有机酸对砷在针铁矿表面吸附影响研究

砷（As）在自然环境下的迁移转化受到矿物质尤其是铁氧化物吸附过程的制约,大量溶解性有机酸影响了砷的吸附过程。 柠檬酸(CA)和As(Ⅴ)不同加入顺序实验表明CA抑制As(Ⅴ)吸附与其促进针铁矿溶解有关。当CA首先加入时，吸附体系溶解铁浓度为~0.3mmol/L，As(Ⅴ)吸附量随初始浓度增加在0.004~0.10mmol/g针铁矿之间；As(Ⅴ)先加入体系，溶解铁浓度为~0.16mmol/L，As(Ⅴ)吸附量在0.007~0.12mmol/g针铁矿之间。为进一步考察有机酸溶解作用对As(Ⅴ)吸附影响，本研究比较了在柠檬酸(1.0 mM)、草酸(1.5 mM)和乙酸(3.0 mM)与As(Ⅴ)共存条件下砷吸附变化和针铁矿溶解状况，结合三种有机酸引起针铁矿表面等质子状态点迁移结果认为：草酸促进针铁矿溶解趋势强于柠檬酸，而抑制砷吸附程度低于柠檬酸，可归因于小分子量有机酸抑制砷吸附是竞争表面位与溶解作用协同作用的结果。 在酸性区域，CA和As(Ⅴ)共存导致二者在针铁矿表面吸附量分别下降28%和29%左右，这与二者在针铁矿表面发生竞争吸附作用有关。在碱性区域，As(Ⅴ)吸附不受CA存在的影响；CA则随加入顺序不同存在明显差异：As(Ⅴ)先于CA加入的体系，CA严重下降达75%左右，而当CA先加入时，As(Ⅴ)的后续加入导致CA吸附少量升高。As(Ⅴ)对CA在碱性区域的影响与二者随pH变化吸附模式不同有关。 本研究采用平衡透析的方式研究了砷在腐殖酸和针铁矿之间的迁移转化问题。结果显示腐殖酸的存在影响了砷向针铁矿表面的迁移，且对As（Ⅴ）的影响比As（Ⅲ）更显著。在酸性区域，腐殖酸导致As（Ⅴ）在针铁矿表面分配系数降低最高可达70%左右；对As（Ⅲ）而言，腐殖酸在弱酸性、中性和弱碱性区域表现出最大抑制效应，As（Ⅲ）分配系数的降低在10%左右。

微生物还原对砷迁移性影响的机理研究

本研究从沈阳冶炼厂旧址采集土壤样品，从中富集厌氧的砷还原菌，并以其为接种微生物，在厌氧条件下考察微生物的作用对砷的还原及迁移的影响，从分子角度探索地下水和土壤体系中砷污染的机理，同时对工业上含砷废渣的长期稳定性进行探讨。 实验在以L-半胱氨酸作为还原剂创造的严格厌氧条件下接种微生物进行培养时，可以观察到As(V)的快速还原并向固体的转移，利用XRD和SEM-EDS技术对固体的分析表明该沉淀为AsS，指出了在周围环境中如果存在足够的含硫化合物时，微生物能够通过形成硫化砷的形式将砷固定下来。 本研究考察了工业上常见的含砷废渣（As:Fe摩尔比为1:8的含砷氢氧化铁）在微生物作用下的长期稳定性，结果表明在厌氧条件下微生物对砷和铁的还原速度都很快，在39天内就将~53%的As(V)还原为As(III)，在一天之内就能将约8.82 mg/L的As(III)释放出来，因此可以得出如果含砷废渣处理不当，就会在长期堆放过程中造成对环境甚至于地下水系统的污染。 本研究进一步采用不同比例（Al:Fe = 1:0, 1:1, 0:1）的铁铝氢氧化物为吸附剂，以As:(Fe+Al)摩尔比为1:100的比例在该介质上吸附砷并进行厌氧培养，考察微生物对吸附于这些载体上的As(V)的还原和迁移作用，结果指出微生物对砷的还原是砷向环境中释放的主要原因，砷的还原发生在铁还原之前，铁的还原和溶解并没有引起砷的迁移量的增加，因此铁的还原性溶解不是砷释放的主要原因；相反，由于氢氧化铝对As(III)几乎不吸附，因此，当铝被引入该体系时，可以观察到As(III)的释放明显增加。该实验结果表明在自然环境中，砷的释放主要是由于微生物对砷的释放以及铝氧化物对As(III)无吸附能力所导致的。

土壤氨基酸和氨基糖聚合物的矿化过程研究

土壤中氨基酸和氨基糖是土壤有机氮的重要组成部分，对土壤氮素供给和土壤碳、氮循环过程有重要贡献。研究氨基酸和氨基糖聚合物的矿化，对于减少氮素损失，提高氮肥利用率能够提供一定的理论依据。 当向土壤中(本试验为黑土)同时添加葡萄糖和(15NH4)2SO4时，在土壤微生物的作用下，(15NH4)2SO4会被用以合成土壤15N-氨基酸和氨基糖聚合物。新合成的这部分氨基酸和氨基糖聚合物与土壤中原有氨基酸和氨基糖聚合物的性质是否不同并且是否受到外源底物的调控。为了解决上述问题，本试验将采用Stanford and Smith的间歇好气矿化淋洗培养法，结合高效液相色谱/质谱、气相色谱/质谱联机技术(HPLC/MS，GC/MS)跟踪测定土壤中15N-氨基酸和氨基糖的同位素富集比例及其含量的变化，探讨土壤中新合成15N-氨基聚合物的矿化特征，通过研究添加葡萄糖、玉米秸秆和无机氮肥对土壤中新合成15N-氨基聚合物矿化过程的影响以及对有机氮聚合物解聚的动力－酶活性的影响，从而阐明土壤氨基聚合物矿化的碳源营养调控机制和氮源反馈调节机制及其解聚机理。研究结果表明： 1. 土壤中新合成的氨基酸和氨基糖聚合物与土壤原有氨基酸和氨基糖聚合物相比具有较高的循环速率，并且不同种氨基酸和氨基糖也分别表现出不同的矿化特征。较高循环速率的存在，将为调控其矿化过程奠定基础，因为只有快速循环的氮素才能够被调控，而且调控新合成有机氮的矿化过程，可以不断地满足作物生长对氮素养分的需求。 2. 土壤中新合成氨基聚合物的矿化受到不同外源底物调控。其中碳源(葡萄糖和玉米秸秆)能够抑制氨基聚合物矿化，但是活性碳源葡萄糖的抑制程度高于活性较低的碳源玉米秸秆，表明氨基聚合物矿化受到不同碳源活性调控。不同浓度以及不同形式氮源也能够调控土壤氨基聚合物的矿化，并且适量氮肥的加入能够抑制土壤中新合成氨基聚合物的矿化，存在氮肥的反馈抑制机制。 3. 土壤中蛋白酶、芳基酰胺酶和几丁质酶活性受到不同碳源和氮源的影响。其中碳源表现为促进作用，而氮源则表现为抑制作用。氮源对土壤酶活性的反馈抑制作用是控制土壤氮素转化的关键，而碳源只是起到维持土壤酶活性的作用。三种酶活性对外源底物的敏感性，将对于调控土壤氮素循环奠定一定的理论依据。 4. 不同处理酶活性与有机氮矿化之间表现出不同的相关性，说明酶与氮矿化之间的关系受到多方面因素影响。总体来看，蛋白酶、芳基酰胺酶和几丁质酶在水解土壤氨基酸和氨基糖聚合物的过程中起到重要作用，是有机氮聚合物重要的解聚酶。

