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 15 N and 13 C 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 Kathmandu valley of Nepal. The higher altitude soil was found to be much more depleted of 13 C 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 δ 15 N and δ 13 C at the research site indicates that the needle isotopic composition is related to nitrogen availability at a site.