鸡粪改良铜尾矿对3种豆科植物生长及基质微生物量和酶活性的影响

基质改良和耐性植物种选择是重金属矿业废弃地人工生态恢复的关键。通过室内盆栽试验研究不同比例腐熟鸡粪改良铜尾矿后对3种豆科植物决明(Cassia tora)、田菁(Sesbania cannabina)、菽麻(Crotalaria juncea)生长和尾矿基质中土壤微生物量C、N及过氧化氢酶、碱性磷酸酶、脲酶和脱氢酶活性的影响。结果表明:添加鸡粪改良处理后3种植物茎叶生物量、根系生物量和体内总磷含量均有提高,植物体内总氮含量则只有菽麻明显增加。添加鸡粪可提高尾矿基质中微生物量C以及脲酶和脱氢酶活性,其中菽麻生长的尾矿基质中微生物量C含量增加最显著。尾矿基质中微生物量C与基质中总氮、有效磷呈显著正相关,菽麻生长的尾矿基质中微生物量C与基质中有效态Cu、Zn呈显著负相关。田菁、菽麻生长的尾矿基质中脲酶、脱氢酶与基质中总氮、有效磷呈显著正相关,决明、菽麻生长的尾矿基质中脱氢酶与基质中微生物量C呈显著正相关,决明生长的尾矿基质中脲酶、脱氢酶与基质中有效态Zn呈显著负相关。综合分析表明,铜尾矿∶鸡粪=250∶1的处理方式可作为鸡粪改良铜尾矿基质较好的一种比例模式,该处理方式下菽麻可作为铜尾矿生态修复优选植物种。     

生物结皮对铜尾矿废弃地土壤微生物量及酶活性的影响

生物结皮是铜尾矿废弃地自然原生演替的最初阶段.本研究以铜陵杨山冲铜尾矿库和铜官山新铜尾矿库为对象,采用熏蒸浸提和化学分析法研究了两尾矿库不同类型生物结皮下土壤微生物量C、N及脱氢酶、过氧化氢酶、碱性磷酸酶和脲酶活性.结果表明：铜尾矿废弃地上的生物结皮能够显著提高表层尾矿中的微生物量和土壤酶活性,其中藻类结皮对土壤微生物量C、N的影响高于藓-藻混合结皮,藓类结皮的影响最小;随着土壤生物结皮类型的变化,土壤微生物区系也随之变化;各类生物结皮下表层尾矿中土壤酶活性无显著差异.相关分析表明,碱性磷酸酶活性与土壤微生物量、脱氢酶和脲酶活性呈显著正相关,但与土壤pH呈显著负相关.此外,藓类植物假根能够显著提高藓类结皮假根层的微生物量和酶活性.     

不同植物群落下酸化尾矿养分状况及土壤酶活性

调查不同植被群落下铜尾矿的养分状况及土壤酶活性的变化动态,通过常规方法测定了尾矿的pH和电导率,以及有机质,总氮,有效磷,速效钾的含量。用底物反应法测定了过氧化氢酶,芳基硫酯酶,脲酶,酸性磷酸化酶和脱氢酶的活性。结果表明,与酸化的裸露尾矿相比,定居其上的芦苇(Phragmites australis)、狗牙根(Cynodon dactylon)和双穗雀稗(Paspalum distichum)均能显著增加尾矿基质pH值(从3.6上升到5.4),降低电导率,减缓尾矿酸化过程。芦苇和狗牙根能够显著提高尾矿基质中N、K和有机质含量(P<0.05),增加尾矿中的养分。3种植物群落下有效磷较裸露尾矿没有显著增加。植物的定居显著提高了尾矿中过氧化氢酶、芳基硫脂酶和脲酶的活性(P<0.05);但酸性磷酸化酶和脱氢酶活性没有显著提高。研究表明,植物对尾矿有明显的改良作用,而且芦苇和狗牙根优于双穗雀稗。在各种植被条件的尾矿中除酸性磷酸化酶以外的其它实验土壤酶活性均与尾矿中有机质和总氮呈极显著正相关(P<0.01)。     

