【作者】 付晓莉；

【导师】 邵明安；

【作者基本信息】 中国科学院研究生院（教育部水土保持与生态环境研究中心） ， 土壤学， 2010， 博士

【摘要】 水蚀风蚀交错带是黄土高原植被退化最严重的地区。该区气候变化剧烈,全年水蚀、风蚀交替进行,土壤下垫面高度异质。水蚀风蚀交错区特殊的植被生境意味着植被恢复措施在减少水土流失、改善土壤肥力和提高碳固持等方面的生态环境服务功效将有别于黄土高原其它地区。本文以灌木、草地、荒地和农地四种植被类型为例,采用中子仪、土壤呼吸仪、植物光合仪以及土样室内分析等仪器与方法,于2007至2009年在中国科学院水利部水土保持研究所神木土壤侵蚀与环境试验站,对典型地形条件下水、碳、氮、磷4种生源要素时空动态分布、植被蒸散、土壤呼吸和植物光合固碳对植被类型的响应进行了系统的研究,取得以下5个方面结果:1.植被类型改变了土壤水分的坡面分布特征与水量平衡。灌木和草地土壤储水量沿坡面分布均匀,而荒地和农地土壤储水量(0-4m)存在由地形驱动的土壤水分侧向运动趋势。四种植被类型蒸散量的大小顺序为:灌木>草地>农地>荒地。雨季初期(六月)灌木和草地的蒸散量高于降雨量。坡长尺度对水量平衡的影响主要体现在径流量上。2.不同植被类型改善土壤质量的能力不同。与农地相比,灌木能显著提高0-100cm土层土壤有机碳和全氮的含量及储量,而草地和荒地可通过减少侵蚀量来间接地增加土壤有机碳和全氮的含量。植被类型对土壤全磷含量影响不显著,但对土壤全磷的坡面分布特征有影响,表现为荒地和农地土壤全磷具有坡下累积现象。植被类型显著改变了坡面土壤速效磷和无机氮的时空动态分布特征。灌草和荒地土壤速效磷始终显著低于农地,而无机氮与农地的差异随季节变化而变化。灌草和荒地土壤速效磷在8月份较高,无坡下累积现象。生长季期间,灌木和草地土壤无机氮的主要形态转变频繁,荒地的主要形态为NH4+-N,农地在生长季前期以NO3--N为主。灌木和荒地土壤无机氮沿坡面随机分布,草地和农地某些月份存在无机氮在坡下部累积现象。研究区农田生态系统存在氮肥淋溶损失风险。3.植被类型对土壤呼吸日变化和月变化的影响与植物生物气候学阶段有关。荒地和农地土壤呼吸日变化幅度在七月与灌木和草地相当,但在八月和十月显著高于灌木和草地。除八月份农地土壤呼吸月均值与灌木和草地一样高外,研究时段内荒地和农地土壤呼吸月均值相当,且显著低于灌木和草地。不同植被类型土壤呼吸月均值变化受不同因子影响,土壤温度对灌草和荒地的土壤呼吸月均值影响明显,而对农地影响不大。生物因素(根生物量、叶面积指数和光合速率)是导致不同植被类型间土壤呼吸差异的主要原因,但主导因子随月份变化。4.碎石存在显著改变了土壤呼吸的降雨脉冲特征和雨季土壤呼吸水平。碎石隔层延迟了土壤呼吸的降雨脉冲峰值,延迟时间随雨强的增大而增长。降雨脉冲和根生物量差别导致生长季碎石隔层处理的土壤呼吸值显著小于无碎石处理。碎石覆盖不影响土壤呼吸的降雨脉冲节奏,但对降雨后土壤呼吸值影响明显。碎石含量对土壤呼吸降雨脉冲特征影响明显,雨后第二天无碎石处理土壤呼吸的增大幅度远高于含碎石处理。碎石覆盖和碎石含量对土壤呼吸生长季均值的影响不显著。碎石存在不改变土壤呼吸的生长季变化趋势。5.植被恢复措施能够提高小流域碳汇能力及生态系统植物光合固碳量。灌木和草地的碳汇功能强于荒地。通过退耕还林还草措施,20hm2小流域的年植被光合固碳量增加25 Mg C,年碳汇量增加2.2 Mg C。本研究表明水蚀风蚀交错区人工灌木在提高土壤养分含量方面的功效优于草地。人工灌草的植被光合固碳量可以抵消由其土壤呼吸导致的高碳排放量,使实施了植被恢复措施的小流域表现为碳汇功能。雨季初期土壤水分亏损加重了人工灌草的土壤干燥化问题,但这一问题可通过合理的植被类型空间布局得到缓解。研究区农田生态系统存在氮肥淋溶风险,故优化的施肥管理方法应取代原有的粗放模式。碎石存在显著地影响土壤呼吸的降雨脉冲特征和雨季土壤呼吸水平这一结果表明考虑土壤下垫面异质性在提高陆地生态系统碳排放估算精度方面不容忽视。该研究将为合理评价水蚀风蚀交错区植被恢复的生态环境效应和进行有效的生态环境建设提供理论依据。更多还原

