Impacts of high-latitude vegetation dynamics on ecosystem carbon turnover under future climate

Abstract:

High-latitude regions store large stocks of soil organic carbon. Most of these regions are underlain by permafrost, and hence much of the soil organic carbon is not accessible to microbial decomposition. However, recent and projected climate warming may accelerate the ecosystem carbon cycle through effects on the rates of carbon uptake and decomposition. The role of potential changes in vegetation in altering the rate of ecosystem carbon turnover is an important component of the global carbon cycle and uncertain. In this study, we used a well-tested mechanistic ecosystem model to examine how climate induced vegetation dynamics affect carbon residence times across Alaska. Our results show that projected 21^st century climate warming will (1) enhance soil warming, deepening of the active layer, soil organic decomposition, and N mineralization which will then enhance plant growth; (2) alter vegetation composition that favors plants with rapid carbon turnover (e.g., deciduous plants); and (3) increase litterfall with lower lignin content and carbon to nitrogen ratios, thus creating a positive feedback to more rapid microbial decomposition and lower overall ecosystem carbon residence times. We modeled a 41% reduction in ecosystem carbon turnover (τ = (C _veg + C _{1m soil}) / GPP) time by 2100 compared to the present. We conclude that high-latitude vegetation change may accelerate ecosystem carbon turnover and associated carbon-climate feedback, which is a major source of uncertainty in Earth System Models.