Bulk partitioning the growing season net ecosystem exchange of CO2 in Siberian tundra reveals the seasonality of its carbon sequestration strength

[摘要] This paper evaluates the relative contribution of light and temperature onnet ecosystem CO₂ uptake during the 2006 growing season in a polygonaltundra ecosystem in the Lena River Delta in Northern Siberia(72°22´ N, 126°30´ E). The occurrence and frequency ofwarm periods may be an important determinant of the magnitude of theecosystem's carbon sink function, as they drive temperature-induced changesin respiration. Hot spells during the early portion of the growing season,when the photosynthetic apparatus of vascular plants is not fully developed,are shown to be more influential in creating positive mid-daysurface-to-atmosphere net ecosystem CO₂ exchange fluxes than thoseoccurring later in the season. In this work we also develop and present amulti-step bulk flux partition model to better account for tundra plantphysiology and the specific light conditions of the arctic region. Theseconditions preclude the successful use of traditional partition methods thatderive a respiration–temperature relationship from all nighttime data orfrom other bulk approaches that are insensitive to temperature or lightstress. Nighttime growing season measurements are rare during the arcticsummer, however, so the new method allows for temporal variation in theparameters describing both ecosystem respiration and gross uptake by fittingboth processes at the same time. Much of the apparent temperature sensitivityof respiration seen in the traditional partition method is revealed in thenew method to reflect seasonal changes in basal respiration rates.Understanding and quantifying the flux partition is an essential precursor todescribing links between assimilation and respiration at different timescales,as it allows a more confident evaluation of measured net exchangeover a broader range of environmental conditions. The growing season CO₂sink estimated by this study is similar to those reported previously for thissite, and is substantial enough to withstand the long, low-level respiratoryCO₂ release during the rest of the year to maintain the site's CO₂ sinkfunction on an annual basis.

[学科分类] 地球化学与岩石