I am thrilled by the invisible: If you look at a plant, you never get the whole picture. Neither do you see its root system, nor the habitat this root system together with soil provides. Indeed, the diverse communities of plants and soils, and their interactions form one of the most fascinating systems I know.
Effects of climate and land use changes on plant-soil system communities and their interactions with regard to ecosystem functions
Process-/ trait-based modeling and machine learning.