A New Theory of Plant-Microbe Nutrient Competition Resolves Inconsistencies between Observations and Model Predictions
Equilibrium Chemistry Approximation (ECA) kinetics explains plant-soil nitrogen competition.
Plants actively compete with soil microbes for nutrients to support photosynthesis and tissue construction. The current suite of Earth System Models (ESMs) has been shown over the past several years to poorly represent these interactions, with very large impacts on predictions of Carbon-Climate interactions and feedbacks. This study aims to test a new theory (ECA) of nutrient competition appropriate for integration in ESMs; we are currently doing so in a version of the ACME Land Model (ALMv1-ECA-CNP).
Our results revealed that competition theories in current ESMs fail to capture observed plant-soil nitrogen competition patterns. Therefore, predicted nutrient limitation effects on terrestrial carbon accumulation by existing ESMs may be biased. Our Equilibrium Chemistry Approximation (ECA) competition theory mechanistically represents plant-microbe nutrient competition, quantitatively matched the observations, and is appropriate for integration in an ESM-scale model.
Terrestrial plants assimilate atmospheric CO2 through photosynthesis and synthesizing new tissues. However, sustaining these processes requires plants to compete with microbes for soil nutrients, which therefore calls for an appropriate understanding and modeling of nutrient competition mechanisms in ESMs. Here, we surveyed existing plant-microbe competition theories and their implementations in Earth System Models (ESMs). We found no consensus regarding the representation of nutrient competition and that observational and theoretical support for current implementations are weak. To reconcile this situation, we applied the Equilibrium Chemistry Approximation (ECA) theory to plant-microbe nitrogen competition in a detailed grassland 15N tracer study and found that competition theories in current ESMs fail to capture observed patterns. The ECA prediction resolves the complex nature of nutrient competition and quantitatively matched the 15N observations. Since plant carbon dynamics are strongly modulated by soil nutrient acquisition, we conclude that (1) predicted nutrient limitation effects on terrestrial carbon sequestration by existing ESMs may be biased and (2) our ECA-based approach will improve predictions by mechanistically representing plant-microbe nutrient competition.
Lawrence Berkeley National Laboratory
DE-AC02-05CH11231 as part of their Regional and Global Climate Modeling and Accelerated Climate Modeling for Energy (ACME) programs.
Zhu, Q., W.J. Riley, J. Tang. “A new theory of plant-microbe nutrient competition resolves inconsistencies between observations and model predictions.” Ecological Applications, 27(3), 875-886 (2017). DOI:10.1002/eap.1490