华南地区5种人工幼林的土壤呼吸及其季节性变化

为了解华南人工林的碳固存机制,对广东鹤山的尾叶桉(Eucalyptus urophylla)纯林、30种树种混交林、10种树种混交林、红椎(Castanopsis hystrix)纯林、厚荚相思(Acacia crassicarpa)纯林5种人工林(林龄2–5 a)的土壤总呼吸(Rs)和自养呼吸(Ra)的季节变化进行了研究。结果表明,从2007年到2012年,5种人工林的Rs为81.3~103.9 mg C m–2h–1,Ra为11.2~22.3 mg C m–2h–1,自养呼吸贡献率(RC)为12.4%~26.9%,且5种人工林间的Rs、Ra及RC差异不显著。5种人工林湿季的Rs均显著大于干季的,平均高出311.4%;Ra、RC的季节性差异不显著。湿季土壤温度与Rs具有显著相关性,土壤温度解释了90.2%的变异,而两者关系在干季不显著。人工林间的微环境和土壤条件差异不明显,可能是由于造林时间短,土壤还处于干扰的恢复过程中,导致人工林间土壤呼吸差异不显著。     

Forest Age and Plant Species Composition Determine the Soil Fungal Community Composition in a Chinese Subtropical Forest

Fungal diversity and community composition are mainly related to soil and vegetation factors. However, the relative contribution of the different drivers remains largely unexplored, especially in subtropical forest ecosystems. We studied the fungal diversity and community composition of soils sampled from 12 comparative study plots representing three forest age classes (Young: 10–40 yrs; Medium: 40–80 yrs; Old: ≥80 yrs) in Gutianshan National Nature Reserve in South-eastern China. Soil fungal communities were assessed employing ITS rDNA pyrotag sequencing. Members of Basidiomycota and Ascomycota dominated the fungal community, with 22 putative ectomycorrhizal fungal families, where Russulaceae and Thelephoraceae were the most abundant taxa. Analysis of similarity showed that the fungal community composition significantly differed among the three forest age classes. Forest age class, elevation of the study plots, and soil organic carbon (SOC) were the most important factors shaping the fungal community composition. We found a significant correlation between plant and fungal communities at different taxonomic and functional group levels, including a strong relationship between ectomycorrhizal fungal and non-ectomycorrhizal plant communities. Our results suggest that in subtropical forests, plant species community composition is the main driver of the soil fungal diversity and community composition.     

Forest Canopy Properties and Variation in Aboveground Net Primary Production over Upper Great Lakes Landscapes

Relationships among aboveground net primary production (ANPP) and forest canopy properties were investigated in secondary successional forests of similar age and disturbance history in northern Lower Michigan, USA. Aboveground biomass, ANPP, canopy leaf area index (LAI), and several canopy nitrogen (N) measures were estimated from 12 stands representing major landform-level ecosystems and vegetation associations. Stand single-date and growing season average normalized difference vegetation indices (NDVI) were derived from Landsat TM. ANPP correlated most strongly with total canopy N content (r ² = 0.81, P < 0.001), followed by LAI (r ² = 0.73, P < 0.001) and area-based canopy-average leaf N concentration (r ² = 0.37, P < 0.05). No significant relationship was detected between ANPP and mass-based canopy-average leaf N concentration. Stand ANPP correlated positively with both total canopy N content (r ² = 0.62, P < 0.05) and mass-based leaf N concentration (r ² = 0.53, P < 0.05) of commonly dominant Populus spp. Relatively higher ANPP, total canopy N content and LAI corresponded to simultaneous presence of shade-intolerant P. grandidentata with shade-tolerant species. Both forms of NDVI were significantly related to ANPP, and more strongly to total canopy N content and LAI; relationships were stronger for seasonally averaged (r ² ≥ 0.75, P < 0.001) than for single-date NDVI (r ² ≥ 0.52, P < 0.01). Results indicate that on the transitioning study landscapes, ANPP was more closely related to canopy N content than to LAI, seasonally averaged NDVI was a more reliable predictor of ANPP and canopy properties than the single-date index, whereas measured canopy characteristics varied significantly between major landform-level ecosystems. The ongoing decline of P. grandidentata is likely to alter aboveground carbon and pools and fluxes in the course of succession.     

