【作者】 丛巍巍；

【导师】 李保国；

【作者基本信息】 中国农业大学 ， 土壤学， 2014， 博士

【摘要】 土壤有机碳(SOC)库地球陆地表面碳库主要组成部分,也是土壤肥力、土壤持水性、土壤生物活性等土壤性质的重要基础。退耕还林是我国近年来防止土壤退化、生物多样性丧失,促进碳固持的重要措施。量化研究退耕还林对于SOC数量和组成的影响对于阐述SOC的稳定机制具有重要意义。本研究选取东北平原造林年限为6年,12年和25年的林地,以林地周围的农地作为对照,分析了退耕还林对剖面土壤SOC含量的影响,利用Daubechies离散小波变换,分析了退耕还林后剖面土壤SOC和全N分布的变化,利用稳定同位素分析和裂解气谱质谱技术,重点研究了林地植被碳进入SOC库的途径以及退耕还林后SOC组成的变化。主要结论如下：(1)退耕还林初期,SOC含量降低,随着造林年限的延长,SOC含量增加。退耕还林6年和25年,0-60cm土层土壤全N含量降低。退耕还林对于SOC和全N的影响主要发生在0-60cm土层,底层土壤(>60cm)的变化较小。25年造林后,0-60cm土层土壤C/N增加,说明了SOC的分解程度降低。造林对于SOC的影响不仅与林地植被碳的投入有关,也受原农地SOC矿化的影响。冲积土的成土过程以及较粗的质地可能使得SOC,N的分布受层次影响显著。(2)在6年林地,退耕还林对于各尺度下剖面SOC含量的分布影响不显著,10cm尺度下农地和林地SOC含量显著变化的位置均在土层80cm左右。在12年林地,退耕还林对于10和40cm尺度下SOC含量的分布影响显著,在25年林地,退耕还林对于20和40cm尺度下SOC含量的分布影响显著。在6年林地,退耕还林对于剖面N含量的分布影响不显著,10cm尺度下农地和林地N含量显著变化的位置均在土层60cm左右。在12年林地,10,20和40cm尺度下N含量差异显著的位置在土层100cm以下。在25年林地,退耕还林对于10和20cm尺度下N含量的分布影响显著。(3)退耕还林降低了6年林地<2.5g cm-3密度组分SOC的含量,增加了25年林地<2.0g cm-3密度组分SOC的含量。退耕还林对于土壤密度组分质量,SOC和N的分布影响不显著。源于林地植被残体的C先进入到低密度组分,然后由低密度组分迁移至高密度组分。在这个过程中,SOC的分解程度增加。少部分林地残体C可以快速的吸附或者扩散到矿物颗粒表面。高密度组分中的农地C分解速率低于低密度组分中的农地C的分解速率。不同密度组分中C的固持和矿化速率的差异说明,微团聚体保护作用以及有机质和矿物的相互作用,对于退耕还林系统中的C固持具有重要的影响。(4)退耕还林影响SOC的分子组成。SOC的分子组成与植被的分子组成相关性不显著。12年林地表层土壤的术质素类化合的丰度,高于6年林地表层土壤的木质素类化合物丰度。可能是受林地的残体投入量增加,而木质素的分解速率受抑制的影响。12年林地和25年林地的SOC分解程度较低。而25年林地的参照农地(5-10cm),SOC受土壤耕作影响,主要由分解程度较高的植被残体和微生物代谢产物组成,同时受植被燃烧的影响。更多还原

【Abstract】 Soil organic carbon (SOC) is important in terrestrial ecosystem carbon pool and have significant influence in soil fertility, water retention, soil microbial activity and other soil physical and chemical properties. In recent years, afforestation is an important project in China for controlling soil degradation, biodiversity loss and increasing C sequestration. To investigate SOC sequestration mechanism, it is nessary to evaluate the the influence of afforestation on SOC content and composition. This study was based on the comparasion between arable lands under continuous cultivation and adjacent afforested lands converted from croplands for6,12and25years, in northeastern China. Changes in SOC content were analysised and impact of afforestation on SOC distribution in soil profile was evaluated with Daubechies discrete wavelet transform. The pathway of forest litter derived C incorporated into SOC was investigated on sequential density fraction with δ13C analysis. SOC composition was analyzed by pyrolysis gas-chromatography-mass-spectrometry. Main conclusions were following:(1) There was an initial decrease in SOC after afforestation followed by a gradual increase. The initial decline was observed to last for at least6years. Subsequent accumulation of C was at25years forest. N content decreased in5and25years forest compared with dajacent arable soil, respectively. The influence of afforestation on SOC and N was significant in0-60cm depth and is not significant in60-160cm depth. After planting trees of25years, C/N increased in0-60cm forest sites compared with adjacent arable sites, indicating the SOC was less decomposed by microbial organism in forest sites than that in arable sites. Effect of afforestation on SOC was related with the annual input of C from forest and the C decompostion of former arable SOC. The SOC and N distribution was influenced by the Fluvents soil forming process and coarse texture.(2) In6years forest, afforestation effect in SOC content distribution is not significant, and forest and arable SOC content changed significantly in about80cm depth in10cm scale. In12years forest, afforestation significantly influenced SOC content distribution in10and40cm scale, and in25years forest, afforestaion significantly influenced SOC content distribution in20and40cm scale. In6years forest, afforestion effect was not significant in N content distribution, and forest and arable N content changed significantly in about60cm depth in10cm scale. In12years forest, N content changed significantly in deeper than100cm in10,20and40cm scale. In25years forest, afforestation significantly influenced N content distribution in10and20cm scale.(3) Afforestation decreased SOC content in<2.5g cm-3fractions of6years forest sites, but increased SOC content in<2.0g cm-3fractions of25years forest sites. No significant incluence in SOC concentration was observed in all density fractions of12years forest. Afforestation did not affect the soil mass, SOC and N proportional weight distribution. Most forest litter-derived C entered the low density fractions of soil firstly, then passed through low density aggregates to higher density organic-mineral associations. A small proportion of the forest litter-derived C could rapidly diffuse and absorb on single mineral particles. Former arable derived C which was associated with denser fractions were depleted slowly than which was associated with lighter fractions. The pattern of forest litter incorporation and former litter derived C depletion suggested that microaggregate protection and association between organic material and mineral controlled the C sequestration within the afforestation soil system.(4) Afforestion influenced the SOC chemical composition. There was no significant correlation between litter composition and SOM composition. Afforestion increased lignin abundance in12years forest topsoil but decreased lignin contribution in6years forest topsoil, likely due to the increasing litter input to the topsoil and inhibited lignin decomposition rates. Twelve years and twenty-five years forest soil contained abundant less-degraded material. While the arable soil (5-10cm), adjacent of25years forest, contained substantial strongly decomposed plant material and microbially altered material and showed the effect of vegetation burning.更多还原