Soil respiration is stimulated by elevated CO₂ and reduced by summer drought: three years of measurements in a multifactor ecosystem manipulation experiment in a temperate heathland (CLIMAITE).

摘要

This study investigated the impact of predicted future climatic and atmospheric conditions on soil respiration (R_S) in a Danish Calluna-Deschampsia-heathland. A fully factorial in situ experiment with treatments of elevated atmospheric CO₂ (+130 ppm), raised soil temperature (+0.4 degrees C) and extended summer drought (5-8% precipitation exclusion) was established in 2005. The average R_S, observed in the control over 3 years of measurements (1.7 micro mol CO₂ m-2 sec-1), increased 38% under elevated CO₂, irrespective of combination with the drought or temperature treatments. In contrast, extended summer drought decreased R_S by 14%, while elevated soil temperature did not affect R_S overall. A significant interaction between elevated temperature and drought resulted in further reduction of R_S when these treatments were combined. A detailed analysis of short-term R_S dynamics associated with drought periods showed that R_S was reduced by ~50% and was strongly correlated with soil moisture during these events. Recovery of R_S to pre-drought levels occurred within 2 weeks of rewetting; however, unexpected drought effects were observed several months after summer drought treatment in 2 of the 3 years, possibly due to reduced plant growth or changes in soil water holding capacity. An empirical model that predicts R_S from soil temperature, soil moisture and plant biomass was developed and accounted for 55% of the observed variability in R_S. The model predicted annual sums of R_S in 2006 and 2007, in the control, were 672 and 719 g C m-2 y-1, respectively. For the full treatment combination, i.e. the future climate scenario, the model predicted that soil respiratory C losses would increase by ~21% (140-150 g C m-2 y-1). Therefore, in the future climate, stimulation of C storage in plant biomass and litter must be in excess of 21% for this ecosystem to not suffer a reduction in net ecosystem exchange.