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DISSIMILATORY NITRATE REDUCTION TO AMMONIUM IN UPLAND TROPICAL FOREST SOILS
Author(s) -
Silver Whendee L.,
Herman Donald J.,
Firestone Mary K.
Publication year - 2001
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(2001)082[2410:dnrtai]2.0.co;2
Subject(s) - nitrogen cycle , soil water , denitrification , nitrification , environmental science , nitrate , environmental chemistry , ecosystem , leaching (pedology) , ammonium , abiotic component , nitrogen , tropical and subtropical moist broadleaf forests , ecology , chemistry , soil science , subtropics , biology , organic chemistry
The internal transformations of nitrogen in terrestrial ecosystems exert strong controls over nitrogen availability to net primary productivity, nitrate leaching into groundwater, and emissions of nitrogen‐based greenhouse gas. Here we report a reductive pathway for nitrogen cycling in upland tropical forest soils that decreases the amount of nitrate susceptible to leaching and denitrification, thus conserving nitrogen in the ecosystem. Using 15 N tracers we measured rates of dissimilatory nitrate reduction to ammonium (DNRA) in upland humid tropical forest soils averaging ∼0.6 μg·g −1 ·d −1 . Rates of DNRA were three times greater than the combined N 2 O and N 2 fluxes from nitrification and denitrification and accounted for 75% of the turnover of the nitrate pool. To determine the relative importance of ambient C, O 2 , and NO 3 concentrations on rates of DNRA, we estimated rates of DNRA in laboratory assays using soils from three tropical forests (cloud forest, palm forest, and wet tropical forest) that differed in ambient C and O 2 concentrations. Rates of DNRA measured in laboratory assays ranged from 0.5 to 9 μg·g −1 ·d −1 in soils from the three different forests and appeared to be primarily limited by the availability of NO 3 , as opposed to C or O 2 . Tests of sterile soils indicated that the dominant reductive pathway for both NO 2 and NO 3 was biotic and not abiotic. Because NH 4 is the form of N generally favored for assimilation by plants and microbes, and NO 3 is easily lost from the ecosystem, the rapid and direct transformation of NO 3 to NH 4 via DNRA has the potential to play an important role in ecosystem N conservation.