自然演替过程中铜尾矿土壤酶活性的变化

铜陵矿区堆放了大量不同时期的铜尾矿,形成大量铜尾矿废弃地,其中的大部分铜尾矿废弃地处于自然生态恢复状态。并形成典型的原生演替系列。为探讨废弃地自然生态恢复中不同演替阶段植物群落变化与土壤酶活性变化的关系,对铜陵3处不同时期弃置的尾矿废弃地进行了调查。随着自然生态系统演替的进行,尾矿中土壤酶活性逐步提高,维管植物群落下尾矿中土壤酶活性〉隐花植物结皮下尾矿中土壤酶活性〉裸地处土壤酶活性;位于植物群落下的尾矿废弃地中脲酶、碱性磷酸酶、过氧化氢酶的活性从表层至下层逐渐降低。不同植物群落对尾矿中土壤酶活性影响有很大差异,位于木贼群落下的尾矿中几种土壤酶的活性高于位于白茅群落和中华结缕草群落下的尾矿中酶的活性。相关分析表明,土壤酶活性与有机质、总N表现出显著的正相关。     

稻鸭与稻鱼生态系统土壤微生物量N和土壤酶活性动态

在一个水稻生长季节,采用田间采样与室内分析的方法,利用氯仿熏蒸培养法、苯酚钠比色法、TTC比色法、高锰酸钾滴定法和茚三酮比色法测定和研究了稻鸭与稻鱼生态系统稻田土壤微生物量N(MBN)和土壤脲酶、脱氢酶、过氧化氢酶和蛋白酶活性的动态变化,及其与土壤养分和水稻吸N量的相关性.结果表明,(1)随着水稻的生长,土壤微生物量N表现为先上升随后下降,于成熟期有所回升趋势;土壤微生物量N与土壤速效N、全N和全P不相关;由于水稻与微生物对养分的竞争,土壤微生物量N与水稻吸N量不相关;稻田养鸭,养鱼显著地提高了土壤微生物量N.(2)土壤脲酶、脱氢酶和蛋白酶活性都表现出先上升后下降趋势,而过氧化氢酶活性变化不大;稻鸭与稻鱼共作显著地提高了土壤脲酶、脱氢酶和蛋白酶活性,而对过氧化氢酶活性影响不大;线性相关分析表明,在一个稻季内,土壤脲酶和脱氢酶活性与土壤速效N负相关,土壤脲酶、脱氢酶、过氧化氢酶和蛋白酶活性与土壤全N和全P不相关;土壤脲酶、脱氢酶和蛋白酶活性与水稻吸N量呈显著相关.(3)稻田土壤微生物量N与土壤酶不相关.     

香根草在铅锌尾矿上生长及其对重金属的吸收

通过野外小区实验 ,研究了垃圾和 NPK肥对铅锌尾矿地中香根草 (Vetiveria zizanioides)生长及其对重金属吸收的影响。结果表明 ,添加垃圾后香根草生物量显著增加 ,而仅加入 NPK肥对其并无显著影响 ,同时添加垃圾和 NPK肥最有利于香根草在铅锌尾矿中生长。尾矿中重金属形态的变化受金属特性和尾矿理化性质的双重影响。对纯尾矿而言 ,种植香根草后尾矿中重金属总量有所减少。尾矿在施加垃圾和 NPK肥后 ,尾矿中 Pb和 Zn总量减少了 13.6 5 %和 32 .4 0 % ,Cu总量则增加了2 3.5 2 %。可交换态和总量 Cu、Pb、Zn变化趋势一致 ,特别是 Cu和 Pb更为显著。香根草积累的 Pb和 Zn显著高于 Cu,并且重金属主要积累在根部。添加垃圾和 NPK肥料对 Cu的积累无显著差异 ,而显著减少香根草茎和根中 Zn和 Pb的积累 ,但显著增加单位面积上茎中 Zn、Pb和 Cu的总积累量 (p<0 .0 5 )。研究表明垃圾和 NPK肥的综合使用是一个较为经济有效的尾矿改良措施 ,但对于尾矿 -植被系统中的重金属迁移问题应引起关注。综合生物量与重金属的吸收特征 ,香根草对于尾矿的植被重建有较高价值     

