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Featured researches published by Richard Wehr.


Nature | 2014

Methane dynamics regulated by microbial community response to permafrost thaw

Carmody K. McCalley; Ben J. Woodcroft; Suzanne B. Hodgkins; Richard Wehr; Eun Hae Kim; Rhiannon Mondav; Patrick M. Crill; Jeffrey P. Chanton; Virginia I. Rich; Gene W. Tyson; Scott R. Saleska

Permafrost contains about 50% of the global soil carbon. It is thought that the thawing of permafrost can lead to a loss of soil carbon in the form of methane and carbon dioxide emissions. The magnitude of the resulting positive climate feedback of such greenhouse gas emissions is still unknown and may to a large extent depend on the poorly understood role of microbial community composition in regulating the metabolic processes that drive such ecosystem-scale greenhouse gas fluxes. Here we show that changes in vegetation and increasing methane emissions with permafrost thaw are associated with a switch from hydrogenotrophic to partly acetoclastic methanogenesis, resulting in a large shift in the δ13C signature (10–15‰) of emitted methane. We used a natural landscape gradient of permafrost thaw in northern Sweden as a model to investigate the role of microbial communities in regulating methane cycling, and to test whether a knowledge of community dynamics could improve predictions of carbon emissions under loss of permafrost. Abundance of the methanogen Candidatus ‘Methanoflorens stordalenmirensis’ is a key predictor of the shifts in methane isotopes, which in turn predicts the proportions of carbon emitted as methane and as carbon dioxide, an important factor for simulating the climate feedback associated with permafrost thaw in global models. By showing that the abundance of key microbial lineages can be used to predict atmospherically relevant patterns in methane isotopes and the proportion of carbon metabolized to methane during permafrost thaw, we establish a basis for scaling changing microbial communities to ecosystem isotope dynamics. Our findings indicate that microbial ecology may be important in ecosystem-scale responses to global change.


Nature | 2016

Seasonality of temperate forest photosynthesis and daytime respiration

Richard Wehr; J. W. Munger; J. B. McManus; D. D. Nelson; M. S. Zahniser; Eric A. Davidson; S. C. Wofsy; Scott R. Saleska

Terrestrial ecosystems currently offset one-quarter of anthropogenic carbon dioxide (CO2) emissions because of a slight imbalance between global terrestrial photosynthesis and respiration. Understanding what controls these two biological fluxes is therefore crucial to predicting climate change. Yet there is no way of directly measuring the photosynthesis or daytime respiration of a whole ecosystem of interacting organisms; instead, these fluxes are generally inferred from measurements of net ecosystem–atmosphere CO2 exchange (NEE), in a way that is based on assumed ecosystem-scale responses to the environment. The consequent view of temperate deciduous forests (an important CO2 sink) is that, first, ecosystem respiration is greater during the day than at night; and second, ecosystem photosynthetic light-use efficiency peaks after leaf expansion in spring and then declines, presumably because of leaf ageing or water stress. This view has underlain the development of terrestrial biosphere models used in climate prediction and of remote sensing indices of global biosphere productivity. Here, we use new isotopic instrumentation to determine ecosystem photosynthesis and daytime respiration in a temperate deciduous forest over a three-year period. We find that ecosystem respiration is lower during the day than at night—the first robust evidence of the inhibition of leaf respiration by light at the ecosystem scale. Because they do not capture this effect, standard approaches overestimate ecosystem photosynthesis and daytime respiration in the first half of the growing season at our site, and inaccurately portray ecosystem photosynthetic light-use efficiency. These findings revise our understanding of forest–atmosphere carbon exchange, and provide a basis for investigating how leaf-level physiological dynamics manifest at the canopy scale in other ecosystems.


