The role of Empodisma robustum litter in CO₂ exchange at Kopuatai bog

Abstract

Respiration from the decomposition of standing dead litter in peatlands influences the ecosystem carbon balance through its contribution to total ecosystem respiration (ER). This research determined the proportion of ER estimated at Kopuatai bog that is sourced from the decomposition of Empodisma robustum litter in the canopy. Canopy harvests were carried out to measure the mass of standing litter in the canopy; laboratory litter incubations were used to measure respiration rates over a range of temperatures and moisture contents; and a simple model was developed to estimate annual litter respiration using inputs of canopy wetness duration and canopy temperature.

E. robustum litter comprised an average of 51% of the total canopy biomass, with 0.92 kg m⁻² standing litter dry matter in 1.8 kg m⁻² of total canopy dry matter. The majority of this litter is located in the lower part of the canopy. Very low respiration rates were measured for the E. robustum litter, although respiration was significantly higher in litter which was more physically decomposed (R₁₀ = 0.44 (± 0.1) μmol kg⁻¹ s⁻¹) than that which was freshly dead (R₁₀ = 0.24 (± 0.05) μmol kg⁻¹ s⁻¹). Litter respiration showed a strong temperature response, and was moisture-limited below approximately 50% moisture content. The model of litter respiration estimated that standing dead E. robustum litter contributed 59 g C m⁻² yr⁻¹ (8.8%) to annual total ER. This represents an estimated litter turnover time of 7 – 8 years. While the contribution of litter respiration to ER is relatively small, the resulting large mass of recalcitrant litter in the canopy may contribute to E. robustum’s ability to engineer its environment.