Human activities are altering a range of environmental conditions, including atmospheric CO2 concentration, climate, and nutrient inputs. However, understanding and predicting their combined impacts on ecosystem structure and functioning and biogeochemical cycles is challenging. Divergent future projections of terrestrial ecosystem models reveal uncertainties about fundamental processes and missing observational constraints. Models are routinely tested and calibrated against data from ecosystem flux measurements, remote sensing, atmospheric inversions and ecosystem inventories. These model projections constrain the current mean state of the terrestrial biosphere, but they provide limited information on the sensitivity of ecophysiological, biogeochemical, and hydrological processes to environmental changes. Observational and ecosystem manipulation studies (e.g., Free-Air Carbon Dioxide Enrichment (FACE), nutrient addition or warming experiments) can complement modelling studies with unique insights and inform model development and evaluation. This session focuses on how ecosystem processes respond to changes in CO2 concentration, warming, altered precipitation patterns, water and nutrient availability. It aims at fostering the interaction between the experimental and modelling communities by advancing the use of observational and experimental data for model evaluation and calibration. We encourage contributions from syntheses of multiple experiments, model intercomparisons and evaluations against ecosystem manipulation experiments, pre-experimental modelling, or the use of observations from "natural experiments". Contributions may span a range of scales and scopes, including plant ecophysiology, soil organic matter dynamics, soil microbial activity, nutrient cycling, plant-soil interactions, or ecosystem dynamics.