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| 中国北方草地土壤阳离子交换量的动态变化及其对氮添加的响应 | |
| 其他题名 | The temporal dynamics of soil cation exchange capacity across northern China' s grasslands and its responses to nitrogen addition |
| 房凯 | |
| 出版年 | 2017 |
| 学位类型 | 硕士 |
| 导师 | 杨元合 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 土壤阳离子交换量和交换性盐基离子在维持植物正常生长和缓冲土壤酸化等方面起着重要作用。过去几十年，全球陆地生态系统经历了显著的环境变化，而环境变化可能会改变土壤阳离子交换量。然而，以往的研究多集中于小尺度，目前仍缺乏关于土壤阳离子交换量动态变化的大尺度证据。此外，在这些全球变化要素中，氮沉降问题尤为明显。然而，目前关于土壤盐基离子对氮沉降响应的相关研究主要集中在酸性土中，而来自碱性土中的观测证据较少。中国北方草地分布区在过去30年间经历了显著的环境变化。鉴于其包括丰富的草地类型、环境梯度大，为研究土壤阳离子交换量的动态变化以及碱性土壤盐基离子对氮添加的响应提供了理想场所。为此，本论文结合历史数据资料与实际样带调查，利用随机森林模型实现两时期数据的匹配，进而考察中国北方草地表层土壤阳离子交换量近30年的动态变化。同时，依托课题组在青海省刚察县设置的高寒草原氮添加控制实验(施氮量分别为0、1、2、4、8、16、24和32 g N m-2 yr-1)，探究土壤盐基离子对氮添加的响应及影响因素。本论文的主要结果如下：(1) 与1980年代相比，2010年代中国北方草地表层土壤阳离子交换量显著降低了14%(P < 0.001)。然而，土壤阳离子交换量的降低程度在不同草地类型存在差异。其中，高寒草甸、高寒草原、草甸草原和典型草原分别显著下降了11%、20%、27%和9%，而荒漠草原并未发生显著变化。阳离子交换量与土壤有机碳含量、粉粒含量、年降雨量等呈显著正相关关系。这些结果意味着过去30年间中国北方草地经历的土壤有机碳含量降低、土地退化、土壤酸化、极端降水等环境变化导致了表层土壤阳离子交换量的下降。(2) 土壤交换性盐基离子(特别是Mg2+与Na+含量)随施氮量的增加显著降低(P < 0.05)。并且，盐基离子与地上植物生物量和土壤无机氮含量呈显著负相关。这些结果意味着施氮一方面促进了植物生长，增加植物对盐基离子的吸收，使盐基离子含量降低；另一方面提高了土壤无机氮含量，导致NH4+与盐基离子交换量增多，同时NO3-淋溶导致大量阳离子损失。需要指出的是，本研究在碱性土中观测到的盐基离子的损失机制与酸性土中有所不同，后者中盐基离子的损失主要由缓冲土壤酸化引起。总体来看，本研究揭示了土壤阳离子交换量动态变化的大尺度证据，发现环境变化造成阳离子交换量的显著降低；考察了关于碱性土中盐基离子对氮添加的响应，发现氮添加促进土壤中盐基离子损失。这些研究结果意味着环境变化造成土壤养分与缓冲能力下降，进而可能影响生态系统结构与功能。这些研究结果也对草原生态系统可持续管理提供了重要启示，即当地政府部门需制订相关政策以减轻环境变化对草原生态系统的危害。 |
| 英文摘要 | Soil cation exchange capacity (CEC) and exchangeable base cations (BCs) play important roles in ensuring plants growth and buffering soil acidification. Over the past few decades, the earth has experienced significant environmental changes, affecting soil CEC in several respects. However, previous studies about CEC dynamics were mostly conducted on small scale, lacking evidence from the large spatial scale. Among these environmental changes, the effects of nitrogen deposition on terrestrial ecosystems attracted wide attention. But relative studies about the effects of nitrogen addition on soil BCs mainly came from acidic soils, with little information available in alkaline soils. The grassland area in Northern China has experienced significant nitrogen deposition and environmental changes in the past three decades. Given that this area covers diverse grassland types and broad environmental gradients, it provides us an ideal place for investigating the CEC dynamics and exploring the responses of BCs to nitrogen addition in alkaline soils.Here, we combined historical inventory data in the 1980s with actual measurements in the 2010s, and then used the Random Forest model to get these two datasets matched. We further explored the topsoil CEC dynamics across northern China’s grasslands in recent 30 years. Meanwhile, based on the manipulative experiment platform in Tibetan alpine steppe established by our research group, we investigated the responses of soil BCs to continuous nitrogen inputs. The main results of this study could be summarized as follows:(1) Compared with the 1980s, topsoil CEC across northern China’s grasslands in the 2010s significantly decreased by 14% (P < 0.001). However, the temporal patterns differed among various vegetation types. Topsoil CEC in alpine meadow, alpine steppe, meadow steppe and typical steppe all decreased significantly (P < 0.001), with the declines of about 11%, 20%, 27% and 9% respectively. In contrast, no significant change was found in desert steppe. Moreover, CEC was positively related to the content of soil organic carbon, silt content and mean annual precipitation, suggesting that the decline of CEC was likely associated with soil organic carbon loss, soil degradation, soil acidification and extreme precipitation across northern China’s grasslands since the 1980s.(2) Exchangeable base cations, especially Mg2+ and Na+, decreased significantly along the gradient of nitrogen addition. The content of base cations was negatively correlated with above-ground biomass and soil inorganic nitrogen. This result suggested that nitrogen addition promoted plant growth, thus strengthening the plant absorption of base cations and making them decrease. Moreover, nitrogen addition increased the content of soil inorganic nitrogen, which increased the exchange quantity of BCs with NH4+ and the loss of BCs resulted from enhanced NO3- leaching. It should be noted that the loss mechanism of BCs in alkaline soils was different from that in acid soils which was mainly caused by buffering soil acidification.This study presented the evidence of temporal dynamics of soil CEC over large spatial scale, showing that CEC declined due to environmental changes. This study also illustrated that BCs decreased along the nitrogen addition gradient. These results suggested that the poor soil nutrient and buffering capacity caused by environmental changes might affect the ecosystem structure and function. To maintain sustainable vegetation production, the local government department should make relative policy to relieve the hazards in grassland ecosystems in the future. |
| 中文关键词 | 中国北方草地 ; 高寒草原 ; 阳离子交换量 ; 交换性盐基离子 ; 动态变化 ; 环境变化 ; 氮沉降 ; 氮添加 |
| 英文关键词 | Northern China’s grasslands Alpine steppe Cation exchange capacity (CEC) Exchangeable base cations (Exchangeable BCs) Temporal dynamics Environmental changes Nitrogen deposition Nitrogen addition |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生物工程 |
| 来源机构 | 中国科学院植物研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288035 |
| 推荐引用方式 GB/T 7714 | 房凯. 中国北方草地土壤阳离子交换量的动态变化及其对氮添加的响应[D]. 中国科学院大学,2017. |
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