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题名: 我国典型森林含氮气体排放潜势研究
作者: 崔娟1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 张晓山 ; 王章玮
关键词: 氧化亚氮,一氧化氮,氨,排放潜势,森林小流域 ; nitrous oxide, nitric oxide, ammonia, emission potentials, forestedcatchments.
其他题名: Emission potentials of nitrogenous gases in some typical forests in China
学位专业: 环境科学
中文摘要: 大气中主要的痕量气体,如氧化亚氮(N2O),氮氧化物(NOx)和氨(NH3) 等对区域乃至全球的大气化学起着至关重要的作用。日趋严重的大气氮(N)沉 降对我国森林生态系统中土壤和植物的含N 气体的排放潜势产生了极其重要的 影响。我国幅员辽阔,存在多种类型的森林。气候,土壤因子以及大气N 沉降都 存在明显的区域差异。森林植物也可以通过叶片气孔和大气进行NH3 的双向交 换。利用冠层NH3 排放潜势这一指标,可以初步判断森林冠层是大气NH3 的排 放源还是汇。基于此,本论文开展了三个方面的工作来研究我国一些典型森林的 含N 气体的排放潜势。 我们利用一个实验室的反硝化培养试验研究了跨气候带的我国南北方八个 典型森林小流域土壤的反硝化特征。在每个森林小流域内,又设置了三到四个采 样样方(分别位于排水良好的坡上,坡下和地下水控制区域),以此来比较不同 土壤的反硝化潜势和N2O 以及NO 的排放潜势。结果表明:与南方亚热带和热 带土壤相比,我国北方温带森林的土壤表现出更高的瞬时反硝化速率,平均值分 别为25.4±23.7 和110.0±104.1 nmol N g-1 dry soil hr-1。六个南方热带/亚热带森林 小流域的土壤表现出更高的潜在N2O 损失(由N2O 被还原为氮气(N2)之前的 反硝化产物的最大累积量计算而来),尤有是在土壤有机碳(C)和总N 含量较 高的森林小流域内;而来自这些森林小流域的土壤也表现出更高的N2O/(N2O+N2) 比率。在同一森林小流域内,与坡上土壤相比,采集自地下水控制区域的土壤也 表现出更高的瞬时反硝化速率和更低的N2O 和NO 排放潜势。这表明,通过反 硝化过程,地下水控制区域的土壤移除硝酸根(NO3 -)的能力更强。同时,我们 的研究还表明,土壤pH 是区域尺度上影响土壤潜在反硝化速率和N2O/(N2O+N2) 比率的重要因子。而土壤pH,C 和N 有效性共同影响土壤N2O 的排放潜势,但 各因子的影响效果因坡位的不同而有所不同。 我们还利用静态箱体法对我国北方一个典型暖温带森林(东灵山)土壤N2O 和甲烷(CH4)的交换通量的时空变化规律进行了较长时间(连续两年)的研究。 小流域内,沿地表水流向,同样设置了四个不同的采样样方(和培养试验采样样 方位置相同)。采样期内,土壤N2O 和CH4 的年交换通量(平均值±标准差)分 别为1.19±0.11 kg N2O-N ha-1 yr-1 和-1.38±0.04 kg CH4-C ha-1 yr-1。时间尺度上, 土壤N2O 的交换通量呈现明显的季节变化,最大排放量出现在春季土壤融化期。 与坡地土壤相比,地下水控制区域表现出更高的N2O 排放通量。由于较高的土 壤含水量,位于地下水控制区域出口位置的土壤,会短暂性地向大气中排放CH4, 而其它三个样方基本都表现为大气CH4 的汇。 本研究还对我国西南一个典型N 饱和的亚热带常绿森林(铁山坪)中六种 优势植物叶片氨(NH3)的排放潜势(叶片中铵离子和氢离子浓度的比率)进行 了研究。结果表明,叶片NH3 的排放潜势和N 含量表现出很小的时间变异性(季 节和周变化),其受植物品种和叶龄的影响更大。杉木(Cunninghamia Lanceolata) 针叶的NH3 排放潜势较高(平均值:46.2±26.3),而含N 量较低(平均值:1.5±0.2% 的干重)。小叶女贞(Ligustrum quihoui Carr.)的NH3 排放潜势在六个品种中居于中间位置(平均值:17.3±9.3),而叶片含N 量最高(2.7±0.3%的干重)。马尾松(Pinus massoniana)的NH3 排放潜势和N 含量都较低。总体而言,六个植物品种的NH3 排放潜势都很低(< 200),从而很难形成足够的叶片NH3 分压。 本研究不仅证明了沿气候带的森林土壤的不同反硝化特性,也证实了在同一森林小流域内,土壤反硝化速率和中间产物累积,以及自然条件下森林土壤的温室气体交换通量都存在空间差异。我们的研究结果凸显了地下水控制区域土壤在 评估森林生态系统温室气体和N 收支方面的特殊性和重要性。因此,未来在评估我国森林温室气体和N 收支时需要考虑水分条件和地形因素的影响。这些结论对评估森林小流域和区域尺度上温室气体的排放和N 收支具有指导意义。此外,我们的结果还表明,以马尾松为主的铁山坪亚热带森林冠层可以作为大气活性NH3 的重要汇。因此,仅以森林穿透水中的N 通量来表征森林生态系统的N收入会显著低估活性N 的收入量,从而影响生态系统N 评估的准确性。这一结 果对未来评价生态系统和区域尺度上植物与大气NH3 的双向交换和N 收支平衡 有指导意义。
英文摘要: Nitrous oxide (N2O), nitrogen oxides (NOx) and ammonia (NH3) are important trace gases in the atmosphere, and play key roles in the atmospheric chemistry on the regional and global scales. The elevated nitrogen (N) deposition in China recently has made great influence on the emission potentials of nitrogenous gases in the forest ecosystems. China has a vast territory, existing many types of forest ecosystems, and the climate, soil factors and N deposition rates vary greatly in regional scales. Furthermore, the exchange of NH3 between plants and the atmosphere is in fact bidirectional, due to the existing of leaf stomata. Using the parameter of leaf NH3 emission potential, we can determine the plants acting as source or sink for the atmospheric NH3 primarily. According to these, we studied the emission potentials of nitrogenous gases in some typical Chinese forests in three respects. Denitrification characteristics of forest soils from eight headwater catchments in China were investigated in this study, along a climatic gradient from the tropics in the south to the temperate zones. Within each catchment, different landscape positions along hydrological flow paths were also considered, including well-drained soils on hill slopes and poorly drained soils in groundwater discharge zones (3-4 sampling plots). The results showed that soils from the northern sites had much greater instantaneous denitrification rates than the southern sites, with the average of 110.0±104.1 and 25.4±23.7 nmol g-1 dry soil hr-1, respectively. Large potentials for N2O loss (evaluated as the maximum denitrified N accumulation before N2O reduced to dinitrogen (N2)) were observed in