Environmental correlates of peatland carbon fluxes in a thawing landscape: do transitional thaw stages matter?

[摘要] Peatlands in discontinuous permafrost regions occur as a mosaic of wetlandtypes, each with variable sensitivity to climate change. Permafrost thawfurther increases the spatial heterogeneity in ecosystem structure andfunction in peatlands. Carbon (C) fluxes are well characterized in end-memberthaw stages such as fully intact or fully thawed permafrost but remainunconstrained for transitional stages that cover a significant area ofthawing peatlands. Furthermore, changes in the environmental correlates of Cfluxes, due to thaw, are not well described – a requirement for modelingfuture changes to C storage of permafrost peatlands. We investigated C fluxesand their correlates in end-member and a number of transitional thawstages in a sub-arctic peatland. Across peatland-lumped CH₄ and CO₂flux data had significant correlations with expected correlates such as watertable depth, thaw depth, temperature, photosynthetically active radiation andvascular green area. Within individual thaw states, bivariate correlations aswell as multiple regressions between C flux and environmental factors changedvariably with increasing thaw. The variability in directions and magnitudesof correlates reflects the range of structural conditions that could bepresent along a thaw gradient. These structural changes correspond to changesin C flux controls, such as temperature and moisture, and their interactions.Temperature sensitivity of CH₄ increased with increasing thaw inbivariate analyses, but lack of this trend in multiple regression analysessuggested cofounding effects of substrate or water limitation on the apparenttemperature sensitivity. Our results emphasize the importance ofincorporating transitional stages of thaw in landscape level C budgets andhighlight that end-member or adjacent thaw stages do not adequately describethe variability in structure-function relationships present along a thawgradient.

[学科分类] 地球化学与岩石