Massive warming-induced carbon loss from subalpine grassland soils in an altitudinal transplantation experiment

[摘要] Climate change is associated with a change in soil organic carbon (SOC)stocks, implying a feedback mechanism on global warming. Grassland soilsrepresent 28 % of the global soil C sink and are therefore important for the atmospheric greenhouse gas concentration. In a field experiment in the Swiss Alps we recorded changes in the ecosystem organic carbon stock under climate change conditions, while quantifying the ecosystem C fluxes at the same time (ecosystem respiration, gross primary productivity, C export in plant material and leachate water). We exposed 216 grassland monoliths to six different climate scenarios (CSs) in an altitudinal transplantation experiment. In addition, we applied anirrigation treatment ( +12  % to 21 % annual precipitation) and an N deposition treatment ( +3 and +15  kg N ha −1  yr −1 ) in a factorial design, simulating summer-drought mitigation and atmospheric N pollution. In 5 years the ecosystem C stock, consisting of plant C and SOC, droppeddramatically by about −14  % ( - 1034 ± 610  g C m −2 ) with the CS treatment representing a +3.0   ∘ C seasonal (April–October) warming. N deposition and the irrigation treatment caused no significant effects. Measurements of C fluxes revealed that ecosystem respiration increased by 10 % at the +1.5   ∘ C warmer CS site and by 38 % at the +3   ∘ C warmer CS site ( P ≤0.001 each), compared to the CS reference site with no warming. However, gross primary productivity was unaffected by warming, as were the amounts of exported C in harvested plant material and leachate water (dissolved organic C). As a result, the 5-year C flux balance resulted in a climate scenario effect of - 936 ± 138  g C m −2 at the +3.0   ∘ C CS, similar to the C stock climate scenario effect. It is likely that this dramatic C loss of the grassland is a transient effect before a new, climate-adjusted steady state is reached.

[学科分类] 大气科学