铁砷共沉淀物长期稳定性研究

有色金属的冶炼过程中会产生大量砷含量很高的酸性废水，其任意排放会造成严重的环境砷污染，必须对其进行除砷处理达标后才能向环境排放。目前，铁砷共沉淀法是一种被广泛应用且较为经济的废水除砷技术，然而由此产生的大量含砷工业废渣中砷的化学形态尚不清楚，其稳定性也较差，容易造成严重的二次砷污染。因此，弄清铁砷共沉淀法产生的工业废渣中砷的化学形态，通过技术改造增强其长期稳定性，探索砷稳定性变化的分子机制具有重要的理论和现实意义。 本文对硫酸盐体系铁砷共沉淀法处理含砷废水所产生的废渣在长期稳定堆放过程中的稳定性及其影响因素进行了系统深入的研究。实验结果表明： （1）铁砷共沉淀物的稳定性受体系的最终pH值影响很大，随体系pH升高，含砷共沉淀物稳定性明显下降。溶液呈弱酸性时(pH 4或5)，含砷共沉淀物的稳定性较好，溶液呈弱碱性时(pH 8或9)，含砷共沉淀物的稳定性较差。 （2）碱类型影响含砷共沉淀物的稳定性，使用CaO中和酸性铁砷溶液显著提高了共沉淀的稳定性。在含砷溶液中添加钙离子也具有明显提高含砷共沉淀物稳定性的作用。 （3）Fe(III)/As(V)比影响铁砷共沉淀物稳定性，Fe(III)/As(V)越大，所形成共沉淀物越稳定。在铁砷酸性溶液的中和过程中，在pH=4时停留一段时间能够明显提高共沉淀物的稳定性，这种特性对于优化工业共沉淀法除砷工艺从而提高共沉淀含砷废渣稳定性具有重要意义。 （4）腐殖酸的加入最终削弱了铁砷共沉淀物中砷的稳定性。 （5）与Fe(III)-As(V)体系相比，Fe(III)-As(III)共沉淀体系中，共沉淀物在弱碱性区稳定性较好，在弱酸性区稳定性较差。在Fe(III)-As(III)-As(V)体系中，使用NaOH作为碱时，在弱碱性区稳定较好，而在弱酸性区稳定性较差。使用CaO作为中和碱在弱碱性区提高了共沉淀体系的稳定性，而在弱酸性区则降低了共沉淀体系的稳定性。

大兴安岭冻土湿地泥炭有机碳矿化对气候变化因子的潜在响应

大兴安岭地区是我国地带性多年冻土和冻土湿地的主要分布区，近30年来，大兴安岭地区整体增温显著，气候变化的幅度加大，加之人类活动的频繁，冻土退化严重，冻土湿地出现了原有湿地萎缩和新生湿地扩张的现象。目前，对大兴安岭多年冻土湿地的研究还非常有限，且定性的研究较多，定量的研究极少，多数研究集中于冻土湿地的分布，冻土与湿地之间的机理探讨及描述多年冻土退化对湿地产生的影响等方面。 本论文通过室内培养实验，分析不同温度和湿度梯度及冻融作用下，大兴安岭不同多年冻土区湿地两层泥炭有机碳的矿化状况。结合回归模型，分析大兴安岭多年冻土湿地泥炭有机碳矿化对不同温度和湿度的响应，探讨在气候预案下，大兴安岭多年冻土湿地对气候变化的潜在响应。获得的主要结论如下： （1）大兴安岭多年冻土湿地存在着碳储层，其不同的冻土湿地区由于自然条件、融深等因素的不同，碳储层的厚度也存在着差异。多年冻土湿地含碳量和含氮量都很高，有机碳含量随剖面深度的增加有降低的趋势，泥炭全氮的含量随剖面深度变化复杂，这与湿地土壤形成的气候条件、微地貌和植被类型等有关。大兴安岭连续多年冻土区泥炭，C/N比要高于不连续多年冻土区湿地，并且有机碳含量与全氮含量存在着很好的耦合关系。 （2）大兴安岭多年冻土湿地泥炭有机碳矿化随温度的升高而升高，在培养温度5-20℃下，总的泥炭有机碳矿化量变化范围为18.55~112.91 mg g-1。虽然连续多年冻土区湿地泥炭有机碳矿化率和矿化量都要高于不连续多年冻土区湿地，但经过温度敏感性系数Q10分析，大兴安岭不连续多年冻土区湿地泥炭矿化对温度的响应更显著。从一元动力学方程分析结果来看，大兴安岭多年冻土湿地泥炭有机碳的矿化对15℃响应更显著。 （3）土壤湿度对大兴安岭多年冻土湿地泥炭有机碳矿化产生一定的影响，泥炭总矿化量出现了先随湿度的增加而增加，达到最适宜值后降低的趋势。从本论文的实验设置来看，大兴安岭多年冻土湿地泥炭有机碳矿化的最适宜湿度为60%WHC。利用二元回归模型很好地反映了湿度对大兴安岭多年冻土湿地泥炭矿化的影响，模型推测大兴安岭连续多年冻土区湿地泥炭有机碳矿化的最优湿度为10-20cm层63%WHC，20-30cm层65%WHC；不连续多年冻土区湿地有机碳矿化的最优湿度为10-20cm层65%WHC，20-30cm层59%WHC。 （4）大兴安岭多年冻土湿地泥炭有机碳矿化受温度和湿度的影响显著，其之间的交互作用同样显著。连续多年冻土区湿地有机碳矿化量要高于不连续多年冻土区湿地，这与其含有更高的有机碳和全氮有关。温度和湿度对泥炭有机碳矿化的影响可以用二元二次回归方程很好的表示（P<0.001），通过回归方程和方差分析，结果表明温度和湿度对大兴安岭多年冻土湿地泥炭有机碳矿化都非常重要。 （5）通过培养实验结果显示，虽然温度仍是影响大兴安岭多年冻土湿地泥炭有机碳矿化的主要因子，但随冻融作用处理次数的增加，冻土湿地泥炭有机碳矿化量和温度敏感性系数Q10值有增加的趋势，这意味着冻融作用对大兴安岭多年冻土湿地泥炭矿化产生了不小的影响。虽然冻融作用对大兴安岭多年冻土湿地的影响并不是很大，但大兴安岭处于寒温带，在气候变暖下，冻融过程的频率将加高，冻融作用对大兴安岭多年冻土湿地的影响不容忽视。 （6）大兴安岭地区近30年气候变化趋势分析表明，年均温增长显著，年降水量变化幅度大。在气候变化下，对于不连续多年冻土区，多年冻土不断的退缩及最终的消失，会使冻土湿地萎缩和消失，原有的典型的贫营养的泥炭藓沼泽湿地可能演化为富营养的苔草沼泽湿地或灌丛沼泽湿地，对于大片连续多年冻土区，冻土湿地的变化更加复杂，出现的湿地类型会更多。通过线性气候预案下的大兴安岭多年冻土湿地泥炭有机碳矿化分析，结果显示大兴安岭多年冻土湿地对气候变化响应显著，特别是对于变湿的环境。气候变化下，大兴安岭多年冻土湿地泥炭存在着潜在的分解，多年冻土湿地与气候变化之间存在着正反馈机制。 目前研究表明，大兴安岭地区对气候变化特别敏感，对大兴安岭冻土湿地的研究既填补了国内研究的空白，又对全球的碳循环研究提供了数据支持，并且加深了对冻土湿地生态过程的了解。

