The land-surface components of several Earth System Models have the capacity to represent the size and compositional structure of terrestrial plants (FATES, ED, SEIB-DGVM, LPJ-GUESS, Ent, etc). Subsequently, these models can represent dynamic processes that operate on single plants, plant cohorts or other similar scaling structures closely tied to plant biology and physiology, that were previously intractable. While the model scaling strategies exist (e.g. cohorts, individuals, etc) to support the representation of allocation and reactive transport of nutrients and carbon isotopes in terrestrial vegetation, these processes are not as well understood as other aspects like leaf physiology and chemistry.

Here we present a software framework designed to enable the testing and intercomparison of different hypotheses for nutrient and carbon isotope allocation and reactive transport in plants. This framework, called the Plant Allocation and Reactive Transport Extensible Hypotheses (PARTEH) is designed with an emphasis on modularity and extensibility, and makes use of modern Fortran programming standards such as inheritance to facilitate the addition of new hypotheses. These hypotheses are evaluated both in a single plant simulation environment, and as coupled with the Functionally Assembled Terrestrial Ecosystem Simulator (FATES). An evaluation of at least two different schemes is presented, a carbon-only allometry based allocation model, and a nitrogen-phosphorous model based on stoichiometric targets with allometrically based carbon. Early results from this framework have shown that plant growth has high sensitivity to the exponent parameter in the power-function leaf carbon-diameter allometry equations. The testing and inclusion of this framework within an ESM highlights the importance of size-structured vegetation and the associated allometric relationships implemented in nutrient transport, as well as areas in need of more research.