Abstract
Wet soil microcosms were established to determine effects of organic matter and nitrate additions on microbial respiration and redox potentials. Organic matter (1%) and nitrate (100 ppm and 200 ppm) treatments were applied in factorial combination. Soil pH, redox potential, and CO2 emissions were measured. Data were analyzed by ANOVA for repeated measures and separately by sampling day. Addition of organic matter significantly (P < 0.05) and consistently increased CO2 emissions and decreased redox potentials. On Day 42 nitrate significantly (P < 0.05) increased redox values. This study indicates a tendency for organic matter to decrease soil redox potential both in absolute terms and relative to the suboxic-anoxic boundary. Our findings portend that additions of organic matter may quickly and markedly decrease soil redox potentials and increase CO2 emissions in wetlands, whereas additions of nitrate may have complex and sporadic effects on redox potentials.
Highlights
Microbial respiration in the soil, accomplished by linking oxidation and reduction half-reactions, directly impacts the redox potential (Eh) of soil-water systems
The data strongly support the hypothesis that adding soil organic matter will decrease soil redox potentials
Ermore, the control treatment having native levels of organic matter and nitrate resulted in intermediate redox potentials through Day 42, after which it produced the highest redox values of all treatments. This further supports the hypothesis that the negative impact on redox values was caused by the organic matter addition, not by the native organic matter in the soil
Summary
Microbial respiration in the soil, accomplished by linking oxidation and reduction half-reactions, directly impacts the redox potential (Eh) of soil-water systems. Is affected by, many attributes of the ecosystem. In soil the primary electron donor for oxidation half-reactions is organic matter. In aerobic soil the prevailing electron acceptor for reduction half-reactions is molecular oxygen (O2). Microbial populations can use electron acceptors less susceptible to reduction than O2, especially in environments where O2 is absent. Where microbes and organic matter are abundant, the absence of O2 (i.e., an anaerobic condition) leads to the reduction of other substances, creating a low redox potential as expressed in units of millivolts or by the term pe implying the negative logarithm of concentration of electrons in search of an electron acceptor
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