Year-round growing conditions explains large CO2 sink strength in a New Zealand raised peat bog

Abstract

We measured net ecosystem CO2 exchange (NEE) for two years in a remnant New Zealand raised peat bog using the eddy covariance technique and estimated the component CO2 fluxes gross primary production (GPP) and ecosystem respiration (ER). Vegetation was dominated by vascular plants belonging to the southern hemisphere family Restionaceae, comprising an overstory of the erect Sporadanthus ferrugineus and a dense understory of Empodisma robustum. Annual NEE (GPP, ER) totals for the two years were −218.2 (1124.2, 906.0)gCm−2yr−1 and −250.3 (1148.3, 897.8)gCm−2yr−1, indicating substantially larger CO2 sink strength than has been reported for peatland ecosystems in the northern hemisphere. The bog was a net sink for CO2 in nine months each year, with small differences in autumn and wintertime NEE accounting for most of the difference in annual NEE totals. Summer daytime average NEE were similar to published values for northern hemisphere peatlands, despite differences in vegetation type and a comparatively deep water table. Fitted ecosystem light response and respiration model parameters were also within the ranges of values reported for peatlands elsewhere. The major distinction compared to northern peatlands was the year-round productivity of the evergreen vegetation cover in New Zealand, which largely offset respiration losses during the short, mild winter season.