若尔盖高寒湿地干湿土壤条件下微生物群落结构特征

土壤水分含量的空间异质性是引起湿地生态系统结构和功能空间变异的关键因素。目前有关低纬度高寒湿地土壤水分对微生物群落结构影响的研究较少。于2007年4月(冷季)和8月(暖季)采集若尔盖高寒湿地常年淹水和无淹水两种水分条件的土壤样品,利用磷脂脂肪酸方法分析其微生物群落结构。结果表明,土壤微生物总生物量、细菌生物量、革兰氏阳性细菌及革兰氏阴性细菌生物量均表现为常年淹水土壤高于无淹水土壤,且4月份高于8月份;与土壤通气量关系密切的真菌、放线菌,其生物量表现为无淹水土壤显著高于常年淹水土壤;反映群落组成的真菌:细菌磷脂脂肪酸比值也表现为无淹水土壤显著高于常年淹水土壤。磷脂脂肪酸的主成分分析表明,水分条件不同的两种土壤中微生物群落结构显著不同,季节变化并未引起土壤微生物群落结构的改变。     

不同种植年限对花椒根际土壤理化性质和微生物群落的影响

为揭示不同种植年限对花椒根际微生态系统的影响,利用磷脂脂肪酸（PLFAs）生物标记法结合土壤养分和酶活性分析,研究了种植年限1、15、30 a的花椒根际土壤的理化性质和微生物群落变化。结果显示,随着种植年限的增加,土壤pH和多酚氧化酶活性呈下降趋势,土壤速效钾和速效磷在15、30 a时显著增加。土壤微生物总PLFA、真菌、革兰氏阴性细菌（G^-）PLFA含量均随种植年限呈增加趋势,30a时达到最大,分别为401.95、88.14、118.61 μg·g^-1。革兰氏阳性细菌（G ⁺ ）和放线菌PLFA含量随种植年限呈先增后降趋势。细菌/真菌和G⁺/G^-随种植年限增加呈下降趋势,与1 a相比,30 a时分别下降34.14%、38.87%。土壤pH与总PLFA、G^-、细菌、真菌呈显著负相关,与G ⁺ /G^-呈显著正相关;多酚氧化酶活性与真菌呈显著负相关,与细菌/真菌、G ⁺ /G^-呈显著正相关。本研究表明：花椒根际理化性质、酶活性和微生物群落结构随种植年限增加发生了显著变化,根际土壤pH、速效磷、速效钾、多酚氧化酶的变化是影响土壤微生物群落与组成的主要环境因子,真菌和G^-的增加及多酚氧化酶活性的降低可能是诱导花椒根腐病发生的重要原因。     

中亚热带地区米槠天然林土壤微生物群落结构的多样性

为了解土壤微生物群落的结构,采用磷脂脂肪酸方法对武夷山和建瓯的米槠(Castanopsis carlesii)天然林土壤微生物群落的结构多样性进行了研究。结果表明,两地米槠天然林的土壤微生物群落组成十分丰富,多样性指数、丰富度指数和均匀度指数分别为2.92~3.01、25.84~28.23 和0.88~0.90。0~10 cm土层的磷脂脂肪酸总量、细菌特征脂肪酸、真菌特征脂肪酸、放线菌特征脂肪酸、革兰氏阳性菌和阴性菌特征脂肪酸含量均高于10~20 cm土层的,且建瓯万木林自然保护区的高于武夷山国家级自然保护区。10~20 cm土层的革兰氏阳性菌/革兰氏阴性菌高于0~10 cm土层的;细菌特征脂肪酸含量显著高于真菌,表明细菌在土壤微生物群落结构中处于优势地位。主成分分析表明,土壤微生物群落结构的差异主要是由采样地点的不同引起。     