Atmospheric Measurement Techniques | 2014

Development and field testing of a rapid and ultra-stable atmospheric carbon dioxide spectrometer

B. Xiang; David D. Nelson; John Barry McManus; Mark S. Zahniser; Richard Wehr; S. C. Wofsy

We present field test results for a new spectroscopic instrument to measure atmospheric carbon dioxide (CO2)with high precision (0.02 μmol mol , or ppm at 1 Hz) and demonstrate high stability (within 0.1 ppm over more than 8 months), without the need for hourly, daily, or even monthly calibration against high-pressure gas cylinders. The technical novelty of this instrument (ABsolute Carbon dioxide, ABC) is the spectral null method using an internal quartz reference cell with known CO2 column density. Compared to a previously described prototype, the field instrument has better stability and benefits from more precise thermal control of the optics and more accurate pressure measurements in the sample cell (at the mTorr level). The instrument has been deployed at a long-term ecological research site (the Harvard Forest, USA), where it has measured for 8 months without on-site calibration and with minimal maintenance, showing drift bounds of less than 0.1 ppm. Field measurements agree well with those of a commercially available cavity ring-down CO2 instrument (Picarro G2301) run with a standard calibration protocol. This field test demonstrates that ABC is capable of performing high-accuracy, unattended, continuous field measurements with minimal use of reference gas cylinders.


Global Change Biology | 2017

Partitioning controls on Amazon forest photosynthesis between environmental and biotic factors at hourly to interannual timescales

Jin Wu; Kaiyu Guan; Matthew Hayek; Natalia Restrepo-Coupe; K. T. Wiedemann; Xiangtao Xu; Richard Wehr; Bradley Christoffersen; Guofang Miao; Rodrigo Marques da Silva; Alessandro C. Araújo; Raimundo Cosme Oliviera; Plínio B. Camargo; Russell K. Monson; Alfredo R. Huete; Scott R. Saleska


Biogeosciences | 2016

Dynamics of canopy stomatal conductance, transpiration, and evaporation in a temperate deciduous forest, validated by carbonyl sulfide uptake

Richard Wehr; R. Commane; J. William Munger; J. Barry McManus; David D. Nelson; Mark S. Zahniser; Scott R. Saleska; Steven C. Wofsy


Agricultural and Forest Meteorology | 2015

An improved isotopic method for partitioning net ecosystem-atmosphere CO2 exchange

Richard Wehr; Scott R. Saleska


Biogeosciences | 2016

The long-solved problem of the best-fit straight line: Application to isotopic mixing lines

Richard Wehr; Scott R. Saleska


Agricultural and Forest Meteorology | 2018

A novel correction for biases in forest eddy covariance carbon balance

Matthew Hayek; Richard Wehr; Marcos Longo; Lucy R. Hutyra; K. T. Wiedemann; J. William Munger; Damien Bonal; Scott R. Saleska; David R. Fitzjarrald; Steven C. Wofsy


Biogeosciences | 2017

Reviews and syntheses: Carbonyl sulfide as a multi-scale tracer for carbon and water cycles

Mary E. Whelan; Sinikka T. Lennartz; Teresa E. Gimeno; Richard Wehr; Georg Wohlfahrt; Yuting Wang; Linda M. J. Kooijmans; Timothy W. Hilton; Sauveur Belviso; Philippe Peylin; R. Commane; Wu Sun; Huilin Chen; Le Kuai; Ivan Mammarella; Kadmiel Maseyk; Max Berkelhammer; King-Fai Li; Dan Yakir; Andrew Zumkehr; Yoko Katayama; Jérôme Ogée; Felix M. Spielmann; Florian Kitz; Bharat Rastogi; J. Kesselmeier; Julia Marshall; Kukka-Maaria Erkkilä; Lisa Wingate; Laura K. Meredith


2015 AGU Fall Meeting | 2015

What Controls the Net Forest-Atmosphere Exchange of Carbonyl Sulfide? Results from 2 Years of Eddy Flux Measurements and SiB Model Simulations

Richard Wehr

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Mark S. Zahniser

National Oceanic and Atmospheric Administration

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David D. Nelson

National Institute of Standards and Technology

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