the six tropical and sub-tropical catchments, particularly in soils with high carbon (C) and N contents. Soils from these southern sites also displayed high N2O/(N2O+N2) stoichiometries. Within the catchments, soils from the groundwater discharge zones showed greater potential denitrification rates but smaller N2O/(N2O+N2) ratios and NO concentrations in comparison with those on the hill slopes, implying large N removal potentials of soils from the groundwater discharge zones. Besides, our findings suggest that soil pH is the prime controller for the potential denitrification rates and the N2O/(N2O+N2) stoichiometries. Additionally, soil pH, C and N availability affect the potential for N2O loss synergistically, while the effecting degree varies with the landscape position. The flux rates of N2O and methane (CH4) were measured in this study by closed chamber technique throughout two years in a warm temperate forested headwater catchment in North China (Donglingshan). The spatial variability in four different positions along the hydrological flow paths within the catchment was also assessed (the four plots were also the positions for soil collection in the former anaerobic incubation study). The annual mean N2O and CH4 flux rates (mean±S.D.) were 1.19±0.11 kg N2ON ha-1 yr-1, and -1.38±0.04 kg CH4-C ha-1 yr-1, respectively. The fluxes of N2O also displayed seasonal variation with higher emission rate in spring due to soil thawing. Additionally, soils from the groundwater discharge zone emitted more N2O than in the hill slope. Soils in the outlet of groundwater discharge zone occasionally emitted CH4 to the atmosphere due to high soil water content contrary to net CH4 uptake at the other three positions. The temporal variability of leaf NH3 emission potentials (the ratio of leaf tissue ammonium to proton concentration) and N pools of six dominant plant species were also investigated at Tieshanping forested catchment, southwest China. The results showed that the NH3 emission potentials and N pools presented small variations in time scales, which were mainly controlled by plant species and leaf age. Also, high emission potential in one species did not correspond to high tissue N content. Specifically, the Chinese fir (Cunninghamia Lanceolata) had higher NH3 emission potential (mean: 46.2±26.3) but lower N content (mean: 1.5±0.2% of Dw). The leaf privet (Ligustrum quihoui Carr.) was with the moderate emission potential (17.3±9.3) and the highest N content (2.7±0.3% of Dw) on average, which for the Masson pine (Pinus massoniana) were both low. Overall, the emission potentials of the six species were too low (< 200)to build up a sufficiently high NH3 partial pressure in the leaves. This paper not only pinpoint the variability of denitrification characteristics of soils along the climatic gradient, but also confirm the small-scale variations in soil N2O and NO emission potentials and in situ greenhouse gas exchange rates within catchments. These indicate the importance of discrimination when modeling N2O and NO emissions and N removals from regional N loading related to different landscape positions. Therefore, the small-scale (within the catchment) spatial variability related to hydrological conditions should be taken into account when understanding of China’s national greenhouse gases budget. Additionally, the Masson pine dominant subtropical forest at Tieshanping acts as a sink for the atmospheric NH3, indicating that using the N flux in throughfall only may significantly underestimate the N income of the ecosystem. The results are informative for future modeling of plant-atmosphere NH3 exchange and estimating N budget in local or regional scales.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38611
Appears in Collections:大气环境研究室_学位论文

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作者单位: 1.中国科学院生态环境研究中心

Recommended Citation:
崔娟. 我国典型森林含氮气体排放潜势研究[D]. 北京. 中国科学院大学. 2017.
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