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Responses of Trace Gas Fluxes and N Availability to Experimentally Elevated Soil Temperatures

Peterjohn, William T., Melillo, Jerry M., Steudler, Paul A., Newkirk, Kathleen M., Bowles, Francis P., Aber, John D.
Ecological applications 1994 v.4 no.3 pp. 617-625
activation energy, air temperature, carbon, carbon dioxide, deciduous forests, equations, field experimentation, gas emissions, heat, leaching, linear models, methane, nitrogen content, nitrous oxide, rooting, soil temperature, soil water
We are conducting a field study to determine the long—term response of belowground processes to elevated soil temperatures in a mixed deciduous forest. We established 18 experimental plots and randomly assigned them to one of three treatments in six blocks. The treatments are: (1) heated plots in which the soil temperature is raised 5°C above ambient using buried heating cables; (2) disturbance control plots (cables but no heat); and (3) undisturbed control plots (no cables and no heat). In each plot we measured indexes of N availability, the concentration of N in soil solutions leaching below the rooting zone, and trace gas emissions (CO₂, N₂O, and CH₄). In this paper we present results from the first 6 mo of this study. The daily average efflux of CO₂ increased exponentially with increasing soil temperature and decreased linearly with increasing soil moisture. A linear regression of temperature and the natural logarithm of CO₂ flux explained 92% of the variability. A linear regression of soil moisture and CO₂ flux could explain only 44% of the variability. The relationship between soil temperature and CO₂ flux is in good agreement with the Arrhenius equation. For these CO₂ flux data, the activation energy was 63 kJ/mol and the Q₁ ₀ was 2.5. The daily average uptake of CH₄ increased linearly with increasing soil temperatures and decreased linearly with increasing soil moisture. Linear regression could explain 46% of the variability in the relationship between temperature and CH₄ uptake and 49% of the variability in the relationship between soil moisture and CH₄ uptake. We predicted the annual CO₂ flux from our study site in 1991 using two empirical relationships: the relationship between air temperature and soil temperature, and the relationship between soil temperature and CO₂ flux. We estimate that the annual CO₂—C flux in 1991 was 712 g/m² from unheated soil and 1250 g/m² from heated soil. By elevating the soil temperature 5°C above ambient, we estimate that an additional carbon flux of 538 g°m— ²°yr— ¹ was released from the soil as CO₂.