Knowledge Resource Center for Ecological Environment in Arid Area
| 榆树疏林草地乔木肥岛效应对土壤有机碳分布与稳定性的影响 | |
| 其他题名 | Effects of tree fertile island on the distribution and stability of soil organic carbon in an elm-dominated savanna ecosystem in north China |
| 孙学凯 | |
| 出版年 | 2013 |
| 学位类型 | 博士 |
| 导师 | 曾德慧 ; 范志平 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 土壤有机碳是全球生物化学循环中极其重要的生态因子，也是土壤碳循环中最活跃的部分，其积累和分解的动态变化能够直接影响全球碳平衡。目前，关于土壤有机碳研究多集中于森林系统、草地生态系统和农田生态系统的，而对于疏林草地生态系统土壤有机碳循环关注较少。疏林草地是由非连续的乔木层和相对连续的林下草本层构成，与草地生态系统相比，疏林草地具有深层的乔木根系，乔木层的“肥岛效应”能提高系统中土壤的固碳潜力。尽管疏林草地生态系统在土壤固碳功能中发挥着重要的作用，但关于乔木层对土壤有机碳分布及其稳定性的影响研究相对薄弱。因此，本研究以半干旱区榆树疏林草地生态系统为对象，探讨了乔木层“肥岛效应”对土壤有机碳分布的影响，利用稳定碳同位素分析了未分组和分组土壤有机碳的植物来源，分析了榆树疏林草地土壤有机碳稳定性特征。得出以下主要结果：\n1）在榆树疏林草地生态系统中，乔木冠幅内、冠幅外和草地区0~100 cm剖面土壤有机碳含量具有显著性差异（p<0.05），而100~200 cm则无显著性差异（p>0.05）。土壤有机碳含量均表现为随着土壤层次加深呈下降趋势，土壤有机碳含量最高值（18.65 g·kg-1）出现在冠幅内0~5 cm土层中，最低值（0.28 g·kg-1）则出现在草地区150~200 cm土层中。\n2）冠幅内、冠幅外和草地区土壤有机碳储量分别为7.08、5.28和3.97 kg·m-2，其中100~200 cm的深层土壤有机碳储量各自占剖面土壤有机碳储量的比例分别为18.08%、16.10%和14.61%。本研究以草地区有机碳储量值为参比，乔木层为冠幅内的土壤有机碳储量提高了3.11 kg·m-2，土壤有机碳储量提升了约78%；冠幅外的土壤有机碳储量提高了1.31 kg·m-2，土壤有机碳储量提升了约33%。可见，疏林草地深层的乔木根系能够提高系统中土壤的固碳能力。\n3）土壤团聚体有机碳分布特征表明，冠幅内、冠幅外和草地区均表现为0.25~0.053 mm的土壤团聚体所占比例最大，且该粒径团聚体有机碳含量最高。由于乔木层冠幅下的地表凋落物和地下深层根系对土壤团聚体有机碳含量的影响，尤其是在表层（0~5 cm和5~10 cm）和深层（100~150 cm）中，冠幅内土壤团聚体有机碳含量显著高于冠幅内和草地区（p<0.05）。\n4）在榆树疏林草地深层土壤中（150~200 cm）同位素值为-23‰左右，通过质量守恒定律估算此土壤层次的有机碳C3来源的贡献率达60%，表明该地区深层土壤是以C3植物来源为主。对C3来源和C4来源的碳贡献影响因素进行双因素（与树干距离，土层深度）和三因素方差分析（与树干距离，土层深度，团聚体大小），结果表明，土壤层次对碳来源有极显著影响（p<0.001）。\n 5）在榆树疏林草地生态系统中，土壤碳矿化速率、土壤碳累积矿化量、微生物量碳和土壤溶解性有机碳含量及其组分在表层土壤中冠幅内显著高于冠幅外和草地区（p<0.05），而在深层土壤中则冠幅内、冠幅外和草地区之间的差异不显著（p>0.05）。随着土壤层次增加，土壤碳矿化速率、土壤碳累积矿化量、微生物量碳和土壤溶解性有机碳含量及其组分呈逐渐降低的趋势。本文以培养29 d的土壤碳累积矿化量与土壤有机碳的比值，作为土壤有机碳矿化释放CO2-C分配比例，结果表明，冠幅内土壤有机碳矿化释放CO2-C分配比例低于冠幅外和草地区，可见乔木层提高了冠幅内的土壤有机碳稳定性。 |
| 英文摘要 | Soil organic carbon (SOC) is one of the most important ecological factors in global biochemical cycles, and an important active component in soil carbon cycles. Dynamic changes of SOC can directly affect global carbon balance. Presently, several studies of soil organic carbon mainly focused on forest, grassland and farmland ecosystems; however, SOC cycle in savanna ecosystem remains largely uncertain. Savanna ecosystem is consisted of a discontinuous woody layer and a relatively continuous understory herbaceous layer. Because of “fertile island” of trees, savanna ecosystem has greater potential to store more carbon in the soil compared with grassland ecosystem. Furthermore, how trees affect SOC distribution and its stability is also poorly understood for the ecosystem. Therefore, in the present study, we selected a natural elm-dominated savanna in semiarid region, and explored the effects of trees on SOC distribution and its stability. In addition, we analyzed plant sources of SOC in non-fractionated and fractionated soils using stable C isotope signatures. The main results are as follows: \n(1) In elm-dominated savanna ecosystem, SOC under canopy was all significantly higher than that outside canopy and in grassland area at depths of 0~100 cm (p<0.05); however, there were no significant differences at depths of 100~200 mm (p>0.05). The results indicated that SOC decreased with depth in soil profiles. In addition, the SOC was highest under canopy at depth of 0~5 cm (18.65 g·kg-1) and lowest was in grassland area at depth of 150~200 cm (0.28 g·kg-1).