氮添加诱导的磷限制改变了亚热带黄山松林土壤微生物群落结构

土壤微生物在陆地生态系统的生物地球化学循环中起着重要作用。然而目前尚不清楚氮(N)添加量及其持续时间如何影响土壤微生物群落结构,以及微生物群落结构变化与微生物相对养分限制状况是否存在关联。本研究在亚热带黄山松林开展了N添加试验以模拟N沉降,并设置3个处理:对照(CK, 0 kg N·hm^-2·a^-1)、低N(LN, 40 kg N·hm^-2·a^-1)和高N(HN, 80 kg N·hm^-2·a^-1)。在N添加满1年和3年时测定土壤基本理化性质、磷脂脂肪酸含量和碳(C)、N、磷(P)获取酶活性,并通过生态酶化学计量分析土壤微生物的相对养分限制状况。结果表明: 1年N添加对土壤微生物群落结构无显著影响,3年LN处理显著提高了革兰氏阳性菌(G⁺)、革兰氏阴性菌(G^-)、放线菌(ACT)和总磷脂脂肪酸(TPLFA)含量,而3年HN处理对微生物的影响不显著,表明细菌和ACT对N添加可能更为敏感。N添加加剧了微生物C和P限制,而P限制是土壤微生物群落结构变化的最佳解释因子。这表明,N添加诱导的P限制可能更有利于部分贫营养菌(如G⁺)和参与P循环的微生物(如ACT)的生长,从而改变亚热带黄山松林土壤微生物群落结构。     

玉米连作及其施肥对土壤微生物群落功能多样性的影响

采用Biolog技术,借助吉林农业大学1984年建立的长期定位试验,以撂荒和非玉米连作(当季作物为芸豆)为对照,研究玉米连作及其不同施肥措施对土壤微生物功能多样性的影响。结果表明,反映土壤微生物活性的平均颜色变化率(AWCD)呈现出以下变化规律:撂荒(UC)非玉米连作(NCC)玉米连作不施肥(CK);玉米连作配施秸秆(S、SN、SNPK)玉米连作配施NPK(NPK)玉米连作不施肥(CK)玉米连作单施N(N)。微生物培养72h活性旺盛,各处理AWCD在0.395—0.732之间,其中撂荒AWCD显著高于非玉米连作和玉米连作不施肥(P0.05);玉米连作配施秸秆明显提高微生物活性,玉米连作配施秸秆(S、SN、SNPK)AWCD是玉米连作不施肥和单施化肥(N、NPK)的1.26—1.62倍。玉米连作不施肥土壤微生物群落多样性指数(H、E、S)低于撂荒处理,但高于非玉米连作处理,非玉米连作提高了土壤微生物优势度指数。玉米连作配施秸秆土壤微生物物种丰富度指数和均匀度指数高于玉米连作不施肥和玉米连作施化肥,玉米连作单施氮肥优势度指数较高,其它多样性指数降低。主成分分析结果表明,不同处理土壤微生物碳源利用特征出现分异:撂荒和玉米连作配施秸秆处理集中在第1主成分正方向,得分系数在2.39—4.17之间,土壤微生物碳源利用特征相似;玉米连作不施肥、玉米连作单施化肥和非玉米连作处理分布在第1主成分负方向,得分系数在-5.43—-1.59之间。土壤微生物利用的碳源主要是糖类、羧酸类、氨基酸和聚合物。玉米连作配施秸秆和撂荒有利于提高土壤微生物代谢活性和土壤微生物群落功能多样性,玉米连作单施化肥尤其单施氮肥土壤微生物活性和功能多样性下降。     

杉木人工林土壤微生物群落结构特征

采用氯仿熏蒸法、稀释平板法和磷脂脂肪酸(phospholipid fatty acid,PLFA)方法,分析了常绿阔叶林转变成杉木人工林后土壤微生物种群数量和群落结构的变化特征.结果表明:常绿阔叶林转变为杉木人工林后,林地土壤的微生物生物量碳、可培养细菌和放线菌数降低.杉木人工林地总PLFAs、细菌PLFAs、真菌PLFAs比常绿阔叶林分别降低了49.4％、52.4％和46.6％,革兰氏阳性和阴性细菌PLFAs远低于常绿阔叶林.杉木人工林根际土壤微生物生物量碳、可培养细菌和放线菌数显著高于杉木人工林林地土壤,根际土壤中总PLFAs、细菌PLFAs、革兰氏阳性和阴性细菌PLFAs的含量也高于林地土壤,但真菌PLFAs和细菌PLFAs之比却低于林地土壤.对土壤微生物群落结构进行主成分分析发现,第1主成分和第2主成分共解释了土壤微生物群落结构变异的78.2％.表明常绿阔叶林与杉木人工林土壤的微生物群落结构间存在差异.     

