Climatic Control on Plant and Soil [delta].sup.13C along an Altitudinal Transect of Lushan Mountain in Subtropical China: Characteristics and Interpretation of Soil Carbon Dynamics

Decreasing temperature and increasing precipitation along altitude gradients are typical mountain climate in subtropical China. In such a climate regime, identifying the patterns of the C stable isotope composition ([delta].sup.13 C) in plants and soils and their relations to the context of climate change is essential. In this study, the patterns of [delta].sup.13 C variation were investigated for tree leaves, litters, and soils in the natural secondary forests at four altitudes (219, 405, 780, and 1268 m a.s.l.) in Lushan Mountain, central subtropical China. For the dominant trees, both leaf and leaf-litter [delta].sup.13 C decreased as altitude increased from low to high altitude, whereas surface soil [delta].sup.13 C increased. The lower leaf [delta].sup.13 C at high altitudes was associated with the high moisture-related discrimination, while the high soil [delta].sup.13 C is attributed to the low temperature-induced decay. At each altitude, soil [delta].sup.13 C became enriched with soil depth. Soil [delta].sup.13 C increased with soil C concentrations and altitude, but decreased with soil depth. A negative relationship was also found between O-alkyl C and [delta].sup.13 C in litter and soil, whereas a positive relationship was observed between aromatic C and [delta].sup.13 C. Lower temperature and higher moisture at high altitudes are the predominant control factors of [delta].sup.13 C variation in plants and soils. These results help understand C dynamics in the context of global warming.