State-of-the-art terrestrial biosphere models require a greater understanding of land surface processes than was previously available. The EU-funded JULIA project helped close the gap between observational science and large scale modelling of biosphere processes at a level of detail suitable for an Earth system model. Two of the most important areas that needed to be addressed were plant-soil interactions and the facctors controlling water fluxes from tree canopies. Both fields have a significant influence on land surface fluxes, ecosystem productivity and long-term carbon sequestration. Scientists used flux measurements, plant characteristics and the outcomes of ecosystem monitoring studies to create sophisticated terrestrial computer models of the biosphere. A particular focus of the JULIA project was the role of the nitrogen cycle in the climate system and its impact on the natural carbon cycle. In addition, JULIA assessed the impact of nitrogen from human activities on terrestrial greenhouse gas fluxes. The studies showed that greater effort is needed to mitigate climate change as the carbon sequestration capacity of the terrestrial biosphere has been previously overestimated. Furthermore, nitrogen management is important for controlling changes to the climate system resulting from human activities. This work resulted in a series of publications on the nitrogen cycle, the modelling of plant soil interaction and the effect of drought on tree canopies. Results were incorporated into a model system that is part of the international Global Carbon Project and provides data for the Intergovernmental Panel on Climate Change (IPCC) and its Fifth Assessment Report (AR5). The JULIA project successfully developed a tool to better quantify interactions of the terrestrial biosphere and the climate system for use in Earth system models, thereby enabling more accurate predictions to be made for future climate conditions.