应用负载型纳米铁去除饮用水中砷的研究

砷是毒性最强的元素之一，水体中砷的污染己经引起人们广泛的关注。我国的新疆、内蒙、山西和台湾等省和地区地下水砷含量严重超标。全球共有5,000多万人遭受高砷饮用水的威胁，其中中国有1,500多万，是饮用水砷污染最严重的国家之一。WHO推荐饮用水砷的最高允许浓度从原来的50 µg•L-1已降至10 µg•L-1。更为严格的砷卫生标准的颁布，对作为饮用水源的地下水中的砷去除工艺提出了更高的要求。吸附法除砷比膜法、混凝法和离子交换法更安全、简便，是砷去除工艺中最有效的方法之一。 首先，本研究通过优化制备条件（包括炭种类的选择、炭的粒径大小、还原剂的浓度及滴定速率、反应温度、铁盐的种类及浓度、分散剂的比例及浓度），制备了负载型纳米铁。考虑到砷的去除效率、工程应用的可行性以及经济性，最优的制备条件如下：选用粒径为20~40目煤质炭，在室温、一定的分散剂比例及浓度，0.2 M KBH4滴速为20 d•min-1时所制备的Fe/炭为82.0 mg•g-1；纳米铁在活性炭孔内呈针状，其直径为30~500 nm，长度为1,000~2,000 nm。绝大多数的铁都负载到活性炭内部，这在处理水时铁不流失很重要。 其次，利用制备的负载型纳米铁作吸附载体，进行了饮用水中As(Ⅴ)的吸附去除实验。研究了该吸附剂对As(Ⅴ)的吸附等温线、动力学以及影响动力学的各种因素（包括As(Ⅴ)的不同初始浓度、吸附剂用量、pH值、共存离子和不同温度）、pH值、共存离子等环境条件对As(Ⅴ)去除的影响；以及吸附剂的再生及再生后的吸附效率等。研究发现在前12 h内吸附较快，72 h时达到了平衡。用Langmuir 吸附等温式估算出As(Ⅴ)的吸附量为12.0 mg•g-1。该吸附剂在pH 6.5， (25±2)℃， As(Ⅴ)初始浓度为2 mg•L-1，吸附剂用量为1.0 g•L-1时，As(Ⅴ)的去除率为75.2%；当把吸附剂的用量增加到1.5 g•L-1时，As(Ⅴ)的去除率可达99.9%以上。吸附剂可以用0.1M的NaOH浸泡12 h后即可再生，再生效率较高。常见的阴离子中PO43-、SiO32-对As(Ⅲ)的去除抑制较大，而SO42-、CO32-、C2O42-等离子对砷的去除影响较小。Fe2+对As(Ⅲ)的吸附抑制作用较大而其它阳离子影响不大。吸附剂可用0.1 M NaOH 有效再生，并且具有良好的机械性能。实验室初步实验数据表明，该吸附剂对饮用水除砷具有较好的应用前景。 第三，利用实验室制备的负载型纳米铁对饮用水中As(Ⅲ)的吸附去除也进行了研究。考察了吸附等温线、动力学以及影响动力学的各种因素、pH值、共存离子等环境条件对As(Ⅲ)去除的影响；以及吸附剂的再生及再生后的吸附效率等。研究发现，该吸附剂在pH 6.5， (25±2)℃， As(Ⅲ)初始浓度为2 mg•L-1，吸附剂用量为1.0 g•L-1时， 对As(Ⅲ)的去除率为99.8%；其吸附容量为1.996mg•g-1。吸附过程中部分As(Ⅲ)被氧化。与As(Ⅴ)的吸附相比，该吸附剂对As(Ⅲ)的效率比较高-而常见的其它除砷吸附剂如载铁纤维棉等，对As(Ⅴ)的效率比As(Ⅲ)高，为有效去除As(Ⅲ)，常常需要专门加上氧化这一过程。 最后，利用负载型纳米铁对饮用水中As(Ⅲ) 的氧化性能进行考察，发现该吸附剂不但能够有效吸附去除饮用水中的砷，而且还能把As(Ⅲ)有效地氧化为As(Ⅴ)。经过对吸附剂的构成组分分析发现，活性炭表面因富含多种官能团而对三价砷的氧化作用最大；其次是纳米铁也能把As(Ⅲ)氧化为As(Ⅴ)。

