Date of Award

Winter 2015

Project Type

Thesis

Program or Major

Microbiology

Degree Name

Master of Science

First Advisor

Serita D Frey

Second Advisor

Linda TA van Diepen

Third Advisor

Louis Tisa

Abstract

Increases in nitrogen (N) deposition have been shown to slow decomposition of organic material including lignin, particularly in forests with high lignin content. Since basidiomycete fungi are the primary decomposers of lignin, their response to increases in available N are of interest. The Chronic Nitrogen Amendment Study at the Harvard Forest Long-Term Ecological Research (CNAS HF-LTER) site is an experimental N gradient in Petersham, MA. Since 1988, three megaplots have received varying levels of NH4NO3: ambient-only deposition (control), 50 kg N ha-1 yr-1 (N50), or 150 kg N ha-1 yr-1 (N150). In order to examine how species of lignin-degrading basidiomycetes might evolve in response to increases in available N, isolates of Stereum complicatum, Irpex lacteus, and Panellus stipticus were reciprocally transplanted from the megaplots at CNAS HF-LTER onto a laboratory-simulated N gradient. These isolates were tested for their ability to decompose oak leaf litter, and were also subjected to an experimental evolution to test whether changes in litter decay capacity are inducible or reversible over shorter time periods. The short-term experimental evolution failed to change litter decay rates or enzyme activity profiles. However, for two of the three species, exposure to 25+ years of N addition significantly changed their decay capacities. S. complicatum isolated from the N150 plot exhibited increased decomposition capacity and N150 isolates of I. lacteus exhibited decreased decomposition capacity compared to control isolates of the same species. These finding suggest that N deposition may have long-lasting effects on the decay capacities of fungi that may help to explain suppression of decomposition which occurs with increases in N deposition.

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