Sensitivity of Tundra Carbon Balance to Ambient Temperature

Summer field observations in thenorth-east European region of Russia (1995–1996) proved thatnatural local and temporal warming could cause similarreversible changes of carbon (C) balance pattern ofsouth tundra ecosystems. Thirty-six diurnal chambermeasurements of carbon dioxide fluxes at two differentsites (67°57′N, 64°40′E; 67°20′N,63°44′E) in 4 main types of ecosystems werestudied. Wide magnitude of ambient mean diurnal airtemperature (from +4.1 to +20.2 °C) allowed toobtain significant linear relationship between thisparameter and variation in ecosystems C net flux (from–2.6 (sink) to +2.0 (source) gC m-2 d-1, R2 = 0.769). In the midst ofthe vegetative season, an increase of mean diurnal airtemperature in the plant canopy over the criticalvalue of +14 °C lead to a change in the C netflux from sink to source. This can revert with atemperature decreases below the critical value. Theabove-mentioned effect is mostly due to thetemperature influenced increase of gross ecosystemrespiration. The summer temperature induced changesmay result in positive (C source) annual C balance insome studied ecosystems. The annual C loss ofshrub-dwarf shrub community in 1996 was estimated at45 gC m-2 yr-1. We consider ourresults to be another evidence of possible positivefeed-back between climate warming and C emission tothe atmosphere on short-term and regional scales.