典型污染海湾河口沉积物中砷的形态分布研究

锦州湾是我国较大的浅水海湾之一，该湾西南五里河沿岸汇集数家工厂排污直接人海， 形成该湾口处的最大污染源。其西南部潮滩地段已成为我国海域污染最严重的区域之一。 本文对葫芦岛3条河流、五里河口和锦州湾水体、沉积物中As的含量、分布、形态及行为进行了系统研究。结果表明，葫芦岛的连山河和五里河未受到明显的As污染，沉积物总As含量一般低于10 mg•kg-1，河水As含量一般低于10 μg•L-1，茨山河下游紧邻葫芦岛锌厂，受到了严重的As污染，沉积物As含量达75.2 mg•kg-1。五里河口区As污染非常严重，锌厂在该区排污口处沉积物As含量高达3176.1 mg•kg-1，超过国家沉积物As标准158倍。受锌厂排污的影响锦州湾As污染也很严重，沉积物中As最高含量达到569.5 mg•kg-1。沉积物和孔隙水As含量在剖面上具有相似的变化趋势，表明孔隙水As含量主要受沉积物As含量影响。锦州湾沉积物中As主要以可交换态存在，残渣态次之，盐酸提取态最少，表明锦州湾沉积物中As的活性很强，有大量的可交换态As随时会进入上覆水体，是重要的As释放源，沉积物中大量As的释放可能会对葫芦岛和锦州湾地区生态系统造成严重的威胁。 以盐度和酸碱度作为环境影响因子进行的释放模拟实验，结果显示：不同盐度条件下，沉积物中的As均在48h左右达到最大释放量。此时，盐度为0‰的水体中As的释放量最大，而其他两种盐度的水体中As的释放量较小且二者相差不大。另外，在室温条件下，随着pH值的升高，沉积物中As的释放量逐渐增加。 通过对不同形态的单一含砷矿物的As提取效果研究得出：对于分级提取方法中吸附态砷的最佳提取条件应为1M KH2PO4 (pH5) 24h, 无定型铁氧化物上结合的砷0.2M oxalic/oxalate (pH3)避光 6h, 硫化亚铁上结合的砷，0.2M oxalic/oxalate (pH3)避光 1h。

有机氮的矿化进程及碳源添加的影响

本文运用室内恒温控湿好气培养试验研究了长期不同施肥制度培育的土壤有机N库的供氮能力；不同C／N比有机物料掺混土壤后有机N的矿化进程以及有机C源添加对其的影响。试验结果表明：长期不同施肥制度培育的土壤有机N库的供氮能力各不相同。与不施肥处理相比，长期施用化肥或有机肥均能提高土壤的供氮能力，但统计分析表明，长期单施化肥（150KgN·hm-2）与单施循环猪圈肥（约60Kg N·hm-2）处理土壤的供氮能力相似，说明有机培肥是保持和提高土壤氮素肥力的根本途径，而二者相结合可明显提高土壤供氮能力。掺混有机物料土壤中有机N的矿化进程与物料的C／N比密切相关，高C／N比的玉米秸粉能提供丰富的能源物质，但因其供应的氮素不足，微生物会固持土壤或空气中的氮而不发生有机N的净矿化释放，而低C／N比的大豆粉加入土壤后立刻会发生有机N的净矿化释放。有机C源的添加只能是暂时地抑制有机N的净矿化，但不能阻滞矿化过程的最终完成，土壤或有机物料中有机N的矿化分解是一个“持续进行、不可抑制的过程”。