节节草生长对铜尾矿砂重金属形态转化和土壤酶活性的影响

通过盆栽模拟栽培试验,研究了节节草生长对铜尾矿砂重金属形态转化和土壤酶活性的影响。结果表明,节节草生长显著提高了尾矿砂中有机物结合态重金属比例(P0.01),降低了交换态和残渣态重金属比例(P0.05)。土壤过氧化氢酶、脲酶、多酚氧化酶和蔗糖酶活性均随着节节草的生长而不同程度的升高,其中过氧化氢酶和脲酶活性均与植物生长时间呈显著正相关(r过氧化氢酶=0.911,P0.05;r脲酶=0.957,P0.01),多酚氧化酶和蔗糖酶活性在植物生长旺盛期达到峰值,分别是对照组的2.40和2.02倍,随后迅速下降;而磷酸酶活性却显著下降(r磷酸酶=-0.923,P0.05)。土壤酶活性与节节草地下部分干重的相关性大于地上部分;且与土壤有机物结合态重金属的含量呈显著正相关,与交换态和残渣态重金属含量呈显著负相关。节节草生长不仅促进了铜尾矿砂重金属朝螯合态方面转化,有效降低重金属的生物有效性,同时还显著地改善了铜尾矿砂的基质环境和土壤肥力。因此,节节草在铜尾矿废弃地恢复实践中具有较大的应用潜力。     

香根草和百喜草对铅锌尾矿重金属的抗性与吸收差异研究

铅锌尾矿是一类重金属含量极高,对植物生长产生毒害的生境.盆栽实验的结果显示,香根草和百喜草在纯尾矿或由尾矿和垃圾组成的混合基质上都能生长,但植物的长势随基质中重金属含量的增加而减弱,其中香根草的生物量所受的影响比百喜草的更大,即百喜草有比香根草更强的重金属抗性.2种植物体内的重金属含量高低均为Zn＞Pb＞Cu,但二者对它们的富集能力大小分别是,香根草为Zn＞Cu＞Pb,百喜草则为Cu＞Zn＞Pb.香根草和百喜草的根系对3种重金属都有较强的滞留效应,滞留率均在50%以上;其中香根草对重金属的滞留率又明显高于百喜草;而且,同一植物对不同的重金属的滞留率也明显不同,香根草对Pb的滞留率最高,而百喜草对Cu的滞留率显著高过对Zn和Pb.由于香根草的生物量明显大于百喜草,结果香根草对Pb、Zn的吸收量比百喜草高.当用25%的垃圾改良金属尾矿时,百喜草对重金属的吸收量即达最大;而香根草则在尾矿和垃圾各占50%的基质中吸收最多的重金属;因此,添加一定量的垃圾(25%～50%左右)用于尾矿改良时,不仅能使尾矿得到更快的植被恢复与更高的植物修复效果,而且能使垃圾资源得到充分合理的利用.总之,当开展对金属尾矿的植被恢复时,可选择种植抗性强、覆盖快的百喜草,但如果要对尾矿中的重金属进行生物净化,则应选择种植生物量大的香根草,种植香根草还可较好地防止重金属的二次污染或生物富集.     

不同主伐方式对兴安落叶松(Larix gmelinii)根际土壤理化性质及微生物群落的影响

对内蒙古根河大兴安岭林区1987年（恢复后期）、2013年（恢复前期）的皆伐与渐伐样地以及未采伐对照样地兴安落叶松的根际土壤理化性质、微生物群落结构和多样性进行了分析,旨在揭示不同主伐方式对兴安落叶松根际土壤理化性质以及微生物群落的影响。结果表明,主伐后兴安落叶松根际土壤的理化性质以及微生物群落的变化特征与非根际土壤存在区别,且不同主伐方式在不同恢复时期会对兴安落叶松根际土壤理化性质以及微生物群落产生不同的影响：（1）根际与非根际土壤微生物群落中真菌均比细菌更容易受到土壤理化性质的影响,但是单一种理化性质的改变对根际与非根际土壤微生物群落均不能造成显著影响。（2）相较于未采伐对照样地,皆伐样地恢复前期兴安落叶松根际土壤理化性质、微生物群落结构和多样性没有显著变化。皆伐样地恢复后期,兴安落叶松根际土壤理化性质（总碳、总氮、速效氮、pH）发生了显著变化,导致了微生物量碳氮、真菌磷脂脂肪酸（PLFA）含量显著降低、细菌/真菌显著升高,辛普森多样性指数显著降低。（3）渐伐样地恢复前期兴安落叶松根际土壤总碳、总氮、速效氮含量以及含水量均显著降低,总钾、速效磷含量显著上升,根际土壤微生物量碳含量显著降低。恢复后期,兴安落叶松根际土壤总磷含量显著升高,根际土壤微生物量碳的含量已恢复到渐伐前水平。渐伐干扰对根际土壤各微生物类群PLFA含量、微生物群落结构以及多样性没有显著影响。     

