The effects of long term nitrogen fertilization on forest soil respiration in a subalpine ecosystem in Rocky Mountain National Park

Allen, Jordan, author
Denning, A. Scott, advisor
Baron, Jill, advisor
Ryan, Mike, committee member
Bowser, Gillian, committee member
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Anthropogenic activities contribute to increased levels of nitrogen deposition and elevated CO2 concentrations in terrestrial ecosystems. The response of soil respiration to nitrogen fertilization in an on going 18- year field nitrogen amendment study was conducted from July 2014 to October 2014. The focus of this study was to determine the effects of nitrogen fertilization on soil carbon cycling, via respiration. Our objectives were to (1) test the hypothesis that N additions would increase soil respiration in Rocky Mountain National Park, and (2) understand the impacts of N additions on carbon flows in subalpine forests. A LiCor LI-820 infrared gas analyzer (IRGA) was used to quantify soil respiration rates. We compared soil respiration from fertilized forest plots (30 x 30 m) with soil respiration from control forests plots (30 x 30 m) that receive only ambient nitrogen deposition (3-5 kg/ N/ha-1/yr-1) during the 2014-growing season. Our results shows that mean soil respiration measurements were not significantly different in the control plots (3.14 µmol m-2 sec-1) than in the fertilized plots (3.02 µmol m-2 sec-1). Treatment was insignificant in influencing soil respiration (p-value greater than 0.5), allowing us to reject our primary hypothesis: that nitrogen additions would lead to an increase in soil respiration. Our results confirm previous research in these plots Advani (2004). The statistically identical soil respiration rates between the control and fertilized plots may result from nitrogen saturation due to elevated levels of ambient N deposition, microbial suppression due to very high levels of N additions in the fertilized plots, or some combination of the two.
2016 Fall.
Includes bibliographical references.
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