Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原草地土壤养分动态变化与空间特征 | |
| 其他题名 | Dynamics and spatial characteristics of soil nutrients across alpine grassland, Qinghai-Tibet Plateau |
| 田黎明 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 赵林 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 气候变化和冻土退化能够改变寒区地表能水平衡和水文循环，进而影响生态环境、植被群落、碳循环、生态系统生产力、沼泽湿地和湖泊萎缩、草地荒漠化、温室气体排放、地表沉降等环境问题；特别是气候变暖和冻土退化对寒区碳氮循环和生物地球化学循环过程的影响是目前相关学科研究的焦点之一。准确了解青藏高原区域尺度上高寒草地土壤养分的动态变化和空间特征，将有助于加深认识青藏高原高寒草地土壤养分循环过程、土壤-植被-冻土系统的相互关系、以及土壤-植被养分对气候变暖、冻土退化和环境变化的响应，进而有助于揭示高寒生态系统养分循环与气候变化之间的内在关系，为高寒草地生态系统的生态修复与保护奠定理论基础。然而，目前关于气候和冻土变化对寒区土壤养分的影响研究主要来自于环北极地区，很少关注区域尺度和长期监测土壤养分及其计量比的动态变化，而在青藏高原高寒草地的相关结果更是稀少。因此，对于高寒草地生态系统土壤养分的动态变化和空间特征仍然不清楚。青藏高原分布着全球面积最大和类型最丰富的高寒草地，也是我国高寒草地分布最为集中的区域。青藏高原多年冻土和草地生态系统处于明显退化状态，可能改变土壤-植被系统的内在关系。本文基于2010s时期青藏高原高寒草地的185个土壤坑探资料和1980s时期全国第二次土壤普查数据库中在青藏高原范围内的319个土壤坑探数据、以及马衔山高寒草地连续样品采集与水热监测，收集区域已发表的文献资料，结合气象资料、植被遥感数据、数理统计方法、以及机器学习算法，研究了青藏高原高寒草地不同植被类型土壤养分及其计量比的垂直分布规律、动态变化、及其空间分布特征和控制因素。主要结果如下：（1）青藏高原东部草地土壤有机碳和全氮储量在高寒草甸和高寒草原随深度递减，但在高寒沼泽草甸随深度变化不显著，这是高寒沼泽草甸频繁的冻结-融化循环引起的冻融扰动现象而导致的。土壤全磷、Ca2+和Mg2+储量在高寒沼泽草甸中随深度有轻微增加趋势。不同植被类型中K+储量随深度显著降低，但Na+储量则随深度增加而显著增加，这是因为植被生长循环作用的结果；相反，SO42-和Cl-储量则随深度没有明显差异。表层1m土壤有机碳和全氮储量随高寒沼泽草甸-高寒草甸-高寒草原逐渐递减；全磷、全钾和Cl-储量在各植被类型中差异较小；Mg2+、K+和Na+储量的最低值出现在高寒沼泽草甸，最高值发生在高寒草原。除碳氮外，沼泽草甸表层20cm土壤养分储量显著低于高寒草甸和高寒草原。土壤有机碳和全氮与植被盖度、土壤水分和细颗粒含量呈现显著正相关，但与砂土含量和土壤pH值呈负相关；相反，离子养分与植被盖度、土壤水分和细颗粒组成含量呈现显著负相关，但与砂土含量和土壤pH值呈正相关。（2）土壤养分及其计量比在冻融循环周期内存在季节波动。土壤pH和电导率在暖湿季节分别显著比干冷季节较低和较高。土壤有机碳、全氮、C:P、C:K、N:P和水分的季节变化一致，但没有显著的变化趋势。季节冻土区表层20cm土壤有效磷和速效钾呈现显著增加趋势，但在多年冻土区变化不显著。土壤养分季节变化特征受土壤微生物活动、植被凋落物、冻融循环特征、根系生长与周转率、土壤水分和温度、地表形变和采样误差等因素影响。（3）近30年来高寒草地土壤有机碳、全氮、全钾、有效磷和速效钾储量分别从2.27kg/m2、0.20kg/m2、2.05kg/m2、0.67g/m2和17.26g/m2显著降低至1.96kg/m2、0.18kg/m2、1.55kg/m2、0.65g/m2和13.24g/m2；分别降低了13.6、10.3、24.4、3.0和23.3%。土壤全磷储量在1980s-2010s期间变化不显著；土壤有效氮从11.94显著升高至14.8g/m2，增加了24.0%。土壤C:N和C:K分别从10.62和1.64显著增加至11.05和1.70；而土壤C:P和N:P分别从36.55和3.04显著降低至31.97和2.92。土壤养分及其计量比的动态变化在不同植被类型中差异较大。土壤养分的动态变化说明高寒草地在过去30年来呈现明显的退化，需要采取围栏封育、补播、飞播、施肥、消除毒杂草、人工草地建植等主要措施，开展天然草地保护工程技术、建设工程技术、以及相关政策保障管理，才能保证退化草地生态恢复工程的可持续发展。（4）高寒草地初始养分储量解释了土壤养分和有效养分变化量的16.4至69.9%；植被类型分别解释了土壤有机碳、全氮和有效氮变化量的10.6、9.1和16.6%；粉土含量分别解释了全磷和全钾变化量的13.5和5.9%；然而，气候、氮沉降和土壤因子综合起来对土壤养分变化量仅仅解释了不到10%。土壤C:N和C:K的变化主要取决于土壤有机碳的变化，但土壤C:P和N:P的变化则取决于养分之间的共同变化。 （5）土壤养分及其计量比在不同植被类型中具有显著差异；高寒沼泽草甸土壤养分及其计量比显著高于高寒草甸、高寒草原和高寒荒漠；土壤养分及其计量比的影响因素在不同植被类型中也不同。黏土和粉土含量解释了土壤C:N变化的32.5%，年平均气温、降水、土壤水分、NDVI、以及黏土和粉土含量共分别解释了土壤C:P、N:P和C:K变化的13.2、11.1和10.3%。另外，土壤碳氮关系是紧密耦合的且随环境变化其变化并不明显，但环境变化可能会削弱土壤碳氮与磷钾的关系，进而打破养分循环之间的平衡，说明高寒生态系统养分限制可能从氮限制转变到磷或钾限制。青藏高原明显的升温能够提升养分的生物循环过程和改变水分条件，结合养分循环之间的耦合作用随干旱程度增加而降低，最终可能会增强青藏高原多年冻土区高寒草地养分之间的耦合作用。 |
| 英文摘要 | Climate change and permafrost degradation could alter surface energy-water balance and hydrological cycle in cold regions, which in turn lead to a series of environmental issues, such as ecological environments, plant communities, carbon cycling, ecosystem primary production, shrinkage of wetlands and lakes, desertification, greenhouse gas emission, and ground deformation. Of which the effects of climate warming and permafrost degradation on carbon and nitrogen cycling and biogeochemical cycles are the main issues concerned by ecologists and permafrost scientists. Accurate understanding of dynamics and spatial characteristics of soil nutrients in alpine grasslands on the Tibetan Plateau at a large scale is essential for increasing our understanding of soil nutrients cycling processes in Tibetan grasslands, relationships among soil-vegetation-permafrost system, and the responses of soil and vegetation nutrients to climate warming, permafrost degradation, and environmental changes, which could help to reveal the inherent associations of nutrient cycling with climate change in alpine ecosystems and to provide a fundamental