【摘要】 选择鼎湖山自然保护区森林植被带 (SL)、灌丛—草甸过渡带土壤剖面 (GC)进行薄层取样 ,根据土壤有机质14 C放射性水平 ,运用模型计算土壤有机质更新速率 (m)。结果表明上部 0～ 10cm土层有机质更新速率 (m)最高 ;向下 ,m锐减 ;剖面下部m值极低 ,这说明土壤有机质由不同更新周期 (T)组分构成。表层快循环组分占绝对优势 ,向下 ,慢循环组分为主 ,剖面下部为稳定组分。根据m、有机碳含量、土壤容重、土层厚度计算有机质更新CO2 产量 ,表层 0～ 10cm层段CO2 产量约为整个剖面的 98%。SL剖面m值及有机质更新CO2 产量均明显大于GC剖面相应值。分析表明在同一气候带植被是制约土壤有机质更新及CO2 产量的第一要素 ,这为通过绿化加强土壤碳汇功能提供重要依据。更多还原

【Abstract】 Two soil profiles were excavated at the forest vegetation zone and the shrub meadow transitional zone of Dinghushan Mt. (23°09′-23°11′N,112°30′-112°33′E), and thin layer sampling were conducted for studies on soil carbon dynamics of mountainous soils in the subtropical area. Based on 14 C radioactivity of soil organic matters (SOM), SOM turnover rate ( m ) is calculated with a numerical model for the upper sections with SOM Δ 14 C value greater than zero, due to incorporation of 14 C produced by atmospheric nuclear weapon testing (Bomb 14 C) in the 1960s. As for the lower section with SOM Δ 14 C value less than zero, the effect of Bomb 14 C may be neglected due to the slow turnover rate of SOM, and value m is calculated by one specific equation. Value m decreases downward, and is greater than 0.01a -1 at the upper 12?cm section of the soil profiles, then, value m reduces abruptly downward, and is about one magnitude less than that of the above specimen. From 12?cm on, value m reduces consistently with depth, till the minimum at the deepest of the profiles. This suggests that soil organic matters are composed of various compartments with different turnover times ( T ). Rapid compartments ( T <10a) are predominated at the upper 12?cm section, slow compartments (100a< T <1?000a) turn to be the main part of SOM downwards, and stable compartments ( T > 1?000a) are predominated at the lower sections of the profiles. CO 2 production resulted from SOM turnover is calculated based on value m , organic carbon content, soil bulk density and soil section thickness. The results suggest that the CO 2 production from the upper 12?cm section is about 98 percent of the total CO 2 production of one profile. Therefore, the upper 12?cm section is the main contributor for CO 2 emission due to SOM decomposition in one soil profile. CO 2 flux of the upper 12?cm section of SL profile is 0.1233gC/cm 2 ·a, which is about one magnitude higher than that of the upper 12?cm section of GC profile. This is ascribed to that value m and organic carbon content of the upper 12?cm section of SL profile are greater than those of the upper 12?cm section of GC profile, respectively. For example, value m of the upper 12?cm section of SL profile are greater than 0.1a -1 , and those of the upper 12?cm section of GC profile are from 0.01a -1 to 0.08a -1 . Value m of the uppermost specimen is 0.402a -1 for SL profile, and is 0.078a -1 for GC profile; the former is about one magnitude higher than the latter. The aboveground vegetation types contrast obviously between SL profile and GC profile, which results in different primary production of aboveground vegetation for the two spots. Soil organic carbon content and value m of SOM are controlled directly by primary production of aboveground vegetation. Therefore, aboveground vegetation is the key factor controlling SOM turnover and the corresponding CO 2 production of soil profiles within one climatic zone, which give scientific supports for increasing soil carbon sink through afforestation. The upper soil section has high SOM content and great value m , and is apt to be eroded away, thus, the upper section of one soil profile is prone to be CO 2 source. Plant debris is the main source for SOM of the upper soil section. Therefore, to reduce plant debris production and to increase the biomass of deep roots, in order to transfer more organic matters into the deep, may be one effective measure for reducing and slowing down the emission of CO 2 due to SOM turnover. For this purpose, vegetation with high underground biomass should be planted firstly under all possible conditions, which needs comprehensive cooperation between soil scientists and botanists.更多还原