铜尾矿废弃地土壤动物多样性特征

土壤动物的恢复、群落演替及其多样性对于铜尾矿废弃地的生态重建具有重要意义.为了解铜尾矿废弃地土壤动物群落多样性特征,在铜陵市铜尾矿区设置4个样地23采样点,共捕获土壤动物4622只个体,隶属5门10纲18目29类.结果表明,铜尾矿自然废弃地与其对照组土壤动物多样性差异明显,自然废弃地土壤动物丰富度指数d、大型土壤动物密度、中小型土壤动物密度、多样性指数H'和D·G指数均小于其对照组且存在显著差异.而复垦废弃地中小型土壤动物密度和D·G指数小于其对照组且存在显著差异,多样性指数H'大于其对照组且差异极显著,其他土壤动物群落指标与其对照组均无显著差异.相似系数q表明,外围林地间土壤动物群落相似性最大,其次是复垦废弃地与外围林地间,自然废弃地与其它3个样地间相似性最小.从垂直分层来看,复垦废弃地土壤动物表聚性强于自然废弃地,尾矿废弃地表聚性强于外围林地.灰色关联分析表明,铜尾矿区土壤理化性质与土壤动物群落结构指标关系密切,其中最重要的因素是土壤含水量和总钾含量,重金属全镉含量也不容忽视,植被因素和土壤全铜含量对土壤动物的影响相对较小.由此可见,土壤含水量、土壤基质的优劣、土壤有机质与营养元素的含量等因素限制了铜尾矿废弃地土壤动物的恢复与重建,而这些因素的改善主要归功于尾矿废弃地的土地复垦和作物种植.所以,尾矿废弃地的复垦与利用有利于土壤动物的恢复与重建.     

Use of Vetiver and Three Other Grasses for Revegetation of Pb/Zn Mine Tailings: Field Experiment

The Lechang Pb/Zn mine is located to the north of the Guangdong Province, South of China. The tailings pond had been abandoned for over 5 years, and revegetation was necessary for stabilizing the bare surface and to reduce its environmental impact. The tailings contained high levels of heavy metals (Pb, Zn, Cu, and Cd) and low levels of major nutrient elements (N, P, and K) and organic matter; therefore, heavy metal toxicity and extreme infertility were the major constraints on revegetation. A field experiment was conducted to compare the growth of Vertiveria zizanioides, Paspalum notatum, Cynodon dactylon, and Imperata cylindrica var. major on the tailings. The tailings were amended with 10 cm domestic refuse + complex fertilizer (NPK) (Treatment A), 10 cm domestic refuse (Treatment B) and complex fertilizer (NPK) (Treatment C), respectively; tailings without any amendment were used as control (Treatment D). Plant growth was improved when either domestic refuse or NPK fertilizer was added to the substrate, but the combination of both amendments gave the best yields. After 6 months' growth, V. zizanioides growing on treatment A had a height of 220 cm, cover of 100% and a yield of 2.1 kg m^-2 (d.w.). The height and biomass of V. zizanioides were significantly greater than the other three grasses growing on the same treatment. Judging from results, V. zizanioides was the best species for tailings revegetation, followed by P. notatum, C. dactylon, and I. cylindrica var. major.     

2株草螺菌的鉴定及其对煤矸石胁迫下香根草的促生作用

【背景】植物-微生物联合修复技术在减轻环境胁迫作用、增强植物抗性、改善矿区景观等方面发挥重要作用,其中根际促生菌可与植物相互作用,促进植物生长,增强植物对非生物胁迫的耐受性。【目的】鉴定铜尾矿中分离得到的2株根际细菌,研究其对植物生长的促生特性,测定2株菌的接种对于煤矸石胁迫下香根草的影响。【方法】对铜尾矿中分离得到的2株菌进行16S rRNA基因序列鉴定和扫描电子显微镜观察,对菌株的促生特性进行测定,并将其分别接种于覆土5 cm的煤矸石和掺土10%的煤矸石中生长的香根草根际,测定2个月后香根草的理化指标和生理学指标。【结果】菌株P5-11和P5-19经鉴定均为草螺菌(Herbaspirillum),2株菌均具有固氮、溶磷、产吲哚乙酸(Indole-3-Acetic Acid,IAA)和产铁载体的特性,其中P5-19的产吲哚乙酸能力约为P5-11的2倍,具有较好的促生能力;2株菌均能提高香根草的株高、生物量、氮积累量和抗氧化酶活性,并降低丙二醛积累量。【结论】2株草螺菌均具有良好的促生特性,能够促进煤矸石胁迫下香根草的生长发育,这不仅为促生菌肥的研制提供了优良菌种,也为香根草在矿区生态恢复中的应用提供了参考价值。     

