Tending towards a fixed value: stoichiometric homeostasis of the nitrogen-to-phosphorus ratio in membrane lipids as an adaptive strategy to nitrogen deficiency

The nitrogen (N) and phosphorus (P) stoichiometry in organisms reflects environmental resources under homeostatic constraints. However, whether and how N and P stoichiometry in plant membrane lipids responds to N deficiency remains untested. This study examined membrane lipid N and P stoichiometry in leaves and roots of Arabidopsis thaliana and its close relative, Crucihimalaya himalaica, under N deficiency. C. himalaica, native to N-poor habitats, exhibits greater N-deficiency tolerance and less membrane lipid reduction than A. thaliana. In leaves, membrane lipid N stoichiometry reflects N supply, with stronger homeostasis in C. himalaica. Lipid P stoichiometry is coupled with N in both: as N supply declines, A. thaliana’s N:P ratio shifts toward 0.61, whereas C. himalaica’s remains stably fixed at 0.61. Roots show stronger N and N:P homeostasis than leaves, with lipid N:P ratios constant at 0.75. Both organs display large negative homeostasis coefficients (H), distinct from whole-plant patterns but indicating tight N:P regulation. These results suggest that membrane lipid N:P homeostasis correlates positively with N-deficiency tolerance, and fixed N:P ratios may represent a novel adaptive strategy, providing new insights into stoichiometric mechanisms for plant survival in extreme N-limited habitats.