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Harvard Forest Symposium Abstract 2012

• Title: The changing diversity and evolution of decomposer fungi in response to soil warming and nitrogen additions
• Primary Author: Linda van Diepen (University of New Hampshire - Main Campus)
• Additional Authors: Serita Frey (University of New Hampshire - Main Campus); Eric Morrison (University of New Hampshire - Main Campus); Anne Pringle (University of Wisconsin - Madison); christopher sthultz (Harvard University Faculty of Arts and Sciences)
• Abstract:

  Fungi are ubiquitous in terrestrial ecosystems and play an important role in biogeochemical cycling because of their function as litter decomposers. Fungi are a highly diverse and non-static group and fungal lineages can evolve in response to climate change. This evolution could redirect fungal function and as a consequence influence nutrient cycling within an ecosystem. Our study focuses on understanding the mechanisms by which fungi persist in a changing climate and explores the potential feedbacks on ecosystem functioning. Our goal is to identify the biodiversity of saprotrophic (decomposer) fungi, understand their evolution (phenotypic plasticity vs. adaptation), and examine the relationship between fungal diversity and litter decay in response to climate change.
  
  
  
  Our study takes place at two of the LTER sites at Harvard forest: the Chronic Nitrogen (N) Addition plots and the Barre Woods Soil Warming Study. The Chronic N Addition Experiment consists of three N treatments (ambient, 5 and 15 g N m-2 y-1) and the Soil Warming Study has two treatments (ambient and +5°C warming). We implemented a litter decomposition study in the fall of 2010 using mesh bags filled with leaf litter. To simulate litter fall as accurately as possible, we used fresh leaf litter collected from the control plots and filled each bag with a proportional representation of the dominant tree species. At the Chronic N experiment we also implemented a reciprocal design using oak litter (most dominant tree species) from each N addition treatment. One set of litterbags was harvested after ~1 year (fall 2011) and another set will be harvested after ~2 years (fall 2012). One third of the litter from each bag was used for analysis of active fungal diversity using molecular techniques. The other 2/3 was used for measurement of biogeochemical parameters (mass loss, C/N, lignin, enzyme activity) and to culture fungi for tests of phenotypic plasticity vs. adaptation.
  
  
  
  Biomass measurements of litter bags harvested after ~1 year indicated suppressed decomposition of mixed litter in the low N and high N plots compared to the control N plot, while soil warming increased decomposition (Figure 1). The single species (oak) litter from the control and low N plots did not show changes in decomposition rate with N addition, but the overall rates were lower compared to the mixed litter. Only the high N oak litter had a suppressed decomposition in the high N treatment compared to low N and control treatments.
  
  
  
  Nitrogen analysis showed an increase in %N for all the litter after one year of decomposition, indicating N immobilization. We found no differences in % N of the decomposed mixed litter among the N amendment treatments, except for the decomposed mixed litter in the high N plot, which had a significantly lower %N compared to the control and low N plot. In the control and low N plots, the % N of decomposed high N oak litter was significantly higher compared to the decomposed control and low N oak litter, but there was no difference in the high N plot (Figure 2). However, total N concentration of decomposed litter (%N multiplied by remaining litter dry weight) was not significantly affected by treatment, litter type, or litter quality (initial % N).
  
  
  
  We now have a well established collection of fungal cultures from sporocarps (2009-2011), fresh litter (2010), and litter from litterbags after one year of decomposition (2011) from the chronic N and warming plots. Using three different media types (PDA, cellulose, lignin) we were able to culture several different morphological species that were present in at least two or all of the N treatments, or in both warming treatments. We have confirmed several morphological species using DNA barcoding of the ITS region, which will be used in tests to measure phenotypic plasticity vs. adaptation. In preliminary tests we found significantly different growth rates of the same fungal species cultured from each of the three N treatments, indicating that our global change factors can affect the physiology of fungal species.
  
  
  
  To assess the fungal diversity of the decomposing litter we used techniques modified from those designed for soil, and were successful in isolating fungal DNA and RNA from the litter harvested in fall 2011. A series of molecular techniques, including cloning and sequencing, were utilized to identify individual members of the fungal communities. Three replicate DNA extractions from fifteen 1cm sections of leaves per bag were performed using a Plant DNA isolation kit (MoBio Laboratories, Inc.). From each extraction, three independent PCR’s of the ITS1 & 2 regions were performed using 454 tagged primers. All extractions from an individual bag were combined and sent for 454 sequencing at Duke University. We are currently awaiting the sequencing to be completed. Preliminary results from some of the fresh litter collected in 2010 indicated that saprophytic fungal communities differed among treatments.
  
  
  
  To complement our litter fungal diversity analysis, an assessment of soil fungal diversity associated with the forest floor (O-horizon) is being conducted at the Chronic N site. Soil samples were taken in November of 2009 at the Chronic N site with three replicate samples per plot. We performed a marker gene study of the fungal community in the organic soil horizon using 454 sequencing of three loci: ITS1, ITS2, and rDNA large subunit D2-D3 region. The dominant fungal family in soils under ambient N deposition was the Russulaceae. This family underwent a significant decrease in relative abundance in N treated soils. Unknown fungi dominated N treated soils. Control soils had significantly fewer unknown OTUs. High N soils had higher numbers of OTUs and singleton OTUs then control soils and low N soils, and had higher predicted richness. Fungal communities in high N soils had different community structure than control and low N soils as predicted with OTU based and phylogenetic β-diversity metrics. Differences in community composition and higher numbers of unknown OTUs in high N soil fungal communities suggests that a previously uncatalogued portion of the community may be released by the decline of the dominant Russulaceae.
  
  
  
  Using all of the above techniques we are starting to bridge the gap in understanding how the interaction between ecosystem function and fungal community dynamics are altered under changing climate conditions.
  
  

• Research Category: Biodiversity Studies
  Group Projects
  Large Experiments and Permanent Plot Studies
  Physiological Ecology, Population Dynamics, and Species Interactions
  Soil Carbon and Nitrogen Dynamics


• Figures:
HF 2012 ECOEVO project Figure1.pdf
HF 2012 ECOEVO project Figure2.pdf