Diversity of free-living nitrogen-fixing microorganisms in the rhizosphere and non-rhizosphere of pioneer plants growing on wastelands of copper mine tailings

The composition of free-living nitrogen-fixing microbial communities in rhizosphere and non-rhizosphere of pioneer plants growing on wastelands of copper mine tailings was studied by the presence of nifH genes using Polymerase Chain Reaction-Denatured Gradient Gel Electrophoresis (PCR-DGGE) approach. Eleven rhizosphere tailing samples and nine non-rhizosphere tailing samples from six plant communities were collected from two wastelands with different discarded periods. The nested PCR method was used to amplify the nifH genes from environmental DNA extracted from tailing samples. Twenty-two of 37 nifH gene sequences retrieved from DGGE gels clustered in Proteobacteria (α-Proteobacteria and β-Proteobacteria) and 15 nifH gene sequences in Cyanobacteria. Most nifH gene fragments sequenced were closely related to uncultured bacteria and cyanobacteria and exhibited less than 90% nucleotide acid identity with bacteria in the database, suggesting that the nifH gene fragments detected in copper mine tailings may represent novel sequences of nitrogen-fixers. Our results indicated that the non-rhizosphere tailings generally presented higher diversity of nitrogen-fixers than rhizosphere tailings and the diversity of free-living nitrogen-fixers in tailing samples was mainly affected by the physico-chemical properties of the wastelands and plant species, especially the changes of nutrient and heavy metal contents caused by the colonization of plant community.     

Spatial variability of soil nutrients and microbiological properties after the establishment of leguminous shrub Caragana microphylla Lam. plantation on sand dune in the Horqin Sandy Land of Northeast China

The objective of this study is to determine the spatial variability of nutrients, microbial biomass, and enzyme activities of soil due to the establishment of shrub plantation on moving sandy dunes, as part of an effort to understand the microenvironmental factors that control the soil microbiological properties. Caragana microphylla Lam., an indigenous leguminous shrub, is the dominant plant species used to control desertification in the semi-arid Horqin Sandy Land of Northeast China. In a 26-year-old C. microphylla plantation, soil samples were collected from three soil depths (0-5 cm, 5-10 cm, and 10-20 cm), three slope positions (windward slope, top slope, and leeward slope), and two microsites (under shrubs and between shrubs). The results showed significant differences in soil EC, nutrient content (except for total K), microbial biomass C and N, and the activities of dehydrogenase, urease, and protease at different slopes, soil depths, and microsites. Significant differences in pH at different microsites and slopes, soil moisture and polyphenol oxidase activity at different soil depths and slopes, and activities of phosphomonoesterase and nitrate reductase at different soil depths were also observed. The soil nutrient contents and microbiological activities were greater in the surface soil layer and decreased with the increase of soil depth. Soil organic C, total N, total P, available P and K, microbial biomass C and N, and the activities of enzymes tested (except for protease) under shrubs were higher than those in between shrubs. Furthermore, significant correlations among soil organic C, microbial biomass C and N, the activities of phosphomonoesterase, dehydrogenase, urease, protease, and nitrate reductase were observed, and correlations were also found among EC, total N, total P, available P and K, enzyme (except for polyphenol oxidase) activities, and microbial biomass C and N contents. These results suggest that microenvironmental factors (slope, soil depth and microsite) have significant influences on the spatial distribution of soil nutrients and microbiological properties when the C. microphylla sand-fixing plantation is established in the moving sand dunes in the Horqin Sandy Land.     

Microbial communities in a porphyry copper tailings impoundment and their impact on the geochemical dynamics of the mine waste

