Nutrient Dynamics in a Coupled Terrestrial Biosphere and Land Model (ELM-FATES)

Abstract

We present a representation of nitrogen and phosphorus cycling in the vegetation demography model the Functionally Assembled Terrestrial Ecosystem Simulator (FATES), within the Energy Exascale Earth System (E3SM) land model. This representation is modular, and designed to allow testing of multiple hypothetical approaches for carbon-nutrient coupling in plants. The model tracks nutrient uptake, losses via turnover from both live plants and mortality into soil decomposition, and allocation during tissue growth for a large number of size- and functional-type-resolved plant cohorts within a time-since-disturbance-resolved ecosystem. Root uptake is governed by fine root biomass, and plants vary in their fine root carbon allocation in order to balance carbon and nutrient limitations to growth. We test the sensitivity of the model to a wide range of parameter variations and structural representations, and in the context of observations at Barro Colorado Island, Panama. A key model prediction is that plants in the high-light-availability canopy positions allocate more carbon to fine roots than plants in low-light understory environments, given the widely different carbon versus nutrient constraints of these two niches within a given ecosystem. This model provides a basis for exploring carbon-nutrient coupling with vegetation demography within Earth System Models (ESMs).

Toward a coordinated understanding of hydro‐biogeochemical root functions in tropical forests for application in vegetation models

“…ELM‐CNP; Yang et al ., 2019); (2) represented the C cost of coarse and fine‐root allocation across depths (e.g. Sakschewski et al ., 2021); and (3) represented water and nutrient foraging functions of roots across depths (Christoffersen et al ., 2016; Xu et al ., 2016; Langan et al ., 2017; Kennedy et al ., 2019; Joshi et al ., 2022; Knox et al ., 2023). Hydro‐biogeochemical model integration would allow a better representation of the fast–slow plant lifestyle continuum (Reich, 2014) by including trade‐offs in nutrient acquisition (shallow‐rooted) vs stable water supply (deep roots).…”