Knowledge Resource Center for Ecological Environment in Arid Area
| 全球草地生态系统根系周转的格局和驱动因子 | |
| 其他题名 | Global patterns and drivers of root turnover in grassland ecosystems |
| 孙元丰 | |
| 出版年 | 2018 |
| 学位类型 | 硕士 |
| 导师 | 白永飞 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 根系周转是陆地生态系统物质循环的关键指标，也是陆地生态系统净初级生产力及固碳潜力估算的核心参数。揭示根系周转的空间分布格局及其影响因素将有助于估算陆地生态系统地下碳收支水平，并预测陆地生态系统对全球变化的响应。草地生态系统占地球陆地总面积的40.5%（不包括格陵兰岛和南极），在全球碳循环中发挥着重要作用。因此，研究草地生态系统的根系周转对估算全球陆地生态系统碳库动态及固碳潜力具有重要意义。然而，由于地下取样困难，长期以来关于草地生态系统根系周转的研究主要局限于局地尺度，区域和全球尺度上的研究十分有限。现有关于草地生态系统根系周转的整合研究存在明显局限性。首先，取样点主要集中于北美和非洲地区，全球分布最广泛的欧亚大陆草原的样点非常稀少。其次，以往研究中根系周转驱动因子只包含气候因子，根系生长的直接载体—土壤的理化性质并未考虑。另外，草地作为承受人类活动干扰最为剧烈的陆地生态系统，以往的整合研究中没有研究土地利用方式（如放牧、打草、火烧等）对根系周转的影响。有鉴于此，本研究整合全球范围内2016年以前已发表文献数据、在线数据库数据及样地实测数据，借助方差分析、混合线性模型、皮尔逊相关、主成分分析、结构方程模型等统计学手段，研究全球草地生态系统根系周转的空间分布格局、驱动因子以及土地利用方式对根系周转的影响和机制。取得的主要结果包括：（1）全球草地生态系统根系周转具有明显的纬度地带性特征，周转速率从赤道向两极递减；不同植被类型根系周转存在显著差异，其中热带稀树草原根系周转最快，平均周转速率为0.82 yr-1，其次是暖温性灌草丛>潘帕斯草原>普列里草原>荒漠草原>欧亚大陆草原>山地草原，周转速率均值最低的是苔原生态系统，为0.12 yr-1, 即苔原生态系统群落水平上根系平均每8年左右周转一次。（2）气候（年平均气温、年平均降水量）、土壤（pH值、碱化度、质地、有机碳含量）和生物因子（地上净初级生产力、地下净初级生产力）共同影响根系周转，对根系周转变异的解释度为44%。年平均气温是影响根系周转的主要因子，既可以直接影响根系周转，也可以通过影响土壤pH值、碱化度和群落净初级生产力进而间接地影响根系周转。根系周转速率随年平均气温的增加呈指数增加（R2=0.35，P<0.001）。根系周转速率随年平均降水量的增加表现出先增加后降低的趋势，在年平均降水量为700-800mm之间达到最高值（R2=0.15，P<0.001）。在pH值为6左右的土壤中，根系周转速率最高，土壤pH值过高或过低均抑制根系周转。粉粒和黏粒含量高的细质土中，由于保水保肥能力高使根系周转较快，而在沙粒含量较高的粗质土中根系周转较慢。地上和地下净初级生产力较高的草地中，根系周转较快。（3）在全球尺度上，放牧、割草、水分添加和CO2倍增对根系周转没有显著的影响。火烧使土壤水分降低并增大地上生物量的分配从而抑制根系周转。酸性土壤中，氮添加会导致土壤微生物活性降低，土壤酸化加剧，根系生物分配减少，从而抑制根系周转。总之，气候因子、土壤理化性质和生物因子通过影响生态系统土壤酶活性、呼吸、矿化、土壤水分及养分的可利用性等直接或间接途径共同影响根系周转。不同草地类型中，根系周转速率存在显著差异。在对全球尺度根系周转的研究中，需要将欧亚大陆草原的数据纳入其中。本研究对全球草地根系周转的空间格局和驱动因子提出了新的观点和证据，为草地生态系统生产力及固碳潜力估算提供了更加可靠的参数，具有重要的现实意义。 |
| 英文摘要 | Root turnover is a key indicator of material cycle for terrestrial ecosystems. It is also a key parameter for estimating net primary productivity and carbon sequestration potential. Understanding the patterns and drivers of root turnover will contribute to better estimating carbon budget and predicting the response of terrestrial ecosystems to global change. Grassland ecosystems, which account for 40.5% of earth's total land area (not including Greenland and Antarctica region), is one of the most important terrestrial ecosystems for global carbon cycle. Thus, it is critical to examine root turnover for accurately estimating carbon sequestration potential in grassland ecosystems. However, studies on root turnover at regional or global scale are mainly limited by the difficulty in root sampling. In addition, previous synthesis studies on root turnover of grassland ecosystems had obvious shortcomings. First, the sampling sites are mainly located in North America or Africa, while study sites in widely distributed Eurasian grassland were sparse. Second, soil properties which can directly affect root growth, was not included. Third, the effects of land use types (e.g. grazing, clipping, burning, etc.) on root turnover rate was not included though human activities had intense impacts on grassland ecosystems. In this study, root turnover data were derived from three sources: Global published literatures on root turnover of grasslands before 2016; Online database for interpolating soil properties and climate data; Field survey data from Grassland Carbon Sequestration project. In this study, the patterns, drivers and mechanisms controlling root turnover were analyzed at global and regional scales (i.e., among different grassland types), by using variance analysis, mixed linear models, Pearson correlation, principal component analysis, structural equation modeling (SEM). The main results are summarized as follows.