basis for ecological rehabilitation and protection in alpine grassland ecosystem. However, most of studies on the effects of climate and permafrost changes on soil nutrients mainly concentrate on the circumpolar permafrost regions, little attention has been paid to the Tibetan ecosystems.The Tibetan Plateau distributes the largest area and the most diverse types of alpine grasslands in China, even around the world. To date, the permafrost and grassland ecosystem on the Tibetan Plateau have been degraded significantly, may altering the inherent relationship between soil and plant. In this study, we collected 185 soil profiles over the Tibetan Plateau and monitored soil nutrients and hydrothermal status on the Mahan Mountain during the 2010s. Moreover, we also applied a comprehensive dataset of 319 soil profiles on the plateau during the 1980s and synthesized relevant published data across the plateau during the 2010s. By using these measured and assembled dataset, combined with meteorological observations, satellite-based vegetation index, mathematical statistics analyses, and machine learning algorithms, we investigated the vertical distributions, seasonal variations, long-term changes, spatial features and controlling factors of soil nutrients and their stoichiometry in the Tibetan grasslands. The principal results are capsuled as follows:(1) On the eastern Tibetan Plateau, soil organic carbon (SOC) and total nitrogen (TN) stocks decreased with increasing depth in alpine meadow (AM) and steppe (AS), while they showed insignificant distributions along soil profiles in alpine swamp meadow (ASM) due to the cryoturbation caused by frequent freezing-thawing cycles. Total phosphorus (TP), Ca2+, and Mg2+ stocks slightly increased with depth in ASM. K+ stock decreased with depth, while Na+ stock increased slightly with depth among different vegetation types because of the plant cycling; however, SO42? and Cl? stocks remained relatively uniform throughout different depth intervals in alpine grassland. The largest and lowest stocks of SOC and TN were observed in ASM and AS, respectively; by contrast, the maximum and minimum stocks of Mg2+, K+, and Na+ were found in AS and ASM, respectively; TP, total potassium (TK), and Cl- stocks did not show any differences among vegetation types. Except for SOC and TN, soil nutrient stocks in the top 20 cm soils were significantly lower in ASM compared to those in AM and AS. SOC and TN stocks in the alpine grassland positively correlated with vegetation coverage, soil moisture, clay content, and silt content, while they negatively related to sand content and soil pH. However, base cation stocks revealed contrary relationships with those environmental variables compared to SOC and TN stocks.(2) Seasonal variations in soil nutrients and their stoichiometry were observed during the freezing-thawing processes in a relict permafrost region on the Mahan Mountain. Soil pH during the warm-humid season was significant lower compared to that during the cold-dry season, while a converse relationship was found for soil electrical conductivity. There were consistent seasonal variations in SOC, TN, C:P, C:K, N:P, and soil moisture, but they exhibited insignificant changes during the observed freezing-thawing cycle. TP and available phosphorus (AP) contents in the top 20 cm soils increased significantly for the seasonally frozen ground, but they did not change for the permafrost soils. Overall, seasonal variations in soil nutrients were affected by microbial activities, litter fall, freezing-thawing processes, root growth and its turnover rate, soil moisture and temperature, ground deformation, sampling errors, etc.