Production and export of dissolved C in arctic tundra mesocosms: the roles of vegetation and water flow

To better understand carbon (C) cycling in arctic tundra we measured dissolved C production and export rates in mesocosms of three tundra vegetation types: tussock, inter-tussock and wet sedge. Three flushing frequencies were used to simulate storm events and determine potential mass export of dissolved C under increased soil water flow scenarios. Dissolved C production and export rates differed between vegetation types (inter-tussock > tussock > wet sedge). In the absence of flushing, dissolved organic C (DOC) dominated production in tussock and inter-tussock soils but was consumed in wet sedge soils (8.3, 32.7, and -0.4 mug C g soil(-1) day(-1)). Soil water dissolved C concentrations declined over time when flushed at high and medium frequencies but were variable at low flushing frequency. Total yield of dissolved C and DOC increased with increased flushing frequency. The ratio of DOC to dissolved inorganic C exported dropped with increased flushing under tussock but not inter-tussock or wet sedge vegetation. Mass export per liter of water added declined as flushing frequency increased in tussock and inter-tussock mesocosms. Export and production of dissolved C were strongly correlated with above ground biomass, but not with photosynthetic rates or below ground biomass. DOC quality was examined by measuring production of Toolik Lake bacteria fed mesocosm soil water. When normalized for DOC concentration, wet sedge soil water supported significantly higher bacterial production. Our results indicate that arctic tundra soils have high potentials for dissolved C export, that water flow and vegetation type mainly control dissolved C export, and that responses of aquatic microbes to terrestrial inputs depend on the vegetation type in the watershed.