Knowledge Resource Center for Ecological Environment in Arid Area
| 祁连山区典型植被土壤有机碳对气候变化及人为干扰的响应机制 | |
| 其他题名 | Response of soil organic carbon for typical vegetation types to climate change and human disturbance in Qilian mountains |
| 陈龙飞 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 何志斌 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 包括青藏高原在内的高海拔及高纬度地区对气候变化响应敏感，被列为全球变化“碳-气候-人类”系统的热点研究区。祁连山位于青藏高原北缘，近年来经历着气候变化和人为干扰（主要为造林及以间伐为主的营林活动）的双重影响：1960年以来，祁连山区年均气温升高了0.29℃/10a，显著高于全国及全球同期水平；随着天然林保护工程及退耕还林（草）工程的实施，1989-2009年间，祁连山区造林面积由43.6万公顷增加至57.96万公顷，增幅达33%。这些剧烈的变化已经对区域植被的生长及格局产生显著影响，进而必将对土壤有机碳的固存产生重要影响。土壤有机碳作为陆地生态系统碳循环的关键组分及最大的碳库载体，其动态变化会对区域碳平衡产生重要影响。然而，目前关于土壤有机碳对气候变化及造林、间伐等典型人为干扰活动响应及机制的认识还不深入，且鲜有研究对其进行系统和定量的评估。本研究针对祁连山区生态恢复建设的实际需求及生态学、土壤学的热点问题，采用样方调查、野外模拟增温实验与室内分析相结合的方法，研究了祁连山区典型植被土壤有机碳对气候变化及造林、间伐的响应，并结合相关的碳循环过程对其响应机制进行了探讨。主要开展了以下四个方面的研究：以典型流域为单元，采用样方调查法研究了典型植被土壤有机碳储量及空间分异特征；采用海拔梯度差增温的方式研究了典型植被土壤有机碳及相关碳循环过程对气候变化的响应；基于空间替代时间法，研究了不同造林年限对土壤有机碳及相关生态过程的影响；采用样方调查法研究了不同间伐强度对土壤有机碳及相关碳循环过程的影响。主要结论如下：（1）典型植被土壤有机碳储量及空间分异特征。研究流域土壤有机碳储量随坡向、植被类型及海拔存在较大变异，0-50cm土层有机碳储量的最大值为31.09kg m-2，最小值为9.50kg m-2，其中阳坡土壤有机碳储量要显著低于阴坡和半阴坡。青海云杉林和草地是流域内分布最广的植被类型，0-50cm土层青海云杉林及草地土壤有机碳总储量分别占流域土壤有机碳总储量的55%和25%，且青海云杉林及草地等植被土壤有机碳密度要高于其它区域同种植被类型，表现出较强的固碳能力。对于整个流域来说，坡向是影响土壤有机碳储量空间异质性最重要环境因子，其次是海拔；对于阴坡来说，由海拔差异引起的温度和降水条件的变化是影响土壤有机碳储量空间异质性最主要的环境因子，其中温度是最重要的因子。青海云杉林土壤有机碳储量随海拔的升高而增加。研究区青海云杉林有着相似的地形条件，且土壤发育于相同的母质，主要的区别在于由海拔梯度引起的温度、降水等气候条件的差异，且随着海拔的降低，温度升高而降水量降低。因此，在温度升高而降水量降低的气候变化条件下，青海云杉林土壤有机碳储量将表现出降低趋势。（2）典型植被土壤有机碳及相关碳循环过程对气候变化的响应。青海云杉林模拟增温实验表明，在温度升高而降雨量降低的气候变化条件下，青海云杉林土壤呼吸速率及凋落物分解速率均显著增加，即增温后，土壤碳排放量增加，而土壤碳的累积量降低。这一结论也佐证了青海云杉林土壤有机碳储量随海拔梯度变化的关系。草地模拟增温实验表明，增温后草本物种数及生物量均显著增加，而土壤有机碳含量却呈降低的趋势。BIOLOG微平板法及磷脂脂肪酸（PLFA）方法分析表明，增温后土壤微生物代谢能力及多样性均呈增加的趋势。土壤微生物代谢能力及活性的增加会提高土壤呼吸速率，促进土壤碳排放。因此，增温后土壤有机碳含量的降低很可能是因为土壤呼吸速率的增加，并超过土壤碳输入部分的增加值的缘故。此外，增温后真菌在土壤微生物群落中所占比例较细菌有明显的提高。真菌的碳同化率一般较细菌高，且真菌的细胞壁较细菌更难分解。因此，增温虽然在短期内可以提高土壤微生物活性及土壤呼吸速率，但从长远来看，真菌在土壤微生物群落中所占比例的提高将会使土壤呼吸对增温产生适应性，一定程度上有利于土壤有机碳的积累。（3）造林对土壤有机碳及相关生态过程的影响。造林显著提高了草地0-70cm土层有机碳储量，且随着年限的延长，土壤有机碳储量呈现增加的趋势。造林后土壤有机碳储量的增加，一方面是因为凋落物产量的增加导致土壤有机碳输入部分升高，另外一方面是因为青海云杉林形成的凋落物较难分解，使得土壤有机碳的输出量降低的缘故。相对于土壤有机碳储量，土壤全氮储量增加的幅度较小，导致造林后土壤C:N值升高。土壤C:N值是指示土壤固碳能力的重要指标，土壤C:N值升高将不利于土壤有机碳分解，在一定程度上促进了土壤有机碳的累积。土壤旱化是祁连山等干旱区山地造林经常出现的突出问题，特别是当造林密度过大时。本研究发现，草地造林后（造林密度为2833-2967棵 ha-1），土壤下层含水量没有显著变化，而土壤上层含水量呈显著增加的趋势。因此，在干旱区山地造林，只要选择合理的造林密度，人工林是可以在充分发挥固碳功能的同时实现可持续发展。（4）间伐对土壤有机碳及相关碳循环过程的影响。间伐（强度为20%及40%）显著提高了青海云杉人工林（造林密度为4500棵 ha-1）土壤呼吸速率，且随着间伐强度的增加，土壤呼吸速率及土壤呼吸对温度的敏感性（Q10）均呈增加趋势；间伐后表层土壤温度的升高是导致土壤呼吸速率增加的主要原因。随着间伐强度的增加，林下植被由苔藓逐渐演变为草本。由于草本形成的凋落物较苔藓更容易分解，间伐后林下植被组成结构的改变将导致表层土壤有机碳组成发生变化，使得土壤呼吸对温度的敏感性升高，在一定程度上也促进了土壤呼吸速率的增加。间伐显著降低了青海云杉人工林0-70cm土层有机碳储量；随着间伐强度的增加，土壤有机碳储量呈显著降低的趋势。土壤有机碳储量的降低，一方面是因为间伐后凋落物产量及林下植被生物量的降低，导致土壤有机碳的输入部分减少；另一方面是因为土壤呼吸速率显著增加，导致土壤有机碳输出部分升高的缘故。间伐显著提高了青海云杉人工林0-70cm土层储水量，且随着间伐强度的增加，土壤储水量呈显著增加的趋势。这对于维持青海云杉人工林稳定健康具有十分重要意义。此外，间伐显著降低了青海云杉人工林土壤C:N值，当土壤C:N值降低时，土壤有机碳将更容易分解，不利于土壤有机碳的积累。 |
| 英文摘要 | The high-altitude and high-latitude ecosystems are more sensitive to climate warming, and have been listed as the hot research areas of global change "carbon - climate - human" ecosystem. Qilian mountains, located in the northern margin of the Tibetan Plateau, have experienced remarkable climate change and human disturbance (grassland afforestation and thinning) recently years. Since 1960, Qilian mountains have experienced a rapid temperature rise of 0.29 ℃ per decade, higher than the national and global average rate. Furthermore, the area of afforestation has increased 33% from 1989 to 2009 due to the implementation of ‘Grain-for-Green’ Program. These changes have had profoundly affect on regional eco-environment and carbon balance. Soil organic carbon as the key component of terrestrial ecosystem carbon cycle and the largest carbon pool is sensitive to environmental change. The change of soil organic carbon pool could directly significantly alter the carbon balance of ecosystem. However, so far there has been little comprehensive assessment of the changes in soil organic carbon and the related carbon cycling process to climate change and anthropogenic activity (grassland afforestation and thinning), and the mechanism is still not well understood. Aimed at the ecological construction demand of Qilian mountains and the hot topics in ecology and soil science, the