The distribution and diversity of acidophilic bacteria of a tailings impoundment at the La Andina copper mine, Chile, was examined. The tailings have low sulfide (1.7% pyrite equivalent) and carbonate (1.4% calcite equivalent) contents and are stratified into three distinct zones: a surface (0-70-80 cm) 'oxidation zone' characterized by low-pH (2.5-4), a 'neutralization zone' (70-80 to 300-400 cm) and an unaltered 'primary zone' below 400 cm. A combined cultivation-dependent and biomolecular approach (terminal restriction enzyme fragment length polymorphism and 16S rRNA clone library analysis) was used to characterize the indigenous prokaryotic communities in the mine tailings. Total cell counts showed that the microbial biomass was greatest in the top 125 cm of the tailings. The largest numbers of bacteria (10(9) g(-1) dry weight of tailings) were found at the oxidation front (the junction between the oxidation and neutralization zones), where sulfide minerals and oxygen were both present. The dominant iron-/sulfur-oxidizing bacteria identified at the oxidation front included bacteria of the genus Leptospirillum (detected by molecular methods), and Gram-positive iron-oxidizing acidophiles related to Sulfobacillus (identified both by molecular and cultivation methods). Acidithiobacillus ferrooxidans was also detected, albeit in relatively small numbers. Heterotrophic acidophiles related to Acidobacterium capsulatum were found by molecular methods, while another Acidobacterium-like bacterium and an Acidiphilium sp. were isolated from oxidation zone samples. A conceptual model was developed, based on microbiological and geochemical data derived from the tailings, to account for the biogeochemical evolution of the Piuquenes tailings impoundment.     

铜陵铜尾矿废弃地生物土壤结皮中的蓝藻多样性

生物土壤结皮是生态系统原生演替过程中的一个早期阶段,在铜陵铜尾矿废弃地自然生态恢复过程中生物土壤结皮在尾矿废弃地表面广泛分布.以生长在铜陵杨山冲和铜官山2处铜尾矿废弃地的生物土壤结皮为研究对象,运用常规培养方法和变性梯度凝胶电泳技术(PCR-DGGE)对不同群落生物土壤结皮中的蓝藻多样性及优势类群进行研究.结果表明2种研究方法所获得的蓝藻种类组成具有明显差异.显微观察结果表明常规培养试验中主要蓝藻类群为微囊藻属(Microcystis)、色球藻属(Chroococcus)、颤藻属(Oscillatoria)、念珠藻属(Nostoc)和浮鞘丝藻属(Planktolyngbya),其中优势种类主要为铜绿微囊藻(Microcystis aeruginosa)、断裂颤藻(Oscillatoria fracta)和细浮鞘丝藻(Planktolyngbya subtilis);提取样品中微生物总DNA,对蓝藻16SrRNA进行PCR-DGGE分析,回收DGGE图谱中24个条带进行测序分析,结果显示,所有序列与GenBank数据库中的近缘蓝藻的相似性系数均在93％以上,其中优势蓝藻类群主要隶属于微鞘藻属(Microcoleus)和细鞘丝藻属(Leptolyngbya),裸地(YL)处和木贼群落下尾矿表面(YM)的生物土壤结皮中优势蓝藻类群主要为微鞘藻属,而黄色真藓-藻类混合结皮(YT)和白茅群落( YB,TG)下的生物土壤结皮中的优势类群主要隶属于细鞘丝藻属.     

Effect of Monospecific and Mixed Sea-Buckthorn (Hippophae rhamnoides) Plantations on the Structure and Activity of Soil Microbial Communities

This study aims to evaluate the effect of different afforestation models on soil microbial composition in the Loess Plateau in China. In particular, we determined soil physicochemical properties, enzyme activities, and microbial community structures in the top 0 cm to 10 cm soil underneath a pure Hippophae rhamnoides (SS) stand and three mixed stands, namely, H. rhamnoides and Robinia pseucdoacacia (SC), H. rhamnoides and Pinus tabulaeformis (SY), and H. rhamnoides and Platycladus orientalis (SB). Results showed that total organic carbon (TOC), total nitrogen, and ammonium (NH₄⁺) contents were higher in SY and SB than in SS. The total microbial biomass, bacterial biomass, and Gram⁺ biomass of the three mixed stands were significantly higher than those of the pure stand. However, no significant difference was found in fungal biomass. Correlation analysis suggested that soil microbial communities are significantly and positively correlated with some chemical parameters of soil, such as TOC, total phosphorus, total potassium, available phosphorus, NH₄⁺ content, nitrate content (NH₃⁻), and the enzyme activities of urease, peroxidase, and phosphatase. Principal component analysis showed that the microbial community structures of SB and SS could clearly be discriminated from each other and from the others, whereas SY and SC were similar. In conclusion, tree species indirectly but significantly affect soil microbial communities and enzyme activities through soil physicochemical properties. In addition, mixing P. tabulaeformis or P. orientalis in H. rhamnoides plantations is a suitable afforestation model in the Loess Plateau, because of significant positive effects on soil nutrient conditions, microbial community, and enzyme activities over pure plantations.