【作者】 王百群；

【导师】 吴金水；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2004， 博士

【摘要】 干旱与水土流失是黄土高原地区农业与生态环境面临的严峻问题。在黄土高原地区,干旱条件直接影响该区农田土壤生产力及土壤有机碳及氮素的动态变化。为了有效地控制水土流失和改善生态环境,进行了退耕还林还草,封山育林,加强植被恢复及自然植被的保护。在干旱与侵蚀环境下的植被恢复过程和不同的植被类型,将地对林地或草地土壤有机碳氮的变化与迁移产生一定的效应。 本论文研究以黄土高原典型区为对象,分别研究旱作农田及林草地土壤有机碳氮的变化特征,坡地植被恢复过程对土壤有机碳累积的影响,土壤矿质氮的迁移与分布,及侵蚀黄土坡地土壤有机质与氮素的流失迁移过程。目标是揭示旱地农田施肥与作物轮作、植被恢复、植被类型对土壤有机碳库收支及生长自然植被和施氮条件下土壤矿质氮迁移的影响机制,明确黄土坡地土壤有机质与氮素流失与坡地地形特征的关系。这些研究对于制定提高土壤肥力、氮肥利用率及控制土壤流失的措施、评价农林生态系统中土壤对有机碳的固定能力、阐明黄土高原区域土壤中有机碳储量及其生态效应具有重要的意义。本文的研究结果如下: (1)黄土区不同区域农田土壤有机碳库动态变化特点 在黄土区的杨陵、长武和安塞等三个不同生态类型区中,施肥管理与农田土壤中有机碳库变化具有密切的关系。单施氮素化肥、氮钾配施或者磷钾配施对土壤有机碳的固定和累积没有明显的影响。在氮磷肥配施、氮磷钾化肥配施条件下,增加土壤有机碳的累积。施有机肥显著提高农田土壤有机碳固定和累积量。三个区域农田土壤有机碳的固定率及有机碳累积量大小为杨陵>长武>安塞。 三个区域农田土壤微生物碳含量与总有机碳含量呈现正相关关系,土壤微生物碳含量与微生物氮含量呈显著正相关关系。在土壤有机碳累积过程中,促使了土壤全氮含量增加,同时也有效地提高了土壤微生物碳、微生物氮的含量,从而提高土壤肥力和土壤养分周转。 (2)黄土丘陵区植被对土壤有机碳库变化的驱动作用与机理 在黄土丘陵区沟壑区不同恢复年限草地中,土壤有机碳、微生物碳含量随土层深度的增加而呈现下降趋势。表层土壤(0-5cm)中有机碳和微生物碳的含量随着植被恢复<WP=6>II 黄土区侵蚀与干旱环境中土壤有机碳氮的变化与迁移年限的增长而提高。土壤微生物碳含量与土壤有机碳含量呈显著正相关关系。土壤微生物碳占总有机碳的比例随土壤有机碳的增加而提高,恢复草地土壤微生物碳的变化可以明显地反应出土壤有机碳的变化趋势。 在干旱半干旱环境条件下,人工柠条林可以有效地提高表层土壤中微生物碳及有机碳的含量。在不同类型林地土壤剖面中,微生物碳与有机碳具有明显的线性关系,微物碳占总有机碳的比例随土层深度增加而降低,表明了微生物碳的增加指示着有机碳发生累积。乔木林比灌木林及短期的人工油松林更显著地提高表层土壤微生物碳及有机碳的含量。 黄土丘陵区恢复草地中,土壤有机碳的固定量随着草地恢复年的增长而增加。在长期草地中,植物有效地促进了土壤中有机碳的固定。在人工柠条林地中,土壤有机碳的固定量,随着柠条林林龄的增加而提高,而有机碳的平均固定率则随柠条林龄的增长而降低。在不同类型的林地中,乔木林地土壤中有机碳的固定量和储量最高,灌木林次之,短期的人工油松林地土壤有机碳的固定量和储量最低。黄土丘陵区林草地土壤能够有效的固定和累积有机碳,显示了该区林草地土壤起到碳汇的作用。 在黄土丘陵区子午岭长期草地中,土壤有机碳、微粒有机碳的含量随土壤剖面深度的增加而下降。草地土壤累积的有机碳主要分布在微粒有机质中,根据微粒有机碳含量的变化可以反映植物促使土壤有机累积的能力。草地土壤剖面中,>2 mm 、1-2 mm、0.5-1 mm、0.25-0.5 mm 及<0.25 mm 各粒级水稳性团聚体中有机碳的含量随土层深度增加而下降。在表层土壤中(0-5 cm),<0.25 mm 微团聚体中有机碳的含量高于>0.25 mm各粒级团聚体中的含量;在 5-15 cm 土层中,各粒级团聚体中有机碳的含量相近;在 15 cm 以下的各土层中,<0.25 mm 微团聚体中有机碳的含量低于>0.25 mm 各粒级团聚体中的含量。草地土壤中<0.25 mm 微团聚体中有机碳所占有机碳库的比例随土层深度的增加而提高,土壤中<0.25 mm 微团聚体中有机碳占有机碳库的 40～90%。<0.25 mm 微团聚体对于固持和稳定土壤有机碳起着重要的作用。根据草地土壤有机碳在不同类型土壤颗粒的自然分布特点,可以反映出土壤有机碳累积和稳定的机理。 (3)黄土丘陵区草地土壤有机碳变化与土壤团聚体稳定性的关系 长期草地土壤剖面中水稳性团聚体的组成中,>2 mm 、1-2 mm、0.5-1 mm 及 0.25-0.5 mm 的各粒级水稳性团聚体的含量随土层深度的增加而降低,<0.25 mm 团聚体的含量随土层深度增加而提高。草地土壤有机碳的含量与水稳性团聚体的稳定性具有明显的正相关关系,水稳性团聚体的稳定性与土壤的抗蚀性密切的正相关关系。因此,草地植被可以通过增加土壤有机碳的与累积,提高土壤水稳性团聚体的稳定性,从而提高土壤的抗蚀性,有效地控制土壤侵蚀。 (4)黄土区自然植被下土壤及农田土壤中矿质氮的?更多还原