Impact of Logging and Forest Conversion to Oil Palm Plantations on Soil Bacterial Communities in Borneo

Tropical forests are being rapidly altered by logging and cleared for agriculture. Understanding the effects of these land use changes on soil bacteria, which constitute a large proportion of total biodiversity and perform important ecosystem functions, is a major conservation frontier. Here we studied the effects of logging history and forest conversion to oil palm plantations in Sabah, Borneo, on the soil bacterial community. We used paired-end Illumina sequencing of the 16S rRNA gene, V3 region, to compare the bacterial communities in primary, once-logged, and twice-logged forest and land converted to oil palm plantations. Bacteria were grouped into operational taxonomic units (OTUs) at the 97% similarity level, and OTU richness and local-scale α-diversity showed no difference between the various forest types and oil palm plantations. Focusing on the turnover of bacteria across space, true β-diversity was higher in oil palm plantation soil than in forest soil, whereas community dissimilarity-based metrics of β-diversity were only marginally different between habitats, suggesting that at large scales, oil palm plantation soil could have higher overall γ-diversity than forest soil, driven by a slightly more heterogeneous community across space. Clearance of primary and logged forest for oil palm plantations did, however, significantly impact the composition of soil bacterial communities, reflecting in part the loss of some forest bacteria, whereas primary and logged forests did not differ in composition. Overall, our results suggest that the soil bacteria of tropical forest are to some extent resilient or resistant to logging but that the impacts of forest conversion to oil palm plantations are more severe.     

Effects of Climate Change and Shifts in Forest Composition on Forest Net Primary Production

Forests are dynamic in both structure and species composition, and these dynamics are strongly Influenced by climate.However, the net effects of future tree species composition on net primary production (NPP) are not well understood. The objective of this work was to model the potential range shifts of tree species (DISTRIB Model) and predict their impacts on NPP (PnET-Ⅱ Model) that will be associated with alterations in species composition. We selected four 200 × 200 km areas In Wisconsin, Maine, Arkansas, and the Ohio-West Virginia area, representing focal areas of potential species range shifts. PnET-Ⅱ model simulations were carried out assuming that all forests achieved steady state, of which the species compositions were predicted by DISTRIB model with no migration limitation. The total NPP under the current climate ranged from 552 to 908 g C/m2 per year. The effects of potential species redistributions on NPP were moderate (-12% to 8%) compared with the influence of future climatic changes (-60% to 25%). The direction and magnitude of climate change effects on NPP were largely dependent on the degree of warming and water balance. Thus, the magnitude of future climate change can affect the feedback system between the atmosphere and biosphere.     

Variation in Microbial Community Composition and Culturability in the Rhizosphere of Leucanthemopsis alpina (L.) Heywood and Adjacent Bare Soil Along an Alpine Chronosequence

We compared the size, culturability, diversity, and dominant species similarity of the bacterial communities of Leucanthemopsis alpina (L.) Heywood rhizosphere and adjacent bare soil (interspace) along a chronosequence of soil development time (5, 50, and 70 years) in the forefield of the Dammaglacier (Switzerland). We found no evidence that the size of the bacterial community was significantly affected by either soil age or the presence of L. alpina. In contrast, the proportion of the bacterial community that could be cultured on nonselective agars, and which was taken as an indication of the proportion of r-selected populations, was significantly higher in the 50- and 70-year-old soils than in the 5-year-old soil, and was also significantly higher in the rhizosphere of L. alpina at all time points. RDA indicated significant correlations between the increased culturability of the bacterial community over time and increasing concentrations of labile N, and between the increased culturability in the rhizosphere and increased concentrations of labile C and N. HaeIII-amplified ribosomal DNA (rDNA) restriction analysis of a library of 120 clones of 16S rDNA revealed 85 distinct phylotypes. Hurlbert's probability of interspecific encounter (PIE) values derived from this library ranged from 0.95 to 1.0, indicating a very high genetic diversity. There was no significant difference in the PIE values of rhizosphere and interspace communities. Detrended correspondence analysis (DCA) of 16S ribosomal RNA (rRNA) denaturing gradient gel electrophoresis (DGGE) community profiles clearly distinguished the rhizosphere from the interspace community in the 5-year-old soils and also clearly distinguished between these communities and the rhizosphere and interspace communities of the 50- and 70-year-old soils. However, 16S rRNA DGGE revealed little difference between rhizosphere and interspace communities in the 50- and 70-year-old soils. The relative similarity of the 16S rRNA profiles strongly reflected labile carbon and nitrogen availability. Overall, our results suggest that improved C and N availability in the rhizosphere of L. alpina increases the size of r-selected bacterial species populations, but that the influence of L. alpina depends on soil age, being maximal in the youngest soils and minimal in the oldest. The reduced influence of L. alpina in the older soils may reflect a feedback between improved nutrient availability and reduced rhizodeposition.     