(3) During the last thirty years, SOC, TN, TK, AP, available potassium (AK) stocks in the top 10 cm soils have significantly decreased from 2.27 kg/m2, 0.20 kg/m2, 2.05 kg/m2, 0.67 g/m2, and 17.26 g/m2 during the 1980s to 1.96 kg/m2, 0.18 kg/m2, 1.55k g/m2, 0.65 g/m2, and13.24 g/m2 during the 2010s for the whole alpine grassland, respectively; they decreased by 13.6, 10.3, 24.4, 3.0, and 23.3%, respectively. TP stock did not change significantly from the 1980s to the 2010, whereas soil available nitrogen (AN) stock increased significantly from 11.94 to 14.8 g/m2 (increasing by 24.0%) during the two sampling intervals. For the soil nutrient stoichiometry, soil C:N and C:K increased significantly from 10.62 and 1.64 to 11.05 and 1.70, respectively, while soil C:P and N:P declined significantly from 36.55 and 3.04 to 31.97 and 2.92, respectively, during the past three decades. In addition, the long-term changing magnitude of soil nutrients and their stoichiometry showed large differences among different vegetation types across the Tibetan grasslands. Furthermore, those variations in soil nutrients demonstrate that alpine grasslands have been degraded severely during the last thirty years. We should carry out fencing, reseeding, aerial sowing, fertilization, elimination of poisonous weeds, establishment of artificial grassland, grassland protection and construction engineering technology, and policies-related guarantee management to ensure the sustainable development of ecological restoration of the degraded grasslands.(4) For the whole alpine ecosystem, the standing nutrient stocks explained 16.4-69.9% for total variations in soil nutrient changes; vegetation types explained 10.6, 9.1, and 16.6% for total variations in SOC, TN, and AN changes, respectively; silt content accounted for 13.5 and 5.9% for total variations in TP and TK changes, respectively; however, combined effects of other factors, such as climatic variables, nitrogen deposition, and edaphic properties, only accounted for less than 10% for soil nutrient changes. Furthermore, soil C:N and C:K changes were dependent on SOC changes, while soil C:P and N:P changes depended on the joint variations of soil nutrients. (5) Topsoil nutrients and their stoichiometry exhibited significant differences among vegetation types across the alpine grasslands. The soil nutrients and their stoichiometry in ASM were significant higher than that in AM, AS, and AD. The controlling factors of soil nutrients and their stoichiometry also showed large differences under different vegetation types. Overall, clay and silt contents explained 32.5% for variations in soil C:N ratio, while climatic, topographic, vegetation, and soil variables together accounted for 13.2, 11.1, and 10.3% for total variations in soil C:P, N:P, and C:K ratios, respectively. Moreover, soil carbon and nitrogen are closely coupled and insignificantly change with environmental factors; while environmental change may decouple carbon and nitrogen with other elements, which may shifts the nutrients limitation in alpine ecosystems from nitrogen-limited to phosphorus or potassium limitation. In addition, the significant warming on the plateau, combined with the increased decoupling of nutrient cycles with aridity, and as a result, it is expected that the Tibetan ecosystem will increase nutrient coupling due to the concurrent enhanced biological cycling of nutrient and improved moisture condition. |
| 中文关键词 | 土壤养分 ; 养分计量学 ; 高寒草地 ; 多年冻土 ; 青藏高原 |
| 英文关键词 | Soil nutrients Nutrient stoichiometry Alpine grassland Permafrost Tibetan Plateau |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 寒区工程与环境 |
| 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/2XILL650/288143 |
| 推荐引用方式 GB/T 7714 | 田黎明. 青藏高原草地土壤养分动态变化与空间特征[D]. 中国科学院大学,2018. |
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