次生植被土壤碳、氮养分季节动态及凋落物输入与温度的影响

土壤微生物量、可溶性有机碳与氮虽然只占土壤有机碳、氮总量的较小部分，但可以在土壤全碳、氮变化之前反映土壤微小的变化，又直接参与土壤生物化学转化过程，因而在植被恢复过程中，较其它土壤理化性质等能够更好地指示土壤恢复情况。在青藏高原东缘存在大面积的次生人工林替代灌丛或采伐迹地，而关于这些人工林替代后的生态效果和生态过程的评估却十分缺乏，本研究通过评估岷江上游植被恢复重建过程中典型人工替代次生植被凋落物层与土壤碳、氮等养分大小，动态监测土壤微生物生物量、水溶性碳、氮等指标，结合温度与凋落物输入等影响土壤活性有机碳、氮因子的控制试验，系统分析不同人工替代次生植被土壤碳、氮等养分的差异原因，试图寻找低效人工林优化调控与持续管理技术，为区域生态公益林持续管理提供理论和技术依据。主要结论如下： 1. 通过对不同人工替代次生植被凋落物层和土壤碳、氮分析发现，油松和华山松人工林替代次生灌丛后土壤碳、氮含量较灌丛和阔叶人工林低，主要原因可能为凋落物质量(C/N)较差，而引起碳、氮等元素难以归还土壤。进而通过对不同人工替代次生植被凋落物层和土壤微生物生物量、水溶性有机碳、氮等指标的季节性动态模式的分析，发现各次生植被土壤微生物生物量C、N，P以及土壤水溶性碳、氮含量均呈明显季节性动态，呈现秋季明显大于其它季节，冬季最低，在表层土壤最为明显。 2. 油松、华山松人工林凋落物层和土壤水溶性有机碳(WDOC)、土壤水溶性有机氮(WDON)明显低于灌丛和连香树，土壤微生物生物量C、N也以油松和华山松人工林最低，而落叶类植被，如灌丛、连香树和落叶松之间没有明显差异，说明可利用底物的数量和质量差异是影响各次生植被凋落物分解和土壤微生物活性的主要原因。MBC/OC和MBN/ON能较好地指示土壤微生物活性的变化，MBC/OC凋落层总体以灌丛和连香树人工林最高，油松和华山松人工林最低；而土壤中MBC/OC连香树人工最高，华山松人工林最低。说明以油松和华山松为主的人工造林替代乡土阔叶灌丛造成土壤C、N等养分严重匮乏，微生物活性低下是影响其养分周转的主要原因。 3. 从各次生植被凋落物产生看，凋落物年归还量最大的为华山松人工林(5.1×103 kg ha-1)，其次为落叶松人工林(4.8×103 kg ha-1)，阔叶灌丛林地凋落物产生总量(4.4×103 kg ha-1)略大于油松人工林(4.2×103 kg ha-1)，最小的为连香树人工林(3.6×103 kg ha-1)；叶是凋落物的主体，落叶类树种月动态表现为单峰型，高峰主要在10-11月，如落叶松、连香树和灌丛林；常绿的松类月动态不明显，各月基本相同，最为明显地为油松林，华山松人工林略有二个小峰，分别出现在11月和5月。落叶阔叶灌丛的凋落物分解速率大于常绿针叶林，如油松和华山松。结合凋落物的产生量和分解速率，不同树种人工林替代次生阔叶灌丛后，人工油松和华山松林枯落物总贮量和厚度明显大于落叶松人工林、灌丛林和连香树人工林，说明以油松和华山松为主的人工造林替代乡土阔叶灌丛延缓了有机物向土壤的顺利归还，不利于土壤C、N等养分循环。 4. 通过控制地面凋落物和地下根系输入有机物对土壤碳、氮的影响研究发现，(1) 单独去除根系以及根系与地面凋落物同时去除处理1年后对表层(0-10cm)土壤WDOC均没有显著影响，而土壤WDON显著增加，油松人工林土壤微生物生物量C、N显著降低，人工落叶松林没有显著差异，说明油松人工林土壤微生物活性对地下碳输入的依赖大于其它次生植被，而落叶松土壤微生物活性对地下碳输入依赖性较小；去除地面凋落物，明显降低了落叶松人工林土壤WDOC，华山松和连香树土壤WDON均较对照显著减少，油松人工林土壤微生物量C较对照显著减少；双倍增加地面凋落物处理对土壤微生物生物量、WDOC和WDON没有明显地增加，相反，连香树、华山松和油松人工林土壤WDON较对照减少。说明油松人工林微生物活性不仅依赖于地下碳输入，而且对地上有机物输入的依赖性也较大；连香树、落叶松和华山松人工林土壤微生物生物量并没有因地面凋落物的去除减少可能与土壤总有机碳含量及活性均较高有关，而双倍增加地面凋落物反而降低了土壤微生物生物量，说明凋落物覆盖后改变了土壤微气候。 5. 碳矿化累积量与有机碳含量和活性有机碳含量之间存在显著地正相关关系。凋落物碳累积矿化量、矿化速率以连香树最高，油松和华山松人工林次之，落叶阔叶灌丛低于常绿针叶纯林，导致其差异的主要原因可能为凋落物产生的时间动态模式不一样，致使凋落物起始分解时间不一致。而土壤层有机碳矿化速率和矿化量以阔叶落叶灌丛和连香树最高，油松和华山松人工土壤最低，再次证实利用针叶纯林恢复植被阻碍了有机质周转与循环。 6. 凋落物累积矿化量与C/N值呈显著地相关关系，并随着温度的升高而明显增加，而土壤累积矿化量与C/N值没有显著相关关系，说明土壤有机碳质量(C/N)对温度的响应不十分明显。通过双指数模型对不同温度下碳矿化过程进行模拟和计算出活性有机碳与惰性有机碳比例，发现温度升高促进了惰性有机碳向活性有机碳的转化，增加了活性有机碳含量，说明温度升高可促进次生植被凋落物与土壤有机质的分解，进而可影响到林地碳源/汇关系的变化。 综上，通过对不同人工替代次生植被凋落物与土壤C、N大小、以及土壤微生物生物量、水溶性C、N等指标动态变化模式研究，结合温度与凋落物数量输入等影响土壤活性C、N因子的综合分析，以油松和华山松人工纯林对山地植被恢复，延缓或阻碍了有机质周转与循环，造成了土壤肥力退化。对现有低效人工纯林改造，应为地面大量有机物分解创造条件。 Although soil microbial biomass, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are a small part of total soil organic carbon and nitrogen, they can directly participate in the process of soil biochemical translation and indicate the fine changes before changes of soil total organic carbon and nitrogen occur. So, they are good indexes to indicate soil restoration condition during the process of vegetation rehabilitation. There are large areas of secondary vegetations which substitute for indigenous shrubs in the eastern fringe of Qinghai-Tibet Plateau. However, it is not well known that the ecological effect and process after substitution by different secondary plantations. Based on comparison of soil organic and nitrogen contents in litter layer and soil under different secondary vegetations in upper reaches of Minjiang River, soil microbial biomass, DOC and DON in litter layer and soil were investigated in order to analyze the seasonal dynamic. Combining the effects of temperature, litter input and root exclusion on soil microbial biomass, DOC and DON, we also aim to understand the reason and mechanism of difference in soil carbon and nitrogen contents among different secondary vegetations. The study would contribute to comprehensively understanding C and N cycling processes and provide optimal control and sustainable technology of low-effect plantations in these regions. The results are as follows: (1) Organic carbon and nitrogen in litter layers and soil under different substitution plantations were investigated. The results showed that contents of soil organic carbon and nitrogen were lower in P. tabulaeformis (PT) and P. armandi Franch(PA) than those in native broad-leaf shrub and broad-leaf plantation. The low quality (C/N) of litter in PT and PA plantations caused carbon and nitrogen returning to soil difficultly. Seasonal dynamic of soil microbial carbon (MBC),-nitrogen (MBN),-phosphor (MBP), and WDOC and WDON showed similar pattern, which had the highest values in autumn and the lowest values in winter. (2) WDOC and WDON in litter layers and soil under PT and PA plantations were significantly lower than those in native broad-leaf shrub and Cercidiphyllum japonicum Sieb. et Zucc.(CJ). Soil MBC and MBN were also the lowest, while there were no significant differences among deciduous vegetations, i.e. native broad-leaf shrub, CJ and Larix kaempferi Lamb.(LK) plantation. The results suggested that difference in quantity and quality of available substance was main reason that affected the activity of microbe in soil and litter layer. MBC/OC and MBN/ON were good indexes to indicate the change of soil microbial activity. MBC/OC of litter had the highest value under native broad-leaf shrub and CJ plantation, and had the lowest value in PT and PA plantations, while MBC/OC of soil was the highest under CJ plantation, and was the lowest in PT and PA plantations. These results indicated that PT and PA plantations substituting for native broad-leaf shrub caused deficit of carbon and nitrogen in soil, low microbial activity was a main reason influencing the cycling and turnover of carbon and nitrogen in soil. (3) The annual litter fall production, composition, seasonal dynamic and decomposition of five typical secondary stands in upper reaches of Minjiang River were studied in this paper. The annual litter productions were: PA (5.1×103 kg ha-1), LK(4.8×103 kg ha-1), native broad-leaf shrub (4.4×103 kg ha-1), PT(4.2×103 kg ha-1)，CJ(3.6×103 kg ha-1). The litter production of leaves in five secondary vegetations occupied a higher percentage in the annual total litter production than those of other components. The litterfall was mostly producted in the cool and dry period (October-November) for deciduous vegetations and relatively equably producted in every season for evergreen coniferous vegetations. The decomposition rate of leaf litter in the broad-leaf stand was higher than those in evergreen coniferous stand. Combined with annual litter fall production and decomposition rate of leaf litter, we found that stock and depth of litter layer were significantly larger in PT and PA plantations than those in native broad-leaf shrub, LK and CJ plantations. The results confirmed that PT and PA plantations substituting for native broad-leaf shrub delayed organic matter returning to soil and hindered cycling of carbon and nitrogen again. (4) We explored plant litter removal, double litter addition, root trenching, and combining root trenching and litter removal treatments to examine the effects of above- and belowground carbon inputs on soil microbial biomass, WDOC and WDON in four secondary plantations. During the experimental period from June 2007 to July 2008, 1 year after initiation of the treatments, WDOC in soil did not vary in root trenching, and combining root trenching and litter removal treatments, while WDON in soil significantly increased compared with CK treatment. Root trenching reduced soil MBC and MBN in PT plantation, while MBC and MBN in soil did not vary in LK plantation. The rasults implied that soil microbial activity was more dependent on belowground carbon input in PT plantation than those in other secondary plantations, on the contrary, soil microbial activity in LK plantation was not dependent on belowground carbon input. Plant litter removal significantly decreased soil WDOC in LK plantation, decreased WDON in PA and CJ plantations, and also significantly reduced soil MBC in PT plantation. However, double litter addition did not increase soil microbial biomass, WDOC and WDON, on the contrary, soil WDON in CJ, PA and PT plantations were decreased. These suggested that soil microbial activity was not only dependent on belowground carbon input, but also on aboveground organic material input. Double litter addition could change the microclimate and result in the decrease of soil microbial activity in CJ, PA and PT plantations. (5) We measured carbon mineralization in a 107 days incubation experiment in 5℃,15℃ and 25℃. Carbon cumulative mineralization was positively correlated with organic matter and labile organic carbon in litter layer and soil. Cumulative carbon mineralization and mineralization rate of litter layers in PT and PA plantations were higher than that in native broad-leaf shrub. This difference between native broad-leaf shrub and coniferous plantations in cumulative carbon mineralization and mineralization rate of litter layers could be attributed to the initiating time of decomposition due to the difference in seasonal dynamic of litter fall production between two types of secondary plantations. However, cumulative carbon mineralization and mineralization rate in soil were the highest in native broad-leaf shrub and CJ plantation, and were the lowest in PT and PA plantations. This also confirmed that PT and PA plantations substituting for native broad-leaf shrub hindered the cycling and turnover of organic matter again. (6) Carbon cumulative mineralization was positively correlated with C/N in litter layer and increased with temperature increasing, while carbon cumulative mineralization was not correlated with C/N in soil. This indicated that soil organic matter quality (C/N) was insensitive to temperature. Applying bi-exponential model, we computed the percent of labile and stable carbon in different temperature incubation and found that temperature increasing would accelerate the transform from stable carbon to labile carbon and increase the percentage of labile organic carbon. This illuminated that temperature incraesing could facilitate the decomposition of litter and soil organic matter in secondary vegetations and hence affect the relationship between carbon source and sink.

