Spectral Indices of Vegetation Condition and Soil Water Content Reflect Controls on CH₄ and CO₂ Exchange in Sphagnum‐Dominated Northern Peatlands

Abstract

Northern peatlands act as globally important carbon (C) sinks (Nichols & Peteet, 2019). Changes in climate and large-scale drainage for agriculture and forestry increase the susceptibility of these C sinks to oxidation, which has the potential to shift some peatlands from being net C sinks to sources (Dinsmore et al., 2010;Trettin et al., 2006), although the warming and drying-to-C-loss scenario is far from certain across all boreal peatlands (Charman et al., 2013;Gallego-Sala et al., 2018). Beyond simply acting as net C sinks, peatlands play

Fresh Air for the Mire-Breathing Hypothesis: Sphagnum Moss and Peat Structure Regulate the Response of CO2 Exchange to Altered Hydrology in a Northern Peatland Ecosystem

“…Spectral indices closely related to Sphagnum primary productivity and water content were calculated and compared to flux measurement data [31,[34][35][36]. Changes in spectral water content (wetness index WI, floating water band index FWBI) and photosynthetic capacity (chlorophyll index CI, normalized difference vegetation index NDVI) were measured using an ASD Fieldspec 3 spectroradiometer (Analytical Spectral Devices, Boulder, CO, USA) under clear, low haze conditions as previously described in detail [31,36]. The spectroradiometer was held 30 cm above the surface of the center of each sphagnocosm, and was white referenced every ten minutes to adjust for changes in sun angle and sky conditions.…”

“…Moss height measurements of each sphagnocosm were taken once a week for five weeks using the method described in the treatment section. Spectral measurements were taken on 6 and 7 August 2020 as described above, with a nominal spectral range spanning 325-1075 nm [36].…”

“…The differing responses of Sphagnum landform types to our treatments and the ability of some moss traits-such as capitula density-to stabilize carbon cycles reveal that Sphagnum and Sphagnum dominated peatlands are not static but are rather responsive ecosystems with a great amount of plasticity. Index) and spectral photosynthetic capacity ("phsyn" in the figure, Chlorophyll Index) (Supplementary File S2, see [36] for greater detail). The box "Landform (hummock)" indicates the effect of the hummock landform relative to the hollow, since that factor is not intrinsically ordered as are the other factors in the SEM.…”

“…However, we also found that hummocks exhibited a compressive mire-breathing technique wherein capitula density increased as the mosses compressed into each other (Figure 3). This compression was as- (Supplementary File S2, see [36] for greater detail). The box "Landform (hummock)" indicates the effect of the hummock landform relative to the hollow, since that factor is not intrinsically ordered as are the other factors in the SEM.…”

“…Linear mixed effects models evaluating water table (WT), rainfall, landform (hummock or hollow) and their interactive effects on two hyperspectral indexes of peat surface moisture and plant/Sphagnum moisture stress. See [36] for details.…”