METHANE FLUX OF AMAZONIAN PEATLAND ECOSYSTEMS: LARGE ECOSYSTEM FLUXES WITH SUBSTANTIAL CONTRIBUTION FROM PALM (MARITIA FLEXUOSA) STEM EMISSIONS

Abstract:

Methane (CH₄) emissions through plants have long been known in wetlands. However, most measurements have focused on stem tops and leaves. Recently, measurements at the lower parts of stems have shown that stem emissions can exceed soil CH₄ emissions in Asian peatlands (Pangala et al. 2013). The addition of stem fluxes to soil fluxes for total ecosystem fluxes has the potential to bridge the discrepancy between modeled to measured and bottom-up to top-down flux estimates. Our measurements in peatlands of Peru show that especially Mauritia flexuosa, a palm species, can emit very large quantities of CH₄, although most trees emitted at least some CH₄.

We used flexible stem chambers to adapt to stems of any size above 5cm in diameter. The chambers were sampled in closed loop with a Gasmet DX4015 for flux measurements, which lasted ~5 minutes after flushing with ambient air. We found that M. flexuosa stem fluxes decrease with height along the stem and were positively correlated with soil fluxes. Most likely CH₄ is transported up the stem with the xylem water. Measured M. flexuosa stem fluxes below 1.5m averaged 11.2±1.5 mg-C m^-2 h^-1 (±95% CI) with a maximum of 123±3.5 mg-C m^-2 h^-1 (±SE), whereas soil fluxes averaged 6.7±1.7 mg-C m^-2 h^-1 (±95% CI) with a maximum of 31.6±0.4 mg-C m^-2 h^-1 (±SE). Significant CH₄ fluxes were measured up to 5 m height along the stems. Combined with the high density of ~150 M. flexuosa individuals per hectare in these peatlands and the consistent diameter of ~30cm, the high flux rates add ~20% to the soil flux. With anywhere between 1 and 5 billion M. flexuosa stems across Amazon basin wetlands, stem fluxes from this palm species could represent a major addition to the overall Amazon basin CH₄ flux.