Carbon dynamics in forests and croplands: influence of management and climate extremes

Management and climate change had and continue to have a strong impact on carbon (C) dynamics in terrestrial ecosystems. In this context, the possible effects due to changes in climate extreme frequency are far to be fully understood as well as mitigation strategies related to forest and agricultural management are still strongly debated. The main objective of this thesis is to bring some additional knowledge on the above mentioned topics through manipulation experiments, medium-term micrometeorological observations and long-term field measurements (chronosequences) in forests and croplands. In particular, after an introduction to the main topic of research (Chapter 1) and a brief summary of the adopted methods (Chapter 2), the thesis is divided into three research papers (one already published, one submitted and one in preparation): - the first paper (Chapter 3) examines, through two forest chronosequences and model simulations, the C pools dynamics in a beech and a spruce forest in Italian Alps. The main objective of the work was to determine the influence of stand age and applied management on the C cycle in these forests. Results showed that shelterwood management had no influence on soil C stock, while model simulations confirmed that the applied management allows a rapid recovery of the ecosystem after disturbance (i.e. final cut); - the second paper (Chapter 4) investigates the effects of conservation agriculture (i.e. minimum tillage + cover crops) on ecosystem C dynamics and crop productivity in a 5-year crop rotation. Continuous micrometeorological measurements on paired plots were used to quantify all C fluxes of the ecosystem. Minimum tillage resulted in a higher net ecosystem productivity than control (conventional tillage), but in a decrease of the overall C budget (net ecosystem C budget, NECB); - the third paper (Chapter 5) focuses on temperature extreme event (i.e. cold and hot waves) impacts on heterotrophic respiration, yield and C budget in a soybean crop. Results showed that both extreme events did not alter the C budget even though an acceleration in decomposition was found in warm treatment.