干旱胁迫与施N条件下白刺花（Sophora davidii）幼苗生长及其适应机制

干旱环境常常由于多变的降水事件和贫瘠土壤的综合作用，表现出较低的生产力和较低的植被覆盖度。全球性的气候变暖和人类干扰必将使得干旱地区缺水现状越来越严竣。贫瘠土壤环境中已经很低的有效养分含量也将会随着干旱的扩大而越来越低。干旱与半干旱系统中不断加剧的水分与养分的缺失将严重限制植物的生长和植被的更新，必然会使得已经恶化的环境恶化速率的加快、恶化范围的加大。如何抑制这种趋势，逐步改善已经恶化的环境是现在和将来干旱系统管理者面临的主要关键问题。了解干旱系统本土植物对未来气候变化的适应机制，不仅是植物生态学研究的重要内容，也对人为调节干旱环境，改善干旱系统植被条件，提高植被覆盖度具有重要的实践意义。 本研究以干旱河谷优势灌木白刺花（Sophora davidii）为研究对象，通过两年大棚水分和施N控制实验和一个生长季野外施N半控制实验，从植物生长－生理－资源利用以及植物生长土壤环境特征入手，系统的研究了白刺花幼苗生长特性对干旱胁迫和施N的响应与适应机制，并试图探讨施N是否可调节干旱系统土壤环境，人工促进干旱条件下幼苗定居，最终贡献于促进植被更新实践。初步研究结论如下： 1）白刺花幼苗生长、生物量积累与分配以及水分利用效率对干旱胁迫和施N处理的适应白刺花幼苗株高、基径、叶片数目、叶面积、根长、生物量生产、相对含水量和水分利用效率随着干旱胁迫程度的增加而明显降低，但地下部分生物量比例和R/S随着干旱胁迫程度的增加而增加。轻度施N处理下幼苗株高、基径、叶片数目、叶片面积和生物量生产有所增加。但重度施N处理下这些生长指标表现出微弱甚至降低的趋势。严重干旱胁迫条件下，幼苗叶面积率、R/S、相对含水量和水分利用效率也以轻度施N处理为最高。 2）白刺花幼苗叶片光合生理特征对干旱胁迫和施N处理的适应叶片光合色素含量和叶片光合效率随着干旱胁迫程度的增加而显著降低，并且PS2系统在干旱胁迫条件下表现出一定程度的光损害。但是比叶面积随着干旱胁迫程度的增加而增加。在相对较好水分条件下幼苗净光合速率的降低可能是因为气孔限制作用，而严重干旱胁迫条件下非气孔限制可能是导致幼苗叶片光合速率下降的主要原因。叶片叶绿素含量、潜在光合能力、羧化效率、光合效率以及RUBP再生能力等在施N处理下得到提高，并因而改善干旱胁迫条件下光合能力和效率。虽然各荧光参数对施N处理并无显著的反应，但是干旱胁迫条件下qN和Fv/Fm在轻度施N处理下维持相对较高的水平，而两年连续处理后在严重干旱胁迫条件下幼苗叶片光合效率受到重度施N处理的抑制，并且Fv/Fm和qN也在重度施N处理下降低。 3）白刺花幼苗C、N和P积累以及N、P利用效率对干旱胁迫和施N处理的适应白刺花幼苗C、N和P的积累，P利用效率以及N和P吸收效率随干旱胁迫程度的增加而显著降低，C、N和P的分配格局也随之改变。在相同水分处理下，C、N和P的积累量、P利用效率以及N和P吸收效率在轻度施N处理下表现为较高的水平。然而，C、N和P的积累量和P利用效率在重度施N处理下不仅没有表现出显著的正效应，而且有降低的趋势。另外，在相同水分条件下白刺花幼苗N利用效率随着施N强度的增加而降低。 4）白刺花幼苗生长土壤化学与微生物特性对干旱胁迫和施N的适应白刺花幼苗生长土壤有机C、有效N和P含量也随干旱胁迫程度的增加而明显降低。干旱胁迫条件下土壤C/N、C/P、转化酶、脲酶和碱性磷酸酶活性的降低可能表明较低的N和P矿化速率。尽管微生物生物量C、N和P对一个生长季干旱胁迫处理无显著反应，但微生物生物量C和N在两年连续干旱胁迫后显著降低。土壤有机C和有效P含量在轻度施N处理下大于重度施N处理，但是有效N含量随着施N强度的增加而增加。微生物生物量C和N、碱性磷酸酶和转化酶活性也在轻度施N处理下有所增加。但是碱性磷酸酶活性在重度施N处理下降低。 5）野外条件下白刺花幼苗生长特征及生长土壤生化特性对施N的适应植物生长、生物生产量、C的固定、N、P等资源的吸收和积累、其它受限资源的利用效率（如P）在轻度施N处理下均有所增加，但N利用效率有所降低。幼苗生物生产量及C、N和P等资源的分配格局在轻度施N处理下也没有明显的改变。白刺花幼苗叶片数目、生物生产量和C、N、P的积累量在重度施N处理下虽然也相对于对照有所增加，但幼苗根系长度显著降低。生物量及资源（生物量、C、N、P）在重度施N处理下较多地分配给地上部分（主要是叶片）。另外，土壤有机C、全N和有效N含量随外源施N的增加而显著增加，土壤pH随之降低，但土壤全P含量并无显著反应。其中有机C含量和有效P含量以轻度施N处理最高。微生物生物量C、N和P在轻度施N处理下也显著增加，而微生物生物量C在重度施N处理下显著降低。同时，转化酶、脲酶、碱性磷酸酶和中性磷酸酶活性在施N处理下也明显的提高，但酸性磷酸酶和过氧化氢酶活性显著降低，其中碱性磷酸酶和中性磷酸酶活性以轻度施N处理最高。 综合分析表明，干旱河谷水分和N严重限制了白刺花幼苗的生长。施N不能完全改变干旱胁迫对白刺花幼苗的抑制的作用，但是由于施N增加土壤N有效性，改善土壤一系列生物与化学过程，幼苗的生长特性也对施N表现出强烈的反应，表现为植物结构与资源分配格局的改善，植物叶片光合能力与效率的提高，植物生长以及利用其他受限资源（如水分和P）的效率的增加，致使植物自身生长及其生长环境在干旱环境下得到改善。但是过度施N不仅不能起到改善干旱胁迫下植物生长环境、促进植物生长的作用，反而在土壤过程以及植物生长过程中加重干旱胁迫对植物的伤害。因此，建议在采用白刺花作为先锋种改善干旱河谷系统环境的实践中，可适当施加N以改善土壤环境，调节植物利用与分配资源的效率，促进植物定居，得到人工促进种群更新的目的。但在实践过程中也要避免过度施N。 Arid regions of the world are generally noted for their low primary productivity which is due to a combination of low, unpredictable water supply and low soil nutrient concentrations. The most serious effects of global climate change and human disturbances may well be those which related to increasing drought since drought stress has already been the principal constraint in plant growth. The decline in total rainfall and/or soil water availability expected for the next decades may turn out to be even more drastic under future warmer conditions. Nevertheless, water deficit is not the only limiting factor in arid and semiarid environments. Soils often suffer from nutrient (especially N and P) deficiencies in these ecosystems, which can also be worsened by climate change. How to improve the poor soil quality and enhance the vegetation coverage is always the problem facing ecosystem managers. The adaptive mechanisms of native plant to future climate change is always the focus in plant ecology, it also plays important roles in improving vegetation coverage by manual controlled programmes. Sophora davidii is a native perennial shrub of arid valleys, which is often predominant on eroded slopes and plays a vital role in retaining ecological stability in this region. It has been found that S. davidii was better adapted to dry environment than other shrubs, prompting its use for re-vegetation of arid lands. A two-years greenhouse experiment and a field experiment were conducted in order to understand the adaptation responses of Sophora davidii seedlings to different water and N conditions, and further explore if additional N supply as a modified role could enhance the adaptation ability of S. davidii seedlings to dry and infertile environment. Two-month old seedlings were subjected to a completely randome design with three water (80%, 40% and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg-1 soil) regimes. Field experiment was arranged only by three N supplies in the dry valley. 1) The growth, biomass partitioning and water-use efficiency of Sophora davidii seedlings in respond to drought stress and N supply Seedlings height, basal diameter, leaf number, leaf area, root length, biomass production, relative water content (RWC) and WUE were decreased with increase of drought stress. An increase in below-ground biomass was observed indicating a higher root/shoot ratio (R/S) under drought stress conditions. Low N supply increased seedlings height, basal diameter, leaf number, leaf area, and biomass production, but decreased root length. In contrast, these growth characteristics showed little or negative effect to high N supply treatment. Leaf percentages increased with increase of N supply, but fine root percentages decreased. In addition, Low N supply rather than the other two N treatments increased leaf area ratio (LAR), leaf/fine root mass ratio (L/FR), R/S and RWC under severe drought stress (20%FC), even though these parameters could increase with the high N supply treatment under well-watered condition (80%FC). Moreover, Low N supply also increased WUE under three water conditions, but high N supply had little effect on WUE under drought stress conditions (40%FC and 20%FC). 