Elevated Nitrogen and Phosphorus Levels Suggest High Metabolic Demands in Himalayan High-Elevation Plants.

Nutrient contents in plant tissues reflect adaptations and environmental constraints, varying across and within species along ecological gradients. Interspecific differences reflect long-term adaptations, while intraspecific variations may indicate acclimation to present conditions. Examining these responses across elevational ranges is therefore crucial for understanding how nutrients influence species performance. We investigated whether organ nutrients play a significant role at the upper limits of the world's highest occurring herbaceous angiosperms by analysing intraspecific and interspecific variations in leaf carbon (C), nitrogen (N), and phosphorus (P) contents in 22 species, and root N and P contents in 15 species along a gradient from 4560 to 6150 m a.s.l. in the Western Himalaya. Our findings reveal contrasting patterns in nutrient contents. Interspecifically, leaf N and P decreased and C:N increased with elevation, indicating selective pressure for adaptations to reduced nutrient availability. In contrast, intraspecific leaf N content generally increased with increasing elevation. Root N trend did not change interspecifically with elevation, while overall intraspecific trends increased. Surprisingly, subnival species at the highest localities around 6000 m had relatively high tissue N and P contents. This suggests that high-elevation Himalayan herbs require high nutrient levels, likely for photosynthesis, to achieve a positive annual carbon gain during the short growing season and to accumulate sufficient root reserves. Elevated N and P content, especially at the highest localities, imply that the upper limits of the world's highest-growing plants may not be limited by nutrient acquisition constraints.