人为干扰对桂西北喀斯特生态系统土壤有机碳、氮、磷和微生物量剖面分布的影响

在桂西北喀斯特地区以原生林地为对照,选取了玉米-红薯轮作地、放牧+火烧草地和自然恢复地3种不同人为干扰的生态系统,研究土壤剖面养分、微生物活性对干扰强度的响应。结果表明,土壤有机碳和全氮随土壤深度的增加而降低,全磷变化较小,说明磷素主要来源于土壤母质,且淋溶作用较小;原生林地0-30 cm土壤有机碳、全氮、全磷、微生物量碳、氮、磷、碱解氮显著高于自然恢复地、放牧+火烧草地和玉米-红薯轮作地(p0.05),说明原生生态系统可维持较高的土壤肥力和微生物活性;3种人为干扰的生态系统,自然恢复地和放牧+火烧草地0-5 cm土壤有机碳含量显著高于玉米-红薯轮作地,说明自然恢复有利于提高表层土壤肥力和有机碳积累;玉米-红薯轮作地表层0-15 cm土壤全磷和有效磷含量显著高于自然恢复地和放牧+火烧草地,主要受施肥影响;60-100 cm,原生林地、自然恢复地和放牧+火烧草地土壤全氮显著高于玉米-红薯轮作地,说明农耕旱地土壤下层氮受雨水影响较大,淋失严重。自然恢复地和放牧+火烧草地表层(0-15 cm)土壤碱解氮、微生物量碳、氮、磷显著高于玉米-红薯轮作地,说明减少人为干扰和实行自然恢复可显著提高土壤氮的有效性和微生物活性。因此,提高农田管理水平、施行保护性耕作,推行自然恢复、减少人为干扰是提高喀斯特退化生态系统土壤生产力和增加土壤有机碳积累的有效措施。     

不同干扰对黄土区典型草原土壤理化性质的影响

以黄土区云雾山典型草原为研究对象,分析4种干扰方式(封育、封育+施肥、封育+火烧和放牧)对土壤理化性质的影响。结果表明:(1)在0-50cm土层,封育、封育+施肥、封育+火烧地的土壤容重随土层深度的增加而增加,放牧地的土壤容重随土层深度的增加而减少。其中,在0-20cm土层,放牧显著高于其他3种干扰方式,封育+施肥显著低于其他3种干扰方式;(2)在0-50cm土层,4种干扰方式的土壤含水量随土层深度的增加而增加,依次为封育+火烧>封育+施肥>封育>放牧;(3)在0-50cm土层,4种干扰方式的土壤有机质、全氮和速效钾含量随土层深度的增加而减少;火烧地的全磷含量随土层深度增加而减少,其他3种干扰方式的全磷含量呈现先增加后减少的趋势。在0-30cm土层,4种干扰方式土壤养分(有机质、全氮、全磷和速效钾)含量为封育+施肥>封育+火烧>封育>放牧,且放牧会导致0-10cm所有养分含量显著降低(P<0.01)。(4)4种干扰方式,有机质与全氮、全磷和速效钾呈极显著的正相关关系(P<0.01)。     

火干扰对径流及土壤侵蚀的模拟研究

为了对比森林火灾与计划烧除两种火干扰对地表径流与土壤侵蚀的影响,在湖南省株洲市高枧林场马尾松林设置22块样地,通过模拟降雨试验,高强度火烧样地的径流比中强度、低强度样地或未烧区大,且差异显著,但是中强度与低强度火烧样地间的径流差异不明显;火干扰对土壤斥水性的影响主要集中在地表1~3 cm的土壤;马尾松高强度火烧样地产沙量比计划烧除样地大30%,分别是中强度火烧样地的5倍、低强度火烧样地的10倍。产沙量与火干扰后土壤裸露的比例正相关,火后土壤裸露面积越大,产沙量越大;坡度对产沙量的影响不明显,研究结果为森林火灾后火灾迹地土壤改良及植被恢复提供理论依据。     

