Soil chemistry versus environmental controls on production of CH4 and CO2 in northern peatlands

Rates of organic carbon mineralization (to CO₂ and CH₄) vary widely in peat soil. We transplanted four peat soils with different chemical composition into six sites with different environmental conditions to help resolve the debate about control of organic carbon mineralization by resource availability (e.g. carbon and nutrient chemistry) versus environmental conditions (e.g. temperature, moisture, pH). The four peat soils were derived from Sphagnum (bog moss). Two transplant sites were in mid‐boreal Alberta, Canada, two were in low‐boreal Ontario, Canada, and two were in the temperate United States. After 3 years in the field, CH₄ production varied significantly as a function of peat type, transplant site, and the type–site interaction. All four peat soils had very small rates of CH₄ production (< 20 nmol g^?1 day^?1) after transplant into two sites, presumably caused by acid site conditions (pH < 4.0). One peat soil had small CH₄ production rates regardless of transplant site. A canonical discriminant analysis revealed that large rates of CH₄ production (4000 nmol g^?1 day^?1) correlated with large holocellulose content, a large concentration of p‐hydroxyl phenolic compounds in the Klason lignin, and small concentrations of N, Ca and Mn in peat. Significant variation in rates of CO₂ production correlated positively with holocellulose content and negatively with N concentrations, regardless of transplant site. The temperature response for CO₂ production varied as a function of climate, being greater for peat formed in a cold climate, but did not apply to transplanted peat. Although we succeeded in elucidating some aspects of peat chemistry controlling production of CH₄ and CO₂ in Sphagnum‐derived peat soils, we also revealed idiosyncratic combinations of peat chemistry and site conditions that will complicate forecasting rates of peat carbon mineralization into the future.