Effects of elevated CO₂ and temperature on methane production and emission from submerged soil microcosm

Abstract

Incubation experiments were conducted under controlled laboratory conditions to study the interactive effects of elevated carbon dioxide (CO₂ ) and temperature on the production and emission of methane (CH₄) from a submerged rice soil microcosm. Soil samples (unamended soil; soil + straw; soil + straw + N fertilizer) were placed in four growth chambers specifically designed for a combination of two levels of temperature (25 ° C or 35 ° C) and two levels of CO₂ concentration (400 or 800 μmol mol^-1) with light intensity of about 3000 Lx for 16 h d^-1. At 7, 15, 30, and 45 d after incubation, CH₄ flux, CH₄ dissolved in floodwater, subsurface soil-entrapped CH₄ and CH₄ production potential of the subsurface soil were determined. The results are summarized as follows: 1) The amendment with rice straw led to a severalfold increase in CH₄ emission rates, especially at 35 “C. However, the CH₄ flux tended to decrease considerably after 15 d of incubation under elevated CO₂ . 2) The amount of entrapped CH₄ in subsurface soil and the CH₄ production potential of the subsurface soil were appreciably larger in the soil samples incubated under elevated CO₂ and temperature during the early incubation period. However, after 15 d, they were similar in the soil samples incubated under elevated or ambient CO₂ levels. These results clearly indicated that elevated CO₂ and temperature accelerated CH₄, formation by the addition of rice straw, while elevated CO₂ reduced CH₄ emission at both temperatures.