I am broadly interested in how ecosystem functioning responds to global climate change impacts such as drought, rainfall intensification, and nitrogen deposition. My research uses interdisciplinary approaches to explore how chemical transformations in natural and managed terrestrial ecosystems respond to global changes.

Dryland nitrogen cycling

Dryland soil N can be lost to the atmosphere as nitric oxide (NO) or nitrous oxide (N2O) following wetting of dry soils. This represents an important N loss pathway in ecosystems where biological productivity is already N limited. Furthermore, gaseous N loss has important implications for regional air quality (NO is a precursor to tropospheric ozone) and Earth’s climate (N2O is a potent greenhouse gas). As a Postdoc at the University of California, Riverside, I work to better understand controls over gaseous N loss from drylands.

Nitrogen trace gas emissions across a N deposition gradient

I am currently investigating controls over N trace gas production from dryland soils across a N deposition gradient spanning the Coachella Valley.

How do altered precipitation regimes affect dryland N cycling?

Precipitation regimes are changing in dryland ecosystems, with important implications for soil N cycling. I investigate how extended periods without rainfall will impact soil microbial community composition and what consequences this has for soil N cycling. This work is done at the Pinyon Flats rainfall manipulation experiment at the Boyd Deep Canyon Desert Research Center.

Soil greenhouse gas emissions in response to intensified precipitation

Global climate change is predicted to increase the intensity and variability of precipitation events throughout much of the United States. Large rain events can lead to flooding of topographic depressions in otherwise flat agricultural fields, stimulating microbial reactions that produce and consume potent greenhouse gases such as nitrous oxide (N2O). My dissertation research examined how soil N2O and carbon dioxide emissions respond to large rain events, and if this response is mediated by topographic position. Specific projects include:

Topographic position mediates soil nitrous oxide emissions in response to rainfall

I have demonstrated that depressional and upslope soils in agricultural ecosystems have distinct controls over N2O emissions. Specifically, upslope soils have higher rates of N2O production via denitrification in response to large rain events, and depressional areas produce more N2O in between large rain events.

Publication: Krichels A, DeLucia EH, Sanford RA, Chee-Sanford, JC, Yang, WH (2019) Historical soil drainage mediates the response of soil greenhouse gas emissions to intense precipitation events. Biogeochemistry 143, 425-442

Microbial community composition varies by landscape position

We have demonstrated that the community composition of denitrifying microorganisms consistently varies between depressional and upslope soils. These differences likely mediate N2O production and consumption in response to intense rainfall.

Publication: Suriyavirun N, Krichels A, Kent A, Yang WH (2019) Microtopographic differences in soil properties and microbial community composition at the field scale. Soil Biology and Biochemistry 131,71-80

Dynamic controls on soil nitrous oxide hot spots and hot moments

I conducted a field experiment to determine if topography can help explain field-scale spatial variation in soil N2O emissions over the course of the growing season. We found evidence that cool temperatures may limit N2O production in response to spring rainfall. However, topography did not consistently explain variation in N2O emissions

Publications: Krichels A, Yang WH. Dynamic controls on soil nitrous oxide hot spots and hot moments. JGR Biogeosciences 124, 3618-3634


Do mycorrhizal associations mediate soil carbon storage in montane tropical forests?

Whether trees associate with arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi has important consequences for soil nutrient cycling. Specifically, EM assicated treees can promote the accumulation of soil organic matter. As part of a NSF Funded IGERT program in association with the Smithsonian Tropical Research Institute, I investigated the mechanisms behind this pattern.

Publication: Yang WH, Lawrence N, Dalling J, Krichels A. Mycorrhizal mediation of soil organic matter characteristics under focal tree species in a diverse lower montane tropical forest. In preparation for submission to Global Biogeochemical Cycles

How does ecosystem respiration respond to increased temperatures?

As part of an NSF funded Research Experience for Undergraduates program through the University of Alaska Anchorage, I worked with Dr. Paddy Sullivan to examine how warming affects ecosystem respiration in the arctic tundra. I also designed an independent project examining the contribution of lichens to ecosystem respiration.


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