Altitudinal gradients of natural abundance of stable isotopes of nitrogen and carbon in the needles and soil of a pine forest in Nepal

Abstract

This paper deals with natural abundance of 15N and 13C in the soil and needles of the pine forest (Pinus roxburghii, Sargent) along an altitudinal gradient. The study area lies in the elevation range of 1,200 m to 2,200 m in Kathmanduvalley of Nepal. The higher altitude soil was found to be much more depleted of 13C than the lower altitude soil. The decreasing trend of C-isotope (as well as the trend of N-isotope) might be attributed to the lower mineralisation rate and net nitrification rate at the higher altitude. The observed differences in isotopic N- and C-contents of needles and soils across altitudinal gradients in this study are a result of the combination of environmentally induced variations in physiological and morphological differences. For example, altitudinal variation in needle δ15N and δ13C at the research site indicates that the needle isotopic composition is related to nitrogen availability at a site.

Keywords

• pine forest
• nepal
• stable isotopes
• carbon
• nitrogen
• soil
• needles
• altitudinal gradients