Knowledge Resource Center for Ecological Environment in Arid Area
| 内蒙古草原氮循环关键过程的时空格局及其影响因子 | |
| 其他题名 | Spatio-temporal variabilities and controls of nitrogen cycling in Inner Mongolian grasslands |
| 施慧秋 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 张新时 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 草地生态系统是陆地生态系统最重要的自然生态系统类型之一，占地球陆地总面积的43 %，是承受全球气候变化和人类活动影响剧烈的植被区域。氮（N）是限制陆地生态系统植物生长、调节生态系统结构和功能、限制群落初级生产力的关键性元素，对草地生态系统尤为重要。在最近的二十年，已经对中国草地生态系统氮循环开展了大量的研究，但大多数在群落或流域水平开展，而对于区域水平的大尺度空间格局研究甚少。另外，已有研究大都关注氮循环多个关键过程中的一个，而综合研究氮循环多个过程的较少出现。本研究在具有明显降水梯度变化的内蒙古草原开展，大致沿中国东北样带（NECT），在1200 km的范围内自东向西设置了12个观测站点，测定了2012-2014年生长季大气干湿混合氮沉降、土壤无机氮及氮矿化作用、氧化亚氮的排放和土壤氨挥发过程，探讨了不同草原类型（草甸草原、典型草原和荒漠草原）氮素输入、转化和输出的时空格局及其影响因素。主要研究结果与结论如下：（1）在所有站点，干湿混合沉降物中铵态氮的浓度比硝态氮浓度高。西部的荒漠草地干湿混合沉降物中的无机氮的浓度较东部的草甸草地和中部的典型草地高。总体来说，样带上氮沉降的季节波动与该地区的降水格局相符，大多数峰值出现在7、8月份。累积氮沉降中硝态氮累积沉降量小于200 mg N m-2，说明该地区受工业燃料、农业肥料及汽车尾气等污染源的影响较小。生长季累积氮沉降量与降水量之间存在显著的相关关系，说明降水量是氮沉降量地理空间格局的重要控制因子。（2）土壤总无机氮含量在生长季期间呈现单峰曲线，其中铵态氮含量呈现先降低后增加的趋势。净氮矿化、硝化和氨化速率的季节波动较大，没有明显的动态规律，且存在年际差异。在时间尺度上，土壤湿度与土壤无机氮含量显著正相关，与土壤氮铵化速率呈正相关，而和土壤氮硝化、矿化速率呈负相关；土壤温度与无机氮含量、氮矿化速率仅在少数站点有相关，而且关系有正有负。在空间尺度上，土壤湿度、地上最大生物量、硝态氮、铵态氮和土壤总无机氮含量、年均的土壤累积氮硝化和矿化作用沿降水梯度呈现正相关关系。土壤无机氮浓度与土壤的物理、化学性质存在显著的相关关系。对于土壤氨态氮，主要的控制因子是土壤pH值和土壤有机碳含量，降水和土壤粘粒含量对土壤硝态氮含量有显著影响，降水量和土壤微生物量碳与土壤总无机氮空间变化相关性更强。氮矿化速率与土壤含水量成正比，土壤累积氮矿化量与降水量也成正比，因此，在样带空间上，降水是影响土壤氮转化过程的主要因子。（3）氧化亚氮排放速率的季节波动较大，在季节、年际间和站点间差异显著。综合分析3个生长季的观测结果，氧化亚氮的排放速率与土壤温度的正相关关系在8个站点发现，在1个站点发现两者存在负相关，而与土壤湿度的关系仅在4个站点发现，均为负相关。在空间尺度上，没有发现土壤温度和湿度与氧化亚氮排放的相关关系，但在2013和2014年生长季，氧化亚氮的排放速率分别与土壤硝态氮含量以及硝态氮沉降、降水量和土壤铵态氮含量有显著的相关关系。氧化亚氮累积排放量在时间和空间上都呈现较大的波动。在空间尺度上，2013年氧化亚氮累积排放量与N沉降量和土壤总氮矿化量有关；而2014年转变为土壤总无机氮含量。（4）沿样带从东至西，土壤氨挥发速率逐渐降低，差异显著。季节的变化对氨气挥发速率的影响不显著，年际间的差异也不显著。2013年，有7个站点的土壤氨挥发速率受温度、土壤湿度和土壤无机氮含量的影响，且各个点的影响因子不同，其余站点没有发现。2014年，温度是大多数站点土壤氨挥发速率的主要控制因子。在空间尺度上，土壤氨挥发速率随降水量的增加而增加；与土壤pH值、土壤硝态氮、土壤氨态氮的含量显著正相关。综上所述，在内蒙古草原，氮沉降、土壤无机氮及氮矿化、氧化亚氮排放和土壤氨挥发均具有较大的时空异质性，其影响因子也随着时间和空间的变化而变化。而氮循环是一个复杂的过程，形成这一区域格局的内在机理需要进一步的整合和分析。为了更好的了解氮循环的关键过程，应该在有条件的情况下进行多点的、长期监测。分析在区域尺度上的关键影响因子以及形成区域格局的内在机制，能够为以后发展氮循环相关模型提供土壤、气候等变量，用于在大尺度上估计草原生态系统的氮循环过程。 |
| 英文摘要 | Grassland ecosystems are one of the most important terrestrial ecosystems, accounting for approximately 43% of the world’s total land area, being rather vulnerable to impacts of unfavourable global climate change and discriminative human activities. Nitrogen (N) is one of the key elements which substantially restricts the growth of plants, regulates the structure and function of ecosystem, and limits the primary productivity level of the community as well, which are particularly true for grassland ecosystems. In recent two decades, a large number of studies on nitrogen cycling have been carried out in Chineses grasslands, however, the vast majority of which were conducted at community or catchment level, whereas those on large-scale spatial-temporal patterns and characteristics are extremely scarce. In addition, most past researches focus on one or a few specific processes of nitrogen cycle, while overall studies of nitrogen cycle are more rarely seen.In Inner Mongolian steppe characterized by an obvious gradient change in precipitation, 12 research sites were set up along the Northeast China Transect (NECT) from east to west, which range for 1200 about kilometers. The spatio-temporal patterns and their influential factors on the mixed nitrogen depositions, soil inorganic nitrogen contents in soils, nitrogen mineralization, nitrous oxide (N2O) emission and soil ammonia volatilization in different grassland types (meadow steppe, typical steppe and desert steppe) were explored during 2012-2014. The main results and conclusions are as follows:(1) Ammonium nitrogen (NH4+-N) concentration was higher than nitrate nitrogen (NO3—-N) in the total mixed (dry plus wet) inorganic N depositions throughout. Relative to the meadow steppe in the East and the typical steppe in the middle, total inorganic N concentration of mixed depositions in the western desert grassland is much higher. In general, seasonal variability of nitrogen deposition is consistent with the precipitation pattern in the area, with the maximum found during July-August at almost all sites in each year. Cumulative nitrate nitrogen deposition is less than 200 mg N m-2, which indicates that the region is less affected by industrial fuel burning, agricultural fertilizer application and automobile exhausts. The growing-season cumulative deposition of nitrogen was significantly correlated with precipitation, suggesting that precipitation is an important factor in controlling the bulk of total nitrogen deposition spatially.