Flavobacterial Community Structure in a Hardwater Rivulet and Adjacent Forest Soil,Harz Mountain,Germany

The great increase in the abundance and phylogenetic diversity of Flavobacterium spp. within a few hundred meters downstream of the discharge site of the Westerhöfer Bach, a hardwater rivulet, raised the question whether adjacent soil may serve as a reservoir of bacteria not detected in discharge water. To address this question, denaturing gradient gel electrophoresis (DGGE) analyses of the V3 region of Flavobacterium 16S rRNA genes were performed on DNA from nine soil samples and five rivulet sites. The resulting patterns were tested for the significance of differences between the sampling habitats using the nonparametric analysis of similarities and multidimensional scaling procedures. Even though both habitats were sampled in two consecutive years DGGE patterns of soil and downstream water samples showed significant overlap (R = 0.614). Sequencing of 57 DGGE bands resulted in 30 different sequences, which, on the basis of BLAST analyses, were between 96% and 100% similar to published clone, DGGE, and strain sequences from a wide range of different habitats. Forty-five percent of the highly similar sequences included those of isolates from the Westerhöfer Bach, while the other sequences were more closely related to clones and cultures from other habitats, especially agricultural soil. Based on these results we suggest that the increase in flavobacterial strain diversity and abundance in the rivulet may originate from soil microflora.     

Climate Variation and Soil Carbon and Nitrogen Cycling Processes in a Northern Hardwood Forest

We exploited the natural climate gradient in the northern hardwood forest at the Hubbard Brook Experimental Forest (HBEF) to evaluate the effects of climate variation similar to what is predicted to occur with global warming over the next 50–100 years for northeastern North America on soil carbon (C) and nitrogen (N) cycle processes. Our objectives were to (1) characterize differences in soil temperature, moisture and frost associated with elevation at the HBEF and (2) evaluate variation in total soil (TSR) and microbial respiration, N mineralization, nitrification, denitrification, nitrous oxide (N₂O) flux, and methane (CH₄) uptake along this gradient. Low elevation sites were consistently warmer (1.5–2.5°C) and drier than high elevation sites. Despite higher temperatures, low elevation plots had less snow and more soil frost than high elevation plots. Net N mineralization and nitrification were slower in warmer, low elevation plots, in both summer and winter. In summer, this pattern was driven by lower soil moisture in warmer soils and in winter the pattern was linked to less snow and more soil freezing in warmer soils. These data suggest that N cycling and supply to plants in northern hardwood ecosystems will be reduced in a warmer climate due to changes in both winter and summer conditions. TSR was consistently faster in the warmer, low elevation plots. N cycling processes appeared to be more sensitive to variation in soil moisture induced by climate variation, whereas C cycling processes appeared to be more strongly influenced by temperature.     

中国农田土壤呼吸速率及驱动因子

土壤呼吸在全球碳收支中具有重要地位.研究中国典型农业区土壤呼吸的时空格局及影响因素,有助于构建区域尺度土壤呼吸定量评价模型,能够为评估中国乃至全球农业生态系统碳/源汇特征提供依据.本研究整合了2000~2012年中国农田生态系统土壤呼吸的主要研究成果,分析了华南、西南、华北、西北和东北5个典型农业区土壤呼吸的季节变化和区域差异,以及影响土壤呼吸的主要驱动因子.结果表明,5个典型农业区的土壤呼吸均存在明显的季节变化特征;中国农田生态系统年均土壤呼吸速率为(682.8±18.3)g C m?2.5个典型农业区年均土壤呼吸速率大小表现为华南区西南区华北区东北区西北区.全国农业土壤的年呼吸通量为(0.90±0.02)Pg C;水作和旱作两种土地利用类型间土壤呼吸速率差异显著(P0.05),旱作土壤呼吸速率约为水作的1.3倍;不同作物类型间土壤呼吸速率差异显著(P0.05),其排序为棉花玉米大豆水稻小麦;农田土壤呼吸与年均气温、土壤温度、土壤含水量和净初级生产力等影响因素呈显著正相关(P0.01),而与年均降水量的相关性不显著.     

