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Harvard Forest Symposium Abstract 2015

  • Title: Fungal community dynamics and soil biogeochemical cycling in response to long-term nitrogen additions and soil warming
  • Primary Author: Linda van Diepen (University of New Hampshire - Main Campus)
  • Additional Authors: Mark Anthony (University of New Hampshire - Main Campus); Serita Frey (University of New Hampshire - Main Campus); Melissa Knorr (University of New Hampshire - Main Campus); Elizabeth Landis (University of New Hampshire - Main Campus); Eric Morrison (University of New Hampshire - Main Campus); Anne Pringle (University of Wisconsin - Madison); Jesse Sadowsky (University of New Hampshire - Main Campus)
  • Abstract:

    Our research takes place at two of the LTER sites at Harvard forest: the Chronic Nitrogen (N) Amendment Study (CNA), and the Soil Warming and Nitrogen Addition Study (SWaN). The CNA experiment consists of three N treatments (ambient, 5 and 15 g N m-2 y-1), and SWaN consists of four treatments (ambient, N (5 g N m-2 y-1), +5°C warming, N and warming). Our goal is to identify the biodiversity of saprotrophic (decomposer) and ectomycorrhizal (ECM) fungi, understand their ecology and physiological response to a changing climate, and examine the relationship between fungal community structure, organic matter decay, and biogeochemical cycling in response to climate change and invasive plant species.

    A litterbag study implemented at the CNA study site showed that N additions resulted in decreased lignolytic and increased cellulolytic enzyme activity, but did not reveal a strong correlation between fungal community composition and extracellular enzyme activity. Several melanized or pathogenic/saprotrophic ascomycete species were associated with enzyme activities in the N treatments, while a Clitocybe species and the family Hydnodontaceae were associated with enzyme activity in control litter. In vivo decomposition experiments in the laboratory, using fungi isolated from the litterbags, showed that fungal isolates from the N addition plots were less able to degrade plant litter as compared to isolates of the same species from control plots, even when the N isolates were grown in control environments. Observed changes in fungal physiology suggest that these species have undergone an evolutionary change that is not readily reversed.

    The CNA plots are also part of a new project to better understand N cycling in Northeastern U.S. forests. Nitrogen retention at CNA is >10-times higher than current atmospheric N deposition rates, while other forests undergo substantial N loss when N deposition is elevated. We designed a study to identify factors contributing to variability in N cycling and retention in Northeastern U.S. forests by in situ labeling of experimental plots with 15N and an intensive time-course sampling. Strengths of below-ground sinks for N will be measured in soil microbial biomass, mycorrhizae, and cell-wall residues, over time after addition of 15N. In addition, relationships will be determined between N-cycle variables and fungal community structure in forested soils of this region.

    Soils (organic and mineral horizon) collected at our SWaN experiment revealed a 30% reduction in C and N stocks in the organic horizon of the warmed plots, but no changes in the mineral horizon. However, incubation measurements of these soils in the laboratory showed no differences in the amount of mineralized C with warming. Furthermore, warming did not affect total soil microbial biomass as measured with phospholipid fatty acids (PLFA). We are currently completing a comprehensive sequencing analysis to assess microbial responses to the treatments.

    Long-term Alliaria petiolata (garlic mustard) invaded and uninvaded plots were set up at Harvard Forest (HF) in the summer of 2013 as part of a regional study to query the impacts and factors facilitating successful garlic mustard invasions with a focus on the effects on fungal community composition and functioning. At HF no differences were found in fungal community structure between invaded and uninvaded plots, and this may be because garlic mustard abundances are lower at HF compared to other forests in MA and NY. At HF, invasion tended to decrease the relative abundance of ECM fungi while several non-mycorrhizal groups strongly increased. In 2015 we will initiate a garlic mustard ”invasion” at SWaN to examine how invasion interacts with soil warming and nitrogen addition. Using the above approaches we are starting to bridge the gap in understanding how the interaction between ecosystem function and fungal community dynamics are altered by anthropogenic changes in climate, nutrient availability, and invasive plant species.

  • Research Category: Biodiversity Studies; Invasive Plants, Pests & Pathogens; Large Experiments and Permanent Plot Studies; Physiological Ecology, Population Dynamics, and Species Interactions; Soil Carbon and Nitrogen Dynamics