Effects of Drainage and Temperature on Carbon Balance of Tussock Tundra Microcosms

• Published in: Oecologia 1996-12, Vol.108 (4), p.737-748
• Main Authors: Johnson, L. C., Shaver, G. R., Giblin, A. E., Nadelhoffer, K. J., E. R. Rastetter, Laundre, J. A., Murray, G. L.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Ecosystems Ecology; Field capacity; Fundamental and applied biological sciences. Psychology; Marine ecosystems; Methane; Microcosms; Organic soils; Respiration; Soil water; Synecology; Terrestrial ecosystems; Tundra soils; Tundras
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00329050

We examined the importance of temperature (7°C or 15°C) and soil moisture regime (saturated or field capacity) on the carbon (C) balance of arctic tussock tundra microcosms (intact blocks of soil and vegetation) in growth chambers over an 81-day simulated growing season. We measured gaseous CO₂ exchanges, methane (CH4) emissions, and dissolved C losses on intact blocks of tussock (Eriophorum vaginatum) and intertussock (moss-dominated). We hypothesized that under increased temperature and/or enhanced drainage, C losses from ecosystem respiration (CO₂ respired by plants and heterotrophs) would exceed gains from gross photosynthesis causing tussock tundra to become a net source of C to the atmosphere. The field capacity moisture regime caused a decrease in net CO₂ storage (NEP) in tussock tundra microcosms. This resulted from a stimulation of ecosystem respiration (probably mostly microbial) with enhanced drainage, rather than a decrease in gross photosynthesis. Elevated temperature alone had no effect on NEP becuase CO₂ losses from increased ecosystem respiration at elevated temperature were compensated by increased CO₂ uptake (gross photosynthesis). Although CO₂ losses from ecosystem respiration were primarily limited by drainage, CH₄ emissions, in contrast, were dependent on temperature. Furthermore, substantial dissolved C losses, especially organic C, and important microhabitat differences must be considered in estimating C balance for the tussock tundra system. As much as ∼ 20% of total C fixed in photosynthesis was lost as dissolved organic C. Tussocks stored ∼ 2x more C and emitted 5x more methane than intertussocks. In spite of the limitations of this microcosm experiment, this study has further elucidated the critical role of soil moisture regime and dissolved C losses in regulating net C balance of arctic tussock tundra.