Abstract: Plant density and nitrogen (N) availability influence plant survival and nutrient use strategies, but the interaction between these two factors for plant growth and the balance of elements remains poorly addressed. Here, we conducted experimental manipulations using Arabidopsis thaliana, with the combination of four levels of plant density and four levels of N addition, and then examined the corresponding changes in plant biomass production (indicated by total plant biomass and biomass partitioning) and nutrient use strategies (indicated by leaf N and phosphorus (P) stoichiometry). The biomass-density relationship was regulated by N availability, with a negative pattern in low N availability but an asymptotic constant final yield pattern at high N availability. Excessive N addition reduced plant growth at low plant density, but this effect was alleviated by increasing plant density. The root to shoot biomass ratio increased with plant density at low N availability, but decreased at high N availability. N availability was more important than plant density in regulating leaf N and P stoichiometry, with the increasing leaf N concentration and decreasing leaf P concentration under increasing N addition, resulting in a negative scaling relationship between these two elemental concentrations. Our results show that N availability and plant density interactively regulate plant biomass production and leaf stoichiometry of A. thaliana, and highlight that the interactive effects of these two factors should be considered when predicting plant growth behaviour under intraspecific competitive environments in the context of nutrient changes.

Key words: Arabidopsis thaliana, constant final yield, biomass partitioning, nitrogen availability, plant density, plant stoichiometry, scaling relationship