纳帕海高原湿地土壤微生物群落对土地利用方式改变的响应

【目的】探明高原湿地不同土地利用方式下土壤理化性质的改变对微生物群落结构及多样性的影响,为纳帕海高原湿地土地利用管理提供理论依据。【方法】以人类活动干扰下形成的放牧草地和耕地为研究对象,以自然沼泽湿地为对照,运用Illumina高通量测序技术比较不同土地利用方式下土壤微生物群落结构和多样性特征,并采用Mantel test分析土壤理化环境改变对土壤微生物群落的影响。【结果】(1)相较于自然沼泽湿地,耕作与放牧显著降低了土壤含水量、有机质、全氮和速效氮,却提高了全磷、碳氮比和容重（P <0.05）。(2)耕作和放牧显著增加土壤细菌与真菌α多样性（P <0.05）,三种利用方式间β多样性差异显著（P <0.01）。(3)耕作和放牧显著改变细菌和真菌群落结构,其中耕作使变形菌门、厚壁菌门和绿弯菌门相对丰度显著增加21.07%～123.61%,酸杆菌门、放线菌门和芽单胞菌门显著减小62.7%～75.29%;耕作使子囊菌门、担子菌门、接合菌门相对丰度显著减小71.33%～96.47%,未分类真菌门相对丰度显著增加722.97%;放牧使细菌浮霉菌门和疣微菌门增加57.46%、17...     

高寒地区不同土地利用方式对土壤抗风蚀能力的影响

采用风洞实验对祁连山东段天祝高寒地区天然放牧草地、退耕自然恢复草地、翻耕地、免耕留茬地和人工种植多年生草地5种土地利用方式下的原状土抗风蚀能力进行了研究。结果表明,多年生草地的临界侵蚀风速最大,免耕留茬地和天然草地次之,翻耕地和退耕自然恢复地最小;风蚀速率与风速变化成正相关,随着风速增大,风蚀速率相应增加;风蚀速率和风速变化服从幂函数变化关系。在近地表0-20cm范围内,降尘量总量依次为退耕自然恢复地翻耕地天然放牧草地多年生草地免耕留茬地;土壤抗风蚀能力表现为退耕自然恢复地天然放牧草地多年生草地免耕留茬地翻耕地。     

藏北高寒草甸土壤线虫群落对围封及自由放牧的响应

为了解放牧干扰对藏北高寒草甸的影响,以及连续围封措施对草地的恢复作用,2013—2015年连续3年对那曲县围封、自由放牧天然高寒草甸土壤线虫群落进行取样调查及数据分析。结果表明:围封、放牧样地的线虫个体数量在年际间的变化均较明显,植食性线虫是整个线虫群落个体数量变化的主要贡献者;围封样地的线虫个体密度、多样性指数H′、丰富度指数SR,以及优势度指数λ的年际变化幅度均大于放牧样地;食细菌性线虫个体数量及线虫通路比值(NCR)表明放牧样地的有机质转化效率高于围封样地;成熟度指数(MI)、植物寄生线虫指数(PPI)分析表明,所研究区域经5年围封,高寒草甸生态系统稳定性没有明显的提高,相反,现有放牧强度维持或者增加了线虫群落的物种多样性,利于物种共存和草地生态系统稳定性的维持。     

放牧干扰后自然恢复的退化沙质草地土壤性状的空间分布

用地统计学的方法 ,研究了科尔沁沙质退化草地不同强度放牧干扰 (重度放牧和适度放牧 )后自然恢复过程中 0～ 15cm土层土壤有机碳、全氮、pH和电导率在 10m尺度上的空间异质性特征。结果表明 ,重牧后的恢复草地比适度放牧后的恢复草地呈现出显著低的有机碳和全氮含量及其显著高的变异性。在取样尺度的空间分布上均表现出显著的空间结构特征 ,自相关尺度分别为 2 2 2～ 2 9 4m和 2 5 5～ 39m ,结构性方差占样本方差的 87 2 %～ 88 2 %和 6 5 5 %～ 85 9%。全氮的自相关尺度大于有机碳。土壤pH和电导率在取样的尺度内不存在局部格局 ,而可能受更大尺度的格局控制。放牧引起的植被斑块状分布和沙化裸斑的出现是土壤碳、氮空间变异的主要因素 ;土壤异质性尺度的改变又可能影响着植被的恢复演替和分布格局。     

