PNNL

Abstract

• Most Earth System Mmodels (ESMs) do not explicitly represent the carbon (C) costs of plant nutrient acquisition, which leads to uncertainty in predictions of the current and future constraints to the land C sink. • We integrate a plant productivity-optimizing nitrogen (N) and phosphorus (P) acquisition model (Fixation & Uptake of Nutrients, FUN) into the Energy Exascale Earth System (E3SM) Land Model (ELM). Global plant N and P uptake are dynamically simulated by E3SM-FUN based on the C costs of nutrient acquisition from mycorrhizae, direct root uptake, retranslocation from senescing leaves, and biological N fixation. • We benchmarked E3SM-FUN with three classes of products: ILAMB, a remotely sensed nutrient limitation product, and CMIP6 models; we, and found significant improvements in C cycle variables. Overall, we found N and P co-limitation for 80% of land area, with the remaining 20% being either predominantly N or P limited. • Globally, the new model predicts that plants invest 4.1 Pg C yr-1 to acquire 841.8 Tg N yr-1 and 48.1 Tg P yr-1, leading to significant downregulation of global Net Primary Production (NPP). Global NPP is reduced by 20% with N costs and 50% with N+P costs. Modeled and observed nutrient limitation agreement increases when N and P are considered together (r2 from 0.734 to 0.83).