【Abstract】 It is well known that aridity and erosion are the severe issues impacting agriculture andecoenvironment on the Loess Plateau. Aridity directly influences on arable land productivityand the dynamics of soil organic carbon(SOC) and nitrogen. In order to control soil and waterlosses and improve ecoenviroment on the Loess Plateau, the conversion of slope farmland tograssland and forestland has been carried out. More attention was paid to restoration ofvegetation and the protection of natural vegetation. In the scenario of aridity and erosion, theprocesses of restoration of vegetation and types of vegetation exert significant influence onthe changes in SOC and nitrogen in these lands.The studies were conducted to investigate the SOC changes in arable dryland, grasslandand forest land, to examine the impacts of vegetation restoration process on SOCaccumulation, mineral nitrogen transfer and distribution in soil profile, the loss process of soilorganic matter and nitrogen in the loessial slope by the means of taking soil samples,analyzing soil samples and field monitoring. The objectives were to understand themechanism of the influences of fertilization, vegetation restoration and types of vegetation onSOC pools and mineral nitrogen transfer in soil profile, to determine relationships betweensoil organic matter and nitrogen losses and slope length or slope gradient. The goals of thesestudies were to work out the measures to improve soil fertility, to raise nitrogen use efficiency,to control soil nutrient losses, to evaluate capacity of SOC sequestration in arable land,grassland and forestland, and to demonstrate the soil carbon storage and its effect onecoenvironment. The results of this thesis were summarized as followings:(1) Dynamics of Soil organic carbon pool in arable lands in different areas<WP=9>II The Dynamics and Transfer of Soil Organic Carbon and Nitrogen in the Scenario of erosion and aridity in the LoessialRegionon the Loss PlateauFertilization management has the close relation to the dynamics of soil organic carbon(SOC) pool in arable lands in Yangling, Changwu and Ansai. Application of nitrogenfertilizer, combination of nitrogen and potassium fertilizer or combination of phosphorus andpotassium fertilizer had no significant effect on SOC sequestration and accumulation.However, application of combination of nitrogen and phosphorus fertilizer or combination ofnitrogen and phosphorus and potassium fertilizer could significantly promote SOCsequestration and storage. Furthermore, application of manure of combination of nitrogen,phosphorus and potassium fertilizer could significantly increase SOC sequestration andstorage fast. The rate of SOC sequestration and storage demonstrated the order ofYangling>Changwu>Ansai. Soil microbial biomass carbon(MBC) had the significantcorrelation with SOC in the arable land in these three regions. MBC also had the significantcorrelation with soil microbial biomass nitrogen. These suggested that size of microbialbiomass and the level of soil nitrogen had been increase the raise of SOC, which was benefitto improve soil fertility and enforce soil nutrient cycling.(2) The driving effect of vegetation on the dynamics of SOC pool and themechanismThe contents of SOC and the sizes of MBC declined with the increase of soil depth in therestored grasslands with different history. The level of SOC and the sizes of MBC in thetopsoil rose with increase in length of conversion. The size of MBC demonstrated thesignificant correlation with the size of MBC, and the rotio of MBC to SOC increased the riseof level of SOC, which suggested that the size of MBC could indicate the trend of SOCevolutioninthe restored grasslands.In the scenario of arid or semiarid environment, planted Caragana could raise the level ofSOC and the size of MBC in the topsoil. MBC had the significant correlation with SOC, andthe ratio of MBC to SOC declined with the increase in soil depth in the soils grown withdifferent kinds of fo更多还原