【作者】 巴才汗尼亚姆达瓦（Batsaikhan Nyamdavaa）；

【导师】 李勇；

【作者基本信息】 中国农业科学院 ， 土壤学， 2013， 博士

【摘要】 十壤在全球碳循环中起着重要作用,并且对碳封存或释放到大气中具有巨大潜在力。由十壤侵蚀引起的土壤有机碳(SOC)再分布过程依然是争议的话题。在全球上,土壤侵蚀导致坡耕地大量有机碳发生横向再分布。在地形系列土壤或田块尺度中,人们普遍认为土壤流失导致SOC含量降低。然而,水库和其他沉积点中的沉积物种富含大量SOC。净源或大气中CO2沉降的结果尚不清楚。全球估计范围从每年大约1Pg C来源到沉降相同的量。基于此背景,本研究调查了中国黄土高原小农业坡地(面积0.07公顷)土壤再分布过程对SOC含量和通量的影响以及相应的碳源和库功能。通过分析3×3m栅格小区表层,包括耕层和底土层(知道0.6m深度)的土壤样品来研究SOC储量的空间格局。在相同的土壤样品中,示踪放射性核素137Cs和过剩的2loPb的空间分布分别用来两国过去50年和100年净侵蚀和净沉积。研究结果表明,SOC在低坡地位置大量累积和稳定化,且含有最高活度的137Cs和210Pb储量。同时强调了对于易受侵蚀农业用地底土碳预算的重要性。基于克里格同归法预测SOC、137Cs和210Pb分布图显示,坡上面SOC弄的减少和穿过坡中部到沿边界的试验地底部坡下部凹面SOC浓度的增加表明SOC和空间分布和137Cs、210Pb相同。为了空间综合分析小规模耕地土壤再分布对SOC动力学的影响,通过SOC浓度与总土壤再分布(TSR)相乘来计算,而总土壤再分布包括由37Cs和210Pb含量和耕作侵蚀预测模型(TEP)得出的耕作和水引起的土壤再分配。该计算方法被用于涵盖每年SOC和由137Cs和210Pb活度测量估计的土壤再分布平衡的两个时期,1911-1954年和1954-2011年。137Cs和210Pb的测量可以提供山坡景观中期(-50年)和长期(100-150年)侵蚀土壤和SOC再分布格局的溯源信息。研究结果表明,由于水力侵蚀的输出作用,SOC在横向大量流失。在1911-1954年和1954-2011年期间,耕作引起的土壤再分布增加了SOC,并且在1911-1954年和1954-2011年期间分别补偿了由水蚀导致SOC流失量的3%、10%。在1911-1954年期间,整个坡面SOC净流失量为6.77t C ha-1(0.157t C ha-1yr-1).在1954-2011年间,SOC净流失量12.58t C ha-1(0.221t C ha-1yr-1)。由于通过铧式犁耕作引起的土壤再分布使得坡麓和背坡底边界区域的SOC显著增加。通过高纯锗伽马谱仪检测的不同坡面深度137Cs和210Pb充分证明了在地边界区域的沉积。土地管理方式对SOC的横向和垂直分布有重要影响。长期耕作的结果是SOC横向输出减少、横向流动增加,导致负C平衡减少。在一个连续的生长期(如在2011年),对最活跃的区域进行关于土壤再分布的土壤呼吸的现场测量。对于测量周期,尚未发现土壤再分布或者其他参数(如土壤特性和地形)空间格局的普遍关系,这凸显了土壤呼吸的变异性。然而,土壤呼吸与耕作侵蚀呈显著线性关系。因此,侵蚀点的碳流失可能在沉积点正将矿化中得到部分补偿。总之,本研究大大提高了关于在小型种植场规模中土壤再分布对SOC含量和通量的影响的认识和理解。更多还原

【Abstract】 Soils play a major role in the global carbon cycle and have a huge potential for either sequestering or releasing carbon (C) to the atmosphere. The fate of SOC redistribution caused by soil erosion is a controversial subject. Globally, large amounts of soil organic carbon (SOC) are laterally redistributed on sloped cultivated land by soil erosion. On the toposequence or a field scale, it is generally recognized that loss of soil results in reduction of SOC. However, significant amounts of carbon might be stored in sediments in reservoirs and other deposition sites. Whether this results in a net source or sink of atmospheric CO2is unclear. Global estimates range from a source of～1Pg C per year to a sink of the same magnitude. Against this background, this study investigates impacts of soil redistribution processes on SOC stocks and fluxes and the corresponding C source or sink function in a small agricultural hillslope (0.07ha) in Chinese Loess Plateau. Spatial patterns of SOC stocks were studied by analysis of soil samples of the top layer, including plough layer and subsoil layers (up to a depth of0.6m) taken in a3x3m grid. In same soil samples, spatial patterns of the radionuclide tracer caesium-137(137Cs) and unsupported lead-210(210Pbcx) were used to quantify net erosion and net deposition within the field over a50-year and100-year period, respectively. Results revealed a substantial accumulation and stabilization of SOC with highest activity of the137Cs and210Pbex inventory at lower slope position, stressing the importance of subsoil C for budgets on agricultural land prone to erosion. Predicted maps of SOC,137Cs and210Pbex based on regression kriging showed that reduced SOC concentrations on the slope convexities at the upper slope and an increase SOC concentrations within the slope concave which traverse the centre of the field, along the boundary of bottom of field, indicates spatial distribution of SOC,137Cs and210Pbex are very similar patterns. For a spatially integrated analysis of the impact of soil redistribution on SOC dynamics at the small cultivated field scale, soil organic carbon redistribution was calculated by multiplying SOC concentration by total soil redistribution (TSR) including both tillage and water-induced soil redistribution derived from137Cs and210Pbex inventories and from the tillage erosion prediction model (TEP). It was applied for two periods from1911to1954and1954to2011, covering periods of the equilibrium of annuals SOC associated to soil redistribution estimated from137Cs and210Pbex measurement, and these measurement provide retrospective information on the medium-term (-50years span) and long-term (100-150years span) redistribution patterns of the eroded soil and SOC within the hillslope landscape. Results indicated that a substantial amount of SOC was lost laterally due to the export by water erosion. Tillage-induced soil redistribution increased SOC and compensated for3%and16%of the SOC losses due to water erosion during1911-1954and1954-2011, respectively. During the period1911-1954, the net SOC loss from the entire slope was6.77t C ha-1(0.157t C ha-1yr-1). Within the period1954-2011, the net SOC loss was12.58t C ha-1(0.221t C ha-1yr-1). Significant increase of SOC at the lower field boundary on the convergent footslope and backslope resulted from tillage-induced soil redistribution by moldboard plowing. Deposition on the lower field boundary was successfully validated by depth profiles of137Cs and210Pbex measured by hyper pure germanium gamma spectrometer. Land management had a profound effect on the lateral and vertical SOC. The effect of long term tillage reduced the lateral SOC export and enhanced the vertical SOC fluxes, leading to a reduced negative C balance. In situ measurements of soil respiration were carried out in the most dynamic area with respect to soil redistribution in one consecutive growing period (2011). No universal relation to spatial patterns of soil redistribution or to other parameters (soil properties and terrain attributes) was found for measurement period, underlining the large variability of soil respiration. However, soil respiration was significantly linearly related to total erosion. Hence, a possible C sink at erosion sites might partly be compensated by enhanced mineralization at depositional sites. Overall, this study substantially improves the knowledge and understands about the impacts of soil redistribution on SOC stocks and fluxes at the small cultivated field scale.更多还原