[Effects of growth stage and altitude on twig functional traits and biomass allocation of Rhododendron przewalskii in the headwater region of Minjiang River, China]

This study aimed at understanding the differences in traits of functional twigs and leaves of a typical alpine shrub species, Rhododendron przewalskii, at Kaka Mountain in the headwater region of Minjiang River. Leaf and twig traits were compared for shrubs at different growth stages (flower bud stage and flowering stage) and altitude (3600 m and 3800 m). The effects of spatial heterogeneity on their correlations and trade-offs were evaluated at leaf and twig levels, respectively. Our results showed that twig length was significantly longer at low altitude than high altitude for the shubs at the same growth stage. The number and mass of flowers at flowering stage were significantly higher at high altitude than those at low altitude. At the same altitude, twig mass, number of leaves, total leaf mass, total leaf area and total petiole mass were all significantly greater at the flower bud stage than those at the flowering stage, while the individual leaf mass and individual petiole mass at flower bud stage were significantly smaller than those at flowering stage. Compared with the flower bud stage, the proportion of leaf mass decreased by 13% at the flowering stage, while biomass proportion of twig significantly increased. At the flower bud stage, twig mass had a higher contribution to total twig mass. In contrast, the contribution of total leaf mass to total twig mass was higher at flowering stage. More biomass of leaf was allocated to individual leaf mass at flower bud stage. More biomass of leaf was allocated to individual petiole mass and individual leaf mass at flowering stage at low altitude and high altitude, respectively. At low altitude, allometric growth patterns presented between twig mass and total leaf area, total leaf mass. Similarly, individual petiole mass and individual leaf area had allometric growth. Our results indicated that the functional traits of twigs and leaves varied across both altitude and plant growth stage.