Shoot growth and seasonal changes of nonstructural carbohydrate concentrations at the upper and lower distribution limits of three conifers

Abstract

Nonstructural carbohydrate (NSC) concentration in plant organs is an indicator of a balance between carbon sources (i.e., photosynthesis) and sinks (i.e., growth). Understanding how NSC concentrations change with altitude would help determine altitudinal changes in plant growth. This study compared shoot growth and seasonal changes in NSC concentrations of current-year and 1-year-old needles and branch woods between the upper and lower distribution limits of subalpine conifers Abies veitchii (1600–2000 m a.s.l.), A. mariesii (2000–2400 m a.s.l.), and Pinus pumila (2400–2800 m a.s.l.) in Japan. The lengths of 1-year-old shoots were shorter at the upper distribution limits for the three species, and concentrations and branch woods were all high in spring but decreased toward summer, increasing from summer to autumn. No clear difference was found for either parameter between upper and lower distribution limits for each species. Therefore, this study suggests that growth reduction at the upper distribution limits is due to reduction of both sink and source activities, with similar degrees for each species. However, further studies of sink and source activities, such as temperature-dependent photosynthesis and growth traits, are necessary to reveal clearly the cause of this growth reduction in high altitudes.