贺兰山不同海拔植被下土壤微生物群落结构特征

为明确海拔变化对干旱区山地森林土壤微生物群落的影响,揭示环境因子改变后土壤微生物群落结构特征及影响因素。对贺兰山5个海拔梯度土壤理化性质进行测定,同时采用磷酸脂肪酸(PLFA)图谱法分析土壤微生物群落组成,通过主成分分析、冗余分析(RDA)探究土壤理化性质与土壤微生物群落相对丰度之间的相关关系。结果表明:土壤养分含量在不同海拔之间差异性显著(P<0.05),土壤有机碳和全氮含量随海拔的升高而升高,全磷含量随海拔升高先升高再降低再升高;土壤微生物量随海拔升高先升高后降低,土壤微生物的相对丰度在不同海拔之间存在差异(P<0.05);主成分分析表明,与第1主成分相关性较强的微生物类群为革兰氏阳性细菌(G~+)、革兰氏阴性细菌(G~-)和真菌;与第2主成分相关性较强的微生物类群为放线菌、原生动物和非特异性细菌。非特异性细菌和真菌与各土壤因子之间均有显著相关关系,而放线菌、G~+和G~-与各土壤因子相关性较弱,原生动物与土壤全磷含量的关系密切。海拔是影响特征微生物分布的重要因素,特征微生物的含量和相对丰度随海拔的升高先升高后降低,符合山地生态学中的"中部膨胀"理论。探明了贺兰山不同海...     

中亚热带地区两种森林植被类型土壤微生物群落结构

利用磷脂脂肪酸(PLFA)生物标记法分析了中亚热带地区罗浮栲天然林和相邻的杉木人工林土壤微生物群落结构特点.结果表明: 两种植被类型的磷脂脂肪酸总量、细菌特征脂肪酸、真菌特征脂肪酸、放线菌特征脂肪酸、革兰氏阳性菌和革兰氏阴性菌特征脂肪酸含量均为0～10 cm高于10～20 cm土层,罗浮栲天然林高于杉木人工林.在两种植被类型的两个土层中,细菌PLFAs含量均显著高于真菌PLFAs含量.两种植被类型中,细菌PLFAs含量约占PLFAs总量的44%～52%,而真菌仅占6%～8%,表明细菌在该地区两种植被类型土壤中处于优势地位.主成分分析表明,土壤微生物群落结构差异主要由植被类型差异引起,土层深度的影响相对较小.相关分析显示,革兰氏阴性菌、革兰氏阳性菌以及细菌的PLFAs含量与pH呈显著负相关,与含水量呈显著正相关;土壤微生物主要类群PLFAs含量与总氮、有机碳、C/N和铵态氮均呈显著正相关.     

亚热带树种转换对林地土壤微生物群落结构和功能的影响

通过分析杉木采伐迹地营造阔叶树种尾巨桉和固氮树种黑木相思人工林后土壤微生物群落组成和酶活性,探讨造林树种转换对于改善杉木林地土壤微生物特性的影响.结果表明: 树种转换对土壤微生物群落组成和酶活性的影响主要局限于0～10 cm土壤层.杉木转换为固氮树种黑木相思后,显著提高了0～10 cm土壤层总脂肪酸含量、真菌、革兰氏阳性细菌、革兰氏阴性细菌和放线菌生物量.主成分分析表明,黑木相思人工林土壤微生物群落组成与杉木和尾巨桉人工林具有显著差异,土壤中革兰氏阳性细菌、阴性细菌和放线菌丰度显著提高.在0～10 cm土壤层,黑木相思人工林土壤纤维素水解酶、乙酰氨基-葡萄糖苷酶和酸性磷酸酶活性均显著高于杉木和尾巨桉人工林.研究表明,杉木转变为固氮树种黑木相思后会显著提高微生物生物量和酶活性,有助于土壤有机质的恢复,加快养分循环过程.     

