Effects of inoculated Microcoleus vaginatus on the structure and function of biological soil crusts of desert

Microcoleus vaginatus Gom., the dominant species in biological soil crusts (BSCs) in desert regions, plays a significant role in maintaining the BSC structure and function. The BSC quality is commonly assessed by the chlorophyll a content, thickness, and compressive strength. Here, we have studied the effect of different proportions of M. vaginatus, collected from the Gurbantunggut Desert in northwestern China, on the BSC structure and function under laboratory conditions. We found that when M. vaginatus was absent in the BSC, the BSC coverage, quantified by the percentage of BSC area to total land surface area, was low with a chlorophyll a content of 4.77 x 10(-2) mg g(-1) dry soil, a thickness of 0.86 mm, and a compressive strength of 12.21 Pa. By increasing the percentage of M. vaginatus in the BSC, the BSC coverage, chlorophyll a content, crust thickness, and compressive strength all significantly increased (P < 0.01). The maximum chlorophyll a content (13.12 mg g(-1)dry soil), the highest crust thickness, and the compressive strength (1.48 mm and 36.60 Pa, respectively) occurred when the percentage of inoculated M. vaginatus reached 80% with a complex network of filaments under scanning electron microscope. The BSC quality indicated by the above variables, however, declined when the BSC was composed of pure M. vaginatus (monoculture). In addition, we found that secretion of filaments and polymer, which stick sands together in the BSC, increased remarkably with the increase of the dominant species until the percentage of M. vaginatus reached 80%. Our results suggest that not only the dominant species but also the accompanying taxa are critical for maintaining the structure and functions of the BSC and thus the stability of the BSC ecosystems.

Capacity of soil to protect organic carbon and biochemical characteristics of density fractions in Ziwulin Haplic Greyxems soil

Physical protection is one of the important ways to stabilize organic carbon in soils. In order to understand the role of soils as a carbon sink or source in global climatic change and carbon cycles and properly manage soils as a carbon sink, we ought to know how many organic carbon (OC) in a given soil could be protected. By a density fractionation approach and ultrasonic technique, each soil sample was divided into three fractions: free light fraction (free-LF), occluded fraction (occluded-LF) and heavy fraction (HF). The obtained fractions were analyzed for total OC content, carbohydrate content and recalcitrant OC content. The results showed: (i) In the whole soil profile, dominance of OC consistently decreased in the following order: HF, free-LF, occluded-LF. This suggested that OC in soils were mostly protected. From 0-10 to 60-80 cm horizons, the OC in free-LF decreased from 25.27% to 3.72%, while OC in HF they were increased from 72.57% to 95.39%. The OC in occluded-LF was between 2.16% and 0.89%. (ii) Organic carbon recalcitrance in free-LF was similar to that in HF, and was even higher than that in HF below the surface horizon. This suggested that free-LF was not always the most fresh and non-decomposed fraction. OM quality of HF was higher than that of free-LF in the surface 10 cm below, namely the protected OM had higher quality than free OM in these horizons.

Slope Stability Analysis Using Anisotropic and Nonlinear Failure Criteria

The shear strength of soils or rocks developed in a landslide usually exhibits anisotropic and nonlinear behavior. The process of sedimentation and subsequent consolidation can cause anisotropy of sedimentary soils or rocks, for instance. Nonlinearity of failure envelope could be attributed to "interlocking" or "dilatancy" of the material, which is generally dependent upon the stress level. An analytical method considering both anisotropy and nonlinearity of the failure envelops of soil and rocks is presented in the paper. The nonlinearfailure envelopes can be determined from routine triaxial tests. A spreadsheet program, which uses the Janbu's Generalized Procedure of Slice and incorporates anisotropic, illustrates the implementation of the approach and nonlinearfailure envelops. In the analysis, an equivalent Mohr-Coulomb linear failure criterion is obtained by drawing a tangent to the nonlinear envelope of an anisotropic soil at an appropriate stress level. An illustrative example is presented to show the feasibility and numerical efficiency of the method.