放牧与围封对沙漠化草地土壤轻组及全土碳氮储量的影响

测定分析了长期放牧与围封对科尔沁沙漠化草地土壤轻组及全土碳氮储量的影响.结果表明:(1)围封与长期放牧草地0-100 cm土壤轻组有机质占土壤质量的比例分别为0.148%和0.053%,围封比放牧增加181%;土壤轻组含量与全土有机碳和氮含量存在极为显著的线性正相关关系;(2)围封草地0-100 cm土壤轻组碳和氮储量分别为271.38,20.36 g/m2,比长期放牧分别增加130%和164%;围封草地全土碳和氮储量分别为1155.86,125.99 g/m2,比长期放牧分别增加58%和24%;(3)轻组有机碳和氮占全土有机碳和氮储量的比例,围封分别为23.48%和16.16%,放牧分别为16.05%和7.59%;(4)围封恢复对轻组有机质的影响主要发生在表层土壤,围封0-10 cm层土壤轻组含量比长期放牧增加537%,10-20 cm层增加216%,但20 cm深度以下两个样地间无统计学上的显著差异.     

基于高通量测序的两种植被恢复类型根际土壤细菌多样性研究

为研究库布齐沙地生态恢复过程中不同植被恢复类型土壤微生物细菌群落结构、多样性的变化特征,以流动沙地为对照,运用高通量测序技术,对自然恢复的油蒿群落、人工种植的中间锦鸡儿群落根际和非根际土壤细菌多样性进行了研究,并分析了土壤理化性质对其分布的影响。结果表明:(1)与流沙对照相比,两种植被恢复类型对细菌多样性产生了正效应,细菌群落丰度、多样性和均匀度明显增加。其中,自然恢复的油蒿群落土壤细菌丰度高于人工种植的中间锦鸡儿群落;(2)变形菌门、酸杆菌门和放线菌门为研究区土壤中的优势细菌类群,其中变形菌门在各样地丰度比例最高,变形菌的4个亚群变化趋势一致,α-变形菌相对含量在油蒿和中间锦鸡儿群落根际土壤中明显增加,尤其是自然恢复的油蒿群落根际土壤中α-变形菌得到了很好的恢复;(3)土壤有机质、全氮、速效氮、速效钾含量和土壤含水量是影响土壤细菌群落丰度和多样性的主要土壤因子,典型相关分析表明土壤有机质、全氮、全钾、速效钾、速效氮含量对于研究区土壤细菌群落遗传多样性的变化起着重要作用。     

放牧对黄土高原典型草原冬季牧场甲烷氧化菌类群及活性的影响

土壤甲烷氧化菌是大气甲烷（CH4）氧化的唯一生物汇。放牧能通过影响甲烷氧化菌的丰度和多样性来调控草地土壤的甲烷氧化活性。采集黄土高原典型草地冬季牧场中不同强度连续放牧的土壤样本,通过室内培养和高通量测序的方法测定不同放牧强度下土壤甲烷氧化活性以及土壤甲烷氧化菌的组成和丰度变化规律。结果表明,该草地是CH4汇,中放牧强度（MG）和高放牧强度（HG）增加了甲烷氧化速率。同时,与未放牧（CK）相比, MG和HG的甲烷氧化菌的平均丰度也显著增加。高通量测序结果显示,放牧对甲烷氧化菌的多样性有显著影响,不同放牧强度下均以USCγ为优势类群,同时存在少量的甲基暖菌属（Methylocaldum）和甲基孢囊菌属（Methylocystis）。皮尔森（Pearson）相关性分析表明,甲烷氧化速率（MOR）与土壤的水分含量和硝态氮的含量存在显著正相关（P < 0.05）,与USCγ的绝对数量存在极显著的正相关关系（P < 0.01）,这说明USCγ在该草地甲烷吸收过程中起主要作用。本研究证明了放牧可提升黄土高原典型草地的甲烷汇功能。     

