Most Earth system models (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 ELM-FUN based on the C costs of nutrient acquisition from mycorrhizae, direct root uptake, retranslocation from senescing leaves, and biological N fixation. We benchmarked ELM-FUN with three classes of products: ILAMB, a remotely sensed nutrient limitation product, and CMIP6 models; we found significant improvements in C cycle variables, although the lack of more observed nutrient data prevents a comprehensive level of benchmarking. 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 invested 4.1 Pg C yr −1 to acquire 841.8 Tg N yr −1 and 48.1 Tg P yr −1 (1994–2005), leading to significant downregulation of global net primary production (NPP). Global NPP is reduced by 20% with C costs of N and 50% with C costs of NP. Modeled and observed nutrient limitation agreement increases when N and P are considered together ( r 2 from 0.73 to 0.83). , Plain Language Summary Climate models do not take into account the carbon (C) spent by plants to acquire nutrients, such as nitrogen (N) and phosphorus (P). This can lead to uncertainties in future climate predictions. In this study, we integrate a model of plant nutrient acquisition using optimization methods (fixation & uptake of nutrients, FUN) into the energy exascale Earth system land model (ELM). Global plant N and P uptake are dynamically simulated by ELM-FUN based on the C costs of nutrient acquisition from multiple acquisition pathways. We benchmarked ELM-FUN with measurements (in situ, remotely sensed, and integrated using artificial intelligence), and other climate CMIP6 models. We found improvements in the global C cycle. Overall, we found N and P co-limitation for 80% of the land. Globally, the new model predicts that plant productivity is reduced by 20% with C costs of N and 50% with C costs of NP. , Key Points We integrate a plant productivity-optimizing nitrogen and phosphorus acquisition model into the Energy Exascale Earth System Land Model We benchmarked the new model and found significant improvements in the carbon cycle. Nitrogen and phosphorus co-limit 80% of the land area Global Net Primary Production is reduced by 50% when the cost of nitrogen and phosphorus acquisitions are considered at the same time