(1) The distribution of root turnover exhibited an obvious latitudinal pattern, decreasing gradually from equator to poles. Root turnover rate was significantly different among different grassland types, the maximum value of root turnover occurred in savanna grassland, with the mean value of 0.82 yr-1, followed by warm-temperate tussock grassland > pampas > prairie > desert grassland > mountain grassland. The lowest average root turnover rate is 0.12 yr-1, which occurred in tundra, indicating that mean turnover time is about eight years.(2) Climatic variables (mean annual temperature, MAT; mean annual precipitation, MAP), soil properties (pH; alkali; soil texture; soil organic carbon content, SOC) and biological factors (aboveground net primary production, ANPP; belowground net primary production, BNPP) together explained 44% of the variation in root turnover rate at global scale. SEM showed that MAT is a primary factor affecting root turnover via direct and indirect pathways. Root turnover rate increased exponentially with MAT (R2=0.35, P<0.001). The form of root turnover-MAP relationship was unimodal, root turnover rate increased at low MAP, peaked at MAP of 700-800mm, and then declined at high MAP (R2=0.35, P<0.001). The root turnover rate was highest in soils with pH value around 6, and root turnover rate was inhibited in soils with pH value higher or lower than 6. Root turnover rate was fast in fine soil with high silt and clay content because of high water and nutrient retention ability. Root turnover rate is low in coarse soils with high proportion of sand. Moreover, positive relationships of root turnover rate with ANPP and BNPP were also observed. (3) Grazing, mowing, burning or water addition had no significant effect on root turnover at global scale. Burning reduces soil moisture and increases the allocation of aboveground biomass, thereby inhibiting root turnover. In acid soil, the nitrogen addition inhibited root turnover due to decreased soil microbial activity, increased soil acidification and decreased biomass allocation to roots.Above all, climate variables, soil properties, ANPP and BNPP drive root turnover by means of regulating soil enzyme activity, respiration, mineralization, soil moisture and nutrient availability directly or indirectly. Root turnover rate differed among different grassland types. Root turnover data from the Eurasian steppe data should be included for global synthesis study. Our findings shed new light on factors and mechanisms controlling global and regional patterns of root turnover. |
| 中文关键词 | 根系周转 ; 驱动因子 ; 碳汇 ; 草地类型 ; 土地利用 |
| 英文关键词 | Root Turnover Driver Carbon Sink Grassland Type Land Use |
| 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/2XILL650/288218 |
| 推荐引用方式 GB/T 7714 | 孙元丰. 全球草地生态系统根系周转的格局和驱动因子[D]. 中国科学院大学,2018. |
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