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Abstract

Soil is a complex media that contains various biotic and abiotic nutrient consumers. Given that terrestrial ecosystems are more or less limited by nitrogen or phosphorus or both, strong nutrient competition is expected. Here, we benchmark existing plant-microbe competition theories that have been implemented in Earth System Models (ESMs), aiming to mechanistically model the competitive interactions among plants, soil microorganisms, and mineral surfaces. We also integrate into ALMv1, parameterize, and evaluate a new competition model (N-COM) based on the Equilibrium Chemistry Approximation (ECA) theory. Short-term ¹⁵N/³³P tracer data and long-term N and P perturbation experiments are used to evaluate model predictability. We show that competition theories in current ESMs (including ALMv0 and ALMv1) fail to capture observed patterns in the short-term (~hours), while our new approach robustly simplifies the complex nature of nutrient competition and quantitatively matches the observations. Over the longer-term (~years) the adjustment of whole-plant resource allocation, investment of nitrogen and phosphorus in phosphatase and nitrogenase production, and adjustment of root traits becomes important. We have integrated representations of these processes in ALMv1 and will discuss their implications. This work provides an ecologically consistent representation of nutrient competition appropriate for the land BGC Experiment planned with ALMv1.