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Fakultät für Biologie, Chemie und Geowissenschaften

Ökologische Mikrobiologie - Prof. Tillmann Lüders

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Limmer, C; Drake, HL: Nonsymbiotic N2 fixation by acidic and pH-neutral forest soils: aerobic and anaerobic differntials, Soil Biology Biochemistry, 28/2, 177-183 (1996)
Abstract:
The effects of aerobic and anaerobic conditions on nitrogenase activities in forest soils (in particular that of a beech forest) obtained from northeast Bavaria (Germany) were assessed by both acetylene reduction and 15N2-fixation methods. Nitrogenase activity occurred without detectable delay under both aerobic and anaerobic conditions; in both cases, initial rates approximated 0.2 nmol C2H2 reduced per g dry weight soil per day. Prolonged anaerobic conditions yielded rates approximating 6 nmol C2H2 reduced per g dry weight soil per day; in contrast, rates remained relatively constant under aerobic conditions independent of the incubation period. When soils were amended with glucose, significantly higher acetylene reduction rates (1-4 µmol C2H2 reduced per gram dry weight soil per day) occurred only under anaerobic conditions. Assays with 15N2 confirmed this N2-fixation activity; based on initial reaction rates with moistened, but otherwise unamended soils, estimated N2 fixation activity approximated 0.2 kg N fixed per hectare per year. Compared to activities obtained under static conditions, shifts from aerobic to anaerobic conditions greatly enhanced N2-fixation activities. High anaerobic/aerobic activity ratios were obtained with both pH neutral and weakly acidic (pH 4.5-5.9) hardwood and coniferous forest soils. These consistently high anaerobic N2-fixation activities indicate that this process is likely limited to O2-deficient microsites in forest soils. No nitrogenase activity was detected with extremely acidic coniferous forest soils (pH 2.7-3.3) under either anaerobic or aerobic conditions.
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