黄土高原植被恢复过程土壤碳库时空变化特征

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	黄土高原植被恢复过程土壤碳库时空变化特征
	魏杰
学位类型	博士
导师	刘卫国
	2013-05
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位专业	环境科学
关键词	植被恢复土壤理化性质有机碳无机碳 Δ13c
其他摘要	近三十年来，黄土高原开始退耕还林还草，大面积的农田自然恢复为草地和森林，这一过程不可避免的导致土壤碳库变化。然而，对于这一区域土壤碳储量及其分布特征的研究还很少。我们选择了黄土高原地区典型的自然恢复草原和天然次生林样地作为研究对象，系统分析了植被恢复过程中土壤有机碳（SOC）、无机碳（SIC）储量及其随深度的分布特征。同时，根据土壤有机和无机碳的稳定同位素信息，探讨了植被恢复过程土壤碳库变化的机制及可能的影响因素。主要研究成果如下：（1）云雾山自然恢复草原：退耕地与禁牧地SOC储量均随着植被恢复时间的延长逐渐增加。退耕过程：耕地、99年退耕地、89年退耕地SOC储量分别为60.02、216.35和222.32 Mg ha-1，显著增加；但是自然草地（82年退牧地）SOC储量显著低于退耕地，这可能是由于根系是草地SOC的主要来源，而自然草地根系生物量略低于89年退耕地，同时其分解速率显著高于退耕地所致。禁牧过程：放牧地、02年退牧地、92年退牧地和82年退牧地SOC储量分别为76.13、102.38、122.54和108.39 Mg ha-1，禁牧的前20年逐渐增加，后有所减少。退耕地的碳库效益优于禁牧地。（2）云雾山自然恢复草原：耕地、99年退耕地、89年退耕地和自然草地SIC平均含量（0-200 cm）分别为18.5、13.2、11.8和18.8 g kg-1，随退耕时间延长逐渐降低，但是当植被演替到自然草地时，SIC含量增加，略高于耕地。99年退耕地与89年退耕地表层80 cm SIC含量显著低于耕地和天然草地。但是，在80-200 cm土层没有出现SIC淀积层，因此我们认为植被恢复后表层SIC含量减少可能不是向下淋溶引起的，而是以CO2的形式暂时释放到大气中。99年退耕地、89年退耕地和天然草地的土壤碳酸盐δ13C值均低于耕地，这可能是由于土壤碳酸盐与根系呼吸释放出来的CO2混合所导致的，表明植被恢复后，次生碳酸盐在总碳酸盐中所占的比例增加。（3）子午岭柴松林和辽东栎林0-100 cm SOC平均含量分别为6.8和9.9 g kg-1，顶级植被辽东栎林SOC含量显著高于柴松林，说明当柴松林演替到顶级植被辽东栎林后，其碳汇潜力非常巨大。柴松林和辽东栎林SOC含量均在表土30 cm快速降低，并在40-100 cm趋于一个平衡值。这说明森林对于提高深层SOC含量的能力有限。柴松林和辽东栎林土壤δ13C值均随深度增加逐渐偏正，表土δ13C值最负，这主要是由于SOC主要来源于地表枯枝落叶所导致的。（4）彬县耕地、10年退耕地、30年退耕地和自然草地0-80 cm SOC平均含量分别为4.18、5.61、4.7和5.67 g kg-1，退耕后SOC含量逐渐增加，但SOC的增加主要发生在表层10 cm。彬县耕地、10年退耕地、30年退耕地和自然草地0-80 cm SIC平均含量分别为16.8、15.43、16.32和23.84 g kg-1，退耕后的前30年SIC含量变化很小，而自然草地SIC含量显著高于耕地和退耕地。总的来看，自然草地的碳库效益优于其他3种土地利用方式。自然草地土壤δ13C最高值达到-18.55‰，处于C3植物δ13C值分布范围之外，说明这一地区的自然植被中有C4植物存在。（5）我们选择了云雾山自然恢复草地的两种典型植物群落：大针茅和赖草；以及子午岭天然次生林的两种典型植物群落：辽东栎和柴松。结果表明：柴松林、辽东栎林、赖草和大针茅群落SOC含量分别为6.8、9.9、17.9和20.4 g kg-1，自然恢复草地SOC含量显著高于次生林。本研究中土壤δ13C值随深度的变化主要由新、老碳混合以及微生物分解有机质过程中的动力学分馏引起的，休斯效应的贡献很少。我们的结果表明，研究区域自然恢复草地的碳库效益高于次生林，这可能是由于草地根系碳输入量高所致。（6）云雾山草地SOC储量显著高于彬县，这可能归因于一方面云雾山草地地上、地下生物量远高于彬县，另一方面彬县土壤温、湿度均较高，有利于微生物分解有机质。彬县和云雾山SIC含量的差异主要表现在退耕地：退耕后，彬县SIC基本没有变化，而云雾山SIC含量显著降低。总体来看，彬县SIC平均含量高于云雾山。彬县SOC δ13C值在表层20 cm显著偏正，而在深层土壤SOC δ13C值变化较小；云雾山SOC δ13C值在表层20 cm变化很小，而在20-100 cm深层土壤SOC δ13C值随深度显著增加。这可能主要是由土壤有机质来源不同引起的。 ; Vegetation restoration has been conducted in the Chinese Loess Plateau (CLP) during the last three decades, and large areas of farmland have been converted to forest and grassland, which largely results in soil organic carbon (SOC) change. However, there has been little research on SOC sequestration and distribution with vegetation restoration. Thus we selected the typical natural restored grassland and secondary forest to analyze the storage and stable isotope composition of SOC and soil inorganic carbon (SIC) and its distribution with depth. Meanwhile we discussed the possible influencing factors on changes of soil carbon with vegetation restoration. The results indicate that: (1) The SOC storage in sites continued cultivation (CC), cultivation abandonment at 1999 (AC-99) and cultivation abandonment at 1989 (AC-89) is 60.02, 216.35 and 222.32 Mg ha-1 in Yunwu Mountain. The SOC storage in natural grassland (NG: grazing abandonment at 1982) is lower than in restored grassland, which is probably because the plant root is the main source of SOC, with similar root boimass between AC-89 and NG but higher decomposition rate of SOC in NG. The SOC storage in sites continued grazing (GC), grazing abandonment at 2002 (AG-02), grazing abandonment at 1992 (AG-92) and grazing abandonment at 1982 (AG-82). The SOC storage in cultivation abandonment is higher than that in grazing abandonment. (2) The average SIC content (0-200 cm) in sites CC, AC-99, AC-89 and NG is 18.5, 13.2, 11.8 and 18.8 g kg-1 in Yunwu Mountain. The SIC content decreases in the first 20 years but increases when plant successes to native climax vegetation, with a slight higher value than CC. A significantly lower SIC content is observed in the top 80 cm in AC-99 and AC-89 than in CC and natural grassland (NG). However, there is no significant SIC accumulation at depths of 