2) Leaf gas exchange and fluorescence parameters of Sophora davidii seedlings in respond to drought stress and N supply Leaf area (LA), photosynthetic pigment contents, and photosynthetic efficiency were decreased with increase of drought stress, but specific leaf area (SLA) increased. Photodamage in photosystem 2 (PS2) was also observed under drought stress condition. The decreased net photosynthetic rate (PN) under relative well-watered water conditions might result from stomatal limitations, but the decreased PN under other hand, photosynthetic capacity by increasing LA, photosynthetic chlorophyll contents, Pnmax, CE, Jmax were increased with increase N supply, and photosynthetic efficiency was improved with N supply treatment under water deficit. Although N supply did a little in alleviating photodamages to PS2 caused by drought stress, low N supply enhanced qN and kept relative high Fv/Fm under drought stress condition. However, high N supply inhibited leaf photosynthetic efficiency, and declined Fv/Fm and qN under severe drought stress condition after two year continues drought stress and N supply. 3) Carbon accumulation, nitrogen and phosphorus use efficiency of Sophora davidii seedlings in respond to drought stress and N supply C, N and P accumulation, NUE , N and P uptake efficiency (NUtE and NUtE ) P N P were decreased with increase of drought stress regardless of N supply. On the other hand, the S. davidii seedlings exhibited strong responses to N supply, but the responses were inconsistent with the various N supply levels. Low N supply rather than the other two N treatments increased C, N and P accumulation, improved NUEP, NUtE and NUtE under corresponding water condition. In contrast, high N supply N P did few even depressed effects on C, N and P accumulation, and NUEP, although NUtEN and NUtEP could increase with high N supply under corresponding water conditions. Even so, a decrease of NUEN was observed with increase of N supply under corresponding water conditions. 4) Soil microbial and chemical characters in respond to drought stress and N supply The content of soil organic C, available N and P were decreased with increase of drought stress. Decreases in C/N and C/P, and invertase, urea and alkaline phosphatase activity were also observed under drought stress conditions, indicating a lower N and P mineralization rate. Although microbial biomass C, N and P showed slight responses to drought stress after one growth period treatment, microbial biomass C and N were also decreased with increase of drought stress after two year continuous treatment. The content of soil organic C and available P showed the stronger positive responses to low N supply than which to high N supply, although than the other two N treatments increased microbial biomass N and invertase activity under severe drought stress condition, even though invertase activity could increase with high N supply treatment under relative well-water conditions. Moreover, low N supply treatment also increased C/P and alkaline phosphatase activity which might result from higher P mineralization, but high N supply did negative effects on alkaline phosphatase activity. 5) The growth characteristics of Sophora davidii seedlings and soil microbial and chemical characters in respond to N supply under field condition Low N supply facilitated seedlings growth by increasing leaf number, basal diameter, root length, biomass production, C, N and P accumulation and absorption, and enhancing the use efficiency of other limited resources as P. Compared to control, however, low N supply did little effect on altering biomass, C, N and P portioning in seedlings components. On the contrary, high N supply treatment also increased leaf number, biomass and C, N and P accumulation relative to control, but significantly decreased root length, and altered more biomass and resources to above-ground, which strongly reduced the ability of absorbing water under drought condition, and thus which might deep the drought stress. In addition, N supply increased soil C, N and available N content, but declined pH and showed little effects on P content. Low N supply showed higher values of soil C and available P content. Low N supply also increased microbial biomass C, N and P, although high N supply decreased microbial biomass C. N supply significantly enhanced soil invertase, urea, alkaline and neutral phosphratase activity, while declined acid phosphratase and catalase activity. Low N supply exhibited higher alkaline and neutral phosphratase activity compared to the others. The results from this study indicated that both drought and N limited the growth of S. davidii seedlings and their biomass production. Regardless of N supply levels, drought stress dramatically reduced the seedlings growth and biomass production. Although plant growth parameters, including basal diameter, height, leaf number, and biomass and their components were observed to be positive responses to low N supply, N supply alone can not alter the diminishing tendency which is caused by drought. available N content increased with increase N supply. In addition, low N supply rather These findings imply that drought played a primary limitation role and N was only the secondary. Even so, appropriate N supply was seemed to enhance the ability that S. davidii seedlings adapted to the xeric and infertile environment by improving soil processes, stimulating plant growth, increasing recourses accumulation, enhancing use efficiency of other limited resources, and balancing biomass and resources partitioning. Appropriate N supply, therefore, would be recommended to improve S. davidii seedling establishment in this region, but excess N supply should be avoided.

