The DOE SC program in Biological and Environmental Research (BER) hereby announces its interest in receiving applications for research in Environmental System Science (ESS). The goal of the ESS program in BER is to advance an integrated, robust, and scale-aware predictive understanding of terrestrial systems and their interdependent microbial, biogeochemical, ecological, hydrological, and physical processes. The ESS program scope advances foundational process knowledge with an emphasis on understudied ecosystems. This NOFO will consider applications that focus on measurements, experiments, field data, modeling, and synthesis to provide improved understanding and representation of ecosystems and watersheds in ways that advance the sophistication and capabilities of models that span from individual processes to Earth-system scales. This NOFO will encompass three Science Research Areas: 1) plant-soil-microbe interactions and their influence on belowground biogeochemical processes; 2) synthesis studies using existing data that address testing of ESS-relevant hypotheses and development of transferable insights into knowledge gaps for U.S. southeast coastal systems; and 3) synthesis studies on contributions and vulnerabilities of Earth system processes in marginal and degraded lands. The BER ESS program goal is to advance an integrated, robust, and scale-aware predictive understanding of terrestrial systems and their interdependent microbial, biogeochemical, ecological, hydrological, and physical processes. To support this goal, the program uses a systems approach to develop an integrative framework to elucidate the complex processes and controls on the structure, function, feedbacks, and dynamics of terrestrial and watershed systems, that span from molecular to global scales and extend from the bedrock through the soil, rhizosphere, and vegetation to the atmosphere. The ESS program scope advances foundational process knowledge with an emphasis on understudied ecosystems. Supported research emphasizes ecological and hydro-biogeochemical linkages among system components and characterization of processes across interfaces (e.g., terrestrial-aquatic, coastal, urban) to address key knowledge gaps and uncertainties across a range of spatial and temporal scales. Incorporation of scientific findings into process and system models is an important aspect of the ESS strategy, both to improve predictive understanding as well as to enable the identification of new research questions and directions.