response of soil organic carbon and related carbon cycling of typical vegetation types to climate change and land use change (grassland afforestation and thinning) has been investigate in the study by the method of combining field investigation, experimental warming and laboratory analysis. The following four aspects of research has been carried out in the study: (1) Storage, patterns and environmental controls of soil organic carbon under different vegetation types in a typical catchment in the Qilian Mountains were determined; (2) Response of soil organic carbon and related carbon cycling of Picea crassifolia forests and grasslands to climate change was investigated by experimental warming; (3) Impacts of grassland afforestation on soil organic carbon storage and related ecological process was investigated by the space-for-time substitution method; (4) Responses of soil organic carbon storage and related carbon cycling to thinning was also investigated. The main results are as follows:(1) Storage and patterns of soil organic carbon under different vegetation types. The results showed that soil organic carbon stocks varied significantly with vegetation type, ranging from 9.50 to 31.09 kg m?2 at 0-50 cm soil depth. Soil organic carbon storage in grasslands on sunny slopes and in Picea crassifolia forest together accounted for about 80% of the total soil organic carbon storage in the catchment due to the extensive distribution area of these vegetation types. Soil organic carbon stocks in grasslands on sunny slopes and in Picea crassifolia forest were generally higher than their counterparts in other regions. For the whole catchment, the distribution of soil organic carbon stocks was significantly affected by topographic aspect and elevation; aspect and elevation together explained 97.49% of the overall variation in soil organic carbon stocks at a soil depth of 0-50 cm, and aspect alone explained 68.16% of the overall variation. Soil organic carbon stocks on shady slopes were mainly regulated by elevation-induced differences in temperature and precipitation, with temperature being the most important factor influencing the distribution of soil organic carbon. Generally, soil organic carbon stocks of Picea crassifolia forests increased with elevation. Soil C:N ratios, though not as well controlled by elevation as soil organic carbon, also tended to increase with elevation. In the study region, forests grow on a uniform geological substrate; elevation, and the divergence of temperature and precipitation induced by elevation create the observed differences in soil organic carbon. We found that soil organic carbon stocks decreased with temperature and increased with precipitation. These results lead us to the conclusion that climate warming together with a decline in precipitation would reduce soil carbon storage in these Picea crassifolia forests. (2) Response of soil organic carbon and related carbon cycling of typical vegetation types to climate change. The results showed that climate warming with a decline in precipitation significantly increased soil respiration rate and litter decomposition rate, and promote soil carbon emissions of Picea crassifolia forests. Our observations confirmed the relationships between soil organic carbon stocks and elevation in Picea crassifolia forests. For the grasslands, climate warming significantly increased herbaceous species number and aboveground biomass, while reduces soil organic carbon content. The response of soil microorganism to climate warming were analyzed using phospholipid fatty acids (PLFA) and BIOLOG carbon utilization technology. The results showed that climate warming had improved the metabolism ability and diversity of soil microorganism. The increase in soil microbial activity and diversity following climate warming had promoted soil respiration and the output of soil carbon, surpassing the input of soil carbon and eventually resulting in the decrease of soil organic carbon content. In addition, climate warming had caused a shift in the soil microbial community structure, leading to the relative dominance of fungi as evidenced by the increased ratio of fungal to bacterial PLFAs. Generally, the carbon assimilation rate of bacteria were higher than fungi, and fungal cell wall is more difficult to decompose than bacteria. In the long term, the acclimatization of soil microbial community structure may therefore weaken soil respiration and the output of soil carbon, thus enhancing the accumulation of soil organic carbon.