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Individual Highlight

Long-term warming increases ecosystem nitrogen cycling

Photo of PSW-2017-250; One of the nine research plots located along a five degree Celcius mean annual temperature gradient on the Island of Hawaii; here the field crew is measuring soil respiration and collecting litterfall. PSW-2017-250; One of the nine research plots located along a five degree Celcius mean annual temperature gradient on the Island of Hawaii; here the field crew is measuring soil respiration and collecting litterfall. Snapshot : In a model ecosystem study where mean annual temperature (MAT) increases with elevation but where many factors such as soils, soil moisture, and forest composition and structure are held constant, Forest Service scientists used replicated plots located across a 5O degrees Celsius (122 degrees Fahrenheit) MAT gradient in Hawaiian montane forest, to examine MAT effects on nitrogen cycling and availability. Their analyses of ammonium oxidation and molecular analyses show that all three ecosystem measures of nitrogen availability increase with rising temperatures.

Principal Investigators(s) :
Giardina, Christian P. 
Research Location : Laupahoehoe Unit of the Hawaii Experimental Tropical Forest and the Hakalau Forest National Wildlife Refuge, Hawaii Island, Hawaii
Research Station : Pacific Southwest Research Station (PSW)
Year : 2017
Highlight ID : 1399

Summary

Functional gene approaches have been used to better understand the roles of microbes in driving forest soil nitrogen (N) cycling rates and bioavailability. Ammonia oxidation is a rate limiting step in nitrification, and is a key area for understanding environmental constraints on N availability in forests. Forest Service scientists studied how increasing temperature affects the role of ammonia oxidizing archaea (AOA) and bacteria in soil N cycling and availability by using a highly constrained natural mean annual temperature (MAT) elevation gradient in a tropical montane wet forest. They identified three distinct phylotypes within the AOA, which differed from one another in abundance and relative gene expression. In addition, one AOA phylotype increased in abundance with MAT, while others did not. They conclude that MAT is the primary driver of ecosystem N availability across this gradient, and AOA population size and structure appear to mediate the relationship between the nitrification and N bioavailability. These findings hold important implications for nutrient limitation in forests and feedbacks to primary production under changing climate.

Forest Service Partners

External Partners

 
  • University of Hawaii at Manoa, Cornell University