不同粘粒含量土壤水分入渗能力模拟试验研究

为研究土壤粘粒含量对土壤入渗能力的影响,通过向自然土壤中添加沙粒、人工粘土的方法配制不同粘粒含量土壤,用土柱积水入渗模拟了人工配制土壤中粘粒含量对其入渗能力的影响。结果表明:(1)土壤粘粒含量对土壤入渗能力有较大影响,随粘粒含量增多,入渗能力递减:<0.001 mm粘粒含量从6%增加至40.4%时,稳定入渗速率从0.0169 cm/min降低至0.0068 cm/min,90 min累积入渗量则从3.66 cm降低至2.02 cm;(2)稳定入渗速率9、0 min累积入渗量与粘粒及物理性粘粒含量分别呈幂函数负相关、指数负相关关系,但与粘粒含量相关性更为显著;(3)通过对Green-Ampt模型、Philip模型及Kostiakov模型的参数拟合及累积入渗量计算,发现在本试验中Kostiakov模型拟合精度最高,Philip模型次之,Green-Ampt模型较差,说明Kostiakov模型对于均质土体是个比较实用的入渗模型。

黄土塬区10m深剖面土壤物理性质研究

土壤水分是影响黄土高原植被生长和生态环境建设的主要因素。已有对黄土高原土壤的持水性能、水分有效性能与移动性能、黄土高原环境的旱化与黄土中水分关系等方面的深入研究[1,2],也有小流域内土壤水分物理性状与地形和利用条件之间关系的具体分析[3,4]。但是这些工作所涉及的土壤剖面深度多为2 m或3 m,深层土壤水分物理参数研究还少有报道。而对于具有深厚土层的黄土塬区,高产农田与多年生林草地在土壤深层产生了不同程度的干燥化[5~7],土壤干燥化的深入探讨需要与剖面土壤物理性质相关联。为此,有必要对植物根系伸展范围以至更深层次的土壤质地、容重、水分特征曲线、饱和导水率、田间持水量以及萎蔫湿度等土壤物理性质进行测定,分析其垂直变化及不同层次的相关性,为土壤深层水分生态和运动规律研究提供基础参数。1材料与方法1·1研究区概况野外测定点位于陕甘交界处的中国科学院长武农业生态试验站的黄土塬面上。所在区域为典型的黄土高塬沟壑区,属暖温带半湿润大陆性季风气候,年平均气温9·1℃。降水年际变异大,多年平均降水量为584·1 mm,主要集中在7月至9月,约占全年降水量的55%以上。塬地主要土壤类型为黑垆土,母质为马兰黄土,非饱和层深厚...

植物与微生物联合修复多环芳烃污染土壤及机理研究

本文以多环芳烃污染土壤为研究对象，以菲（Phe）、芘（Pyr）和苯并[a]芘（BaP）为目标污染物，以建立生态、经济、高效污染土壤修复技术为目标，在研究植物与微生物联合修复多环芳烃污染土壤效果的基础上，重点研究了植物与微生物联合修复污染土壤过程中多环芳烃的去除机制。 研究结果表明：种植苜蓿和黑麦草能够促进土壤中多环芳烃的去除，提高土壤中多环芳烃的去除率。植物根际土壤中多环芳烃的去除速度快于于非根际土壤。在植物与高效降解菌联合作用过程中，植物的存在强化了菌剂对土壤中多环芳烃的去除作用。苜蓿和黑麦草与高效降解菌的联合作用使菲、芘和苯并[a]芘去除率分别比对照土壤提高了26.64%、30.41%、32.04%和26.93%、27.43%、30.15%。 植物根和茎叶中菲、芘和苯并[a]芘的含量与土壤污染物浓度正相关，但其吸收积累作用对土壤中多环芳烃去除的贡献率小于0.34%。植物对土壤多环芳烃污染的修复作用主要源于植物生长显著提高了根际微生物的降解活性。 植物根际微生物的数量和土壤酶活性显著高于非根际土壤。植物根系的存在提高了土壤中微生物的数量和酶活性，从而提高了土壤中PAHs的去除率。这是根际土壤中多环芳烃去除的主要机制。 模拟根际修复，研究了添加根系分泌物对土壤中芘降解的影响。添加20mg/kg根系分泌物土壤中细菌数量为未添加根系分泌物土壤的19.43-36.29倍，真菌为3.05-6.60倍，土壤中芘的半衰期比未添加根系分泌物处理减少10.91天。植物根系分泌物是影响根际修复的一个重要原因。

