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Harvard Forest Symposium Abstract 2016

• Title: Characterizing the Response of Nitrogen-Cycling Microbial Communities to Increasing Temperature and Nitrogen Deposition at Harvard Forest
• Primary Author: George Hamaoui (Massachusetts College of Liberal Arts)
• Additional Authors: Serita Frey (University of New Hampshire - Main Campus); Klaus Nusslein (University of Massachusetts - Amherst )
• Abstract:

  As industrialization and climate change progress, increasing atmospheric temperatures and nitrogen (N) deposition are acting as stressors on natural habitats, especially in the forests of the Northeastern United States. Previous research in the Harvard Forest chronic soil warming and N-fertilization experiments has shown that soil microbial communities can be altered by such temperature and nutrient stressors. However, little work has been performed to characterize the response of nitrogen cycling microbial communities in these forest soils. Toward this end, our research goal was to determine how soil N-cycling microbial communities respond to the combinatorial stress of increased soil temperature and N-deposition in the soil warming and nitrogen fertilization (SWaN) experiment. Soil samples from both the organic and mineral soil horizons were collected in September 2012 from triplicate plots of the four different treatments: control, heated (5°C above ambient soil temperature), fertilized (5.0 g N m-2 yr-1), or both heated and fertilized. Soil chemical parameters (ammonium and nitrate), N-mineralization rate measurements (potential N-mineralization and N-acetylglucosaminidase enzyme activity), and culture-independent abundances of total bacteria, fungi, and archaea were determined. Additionally, abundances of nitrifying and denitrifying bacteria and archaea were ascertained. No significant differences in ammonium levels (p > 0.05) were seen between the different treatments regardless of the soil layer analyzed. Nitrate was below the detection limit in both soil horizons from all treatments. Potential N-mineralization rates and N-acetylglucosamindase activities showed no significant differences between treatments. While ammonia oxidizing archaea (AOA) and bacterial denitrifers were detected in all plots, no ammonia oxidizing bacteria were detected. Also, no differences in AOA or bacterial denitrifier abundances were seen in either soil layer for any of the treatments. Additionally, there were no differences between treatments and soil layers for total bacteria, archaea, and fungi. Microbial community sequencing analyses currently being performed will elucidate if the temperature and fertilization disturbances effect microbial community structure and diversity. Taken together, these results may indicate that the soil system in the SWaN experiment is resistant to both applied disturbances or that the experiment has not been established for a long enough time period to detect differences.

• Research Category: Large Experiments and Permanent Plot Studies
  Soil Carbon and Nitrogen Dynamics