Variation in diazotrophic community structure in forest soils reflects land use history

Microbial nitrogen fixation is an important source of nitrogen in soils of both old and secondary-growth forests. Considering that many soils, which today support secondary-growth forests were once under cultivation, no studies have examined how this kind of disturbance history affects contemporary populations of nitrogen-fixing microbes in forest soils. In the work presented here, we compare secondary-growth forest sites, which were under cultivation more than 150 years ago, to old-growth forest sites in Cadwell Forest, Massachusetts. For each site, nitrogenase activity was measured and the diversity of the nifH gene pools was examined. Three sites with prior agricultural history exhibited higher nitrogenase activity and were dominated by diazotrophs closely related to the α- and γ-Proteobacteria. In contrast, lower nitrogenase activity and the dominance of the anaerobic Cluster III diazotrophs characterized the three old forest sites. Further analyses of species overlap among all six sites revealed that the diazotrophic composition was closely related to previous management history, with agricultural sites clustering together and separate from old forest sites, independent of the proximity between sites. By specifically targeting one of the main functions of microbial communities in soils, the activity and diversity of nitrogen-fixing microorganisms, this work points to a long-lasting effect of former agricultural activities on secondary-growth forest soils, more than one hundred years after succession.     

放牧干扰对岷江上游山地森林-干旱河谷交错带土壤微生物量及呼吸熵的影响

选择岷江上游理县山地森林/干旱河谷交错带地区人工刺槐林、人工杨柳林、草地和锥花小檗灌丛这4种植被类型为研究对象,对4种植被下的土壤微生物量及呼吸熵对放牧干扰的响应进行了研究。以距牧道距离远近的不同设置了3种放牧干扰强度处理,分别对各植被类型3种放牧干扰强度的土壤进行了分析。结果表明,在各植被类型下,土壤有机碳(SOC)和土壤微生物量碳(MBC)含量随放牧干扰强度的增加而降低。各植被类型下表层土壤呼吸熵值(qCO2)值随放牧压力的增加而增大(除灌丛中度干扰外),增加幅度为15.14%~100.54%,说明放牧干扰使微生物体的周转率加快,对SOC的利用率降低,释放的CO2增多,土壤碳保存率降低。     

The effect of soil compaction, profile disturbance and fertilizer application on the growth of eucalypt seedlings in two glasshouse studies

Soil damage, compaction and displacement, during logging or clearing and cultivation affects both soil physical and chemical properties and reduces growth of regenerated or planted tree seedlings. Understanding the factors involved will aid management and set limits for indicators of sustainable management in eucalypt forests. In the first of two glasshouse studies, three Eucalyptus species were grown for 110 days in soils from six forest sites in Tasmania, Australia. Sites sampled ranged from low rainfall dry forest to very high rainfall wet forest. Soil was collected from three soil depths, in 10 cm increments to 30 cm, each packed in pots to four different bulk densities, ranging from that present in undisturbed field sites to that plus 0.17 g cm⁻³. In the second study Eucalyptus globulus Labill. seedlings were grown in soil collected from disturbed and undisturbed sites, packed to two bulk densities, and fertilized with combinations of N and P. Increasing soil compaction, in Study 1, caused a proportional decrease in final mass of seedlings of up to 25%. Growth on soil from lower horizons (10–30 cm) averaged only 41% of that on topsoil, a significantly greater restriction of growth than that achieved through compaction. It was concluded that topsoil displacement and profile disturbance was a more significant form of soil damage than compaction. Above-ground dry weight of seedlings was most strongly correlated with soil total N but poorly correlated with other macronutrients. Growth of E. globulus seedlings grown on disturbed soils, in Study 2, averaged 30% of that on undisturbed sites. With added P and N on undisturbed sites growth averaged seven times that of the unfertilized seedlings indicating a general deficit of available P and N on the three soils tested. On soils from disturbed areas, there was also a response to fertilizing with N and P together but the response varied on the three soils. The effects of profile disturbance were ameliorated with fertilizer applications on only one of the soils. The results highlighted the importance of retaining topsoil in situ during forest operations.     