Ranging Behavior of Proboscis Monkeys in a Riverine Forest with Special Reference to Ranging in Inland Forest

We observed a unimale group (BE-Group) of proboscis monkeys (Nasalis larvatus) comprising an α-male, 6 adult females, and several immatures from May 2005 to May 2006. We followed the group for 2014 h along the Menanggul River, Sabah, Malaysia (118°30′E, 5°30′N). Observations focused mainly on ranging behavior. We determined availability and seasonal changes in plant species consumed by the members of the group by vegetation surveys in a 2.15-ha area along 200–500 m trails in the riverine forest. During the observation period, the group ranged ≤800 m from the riverbank, within a total range of 138.3 ha. The daily path length of the group ranged from 220 to 1734 m (mean, 799 m), and daily path length correlates negatively with fruit availability. The monkeys were apt to remain within a small range in fruit-abundant seasons. Because the monkeys preferred to feed on fruits of dominant plant species in the study area, their daily path length may decrease on days when they feed on fruits. The core areas of the group’s home range were along the river because the monkeys typically returned to riverside trees to sleep. The group most often used areas that were nearer the riverbank and where the availability of fruits was higher. The most frequently used grids were the ones where the group often had sleeping sites and crossed the river. Avoiding predation may be the main reason for river crossing and selecting particular sleeping sites; hence not only food availability but also the risk of predation appears to influence the ranging of the BE-Group.     

Spatial Variability of Soil Properties in a Floodplain Forest in Northwest Spain

Floodplain forests are generally areas of high plant diversity compared with upland forests. Higher environmental heterogeneity, especially variation in belowground properties may help explain this high diversity. However, there is little information available on the spatial scale and pattern of belowground resources in floodplain forests. Geostatistics and coefficient of variation (CV) were used to describe the spatial variability of 20 soil properties ranging from essential plant nutrients, such as NH₄ or PO₄, to nonessential elements like Ti or V. The spatial variation of Si-to-(Al + Fe) ratio, an index of soil development, was also analyzed. Semivariograms and maps of selected properties were used to discriminate between the effect of flooding (and other mechanisms that may contribute to large scale trends in data) and local heterogeneity. The hypothesis that elements mainly cycled through biological processes (such as N) show different spatial properties than elements cycled through both biological and geological processes (such as P) or elements under strict geological control (such as Ti or V) is also presented. Redox potential was the most variable property (CV = 1.35) followed by mineral N, phosphate, organic matter, and carbon. Nonessential elements for organisms such as Si, Al, Ti, Rh, or V were less variable, supporting the hypothesis that biological control on soil properties leads to higher spatial variability. The range (the average distance within which the samples correlate spatially) varied between 3.89 m for water content to 18.5 m for the Si-to-(Al + Fe) ratio. The proportion of the total variance that can be modeled as spatial dependence (structural variance) was very variable, ranging between 0.34 for Fe and 0.96 for K. The addition of the large trend had a strong influence on the CV of most soil variables and created a gradient in C accumulation and the mineral weathering rate. The results suggest that flooding and other processes that are responsible for large spatial trends in the floodplain forest differentially affect biologically and geologically controlled variables with different turnover rates, thus providing a heterogeneous edaphic environment.     

Numerical and Functional Responses of Forest Bats to a Major Insect Pest in Pine Plantations

Global change is expected to modify the frequency and magnitude of defoliating insect outbreaks in forest ecosystems. Bats are increasingly acknowledged as effective biocontrol agents for pest insect populations. However, a better understanding is required of whether and how bat communities contribute to the resilience of forests to man- and climate-driven biotic disturbances. We studied the responses of forest insectivorous bats to a major pine defoliator, the pine processionary moth pityocampa, which is currently expanding its range in response to global warming. We used pheromone traps and ultrasound bat recorders to estimate the abundance and activity of moths and predatory bats along the edge of infested pine stands. We used synthetic pheromone to evaluate the effects of experimentally increased moth availability on bat foraging activity. We also evaluated the top-down regulation of moth population by estimating T. pityocampa larval colonies abundance on the same edges the following winter. We observed a close spatio-temporal matching between emergent moths and foraging bats, with bat activity significantly increasing with moth abundance. The foraging activity of some bat species was significantly higher near pheromone lures, i.e. in areas of expected increased prey availability. Furthermore moth reproductive success significantly decreased with increasing bat activity during the flight period of adult moths. These findings suggest that bats, at least in condition of low prey density, exhibit numerical and functional responses to a specific and abundant prey, which may ultimately result in an effective top-down regulation of the population of the prey. These observations are consistent with bats being useful agents for the biocontrol of insect pest populations in plantation forests.     