【Abstract】 The transitional belt with both water and wind erosion is the center of the intensive erosion and subject to severe vegetation degradation. The wind-water erosion region is characterized by dramatic change of climate and quite heterogeneous soil substrate, suffering wind and/or water erosion through the year. Such unique and harsh habitat quality indicates that the performance of vegetation restoration in eco-environmental serve, e.g. remedy soil and water erosion, improve soil fertility and ecosystem carbon sequestration, in the wind-water erosion region should be different from the other parts of the Loess plateau. In 2007-2009 years, experiments were conducted in Shenmu Erosion and Environment Research Station of the Institute of Soil and Water Conservation, CAS&WRR to study the dynamic temporal and spatial distribution of four biogenic elements (water, carbon, nitrogen and phosphorus), vegetation evapotranspiration, soil respiration and plant photosynthesis rate, and their responses to four vegetation types (shrub, grass, fallow and cropland). The main results are:1. Vegetation types changed the soil moisture distribution and water balance on the hillslopes. The soil moisture distribution was uniform along the hillslopes for shrub and grass. However, soil water storage to 4 m depth for fallow and cropland showed a water lateral movement driven by the topography. The evapotranspiration order of four vegetation types was shrub > grass > cropland > fallow. At the beginning of the rain season (June), the evapotranspiration from shrub and grass were quite larger than the precipitation. The slope scale in length mainly influenced the runoff.2. The performances in soil quality recovery were quite different among vegetation types. Compared with the cropland, shrub directly increased soil organic carbon and total nitrogen in the 0-100 cm soil depth, however, grass and fallow could indirectly improve soil organic carbon and nitrogen by decreasing sediments losses and runoff. The effect of vegetation types was not significant on soil total phosphorus concentration but pronounced on soil total phosphorus distribution along the hillslopes. A downward accumulation trend of soil total phosphorus along the hillslope was observed for fallow and cropland. Pronounced influences of vegetation types on the temporal and spatial variability of soil available phosphorus and inorganic nitrogen were detected. Soil available phosphorus of shrub, grass and fallow was consistently lower than that of cropland. However, the order of soil inorganic nitrogen between shrub, grass, fallow and cropland varied with season. In contrast to cropland, soil available phosphorus was higher in August and had no downward accumulation along the hillslopes for shrub, grass and fallow. During the study period, the dominant form of soil inorganic nitrogen for shrub and grass changed frequently, however, the dominant form was NH4+-N and NO3--N for fallow and cropland, respectively. Soil inorganic nitrogen distributed randomly along the hillslopes for shrub and fallow but had downward accumulation trend in certain months for grass and cropland. Besides, fertilizer derived nitrogen leaching was at risk in this semiarid rainfed agriculture ecosystem.3. Vegetation phonological stage mediated the effects of vegetation types on daytime and monthly soil respiration. The soil respiration variation amplitude of fallow and cropland was comparable to that of shrub and grass in July but obviously larger than that of shrub and grass in August and October. During the study period, monthly soil respiration of fallow and cropland were comparable and significantly lower than that of shrub and grass, with an exception in August when soil respiration of cropland was as larger as shrub and grass. The main controlling factor of monthly soil respiration variation differed among vegetation types, e.g. soil temperature highly mediated the monthly soil respiration variation for the three vegetation types but contributed little when went to the cropland. The biotic factors, root biomass, leaf area index and photosynthesis rate, are mainly responsible for the monthly differences in soil respiration among vegetation types. Moreover, the dominant controlling factor varied with vegetation stage.4. Rock fragments changed the rain pulse characteristics and the level of soil respiration during the rain season. Rock fragment layer delayed the rain pulse peak of soil respiration, and the delay duration increased with the increase of rainfall. Average soil respiration during the study period was significantly lower than the control because of the lower root biomass and different rain pulse properties. Rock fragment coverage showed a significant effect on soil respiration following rainfall but had no influence on rain pulse rhythm of soil respiration. Soil respiration of the treatment mixed with rock fragment was quite lower than that of control. Effect of rock fragment coverage and content on average soil respiration of the study period was not significant. Additionally, rock fragment did not change the seasonal variation of soil respiration.5. Compared with fallow, shrub and grass had better performance in carbon sequestration. Vegetation restoration improved the carbon sequestration and photosynthetic C uptake of the vegetation in a small watershed with the area of 20 hm2. Vegetation restoration in this small watershed annually increased photosynthetic carbon uptake and carbon sequestration with the values of 25 and 2.2 Mg C, respectively.The results showed that shrub performed better than grass in improving soil nutrient content. The large carbon emission caused by soil respiration of shrub and grass was offset by the corresponding large photosynthetic carbon uptake. Therefore, the small watershed involved with vegetation restoration program served as carbon sink. Soil water deficit at the beginning of the rain season aggravated the soil desiccation of planting perennial vegetations. However, this problem would be alleviated by adopting instructive spatial distribution pattern of vegetation types. Because urea-derived nitrogen loss by leaching was at risk in the agroecosystem, optimized fertilizer management should be adopted instead of the traditional extensive style. The result that rock fragment significantly changed the rain pulse properties and rain season mean value of soil respiration suggests that considering soil heterogeneous is important in terrestrial ecosystem carbon emission. The conclusions of this study can be used to evaluate the eco-environmental performance of the vegetation restoration program in the wind-water erosion region and be beneficial in constructing effective management of eco-environment restoration.更多还原