放牧对荒漠草原土壤养分及微生物量的影响

[目的]探讨不同放牧强度对荒漠草原植被多样性、土壤理化性状、土壤养分及土壤微生物量的影响。[方法]以围封禁牧草地为对照,采用野外调查和室内分析的方法,对不同放牧强度下的草地土壤及植被展开调查。[结果]随放牧强度的增加,荒漠草原植被盖度、物种多样性、地上生物量、土壤养分和微生物量显著降低,土壤容重和pH值呈增加趋势,土壤电导率呈先增加后降低趋势,地下生物量则没有明显变化趋势;在植被作用下土壤养分和微生物量垂直方向表现递减规律并且在表层富集,"表聚性"较为明显;在放牧干扰下土壤全磷变异系数最高;放牧并没有改变荒漠草原土壤养分和微生物量的垂直分布特征;相关分析表明,放牧干扰下土壤微生物量与土壤养分之间具有较强的相关性,二者与土壤含水量也有较强的相关性。[结论]放牧强度对土壤全磷的空间变异影响较大,并且土壤微生物量对于放牧干扰的敏感性高于土壤养分全量;土壤养分和微生物量等地下生态系统各指标之间具有统一性。     

东祁连山不同干扰生境草地土壤养分时空变化特征

为探究东祁连山不同干扰高寒草地土壤养分及其生态化学计量学特征时空变化特征规律。研究了2017年8月在东祁连山不同干扰高寒草地土壤养分含量及其生态计量学特征,以及与2003年和2011年在相同地点、相同研究方法对该地区的土壤理化性质进行比较。结果表明:(1)在同一干扰生境不同土层下,土壤pH、电导率、含水量、土壤全量和速效养分均随着土层深度增加而逐渐减小,变化各异;在同一土层不同干扰生境下土壤养分间变化差异各不相同。(2)不同干扰生境土壤C/N为7.64~18.21,与我国陆地土壤平均值(10~12)基本接近,土壤C/P和N/P分别为109.16~144.79和7.52~15.65,远高于中国陆地土壤的C/P平均值52.7和N/P平均值3.9。(3)主成分分析结果表明,土壤理化性质(pH、电导率、含水量、全磷、全钾、速效磷、有机质、有机碳和速效氮)和土壤生态化学计量比(C/N、C/P和N/P)可以敏感的反映出不同干扰对草地土壤质量影响状况。土壤质量综合评价可知,不同干扰生境下草地土壤质量水平差异较大,多年生草地土壤质量较高,围栏外草地质量最差,在0-20,20-40cm土层中,均表现为多年生围栏内一年生围栏外。(4)与2003年和2011年相比较,4种不同干扰生境高寒草地土壤pH和含水量,总体呈上升的趋势,土壤有机质、全氮和全磷含量则呈现出明显下降趋势。综上,放牧干扰、人为种植对东祁连山4种干扰生境草地土壤养分含量有很大影响,为此应对该地区草地的利用和保护给予足够的重视,合理利用和科学管理草地。     

