Abstract: Based on the determinations of soil organic matter (SOM) content,SOM Δ¹⁴C,and SOMδ¹³C of the samples collected by thin-layered sampling method, this paper studied the spatial and temporal differentiation of SOM δ¹³C in the soil profiles at different altitudes in Dinghushan Biosphere Reserve.The results showed that the vertical differentiation of SOM δ¹³C at different altitudes was controlled by the development of soil profile,and closely correlated with the composition of SOM and its turnover processes.The fractionation of carbon isotope was happened during both the transformation of vegetation debris into topsoil organic matter (OM) and its regeneration after the topsoil buried,which resulted in a significant increase of SOM δ¹³C.Relative to plant debris δ¹³C,the δ¹³C increment of topsoil OM was more dependent on its turnover rate.Both the δ¹³C of plant debris and topsoil OM increased with altitude,indicating the regular variation of vegetations with altitude,which was consensus to the vertical distribution of vegetations in Dinghushan Biosphere Reserve.Soil profiles at different altitudes had similar characteristics in vertical differentiation of SOM δ¹³C, vertical distribution of SOM content,and increasing apparent age of SOM ¹⁴C with soil depth,which were resulted from the successive turnover of SOM during the development of soil profile.The maximum depth of SOM δ¹³C in soil profile was different in origin and magnitude with the penetration depth of ¹⁴C produced by nuclear explosion in the atmosphere,indicating the controlling effects of topography and vegetation on the distribution of SOM carbon isotope with soil depth.

Key words: Growth irradiance, Photosynthetic characteristics, Protective enzymes, Tropical woody plant seedlings