opportunity granted by course directors Steve Zinder and Dan Buckley of Cornell, this budding atmospheric chemist plunged head on into the world of microbiology. I was eager to learn the theory and hands-on methods to study the microbial world, which has such a profound impact on atmospheric composition, and this course gave me a chance to explore my interests in a way not offered anywhere else. Continue reading