<Emphasis Type="Italic"> Picea</Emphasis> seedlings show apparent acclimation to drought with increasing altitude in the eastern Himalaya

Abstract We measured plant structural and physiological responses of two sympatric Picea species, Picea likiangensis (Franchet) E. Pritzel var. balfouriana and Picea asperata Masters var. retroflexa to altitude close to the treeline in the eastern Himalaya. Most measured tree characteristics differed between different altitudes, between different ages, and between shaded and un-shaded treatments. Both P. likiangensis and P. asperata had lower foliage area/stem cross-sectional area ratios, smaller specific leaf areas, higher root mass/foliage area ratios, and less negative ¹³C at 3,900 m than at 3,600 m altitude, and in the un-shaded treatment than in the shaded treatment. The 7- and 9-year-old seedlings also showed lower foliage area/stem cross-sectional area ratios, higher root mass/foliage area ratios and less negative ¹³C than younger seedlings. Shading resulted in an increase of biomass accumulation at all altitudes. A close relationship, independent of altitude, was observed between ¹³C and specific leaf area, suggesting that internal resistance could limit CO₂ diffusion to the site of carboxylation. The results indicate that, in spite of greater water availability, trees at higher altitudes show quite a number of apparent acclimations to drought.