火烧和保留采伐剩余物对土壤有机碳矿化的影响

Effect of prescribed bruning and reservation of logging residues on soil organic carbon mineralization

摘要:

采用室内培养法，比较分析了福建三明地区米槠次生林皆伐后火烧、保留采伐剩余物处理对土壤有机碳累积矿化量的影响，分析了土壤有机碳累积矿化量和土壤初始有机碳、微生物生物量碳及可溶性有机碳的关系。结果表明，火烧、保留采伐剩余物处理6个月和18个月后，火烧处理表层0~10 cm土壤有机碳含量较对照处理分别下降了6.0%和1.9%，保留采伐物处理土壤表层有机碳增加了15.6%和25.0%。两次培养中，火烧处理各土层累积矿化量显著低于对照和保留采伐剩余物处理；火烧6个月后，保留采伐剩余物处理各土层累积矿化量显著低于对照，18个月后10~20和20~40 cm土层累积矿化量显著高于对照处理。火烧18个月后，保留采伐剩余物处理各土层累积矿化量显著高于1年前的累积矿化量，分别高57.0%、112.0%和49.9%；火烧和对照处理前后两次培养各土层累积矿化量变化并无明显规律。土壤有机碳累积矿化量与土壤初始有机碳、微生物生物量碳和可溶性有机碳呈显著地线性相关关系(p < 0.05)。营林活动初期，皆伐后保留采伐剩余物措施较火烧能够增加土壤有机碳库，对土壤肥力及后期林木生长有重要的促进作用。

Abstract:

Soil organic carbon (SOC) plays an important role in maintaining carbon pools in terrestrial ecosystems. Any of its subtle changes may cause great changes in the environment we live in. Therefore, dynamics of soil organic carbon mineralization is an issue of great significance in global climate change, because SOC mineralization plays a critical role in regulating CO₂ concentration in the atmosphere. There are a number of factors, such as soil temperature, soil structure, soil moisture, characteristics of soil micro-organisms and microbial communities, as well as quality and quantity of the substrate, that affect mineralization of SOC. However, human activities are the factor that may generate direct impact on the above-listed factors affecting SOC mineralization. In China, especially in South China where there are rich forest resources, silvicultural activities have a history of over 1 000 years. Although traditional silvicultural activities, such as clear-cutting and burning, are easier and faster, they cause a substantial loss and redistribution of soil organic carbon, while only trunks are harvested, leaving logging residues in the field can increase SOC content in the soil. Studies have been reported all over the world on SOC mineralization in forest soils, but little has been done on impact of silvicultural activities on SOC mineralization, especially at the early stage of silvicultural activities. This research project is oriented to explore effects of management of logging residues on soil organic carbon mineralization at the early stage of the silvicultural activities. The Chenda Town Forestry Farm in Fujian Province, Southeast China, was selected for this project. The farm had a tract of 36-year-old secondary Castanopsis carlesii forest, which was divided into three plots. Clear-cutting was done in Plots 1 and 2 with logging residues burnt in Plot 1 and left intact in Plot 2, and Plot 3 still had trees standing as Control (without clear-cutting). Soil samples were collected from the plots for incubation to determine mineralization of SOC. The first sampling occurred 6 months after burning of logging residues and the second did 18 months after burning. The incubation of soil samples lasted two months, each time. Though the two incubation experiments, results show that: 1, Management of logging residue managements had a significant impact on soil organic carbon mineralization, mainly through altering quality and quantity of the substrate. 2, After two incubations, Plot 1 was obviously lower than Plot 2 and Plot 3 in cumulative SOC mineralization in all soil layers; however, after the first incubation, Plot 2 was significantly lower than Plot 3 in cumulative SOC mineralization in all the soil layers, while after the second incubation, Plot 2 was much higher than Plot 3 in cumulative SOC mineralization in the 10~20 cm and 20~40 cm soil layers. And what is more, in Plot 2, the cumulative SOC mineralization after the second incubation was much higher than that after the first incubation or 57.0%, 112.0% and 49.9% higher in the 0~10, 10~20 and 20~40cm soil layers, respectively. However, there were no such variations in Plot 1 and Plot 3. 3, After both the first and second incubations, Plot 1 was 6.0% and 1.9%, respectively, lower than Plot 3 in organic carbon content in the 0~10cm soil layer, but Plot 2 was 15.6% and 25.0% higher, respectively, than Plot 3. In Plot 2, the contents of dissolvable organic carbon and microbial biomass carbon in all the soil layers were significantly higher after the second incubation than after the first incubation, while in Plot 1 they were in an opposite way. 4, Cumulative SOC mineralization was in significantly liner relationships with the initial contents of organic carbon, dissolvable organic carbon and microbial biomass carbon (p < 0.05), indicating that the latter three are the major factors affecting the former. 5, It can be concluded that the management of keeping logging residues in the field after clear-cutting is superior to that of burning the residues in many aspects at the early stage of silvicultural activities, for instance, it can raise quality and quantity of the substrate, and also raise the soil organic carbon stock.