(2) The seasonal dynamics trend of total inorganic nitrogen mostly shows a single peaked curve during the growing season, while NH4+-N concentration decreased firstly and then on the rise during the growing season. The net nitrogen mineralization, nitrification and ammonification rates varied significantly during the growing season, showing no consistent seasonal patterns, with substantial inter-annual differences. At the temporal scale, soil moisture was positive related to soil inorganic N concentrations and soil ammonium nitrogen rate, while negatively correlated to soil nitrogen mineralization and nitrification rate. The relationships between soil inorganic N, soil nitrogen mineralization rate and soil temperature were only found in several sites but with rather inconsistent trends. Spatially, soil moisture, the maximum aboveground biomass, NH4+-N, NO3—-N, and total inorganic N, 3-year averaged cumulative soil nitrogen nitrification and mineralization increased along the precipitation gradient. There were significant correlations between soil inorganic N concentration and soil physical and chemical properties. The main controlling factors related to soil NH4+-N contents were soil pH and soil organic carbon content, and precipitation and soil clay content were more influential on soil NO3—-N, while precipitation and soil microbial biomass carbon were most closely related to soil inorganic nitrogen. The rate of nitrogen mineralization is positively correlated to soil mositure, and cumulative soil nitrogen mineralization is increased with precipitation, suggesting that in the region, precipitation plays an important role in controlling the minerlization process of soil nitrogen.(3) N2O emission rate varied substantially in growing seasons, with significantly differences in seasonal, inter-annual and inter-site. Analysis of all three growth seasons show positive correlations between N2O emission rate and soil temperature at 8 sites, a negative correlation at one site; by contrast, negative relationships with soil moisture were found at 4 sites. Spatially, no distinct relationships between N2O emissions and the soil temperatures or mositure were ever found. Significant correlation of N2O emission rate with soil nitrate content and nitrate nitrogen deposition were found in 2013, and with precipitation and soil ammonium nitrogen content in 2014. Cumulative N2O emissions displayed large fluctuations both temporally and spatially. At the spatial scale, cumulative N2O emissions were significantly correlated with N deposition and total soil nitrogen mineralization in 2013; by contrast, there was a significant correlation between total soil inorganic nitrogen concentration and cumulative N2O emissions in 2014. (4) Annual soil ammonia volatilization rates were significantly different among sites, decreased gradually from east to west along the transect. The effect of seasonal and inter-annual variation on soil ammonia volatilization rate was not significant. In 2013, cases in which soil ammonia volatilization rate was related to temperature, soil moisture and soil inorganic nitrogen content were found at 7 sites, and the degree of impacts of various factors was different. Temperature appeared to be the main controlling factor for the soil ammonia volatilization rate at most sites in 2014. At the spatial scale, soil ammonia volatilization rate increased with increases in precipitation, and was significantly positively correlated with soil pH, soil nitrate nitrogen and ammonium nitrogen content.In general, in the Inner Mongolian grassland, nitrogen deposition, soil inorganic nitrogen, nitrogen mineralization, N2O emission and soil ammonia volatilization all had a large spatial heterogeneity, and their controlling factors changed with season and site. Due to the complexity of nitrogen cycling, moer analysis and integration are needed to explore the underlying mechanisms. In order to better understand the key process in the nitrogen cycle, multi-point and long-term monitoring should be carried out in the region. Analysis of the key factors and internal mechanisms at the regional scale can be used for developing future models of nitrogen cycle driven by site climatic and soil cariables, applicable for large-sacle estimates of nitrogen cycle in grassland ecosystem. |
| 中文关键词 | 草地生态系统 ; 氮循环 ; 降水梯度 ; 氧化亚氮排放 ; 氨挥发 |
| 英文关键词 | Grassland ecosystem Nitrogen cycling Precipitation gradient N2O emission Soil ammonia volatilization |
| 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/2XILL650/288034 |
| 推荐引用方式 GB/T 7714 | 施慧秋. 内蒙古草原氮循环关键过程的时空格局及其影响因子[D]. 中国科学院大学,2017. |
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