\n(2) SOC storage under canopy, outside canopy and grassland area were 7.08, 5.28 and 3.97 kg·m-2, respectively. The percentage of deeper SOC storage in whole soil profile for three distances were 18.08%, 16.10% and 14.61%, respectively. SOC storage under canopy and outside canopy increased by 3.11 and 1.31 kg·m-2, respectively. The results showed that savanna ecosystem has greater potential to store more carbon in the soil because of the presence of deep-rooted trees.\n(3) The percentage of 0.25~0.053 mm fraction in whole soil was the highest, and the fraction had the highest SOC concentration. Our research indicated SOC in fractions under canopy were all significantly higher than that outside canopy and in grassland area at three depths (0~5 cm, 5~10 cm and 100~150 cm) (p<0.05). Therefore, the litterfall from the tree as well as effects of the roots could have contributed to the SOC of fractions accumulation in the surface soil and deeper soil.\n(4) The δ13C value was about -23‰ in deeper soil (150~200 cm). Based on the value and mass balance, we calculated that the contribution of C3 plants to C stock was about 60% at depth of 150~200 cm. Our results indicated that C3-dominated plants had emerged in study sites during previous land-use history. Two-factorial (distance and depth) and three-factorial (distance, depth, and fraction size) ANOVA showed that only depth was significant (p<0.001). Testing C3-origin C and C4-origin C separately showed that distance and fraction size were not found to be a significant factor for C3-origin C data and C4-origin C data, but depth was.\n (5) In elm-dominated savanna ecosystem, soil C mineralization rate, soil C cumulative mineralization, soil microbial biomass carbon (MBC) and soil dissolved organic carbon (DOC) under canopy were all significantly higher than that outside canopy and in grassland area at surface layer (p<0.05); otherwise, there were no significant differences at deeper layer (p>0.05). Soil C mineralization rate, MBC and DOC decreased with depth in whole profiles. In addition, rates of soil carbon cumulative mineralization to soil organic carbon under canopy were lower than that outside canopy and in grassland area at depths of 0~200 cm. The results indicated that tree enhanced SOC stability in elm-dominated savanna. |
| 中文关键词 | 榆树疏林草地 ; 土壤有机碳 ; 土壤团聚体 ; 溶解性有机碳 ; 稳定碳同位素 |
| 英文关键词 | Elm-dominated savanna Soil organic carbon Soil aggregate |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院沈阳应用生态研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287264 |
| 推荐引用方式 GB/T 7714 | 孙学凯. 榆树疏林草地乔木肥岛效应对土壤有机碳分布与稳定性的影响[D]. 中国科学院大学,2013. |
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