不同坡向凋落物分解对土壤微生物群落的影响

采用空间与时间序列并用的方法,对贵州茂兰喀斯特森林阳坡和阴坡凋落物的分解特征及土壤微生物进行1年的野外调查和测定,探讨凋落物分解规律及其对土壤微生物群落的影响。凋落物在分解1年后的质量损失率约为72%,在分解过程中的碳、磷元素表现为释放,氮元素表现出富集;土壤微生物各群落磷脂脂肪酸(PLFA)在分解过程中的平均含量表现为:细菌(149.8 nmol/g)放线菌(63.9 nmol/g)真菌(31.3 nmol/g),阳坡和阴坡的微生物总PLFA在180d(559.2 nmol/g)和360d(513.6 nmol/g)的含量显著高于分解前;随分解时间的增加,阳坡细菌特征磷脂脂肪酸18:1ω7c的含量增加最大,其次是cy19:0和真菌特征磷脂脂肪酸18:1ω9c,阴坡土壤微生物PLFA含量表现出减少的趋势,细菌特征脂肪酸18:1ω7c减少量最大,约9.42 nmol/g,其次是i15:0和真菌特征脂肪酸18:1ω9c,约减少4.29—4.86 nmol/g;凋落物养分释放特征与微生物群落间的Spearman相关分析表明,真菌群落与碳元素释放率呈显著正相关关系,细菌群落与凋落物碳、磷元素的释放呈极显著正相关关系,且阳坡凋落物分解对微生物群落的影响高于阴坡。坡向和凋落物养分释放量对喀斯特森林凋落物的分解及土壤微生物群落的影响较显著,特征磷脂脂肪酸18:1ω7c、cy19:0、i15:0和18:1ω9c对环境变化的响应较为敏感。     

Characterization of Microbial Consortia in Paddy Rice Soil by Phospholipid Analysis

Abstract Microbial biomass and community structure in paddy rice soil during the vegetation period of rice were estimated by analysis of their phospholipid fatty acids (PLFA), hydroxy fatty acids of lipopolysaccharides (LPS-HYFA), and phospholipid ether lipids (PLEL) directly extracted from the soil. A clear change in the composition of the community structure at different sampling periods was observed, indicated by the principal component analysis of the PLFA. A dramatic decline of ester-linked PLFA was observed in the soil samples taken at the second sampling time. In contrast to the ester-linked PLFA, the non-ester-linked PLFA composition did not change. The hydroxy fatty acids of lipopolysaccharides as well as ether lipids decreased consecutively during the observation period. Total microbial abundance was estimated to be (4.1–7.3) × 10⁹ cells g^-1 soil (dry weight). About 44% account for aerobic and 32% for facultative anaerobic bacteria, and 24% for archaea, on average. According to the profile and patterns of PLFA in the soil sample, it may be suggested that the paddy soil at the August sampling period contained more abundant facultative anaerobic bacteria (ca. 36%) and archaea (ca. 37%), but the total microbial biomass was significantly lower than in the remaining sampling periods. As the plant approached maturity, the microbial community structure in the soil changed to contain more abundant Gram-negative bacteria and methanotrophs. Received: 23 September 1999; Accepted: 28 February 2000; Online Publication: 12 May 2000     

西藏那曲地区高寒草甸不同放牧方式下土壤微生物群落结构特征

以不同放牧方式下那曲高寒草甸为研究对象,通过比较土壤化学性质和土壤磷脂脂肪酸(PLFA)研究土壤微生物群落结构的变化.结果表明： 土壤化学性质(总有机碳、全磷和硝态氮含量)和微生物生物量碳总体表现为休牧7年>自由放牧>禁牧;除真菌细菌比外,土壤PLFA总值、细菌PLFA值、真菌PLFA值、革兰氏阴性菌和革兰氏阳性菌PLFA值均表现为休牧7年>禁牧5年>自由放牧>禁牧7和9年.主成分分析(PCA)表明：第1主成分(PC1=74.6%)主要由单烯脂肪酸、多烯脂肪酸、支链饱和脂肪酸组成;第2主成分(PC2=13.2%)主要由直链脂肪酸和部分单烯脂肪酸组成.土壤微生物生物量碳(MBC)和PLFA总值之间有较好的相关性.与禁牧方式相比,休牧最适宜于那曲高寒草甸健康稳定,轻度放牧也有利于高寒草甸的稳定.     

