Carbon quality and nutrient status drive the temperature sensitivity of organic matter decomposition in subtropical peat soils

Estimates of gaseous carbon (C) fluxes in wetlands are heavily based on temperature. However, isolating specific effects of temperature on anaerobic C processing from other controls (C quality and nutrients) has proven difficult. Here, we test the hypothesis that temperature sensitivity of soil organic matter (SOM) decomposition is more influenced by C quality than nutrient availability in subtropical freshwater, sawgrass (Cladium jamaicense)-based peats. Carbon age (characterized by depth: 0-10 and 10-20 cm) was used as a surrogate of C quality while two sites were selected with contrasting levels of nutrient (P) availability. In anaerobic laboratory incubations temperature was increased in 5 degrees C steps to assess the proportion of C available at a given temperature (i.e. thermo-labile C) as productions of gaseous (CO2 and CH4) and dissolved organic C (DOC) fractions. Thermo-labile C increased 3.1-3.6 times from 15 degrees C to 30 degrees C in all soils. Disproportionate increase in the production of gaseous forms versus DOC as well as CH4:CO2 was observed with warming. Observed Q(10) values followed the trend of CH4 (similar to 14) >> CO2 (similar to 2.5) > DOC (similar to 1.7) and temperature sensitivity was more dependent on C quality than nutrient availability over the entire temperature range. Spectral analysis indicated more bio-available DOC production at higher temperature. Regression analysis also indicated that C quality primarily influenced SOM decomposition at lower temperature, while at higher temperature nutrient limitation dominantly controlled SOM decomposition. These findings confirm the role of C quality in temperature sensitivity of warm peat soils, but also indicate an increased importance of nutrient limitation at higher temperature.