瓦屋山扁刺栲-中华木荷常绿阔叶次生林土壤有机碳组分特征

次生林在全球碳循环中占有重要地位,为了研究中国中亚热带次生林土壤有机碳组分特征,以四川瓦屋山中山段扁刺栲-中华木荷常绿阔叶次生林为对象,通过挖取土壤剖面分层(0—10、10—40、40—70 cm和70—100 cm)取样方式,研究土壤各有机碳组分特征。结果表明:土壤有机碳、微生物生物量碳、可浸提溶解性有机碳和易氧化碳含量均随土层深度增加而减小,0—10 cm土层有机碳含量为121.89 g/kg,高于已报道的亚热带其他常绿阔叶林和四川各类森林;0—10 cm层微生物生物量碳含量为1931.82 mg/kg,可浸提溶解性有机碳含量为697.42 mg/kg,易氧化碳含量为20.98 g/kg,高于已报道的许多相似天然林和人工林活性碳含量。土壤有机碳储量为154.87 t/hm2,在四川省各类森林中处于中等水平。研究表明瓦屋山扁刺栲-中华木荷常绿阔叶次生林活性碳含量较大,微生物活动和养分流动较为活跃,凋落物层转化为土壤碳的潜力较大,这类生态系统可能会在区域碳循环过程中扮演更为重要的角色。

Characteristics of soil organic carbon components in a secondary Castanopsis platyacantha-Schima sinensis evergreen broad-leaved forest, Wawushan Mountain

Secondary forests are one of the most important fast-growth forest types, with a large distribution area and high potential carbon sequestration capacity. In order to investigate the component characteristics of soil organic carbon in a subtropical secondary evergreen broad-leaved forest, an experiment was conducted in a typical evergreen broad-leaved secondary forest (Castanopsis platyacantha-Schima sinensis) in the middle section of Wawushan Mountain, southwest China. The physical soil properties and soil carbon fractions were studied, with the soil profile divided (0-10, 10-40, 40-70 cm and 70-100 cm) and sampled. Results showed that the soil at each level was acidic. Soil potential acidity was between 3.2 and 4.0, field moisture capacity was 63%-190%, and total porosity and bulk density were 63.0%-83.3% and 0.41-0.99 g/cm³ respectively. Soil pH value and bulk density increased with increased soil depth, while the field moisture capacity and total porosity showed the opposite trend. The organic carbon content of litter was 443 g/kg, and the litter stock and litter carbon stock were 10.4 t/hm² and 4.5 t/hm², respectively. Litter organic C stock in the studied forest was higher than in the majority of the plantations and natural forests in Sichuan Province. Soil organic carbon, microbial biomass carbon, extractable dissolved organic carbon, and readily oxidizable carbon decreased with an increase in soil depth. The soil organic carbon content in the 0-10 cm layer was 121.9 g/kg, which was higher than reported in other subtropical evergreen broad-leaved forests and in all types of forests in Sichuan (3.6, 8.6, and 14.6 times the soil organic content of the soil layers at 10-40 cm, 40-70 cm, and 70-100 cm respectively). The content of microbial biomass carbon in the 0-10 cm layer was 1931.82 mg/kg, which was 2.6, 5.7, and 7.8 times that in the following three layers. The contents of extractable dissolved organic carbon and readily oxidizable carbon in the 0-10 cm layer were 697.42 mg/kg and 20.98 g/kg, respectively. The contents of labile organic carbon in the 0-10 cm layer were higher than in many other reported similar natural forests and plantations. The density of soil organic carbon, microbial biomass carbon, extractable dissolved organic carbon, and readily oxidizable carbon were 7.5-48, 0.20-0.81, 0.25-0.37, and 0.8-8.4 kg/m³, respectively. The density of soil organic carbon, extractable dissolved carbon, and readily oxidizable carbon decreased with an increase in soil depth, while the microbial biomass carbon first increased and then decreased and peaked at the horizon, 10-40 cm. Soil organic carbon stock was 154.9 t/hm², which was at the mid-level in Sichuan Province. The stocks of microbial biomass carbon, extractable dissolved organic carbon, and readily oxidizable carbon were 3.1, 3.0 and 21.0 t/hm², respectively. This study suggests that (1) the content of the soil labile organic carbon was relatively high, (2) the activity of microorganisms and the flow of nutrients were relatively active, and (3) there is a huge amount of forest litter in the C. platyacantha-S. sinensis evergreen broad-leaved secondary forest that can be transformed into soil carbon in the future. These ecosystems will play a more important role in regional carbon cycles in the future.