|Venterea, Rodney - Rod|
Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2003
Publication Date: 11/1/2003
Citation: Fitzhugh, R.D., Lovett, G.M., Venterea, R.T. 2003. Biotic and abiotic immobilization of ammonium, nitrite, and nitrate in soils developed under different tree species in the Catskill Mountains, New York, USA. Global Change Biology. 9:(11)1591-1601. Interpretive Summary: Air pollution deriving from fossil fuel combustion and agricultural fertilizer use results in increased amounts of nitrogen (N)-containing chemicals in the atmosphere, which can subsequently be deposited on land. Additions of atmospheric N to forest ecosystems may have several negative effects, including loss of nutrients, acidification of soils and streams, and leaching of nitrate into groundwater. Forests soils apparently can buffer against these negative effects, at least partly and at least temporarily, by retaining the added N within mineral, chemical, and/or biological soil components. However, very little is known regarding exactly which chemical and biological reactions are most important in retaining added N. The objective of this research was to investigate which chemical forms of N are most readily subject to retention in the soil, and to what extent this retention is mediated by strictly chemical versus biological processes. A laboratory experiment was performed where 15-N isotope labelled N was added as ammonium, nitrite, and nitrate to live and sterilized soils from three tree species (American beech, northern red oak, sugar maple) in the Catskills Mountains of New York State. Incorporation of nitrite into soil organic matter occurred very rapidly (< 15 minutes) via chemical reactions, and occurred to a greater extent than incorporaion of ammonium or nitrate. These results suggest that chemical fixation of nitrite may be an important mechanism of N retention in forest soils. The incorporation of nitrite did not vary significantly among tree species, so this mechanism likely does not contribute to differences in soil N dynamics among species. Further research is required to determine the importance of this process in field situations. These findings contribute to our understanding of how fundamental soil processes respond to N additions, and will also aid in the evaluation of regulations governing the emissions of N oxides from fossil fuel burning plants and other sources which may impact terrestrial ecosystems via N deposition.
Technical Abstract: Nitrogen retention in soil organic matter (SOM) is a key process influencing the accumulation and loss of N in forest ecosystems, but the rates and mechanisms of inorganic N retention in soils are not well understood. The primary objectives of this study were to compare ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-) immobilization among soils under different tree species from the Catskill Mountains in New York state, and to determine the relative roles of biotic or abiotic processes in soil N retention. A laboratory experiment was performed, where 15N was added as NH4+, NO2-, and NO3- to live and sterilized soils from three tree species (American beech, northern red oak, sugar maple), and 15N recoveries were determined in the soil pool following extraction of the soil with potassium chloride (KCl). Mercuric chloride (HgCl2) was utilized to sterilize soils as this chemical has been shown previously to effectively inhibit microbial metabolism without significantly altering the chemistry of SOM. Immobilization of NH4+ and NO2- into SOM was almost always greater than immobilization of NO3-. Ammonium immobilization increased over the 28-d incubations and occurred primarily by biotic processes. Incorporation of NO2- into SOM occurred rapidly (< 15 minutes) via abiotic processes. Abiotic immobilization of NO2- was significantly greater than abiotic immobilization of NH4+ or NO3-. As over 30% of the 15NO2- label was recovered in SOM within 15 minutes in live soils, and the products of NO2- fixation remained relatively stable throughout the 28 day incubation, our results suggest that NO2- fixation may be an important mechanism of N retention in forest soils. The importance of NO2- fixation in N retention in field soils, however, will depend on competition between fixation and nitrification for transiently available NO2-. The incorporation of NO2- into SOM did not vary significantly among tree species, so this mechanism likely does not contribute to differences in soil NO3- dynamics among species. Our results suggest that the incorporation of NO2- into SOM could be an important component of the N cycle in forest ecosystems. Further research is required to determine the importance of this process in field situations.