Methods for physical separation and characterization of soil organic matter fractions

Turnover of soil organic matter (SOM) is coupled to the cycling of nutrients in soil through the activity of soil microorganisms. Biological availability of organic substrate in soil is related to the chemical quality of the organic material and to its degree of physical protection. SOM fractions can provide information on the turnover of organic matter (OM), provided the fractions can be related to functional or structural components in soil. Ultrasonication is commonly used to disrupt the soil structure prior to physical fractionation according to particle size, but may cause redistribution of OM among size fractions. The presence of mineral particles in size fractions can complicate estimations of OM turnover time within the fractions. Densiometric separation allows one to physically separate OM found within a specific size class from the heavier-density mineral particles. Nutrient contents and mineralization potential were determined for discrete size/density OM fractions isolated from within the macroaggregate structure of cultivated grassland soils. Eighteen percent of the total soil C and 25% of the total soil N in no-till soil was associated with fine-silt size particles having a density of 2.07-2.21 g/cm3 isolated from inside macroaggregates (enriched labile fraction or ELF). The amount of C and N sequestered in the ELF fraction decreased as the intensity of tillage increased. The specific rate of mineralization (mug net mineral N/mug total N in the fraction) for macroaggregate-derived ELF was not different for the three tillage treatments but was greater than for intact macroaggregates. The methods described here have improved our ability to quantitatively estimate SOM fractions, which in turn has increased our understanding of SOM dynamics in cultivated grassland systems.