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Student Spotlight

Alix Contosta

Alumna Profile: Alexandra R. Contosta

Degree: Earth and Environmental Science


Dissertation Title: Seasonal, Biogeochemical, and Microbial Response of Soils to Simultaneous Warming and Nitrogen Additions

Advisor: Dr. Serita Frey

Description of Research

My proposed doctoral research examines how soils respond to simultaneous warming and nitrogen fertilization. Both increased temperatures and elevated nitrogen loads can alter soil carbon and nitrogen dynamics, which in turn can influence atmospheric carbon dioxide concentrations, soil nitrogen availability, primary productivity, and can even impact water quality.   The magnitude and the direction of the response of soils to warming and nitrogen fertilization are ambiguous given the lack of consensus in the published literature.  Further, because most data have been collected primarily during the growing season from single manipulation experiments, we currently either under- or overestimate how soils respond to increased temperatures and nitrogen loads.  Preliminary data suggests that soils experiencing multiple disturbances, as they do in the natural world, behave differently than they would if exposed to a single manipulation.  Recent work also reports that soils are active in the winter in ways that we do not yet understand.   My research aims to improve our understanding of how soils respond to simultaneous warming and fertilization, both inside and outside of the growing season.  My dissertation also incorporates a theoretical component, in the sense that it examines the long-debated question of whether species composition and diversity influence ecosystem processes.  Using decomposer fungi as a case study, I can evaluate whether the diversity of these fungi correlates to the functions they perform, such as decomposition and carbon and nitrogen storage and loss from soil.  I can also ask whether some of these fungi are more vulnerable to extirpation than others, and whether changing environmental conditions such as increased temperature and nitrogen inputs eradicate some species while promoting others.


In short, my doctoral research aims to determine:

  1. How soil carbon and nitrogen cycles respond to separate and simultaneous warming and fertilization treatments
  2. The response of the soil microbial biomass and the fungal decomposer community to the experimental manipulations
  3. The link between changes in the decomposer community and its functional role in the ecosystem
  4. Whether soils display a seasonal pattern in nutrient cycling and microbial community dynamics; and
  5. If a seasonal trend exists, whether increased temperatures and nitrogen inputs alter that pattern.

To address my research objectives, I installed a multifactorial experiment at the Harvard Forest Long Term Ecological Research site that includes control, warming, nitrogen, and warming plus nitrogen addition treatments. Data collected from these plots fall into one of three broad categories. First, soil carbon and nitrogen cycles will be quantified as CO2 emissions, labile carbon availability, nitrogen mineralization, and DIN, DON, and DOC in soil water. Second, the microbial community will be measured using two different types of assays. The first will determine the overall biomass of the microbial community. The other microbial assay will be more targeted, and will use a genetic approach to measure the community composition of a specific group of microbes, the ligninolytic fungi, in response to the experimental manipulations. These fungi have been chosen because they are functionally unique, are vulnerable to environmental stress, and are essential to the ecosystem. Third, the work will examine potential links between shifts in lignin decomposer community structure and activity, and the dynamics of the larger ecosystem, such as soil enzyme activity and decomposition. In order to asses whether soils display a seasonal pattern in their structure and function, data collection for carbon and nitrogen fluxes and microbial community composition and activity will be collected year-round.


Prior to beginning my work at the University of New Hampshire, I worked as a research technician for the U.S. Forest Service Northeastern Research Station in Durham, NH.   I collected field data for forest health, carbon sequestration, and hemlock woolly adelgid studies.  I also worked in the lab and analyzed foliage samples for nutrient concentrations.  My work with the Forest Service began while I was completing my master’s degree at Antioch New England Graduate School in Keene, NH.  For my master’s thesis, I collaborated with research scientists at the Forest Service in studying ways to assess sugar maple health along a nutrient availability gradient in the White Mountain National Forest. 

In addition to research, I also have experience with writing, teaching, and community service.  At Antioch, I acted as editor of Whole Terrain, a journal that addresses emerging trends in ecology and environmental thought.  Whole Terrain enjoys a national distribution, bringing together prominent authors, students, land managers, teachers, and many others to discuss their perspectives on a specific theme.  I now serve on the board of Whole Terrain, and in this way can keep my creative and literary selves active even as I pursue my research.

I have enjoyed the opportunity to teach several courses at the undergraduate and graduate level.  In the fall of 2007, I taught the lab section of a Soil Ecology course.  The preceding autumn, I lectured for Introduction to Soil Science.  While at Antioch, I also served as a teaching assistant, and helped students formulate and carry out research in a Soil Ecology class.  Before I started graduate school, I held several jobs as an environmental educator in both daytime and residential programs.   I was also a youth mentor for a program called Visions, which conducted cross-cultural and community service trips for high school kids to locations all over the world.  I was lucky to spend two summers in the Caribbean working for Visions, in Guadeloupe, the Dominican Republic, and the British Virgin Islands.   

Selected Presentations and Publications

Oral Presentations

Poster Presentations

Professional Positions



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