[Spatial and temporal differentiation of mountainous soil organic matter delta 13C in Dinghushan Biosphere Reserve].

Based on the determinations of soil organic matter (SOM) content, SOM delta 14C, and SOM delta13C of the samples collected by thin-layered sampling method, this paper studied the spatial and temporal differentiation of SOM delta13 C in the soil profiles at different altitudes in Dinghushan Biosphere Reserve. The results showed that the vertical differentiation of SOM delta13C 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 delta13C. Relative to plant debris delta13C, the delta13 C increment of topsoil OM was more dependent on its turnover rate. Both the delta13C 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 delta13C, 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 delta13C 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.

[Quantitative simulation on the vertical distribution of soil organic matters in mountainous soil profiles in the subtropical area, south China].

Quantitative descriptions of soil organic matter (SOM) dynamics, i.e., their distribution, turnover and movement, are essential for the running of the simulation of terrestrial ecosystem organic matter models. In this study, based on utilizing SOM diffusion-translation-decomposition model, two soil profiles were selected in different vegetation zones at Dinghushan Mountain for quantitative studies on SOM dynamics and their controlling factors. SOM were divided into three kinds of compartments: rapid compartment with turnover rate of 0.1-1.yr-1, slow compartment with turnover rate of 0.002-0.02.yr-1, and stable compartment with turnover rate of 0.0001-0.001.yr-1. The numerical results suggested that SOM distribution in soil profile in subtropical mountainous areas of south China obeyed the law of diffusion motion, translation motion and decomposition. The turnover rate of SOM rapid compartment was 0.483.yr-1 in the forest vegetation zone, and was 0.694.yr-1 in the shrub vegetation zone. The turnover rates of SOM slow compartment in the two kinds of vegetation zones were both 0.02.yr-1, and the turnover rates of SOM stable compartment in the two kinds of vegetation zones were both 0.001.yr-1. SOM diffusion rate and translation rate for the forest vegetation zone was 4 cm2.yr-1 and 0.2 mm.yr-1, respectively, and the two rates of the shrub vegetation zone were 1 cm2.yr-1 and 0.5 mm.yr-1, respectively. The obvious discrepancy between numerical values and measuring values for SOM content occurred in the 0-10 cm sections of the profiles, which might be due to the fact that the upper sections were at the interface between lithosphere and atmosphere, and were influenced directly by changes of climatic and environmental factors. The two kinds of values for SOM content were identical below the upper section of the profiles, and it indicated stable pedogenesis environments. Diffusion motion had obvious influences on SOM vertical distribution, and translation motion had clear impacts on SOM distribution only in the upper 0-10 cm section. Comparison analysis suggested that SOM dynamics were controlled mainly by soil profile qualities such as SOM content, clay content, soil fabric, void types and their developments, soil fauna and microorganism activities, etc. With the increasing of primary production of aboveground vegetation, the turnover rate of SOM rapid compartment decreased and SOM content increased, which provided scientific basis for increasing soil carbon sink through anthropogenic effects.