#L19 Global terrestrial nutrient uptake

Abstract

The ACME BGC inter-comparison has a primary goal of evaluating two ALMv1 representations of nutrient controls on the terrestrial C cycle: ALMv1-ECA-CNP and ALMv1-CTC-CNP. These models take fundamentally different approaches to representing nutrient competition, plant nutrient acquisition, and plant nutrient use, resulting in distinct C cycle dynamics. We focus here on one important aspect of these interactions: nutrient competition and acquisition at the root-soil interface. In this regard, an important distinction between the two model structures is the Equilibrium Chemistry Approximation (ECA) versus Relative Demand (RD) concepts. Decades of observations indicate that plant nutrient uptake is de-coupled from instantaneous photosynthetic nutrient demand in terrestrial systems, contradicting a fundamental basis of the RD approach integrated in ALMv1-CTC-CNP. Our analysis using ALMv1-ECA-CNP indicates that about half of global N and P uptake occur outside of photosynthetically active periods, with non-growing season uptake being particularly important in high latitudes and nighttime uptake being particularly important at lower latitudes. In this presentation, we describe ALMv1-ECA-CNP concepts, benchmarking, and estimates of the implications of non photosynthetically active period nutrient acquisition on global C, N, and P cycles.