连作条件下毛鸡骨草根际土壤微生物群落功能多样性变化特征

毛鸡骨草是治疗肝病的重要中草药之一,而连作障碍致其产量和品质下降。从主产区广西玉林分别采集正茬、重茬和连作三年的毛鸡骨草根际土壤样品,以种植前水稻土壤为对照,采用Biolog GN2 平板碳源分析技术,研究连作条件下根际土壤微生物群落功能多样性变化特征,以揭示其连作障碍的原因。结果表明,连作导致根际土壤微生物功能多样性显著降低,微生物利用各类碳源的能力下降。主成分分析(PCA)表明,不同种植年限的毛鸡骨草根际土壤微生物群落结构之间存在显著差异,且均与种植前对照明显不同,而同一种植年限不同生长期土壤微生物碳代谢群落结构虽有差异,但并不显著。相关分析表明,其产量与微生物功能多样性指数(如Shannon,Simpson,Mclntosh)以及平均吸光值(AWCD)值正相关,而与第一主成分(PC1)呈显著负相关,说明连作条件下其产量的降低在一定程度上与土壤微生物功能多样性的降低和群落结构的改变有关。     

Decomposition rates and nutrient dynamics of Picea abies needles,twigs and fine roots after stem-only harvesting in eastern and western Norway

Objectives

Afforestation changes soil chemical properties over several decades. In contrast, microbial community structure can be shifted within the first decade and so, the direct effects of tree species can be revealed. The aim of this study was to determine the alteration of soil microbial community composition 10 years after afforestation by trees with contrasting functional traits.

Methods

The study was conducted at the BangorDIVERSE temperate forest experiment. Soil samples were collected under single, two and three species mixtures of alder and birch, beech and oak - early and secondary successional species, respectively, and contiguous agricultural field. Soil was analysed for total carbon (C) and nitrogen (N) contents, and microbial community structure (phospholipid fatty acids (PLFAs) analysis).

Results and conclusions

The total PLFAs content (370–640 nmol g^?1 soil) in forest plots increased for 30 to 110 % compared to the agricultural soil (290 nmol g^?1 soil). In contrast, soil C, N and C/N ratios were altered over 10 years much less - increased only up to 20 % or even decreased (for beech forest).

Afforestation increased bacterial PLFAs by 20–120 %, whereas it had stronger impact on the development of fungal communities (increased by 50–200 %). These effects were proved for all forests, but were more pronounced under the monocultures compared to mixtures. This indicates that species identity has a stronger effect than species diversity. Principal component analysis of PLFAs revealed that under mono and three species mixtures similar microbial communities were formed. In contrast, gram-positive PLFAs and actinomycete PLFAs contributed mainly to differentiation of two species mixtures from other forests. Thus, at the early afforestation stage: i) soil biological properties are altered more than chemical, and ii) tree species identity affects more than species amount on both processes.

     

新疆绿洲农田不同连作年限棉花根际土壤微生物群落多样性

以南北疆不同连作年限棉花根际土壤为研究对象,采用Biolog技术,并结合传统平板培养法和土壤酶的测定,研究连作对棉花根际土壤微生物群落多样性的影响。Biolog分析结果表明,不同连作年限棉花根际土壤微生物碳源利用和功能多样性差异显著。荒地土壤微生物活性较低;在连作年限较短时(5—10a),根际土壤微生物群落的平均颜色变化率(AWCD)和Shannon指数较高;长期连作(15—20a),则呈明显下降趋势。主成分分析表明,不同连作年限的棉花根际土壤微生物碳源利用特征有明显不同。第一、二组开垦与未开垦土壤分别在PC1和PC2上出现差异,未开垦土壤得分均为负值,开垦土壤均为正值;而正茬与连作多年的棉花土壤在PC1上差异显著。其中在PC1上起分异作用的碳源主要是羧酸类和聚合物类,这两类碳源可能是影响连作棉花根际土壤微生物的主要碳源。可培养微生物数量的测定结果表明,荒地细菌数量最少;在连作年限较低时(5—10a左右),细菌数量呈上升趋势;而长期连作(>15a)后,细菌数量呈现下降趋势。真菌数量在连作多年后(10—15a)也开始增加。放线菌变化趋势不明显。四种土壤酶活性在连作的初中期(5—15a),连作障碍表现明显,土壤酶活性呈下降(过氧化氢酶和磷酸酶)或先升高后下降(脲酶和蔗糖酶)趋势,但随着连作年限的延长(15—20a),这4种土壤酶活性均表现出增高趋势。综上所述,棉花长期连作使棉花根际土壤微生物群落多样性降低,发生连作障碍,进而导致棉花产量降低。     

The use of phospholipid fatty acids (PL-FA) in the determination of rhizosphere specific microbial communities (RSMC) of two wheat cultivars