80-200 cm. Meanwhile, the SIC content in AC-99 and AC-89 wasclose to CC and NG at depths of 160-200 cm, which tended to reach an equilibrium value. This finding illustrated that the portion of carbonate was most likely released to the atmosphere as CO2 temporarily. The lower δ13C value of SIC in AC-99, AC-89 and NG than in CC was most likely due to the soil carbonate admixing with more soil respired CO2, suggesting that more secondary carbonate formed in restored grassland. (3) The average SOC content in secondary forest Pinus shenkaneusis (SF-1) and Quercus liaotungensis (SF-2) is 6.8 and 9.9 g kg-1 at depths of 0-100 cm in Ziwuling Mountain. The SOC content in SF-2 is higher than that in SF-1, suggesting that there was a substantial potential for carbon sequestration at SF-1 if the plants succeeded to natural climax vegetation (Quercus liaotungensis) in Ziwuling Mountain. The SOC content decreases significantly in the top 30 cm and reaches a equilibrium value at depths of 40-100 cm both in SF-1 and in SF-2, indicating that the contribution of secondary forest to SOC storage in deep soil is much smaller. The δ13C value is lowest in the topsoil and increases with depth, which is probably because the main source of SOC comes from aboveground plant litter in secondary forest. (4) The average SOC content in sites continued cultivation (CC), cultivation abandonment for 10 years (AC-10), cultivation abandonment for 30 years (AC-30) and natural grassland (NG) is 4.18, 5.61, 4.7 and 5.67 g kg-1 at depths of 0-80 cm in Binxian. The SOC content mainly increases in the topsoil with vegetation restoration. The SIC content in CC, AC-10, AC-30 and NG averages 16.8, 15.43, 16.32 and 23.84 g kg-1. There is little influence of vegetation restoration on SIC accumulation during the first 30 years. On the whole, the soil carbon storage is higher in NG than in CC, AC-10 and AC-30. The highest soil δ13C value of -18.55‰ is found in NG, which is outside the range of δ13C value of C3 plant, indicating that there is C4 plant in this region. (5) We selected two typical restored grass Leymus secalinus (RG-1) and Stipa grandis (RG-2) in Yunwu Mountain and two typical secondary forest Pinus shenkaneusis (SF-1) and Quercus liaotungensis (SF-2) in Ziwuling Mountain. The average SOC content in SF-1, SF-2, RG-1 and RG-2 is 6.8, 9.9, 17.9 and 20.4 g kg-1. The SOC storage in restored grassland is significantly higher than in secondary forest. The variation of soil δ13C values with depth in this study might be attributed to the mixing of new and old carbon and kinetic fractionation during the decomposition of SOM by microbes, whereas the impact of the Suess effect (the decline of 13C atmospheric CO2 values with the burning of fossil fuel since the Industrial Revolution) is minimal. We suggest that naturally restored grassland would be a more effective vegetation type for SOC sequestration due to higher carbon input from roots in the CLP. (6) The SOC storage is higher in Yunwu Mountain than in Binxian, which is probably due to the higher biomass input in Yunwu Mountain and the hihger decomposition rate of organic matter because of higher soil tempreture and higher soil water content in Binxian. The main variance in SIC between Binxian and Yunwu Mountain is in sites of cultivation abandonment. The SIC content shows little changes in Binxian but significnat changes in Yunwu Mountain with vegetation restoration. On the whole, the SIC content is higher in Binxian than in Yunwu Mountain. The δ13C value increases significantly in the top 20 cm but changes little in deep soil in Binxian. On the contrary, The δ13C value changes little in the top 20 cm but increases significantly in deep soil in Yunwu Mountain. It is probably due to the different carbon source between the two sites.
学科领域	地球化学 ; 环境科学
语种	中文
文献类型	学位论文
条目标识符	http://ir.ieecas.cn/handle/361006/2601
专题	博士研究生论文
推荐引用方式 GB/T 7714	魏杰. 黄土高原植被恢复过程土壤碳库时空变化特征[D]. 北京. 中国科学院研究生院,2013.