用植物油淋洗修复多环芳烃污染土壤

研究用植物油淋洗修复多环芳烃污染土壤的效果、植物油淋洗剂再生与回用的可行性、植物油的生态效应。采用了批处理法和土柱法对多环芳烃污染土壤进行修复，结果表明：油土比1：1的条件下，批处理法可以去除土壤中90％以上的多环芳烃，多环芳烃的质量转移过程可以用经验模型模拟。恰当的运行条件下，土柱法可去除土壤中90％以上的多环芳烃，但是根据土壤中多环芳烃浓度的高低，植物油的用量是批处理法的2～4倍。无论是批处理法，还是土柱法，土壤水分含量都影响了植物油去除土壤中多环芳烃的能力。采用了化学氧化法、溶剂提取法和吸收剂吸收法对植物油进行再生，结果表明：臭氧和双氧水能氧化植物油中的多环芳烃，但不理想，紫外线及双氧水在pH＝3的条件下可氧化植物油中76.5％的多环芳烃。按植物油／乙醇1:3的比例对植物油进行6级处理可氧化植物油中87％的多环芳烃。活性炭二级处理可去除植物油中87％的多环芳烃，实现植物油的再生。高等植物生长实验说明土壤中的植物油对燕麦及萝卜的生长起了抑制作用，土壤呼吸实验证明，残留在土壤中的植物油可被生物降解，但是必须保证良好的氧气及营养供应。用植物油修复多环芳烃污染土壤具有可行性。

石油烃污染土壤植物-微生物联合修复及机理研究

运用土壤学、微生物学、生态学和统计学方法，系统地开展了石油污染土壤的植物-微生物联合修复研究，对植物-微生物修复的生态影响进行了分析，并从根际微生物区系变化与根分泌物特性两个角度深入探讨了污染土壤植物一微生物联合修复的机理。室内模拟、室外盆栽、田间微区实验的结果表明：（1）植物-微生物联合修复对不同浓度石油烃污染土壤有较好的修复效果，125d的修复周期中对土壤中石油污染物的降解率为7.1％-69.8％，随污染物浓度的升高，联合修复对土壤中污染物的降解作川增强；（2）植物一微生物联合修复作用可能会长期持续，并对难降解物质PAHs存在修复潜力；（3）在本实验条件下，采用经济作物与降解微生物联合修复会降低土壤有机质含量，对土壤生态系统的结构和功能不会产生严重的干扰，对土壤生态环境的影响可以在短时间恢复；（4）植物一微生物联合作用方式在于植物与微生物的相互作用，作用区为植物根际，微生物在植物根际区域的种类数量和生化特征存在差异；植物分泌物对于微生物具有调节作用，促使污染物的生物降解。并以本试验研究为例，进一步探讨石油污染土壤植物一微生物联合修复的机理，利石油污染土壤的植物一微生物联合修复的影响因子进行调控研究，联合修复的主要影响因子是营养因子，其次是污染物浓度。石油污染土壤的植物一微生物联合修复研究，对土壤微生物群落，植物根际效应及潜在自然生物降解获得了进一步的理解，为污染土壤修复技术提供了科学依据和理论支持。