| 28 Sep 2026
Revised nitrogen balance for plant photosynthesis and growth in the dynamic global vegetation, hydrology and agriculture model LPJmL (5.10)
Abstract. The balance between the supply of reactive nitrogen to plants and their nitrogen demand determines the extent to which plant growth, and the associated terrestrial carbon and water cycles, are limited by nitrogen (N). While developing recent versions of the Lund-Potsdam-Jena managed land (LPJmL) model, we identified a legacy scaling error in the nitrogen demand formulation that artificially inflated plant leaf N demand by a factor of approximately two. Correcting this structural inconsistency fundamentally altered the modeled terrestrial N balance and effectively eliminated N limitation on simulated vegetation growth. To restore process realism, we present LPJmL version 5.10, which resolves this legacy formulation by implementing a comprehensive re-evaluation of plant uptake, recycling, and phenological dynamics. Specifically, this model update introduces: (1) a corrected leaf N demand calculation that removes inappropriate daylength scaling; (2) updated root uptake kinetics for separate nitrate (NO3-) and ammonium (NH4+) uptake based on experimental data; (3) changes to N recovery and turnover in plants; and (4) revised tree phenology to improve seasonal canopy dynamics. We evaluated the resulting model behavior using the International Land Model Benchmarking (ILAMB) tool, spatial vegetation patterns against satellite observations, and comparisons with global literature values for N cycle components. LPJmL 5.10 preserves aggregate land-surface performance for energy and hydrological diagnostics while establishing a more self-consistent and realistic internal N cycle. Relative to its predecessor, global vegetation N stocks and N uptake decreased by ~35 %. This reduction in plant demand shifted mineral soil nitrogen toward a larger nitrate pool, which subsequently increased immobilization, leaching, and denitrification fluxes. These altered pathways bring global N losses into closer agreement with absolute empirical literature estimates. As the final release of the LPJmL 5 series, version 5.10 documents the exact model configuration used for the TRENDY simulations in the Global Carbon Budget 2025 and provides a structurally sound foundation for future model development in the LPJmL 6 series.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Geoscientific Model Development.
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