【摘要】 选择鼎湖山自然保护区及中国科学院华南植物研究所小良生态站 6个土壤剖面 ,根据土壤有机质碳稳定同位素特征、14 C放射性水平、有机质含量、粒度特征 ,研究土壤有机质更新特征及其制约因素。结果表明 ,土壤有机质分解呈明显阶段性 :有机质快速分解发生在 0～ 1 0 0 a之内 ,自地表向下 ,有机质含量急剧降低 ,因碳同位素分馏效应 ,有机质 δ13C值迅速增加 ;至 1 70 /2 40 a,有机质 δ13C值达最大 ;自 1 70 /2 40～ 80 0 /1 40 0 a,有机质分解速度变慢 ,有机质含量缓慢降低 ,因高 δ13C值组分分解 ,δ13C值逐渐减小 ;约在 1 5 0 0 a之后 ,有机质含量变化甚微 ,δ13C值趋于稳定。对比研究表明 ,粘粒对有机质赋存状态及其更新有直接影响 ,粒度是制约土壤有机质动态的重要因子 ;地表植被类型及其发育特征直接影响土壤有机质更新 ,在植被类型相似情况下 ,植被覆盖史对土壤剖面有机质动态有明显影响。更多还原

【Abstract】 Six soil profiles were selected in the Dinghushan Biosphere Reserve (DHSBR) (23°09′～23°11′N, 112°30′～112°33′E), and the Xiaoliang Ecological Station established by South China Institute of Botany, Chinese Academy of Sciences, for our studies on dynamics of soil organic matters (SOM) in the south subtropical areas. Each selected profile was sampled using thin layered methods, and every sample is about 1 5 to 2 0 kg weight. Two soil profiles were excavated in July 1998, at the forest vegetation zone (SL) and shrub meadow zone (GC) of DHSBR, respectively. The purpose to select natural soil profiles is to avoid anthropogenic disturbances upon the soils, so as to recover natural characteristics of SOM distribution and turnover processes. Two different vegetation zones were considered in order to study the effect of primary production (PPT) of aboveground vegetation on SOM turnover processes. Four locations with different vegetation covering histories were selected in August 1998, in the Xiaoliang Ecological Station and its surrounding areas within the scope of 2 kilometers. They are bare ground (GBD) which had been deforested about one hundred years ago, restoring forests at former bare ground, with mix typed vegetation that were planted in 1964 (HJ64) and 1974 (HJ74), respectively, and a patch of primary forest (CB) where the vegetation has not been disturbed by anthropogenic activities. One soil profile was excavated at each of the four places. The purpose to select four locations in the same area is to study the impacts of vegetation covering histories upon SOM dynamics of the profiles, and characteristics of SOM dynamics during restoration of the degraded ecosystems. The study is based on analyses of SOM δ 13 C and Δ 14 C, soil grain size characteristics and soil organic carbon (SOC) contents. The results indicate that the turnover processes of SOM include three obvious stages. (1) Rapid turnover of SOM occurs within one hundred years, SOC contents decrease sharply with depth from ground surface, and SOM δ 13 C values increase correspondingly due to carbon isotope fractionation effect in the SOM turnover processes, and reach the maximum till about 170~240 year, with increment of 6.9‰~5.6‰. (2) From about 170~240 year to 800~1400 year, SOM turnover rates reduce, SOC contents decrease slowly with depth, and SOM δ 13 C values decrease gradually due to the decomposition of SOM compartments with higher δ 13 C values, the difference between the highest value and the stable value of δ 13 C varies from 3.9‰ to 2.7‰. (3) Till about 1500 years, SOC contents get close to the minimum, with slight fluctuations, which suggest that SOM are mainly of stable compartments; SOM δ 13 C values turn to be stable, and are generally greater than those of the plant materials at the commence of decomposition. Variations of SOM δ 13 C values with depth are correlated well to those of SOC contents with depth, showing that SOM are composed of various compartments with different turnover rates, and SOM turnover processes include obvious stages. The upper 10 cm section of GC profile and the upper 24 cm section of SL profile are the main contributors to CO 2 emissions for the two profiles, respectively, and the clay contents of the two sections are both less than 20%. From these horizons downward, soil clay contents increase, and are greater than 20%. Section below 30 cm depth of GC profile and section beneath 40 cm depth of SL profile, have high clay contents of 25%~30%. In these sections, SOC contents show slight variations with depth, and SOM δ 13 C values turn to be stable downwards, suggesting that SOM are mainly of stable compartments. Comparison analysis suggests that soil clayey materials exert direct controls upon existing forms and turnover processes of SOM, due to absorption and protection of organic mineral complexes. Soil grain size composition, as one important aspect of soil properties, is a fundamental factor controlling SOM dynamics. The aboveground更多还原