市域尺度的稀有濒危土壤类型的界定与评价——以郑州市为例

在当今世界城市化高速发展的背景下,土壤资源的保护也越来越受到人们的关注,土壤多样性骤减也成为了全球关注的焦点,界定和评价稀有濒危土壤对于保护土壤资源及其多样性具有非常重要的指导意义。本文以郑州市为例,应用土壤类型密度和土壤多样性两种多样性测度方法分别对郑州市1 km×1 km和5 km×5 km网格尺度下基于不同分类级别的土壤空间多样性分布格局进行了分析和定量化研究;利用1988、2001、2007和2013年4期遥感资料进行土地利用分类,结合基于第二次土壤普查的1∶20万郑州市土壤图,采用多时相连续对比法对郑州市近25年来土地利用变化对土壤的扰动情况进行了分析;结合土壤多样性方法和传统评价方法界定和评价了稀有濒危土壤。结果表明,郑州市土壤整体分布较为均匀,且随着分类单元级别的降低,构成组分多样性指数升高,即分类越细,土壤类型分布越均匀;1988~2013年郑州市土壤受到非农建设扰动剧烈,干扰比例为16.01%,随着时间的推移,土壤受扰动的速度是呈上升趋势的;稀有土属有16种,濒危土属有2种,稀有濒危土属有4种。截止2013年濒危土属整体受到扰动比例高达35.38%,而稀有土属受到扰动比例为8.76%。     

Succession and Phylogenetic Profile of Eubacterial Communities in Rice Straw Incorporated into a Rice Field: Estimation by PCR-DGGE Analysis

PCR-DGGE analysis followed by sequencing was conducted to estimate the succession and the phylogenetic profile of the eubacterial communities responsible for the decomposition of rice straw (RS) that was incorporated into a rice field. Leaf sheath and leaf blade parts were separately put in nylon mesh bags, and were placed in the rice field soil under drained conditions during the off-cropping season and under flooded conditions after transplantation of rice. In addition, RS samples that had been placed under drained conditions in the off-cropping season were placed again in flooded rice field soil after transplantation of rice. DGGE patterns of the bacterial communities in the RS samples were classified into two groups, namely leaf sheaths and leaf blades. Principal component analysis of the DGGE patterns revealed the succession along with the duration of placement. These results indicated that the RS part (sheath or blade) mainly determined the structure of the bacterial communities responsible for the RS decomposition, followed by the duration of placement. Sequence analysis of the characteristic DGGE bands indicated that most of the closest relatives associated with the bands belonged to α-, β-, γ-, and δ-Proteobacteria, CFB group, and Spirochaetes. Some bands were closely related to Acidobacteria and Verrucomicrobia. CFB members and α-Proteobacteria predominated commonly in both RS parts, while γ- and δ-Proteobacteria, and Spirochaetes and β-Proteobacteria specifically colonized sheath and blade parts, respectively. In addition, Proteobacteria and CFB members characterized the differences in the bacterial communities under flooded or drained conditions. These results suggest that Proteobacteria, CFB group, and Spirochaetes were responsible for RS decomposition in rice field soil under both flooded and drained conditions.     

Phylogenetic characterization of dwarf archaea and bacteria from a semiarid soil

Microscopic studies have shown that most microbes exist in soils as dwarf cells that are thought to be an adaptation to nutrient limitation. Most dwarfs are uncultured by current approaches and have not been identified phylogenetically. Only a few dwarf bacteria have been isolated in culture and dwarf archaea have received little study. We selected a semiarid creosotebush shrubland site for studying dwarf microorganisms because arid and semiarid soils are generally nutrient-poor. Soils were collected beneath creosotebush canopies and in open areas between shrubs. Cells were eluted in sodium pyrophosphate and filtered with a 0.45-μm pore-size filter. Filtrate DNA was extracted, PCR-amplified using universal bacterial and archaeal 16S rDNA primers, cloned, RFLP-screened, and sequenced. The eluted cell filtrates were also inoculated into R2B medium. After incubation, cultures were filtered to select against populations of dwarfs that formed large cells in the presence of nutrients (pleomorphic dwarfs) and to select for populations that retained dwarf size (intrinsic dwarfs). Dwarf archaea and bacteria were present in the initial filtrate and in the cultures. A single dwarf archaeon (SevArch-01) that is related to other soil Crenarchaeota sequences was found in the initial filtrates and in subsequent filtrate cultures, indicating an intrinsically dwarf archaeon. Dwarf bacteria fell into four bacterial phyla: Proteobacteria, Firmicutes, Actinobacteria, and the TM-7 group. Intrinsically dwarf bacteria in enrichment cultures were identified as α- and β-Proteobacteria. Dwarf bacteria related to Arthrobacter, Propionibacterium, and other actinobacteria were detected. Several sequences showed no close relationships to any microorganisms that have been grown in culture.     

