Human generation of nitrogen pollution and the subsequent deposition of nitrogen on soils is a phenomenon of changing environments and a potentially enormous stress on organisms and their ecosystems. Fungi are critical to biogeochemical cycles, but because individuals grow hidden in substrates, fungi are difficult to observe or manipulate in natural contexts. Measuring adaptation is difficult, and the ability of fungi to adapt their metabolisms to nitrogen stress is unknown. I am testing physiological functional traits of decomposer fungi which have experienced nitrogen pollution for multiple decades, and am comparing those to the traits of closely related fungi which have not been exposed to nitrogen pollution. I aim to demonstrate whether fungi experiencing nitrogen pollution have adapted to grow differently in nitrogen rich environments. Fungi were isolated from the Long-Term Ecological Research (LTER) Chronic Nitrogen Amendment study (CNAS) at Harvard Forest, and grown in the lab in minimal nutrient liquid culture at three concentrations of nitrogen, mimicking the CNAS plots. Each isolate was grown in shaking culture and biomass was destructively harvested daily to measure growth rate and other physiological functional traits. Growth rate will be reported here, and ongoing measurements of respiration and nitrogen in biomass are being collected.
Results/Conclusions
Preliminary tests are intriguing: fungi isolated from the amended nitrogen environments grow significantly more slowly than fungi from the control nitrogen environment. At day six, average biomass of the Ascomycete leaf decomposer fungus Epicoccum sp. from the control plot was 133.2 mg (dry weight), while average biomass of Epicoccum sp. from nitrogen amended plots was 65.8 mg. Similarly, for Irpex sp., a Basidiomycete wood decomposer, biomass at day six from the control plot was 53.2 mg while biomass from the nitrogen amended plot was 31.4 mg. Observed slower growth rate of isolates from nitrogen amended plots suggests these organisms have adapted to the pressure of nitrogen pollution. By quantifying growth rate, respiration rate, and total nitrogen in biomass for isolates of the same species exposed or not exposed to nitrogen pollution, I am testing whether adaptation has occurred, a key to understanding how evolution will impact decomposition in contexts of global change.