Identifying the sources and uncertainties of ecosystem respiration in Arctic tussock tundra
2014
Segal, Aliza D. | Sullivan, Patrick F.
Ecosystem respiration (ER) is the largest flux of carbon (C) from terrestrial ecosystems to the atmosphere, yet our ability to model this aggregate flux lags considerably behind our ability to model photosynthesis. Arctic ecosystems hold large stocks of potentially labile soil C and are dominated by plants with high root: shoot ratios. However, simple models of Arctic tundra ER typically use only aboveground drivers, such as air temperature and leaf area index. To investigate this apparent discrepancy, we partitioned ER into its component fluxes in moist acidic tussock tundra, which is among the most widespread of Arctic ecosystems. To partition ER, we combined tissue-scale measurements of leaf, wood, moss, lichen, and root respiration with seasonal biomass estimates. Simple respiration models were fit to the data for each tissue type. Our results suggest that belowground respiration is a large proportion of ER and that its contribution increases over the course of the growing season with soil thaw. We estimated that bulk soil heterotrophic respiration made up approximately 40 %, root respiration made up 35 %, mosses contributed 8.5 % and all vascular plant leaves combined made up a mere 13.5 % of ER during the 2012 growing season. Our ability to model aboveground tissue respiration exceeded our ability to model belowground respiration. We hypothesize that effects of the aboveground climate on rhizosphere respiration, mediated by the production and delivery of photosynthate, may be a critical determinant of ER, as this would reconcile our results with simple models of ER.
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