Age-related variations of needles and twigs in nutrient, nonstructural carbon and isotope composition along altitudinal gradients

The biochemical and physiological properties of alpine woody plants responding to elevation are associated with needles and twigs age. However, the interactions with elevation were not well studied. In this study, we investigated age-related (current, one-year and two-year old) functional traits of Abies faxoniana in needles and twigs with elevation (2500 m, 2750 m, 3000 m, 3250 m, and 3500 m a.s.l) at the eastern edge of the Tibetan Plateau. The macro-elements (C, N, P, K, Ca, and Mg), nonstructural carbons (soluble sugar, sucrose, and starch) and isotope composition (δ 13 C) were measured in needles and twigs of adult A. faxoniana trees (breast height diameter about 30 cm). There were significant age, elevation and their interaction effects on these traits (except for δ 13 C). Compared with two-year-old needles and twigs, the current and one-year-old tissues possessed higher concentrations of P and K, lower Ca concentrations, as well as a lower δ 13 C values and C: P and N: P ratios in needles. The current-year twigs generally had higher sucrose concentration and sucrose: starch ratio than the old ones. This study suggested that more nutrients were invested to young needles and twigs to cope with elevation for A. faxoniana than the old ones.