The age-related changes of leaf structure and biochemistry in juvenile and mature subalpine fir trees (Abies faxoniana Rehder and E.H. Wilson.) along an altitudinal gradient

Abstract

In woody perennials, leaf structure and biochemistry vary with tree age under changing environments. However, the related eco-physiological mechanisms have not been elucidated yet. In this study, we investigated age-related responses of juvenile and mature subalpine fir trees (Abies faxoniana Rehder & E.H. Wilson.) growing at altitudes between 2,500 and 3,500 m in the Wanglang Natural Reserve in southwest China, to study the adaptive strategies of different age trees to suit changing environments. We found that there were distinct age- and altitude-related changes in the structural and biochemical characteristics of leaves. At all altitudes, mature trees exhibited higher area- and mass-based leaf nitrogen content (N-area, N-mass), leaf mass per area (LMA) and stable isotope carbon composition (delta C-13), and a lower chlorophyll (Chl) content than those juvenile trees, except for N-mass at 3,000 m as well as LMA at 2,750 in, where the values of N-mass and LMA in mature trees were slightly lower than those in juvenile trees. Furthermore, leaf characteristics showed significant differences in the change rates with altitude between different age groups. Our results indicated that assimilative organs in mature trees do not suffering from nutrient deficiency and that juvenile and mature trees possess different adaptive growth strategies under changing environments, as indicated by higher leaf N content in mature trees and the opposite patterns of LMA and Chl content between two age groups. We also concluded that juvenile could be more sensitive to global warming due to a greater altitudinal influence on the leaf traits in juvenile trees than those in mature trees.