(3) Impacts of grassland afforestation on soil organic carbon storage and related ecological process. Grassland afforestation resulted in a significant increase in soil organic carbon stocks, and soil organic carbon stocks tended to increase with stand development. The dynamics of carbon stored in soils depend on the balance between inputs, primarily from plant leaf and root detritus, and outputs through decomposition. Litter of coniferous trees, with higher amounts of secondary compounds such as lignin and polyphenols, decomposes more slowly than that of grass, which typically has lower phenolic and lignin concentrations. Thus, increased soil organic carbon stocks in afforested grasslands may be partially explained by the reduced decomposition rates of conifer litter. In our study, accumulation of an organic layer was observed in afforested grasslands, thus the larger annual cabon inputs through litter production may have contributed to the increase in soil organic carbon stocks. In contrast to the cumulative soil organic carbon storage, total nitrogen stocks did not differ significantly between plantation forests and adjacent grasslands, which had resulted in an increase in soil C:N ratios. Soil C:N ratios is one of the most important indexes to indicate soil carbon sequestration capacity, and soil organic matter with higher C: N value will be less liable to decompose, thus enhancing the accumulation of soil organic carbon. In the arid and semi-arid region of northwestern China, water supply is the main factor limiting sustainable development of planted forests, and water deficit had often been observed following afforestation. In our study, we did not observe a water deficit in the subsoil, and a significant increase was observed in the topsoil at a density ranging from 2833 to 2967 trees ha-1. We conclude that it is feasible to pursue carbon sequestration and maintain sustainable development of planted forests in this semiarid area if appropriate stand density is chosen for afforestation. (4) Responses of soil organic carbon storage and related carbon cycling to thinning. Generally, thinning resulted in a significant increase in soil respiration and soil temperature, and both soil respiration and its temperature sensitivity tended to increase with thinning densities in Picea crassifolia plantation forests. The increase in soil respiration were primarily driven by soil temperature. Thinning also changed the composition and structure of understory vegetation (moss gradually excluded while herbs expanded with thinning densities), which would influence the composition of surface soil organic carbon, and improve the temperature sensitivity of soil respiration. Thinning resulted in a significant decrease in soil organic carbon stocks, and soil organic carbon stocks tended to decrease with thinning densities. Furthermore, soil organic carbon in the upper soil were more vulnerable to thin-induced loss than the subsoil. The decline in soil organic carbon stocks following thinning may be partially explained by the increased soil respiration. In addition, the lower annual carbon inputs through litter production may have contributed to the decrease in soil organic carbon stocks. Thinning had resulted in a significant increase in soil water storage (0-70cm), and soil water storage tended to increase with thinning densities, which would have important implications for sustainable development of Picea crassifolia planted forests. Furthermore, thinning had significantly decreased soil C:N ratios, and soil organic matter with lower C: N value would be more liable to decompose, thus accelerate the decrease of soil organic carbon. |
| 中文关键词 | 祁连山区 ; 土壤有机碳 ; 造林活动 ; 间伐强度 ; 模拟增温 |
| 英文关键词 | Qilian Mountains Soil organic carbon Grassland afforestation Thinning densities Experimental warming |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287723 |
| 推荐引用方式 GB/T 7714 | 陈龙飞. 祁连山区典型植被土壤有机碳对气候变化及人为干扰的响应机制[D]. 中国科学院大学,2016. |
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