Discipline: Ecology Environmental and Earth Sciences
Aleah Dungee - Norfolk State University
Co-Author(s): Di Liang and G. Philip Robertson, W.K. Kellogg Biological Station, Hickory Corners, MI/Michigan State University, East Lansing, MI
Soil nitrification is a biological process that converts ammonia to nitrate. Excess nitrate is prone to leaching, which results in financial loss for farmers and water pollution. It is known that ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) are able to nitrify, but it is unclear how much they contribute to this process individually. To answer this question, we conducted an experiment at the Kellogg Biological Station Long Term Ecological Research (LTER) to determine how AOA and AOB contribute to soil nitrification. We hypothesized that AOA and AOB would contribute differently to nitrification in regards to annual vs. perennial crops and fertilized vs. non-fertilized treatments. We sampled soils two days after rainfall on June 19, 2016. Soil samples were taken from seven different land treatments including T1 (conventional wheat), T4 (biologically based wheat with cover crop), T5 (poplar), T7 (early successional community), T7 Fertilized subplots, DF (Deciduous Forest), and DF Fertilized subplots. Soil was then sieved through 4mm meshes. 12 grams of sieved soil was placed in Wheaton bottles in triplicate. Chemical inhibitors including 10 Pa C2H2 (inhibits both AOA and AOB) and octyne (inhibits AOB only) were injected into the bottles to separate the relative contribution of heterotrophs, AOA and AOB to soil nitrification. The bottles were incubated in their respective ecosystems (buried in soil: 15 cm deep) for four weeks. Every week, we removed the bottles and flushed with water-saturated air and then injected inhibitors again. CO2 samples were taken at the first week of the experiment and measured at 2 hours and 24 hours. The accumulation of CO2 over the 22 hour period was used to calculate the CO2 emission rates of different ecosystems. At the 28th day, the bottles were removed and soil nitrate was extracted with KCL and analyzed with Latchat. We also tested soil pH immediately after the soils were brought back to the lab. The amount of nitrate accumulation with different inhibitors over a four-week period was used to calculate the nitrification rates by AOA and AOB. CO2 emission rates in T7 fertilized subplots were significantly higher than T1, T4 and T5. This might be because there is more organic carbon that accumulated in T7 fertilized subplots. T4 and DF had the highest field net nitrification rates. This reflects the constant supply of organic matter from the cover crop in T4 and plant detritus in DF. Heterotrophs dominated nitrification in T1 and T4; however, in DF there were no evidence of heterotrophic nitrification. The pH of the fertilized subplots was significantly lower than their non-fertilized treatments (as shown in T7 and DF). This was expected because fertilizer facilitates nitrification, which causes soil acidification. Future research involves a deeper understanding of how AOA and AOB affect the emission of greenhouse gases.
Funder Acknowledgement(s): Funding was provided by the NSF. Funding was also provided by Michigan State University AgBIO Research and the Kellogg Biological Station Long-Term Ecological Research.
Faculty Advisor: Di Liang, firstname.lastname@example.org
Role: The part of the research I did included the field work, lab work, and data analysis. My mentor Di Liang and I worked together in the lab to analyze the data collected in the experiment. During the beginning of the experiment, I went out to the field to collect soil samples for analysis.