OP-I5.3 Non-growing season high-latitude plant nitrogen and phosphorus uptake impact land C cycle

Abstract

High-latitude systems have very large soil organic carbon (C) stocks which are vulnerable to be released to the atmosphere as CO₂ and CH₄ over the 21^st century. On the other hand, CO₂ sequestration by plants may counteract these emissions. High-latitude plant photosynthesis is strongly limited by nutrient (nitrogen (N), phosphorus (P)) availability, and these limitations are expected to increase in the coming decades. Further, high-latitude plant representations in global land models remain uncertain and these models have fared poorly in recent confrontations with observations. We show here that one relevant factor may be plant nutrient acquisition during the non-growing season, a widely observed process ignored by most large-scale land models. To quantify high-latitude nutrient acquisition, we apply ELMv1, a model that explicitly represents nutrient acquisition based on competitor traits (e.g., fine-root biomass and transporter density, microbial V_max and affinity). Our results indicate that high-latitude plant nutrient uptake during the non-growing season ranges between ~10 - 60% of annual uptake, with large spatial variability and dependence on plant type. Model experiments excluding non-growing season nutrient uptake demonstrate large effects on N retention and the C cycle, and therefore interactions with the atmosphere and climate.

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