To determine differences in microbial community structure, phospholipid fatty acids (PL-FA) from rhizosphere bacteria of two different wheat cultivars Triticum aestivum L. (cv. Bohouth-6 and cv. Salamouni) were extracted and analyzed by gas chromatography. This approach was used to overcome the methodological underestimation of microbial densities obtained with isolation, culture techniques and microscopic observations. Our objective was to verify differences in PL-FA profiles from two wheat cultivars grown under controlled environmental conditions. Principal component analysis (PCA) and cluster analysis were used to detect dissimilarities between rhizosphere microbial communities of the two wheat cultivars and signature fatty acids (FA) were used to determine specific differences in the community structures. PCA of the two cultivars explained 79.18% of the variance on principal component 1 (PC1), which accounted for Bohouth-6 rhizosphere soil. The rhizosphere soil of Salamouni accounted for 11.66% of the variance on principal component 2 (PC2). The results demonstrated repeatedly the clustering of the samples into two distinct groups; each group belonging specifically to one of the two wheat cultivars. Profiles of Bohouth-6 showed higher amounts of cyclopropane acid 19:0cy and Sif 7 (Sum in feature 7) than Salamouni. Those FA are known as signature molecules for Gram-negative bacteria. This was also reflected by the higher bacterial counts (cfu g^–1 fresh root weight) of Gram-negative bacteria from the rhizosphere of the former than the latter. The results indicated that under controlled environmental conditions, wheat cultivars of different genotypes exhibit distinct microbial colonization in their rhizosphere.     

Changes in soil microbial functional diversity under different vegetation restoration patterns for Hulunbeier Sandy Land

Grassland desertification seriously threatens economic and social sustainable development. How to control grassland desertification, and even to restore and reconstruct grassland has been paid much attention. Vegetation restoration is considered to be a very effective solution. Soil contains an immense diversity of microbes, and the characteristics of soil microbial communities are sensitive indicators of soil. It is important to understand the relationship between vegetation and soil microbial diversity during the restoration process. Based on Biolog-Eco technology, a case study was carried out to investigate the effects of five different vegetation restoration patterns on soil microbial functional diversity after four years in sandy land in Hulunbeier, China. The five vegetation restoration patterns included mono-cultivar planting of Agropyron cristatum (UA), mono-cultivar planting of Hedysarum fruticosum (UH), mono-cultivar planting of Caragana korshinskii (UC), and mixed-cultivar planting of A. cristatum and H. fruticosum (AC), mixed-cultivar planting of A. cristatum, H. fruticosum, C. korshinskii and Elymus nutans (ACHE). Completely degraded sandy land was used as control.The results indicated that the vegetation restoration significantly increased soil microbial activity. The Average Well Color Development (AWCD), which represents soil microbial metabolic activity, followed the order of UC > UH > UA > ACHE > AC > control. AWCD of five vegetation restoration patterns were all higher than that of control, and the highest soil microbial metabolic activity in mono-cultivar planting of C. korshinskii treatment was found. Five vegetation restoration patterns resulted in significant increase in Shannon index (H), evenness (E) and Simpson’s Dominance (D) of soil microbial community. Greater Shannon index and Simpson’s Dominance was observed in UC treatment than in other four vegetation restoration treatments and control. ACHE treatment had the highest evenness index (E) of soil microbial community. The principal component analysis (PCA) indicated a similar mode in carbon utilization for soil microbial community of UA, AC, ACHE and CK. However, UH and UC treatments had special carbon utilization mode. Treatments of UA, AC, ACHE and CK concentrated in the negative direction of the first principal component. Conversely, treatments of UH and UC concentrated in the positive direction of the first and second principal component respectively. The carbon sources mostly used by soil microbes were carbohydrates, amino acids, metabolic mediates and secondary metabolites. Therefore, vegetation restoration enhanced the metabolic activity and functional diversity of microbial community in sandy soil.     

Diversity of Microorganisms within Rock Varnish in the Whipple Mountains, California

Rock varnish from Arizona's Whipple Mountains harbors a microbial community containing about 10⁸ microorganisms g⁻¹ of varnish. Analyses of varnish phospholipid fatty acids and rRNA gene libraries reveal a community comprised of mostly Proteobacteria but also including Actinobacteria, eukaryota, and a few members of the Archaea. Rock varnish represents a significant niche for microbial colonization.