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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.