The microbial diversity and structure in peatland forest in Indonesia

The microbial community structure and function under forest in tropical peatlands are poorly understood. In this study, we investigated the microbial community structure and diversity in natural peat swamp forest soil, disturbed peat soil and mineral soil in Central Kalimantan, Indonesia, using 454 pyrosequencing. The results showed that the natural peat soil had the greatest fungal species richness (Chao1), which was significantly (p < .05) larger than that in the other two soils. Community structure of both fungi and bacteria in natural peat soil differed significantly from that in the disturbed peat soil (p = .039 and p = .045, respectively). Ascomycota (40.5%) was the most abundant phylum across the three soils followed by Basidiomycota (18.8%), Zygomycota (<0.1%) and Glomeromycota (<0.1%). The linear discriminant analysis with effect size (LEfSe) showed that Ascomycota (p < .05) and genus Gliocephalotrichum (p < .05) dominated in natural peat soil. Functionally, pathotrophs were more abundant in disturbed peat soil (p < .05). Proteobacteria (43.8%) were the most abundant phylum followed by Acidobacteria (32.6%), Actinobacteria (9.8%), Planctomycetes (1.7%). Methylocystis, Telmatospirillum, Syntrophobacter, Sorangium and Opitutus were the more abundant genera in disturbed peat soil, whereas Nevskia and Schlesneria were more abundant in mineral soil and natural peat soil, respectively. The natural peat forest soil supported a more diverse microbiology; however, the land use of such a soil can change its microbial community structure. The results provide evidence that the disturbance of tropical peat land could lead to the introduction and spread of a large number of fungal diseases     

Characterization of bacterial diversity at different depths in the Moravia Hill landfill site at Medellín, Colombia

A combination of culture-dependent and culture-independent methods was used to assess bacterial diversity at different depths within a former solid waste dump in Medellín, Colombia. Sampling sites included a densely populated area, which is built upon 40 m of solid waste (domestic, industrial, agricultural, and medical). The soil and leachate contain high levels of contaminants and the natural soil is highly disturbed with solid anthropogenic materials, disrupting natural aggregation and resulting in a loose, porous matrix with irregular aggregate structure. The unusual physical structure and contaminant levels at the site made it unclear if the indigenous bacterial community would possess the complexity commonly observed for natural soils, and thus may limit potential for remediating the site using monitored natural attenuation. Bacterial diversity patterns were determined through 16S-TTGE and T-RFLP at depths of 0, 10, 20 and 30 m. Abundance and diversity patterns, as estimated by number and intensity of terminal restriction fragments and TTGE bands, varied among the 4 different depths, showing more complex patterns in deeper samples (20 and 30 m), which also contained greater concentrations of organic carbon. General diversity patterns were dominated by the phylum Proteobacteria (λ, β, and α divisions). These findings were reinforced by analysis of the culturable fraction able to use n-hexadecane as sole carbon source, in which the genera Acinetobacter sp. (λ-Proteobacteria) was dominant. This research offers new clues regarding bacterial diversity patterns through different depths in polluted environments with unique physicochemical conditions, suggesting that bacterial diversity profiles may be highly influenced by the nature of pollutants present. Additionally, results imply that the culturable fraction at the site has a very important role in the community.