Variation in Canopy Litterfall Along a Precipitation and Soil Fertility Gradient in a Panamanian Lower Montane Forest

Fertilization experiments in tropical forests have shown that litterfall increases in response to the addition of one or more soil nutrients. However, the relationship between soil nutrient availability and litterfall is poorly defined along natural soil fertility gradients, especially in tropical montane forests. Here, we measured litterfall for two years in five lower montane 1‐ha plots spanning a soil fertility and precipitation gradient in lower montane forest at Fortuna, Panama. Litterfall was also measured in a concurrent nitrogen fertilization experiment at one site. Repeated‐measures ANOVA was used to test for site (or treatment), year, and season effects on vegetative, reproductive and total litterfall. We predicted that total litterfall, and the ratio of reproductive to leaf litterfall, would increase with nutrient availability along the fertility gradient, and in response to nitrogen addition. We found that total annual litterfall varied substantially among 1‐ha plots (4.78 Mg/ha/yr to 7.96 Mg/ha/yr), and all but the most aseasonal plot showed significant seasonality in litterfall. However, litterfall accumulation did not track soil nutrient availability; instead forest growing on relatively infertile soil, but dominated by an ectomycorrhizal tree species, had the highest total litterfall accumulation. In the fertilization plots, significantly more total litter fell in nitrogen addition relative to control plots, but this increase in response to nitrogen (13%) was small compared to variation observed among 1‐ha plots. These results suggest that while litterfall at Fortuna is nutrient‐limited, compositional and functional turnover along the fertility gradient obscure any direct relationship between soil resource availability and canopy productivity.     

小兴安岭原始阔叶红松林与枫桦次生林土壤呼吸及其各组分特征的比较研究

原始阔叶红松林是我国温带典型的地带性顶极植被类型,枫桦次生林是其典型的次生林类型之一,对二者土壤呼吸及其各组分特征的研究有助于准确评价该地区的碳平衡。本研究主要测定了2013和2014年2个生长季原始阔叶红松林和枫桦次生林土壤呼吸（R_S）,并量化了土壤呼吸的各个组分（异养呼吸R_H和自养呼吸R_A）,与此同时测量了土壤10 cm处温度以及土壤含水率。研究结果表明,土壤呼吸及其各组分有着明显的季节变化特性,其大小的变化主要受温度的影响,土壤10 cm处的温度可以解释R_S 64%~70%、R_H 56%~65%、R_A 77%~79%的变异。对于温度的敏感性,原始阔叶红松林土壤呼吸Q₁₀值>枫桦次生林土壤呼吸Q₁₀值,而在单一林型中的比较,R_A Q₁₀值 > R_S Q₁₀值 > R_H Q₁₀值。此外,总体Q₁₀值随着季节有着明显的变化,且随着温度的升高有降低的趋势。原始阔叶红松林和枫桦次生林R_S年平均速率分别为3.92和4.06 μmol·m^-2·s^-1,R_H年平均速率分别为2.97和2.85 μmol·m^-2·s^-1,R_A年平均速率则分别为0.96和1.17 μmol·m^-2·s^-1。原始阔叶红松林土壤呼吸以及土壤土壤自养呼吸要稍低于枫桦次生林,而原始阔叶红松林异养呼吸则高于枫桦次生林异养呼吸,但差异不显著。原始阔叶红松林和枫桦次生林R_S平均年通量分别为942和971 g C·m^-2·a^-1,R_H年通量分别为709和677 g C·m^-2·a^-1,R_A年通量则分别为215和276 g C·m^-2·a^-1。原始阔叶红松林R_S年通量略高于枫桦次生林R_S年通量,但差异不显著。我们的实验结果表明,小兴安岭地区枫桦次生林正向演替的过程中,植被演替变化对土壤呼吸及各组分的影响并不明显,相较于环境因子温度和湿度要小的多。     

Plant Species Composition Effects on Belowground Properties and the Resistance and Resilience of the Soil Microflora to a Drying Disturbance

We hypothesised that plant species composition and richness would affect soil chemical and microbial community properties, and that these in turn would affect soil microbial resistance and resilience to an experimentally imposed drying disturbance. We performed a container experiment that manipulated the composition and species richness of common pasture plant species (Trifolium repens, Lolium perenne, and Plantago lanceolata) by growing them in monoculture, and in all the possible two and three-way combinations, along with an unplanted control soil. Experimental units were harvested at four different times over a 16-month period to determine the effect of plant community development and seasonal changes in temperature and moisture on belowground properties. Results showed that plant species composition influenced soil chemistry, soil microbial community properties and soil microbial resistance and resilience. Soil from planted treatments generally showed reduced soil microbial resistance to drying compared to unplanted control soils. Soils from under T. repens showed a higher resistance and resilience than the soils from under P. lanceolata, and a higher resistance than soils from under L. perenne. We suggest that differences across soils in either resource limitation or soil microbial community structure may be responsible for these results. Plant species richness rarely affected soil microbial community properties or soil microbial resistance and resilience, despite having some significant effects on plant community biomass and soil nitrogen contents in some harvests. The effect that treatments had for most variables differed between harvests, suggesting that results can be altered by the stage of plant community development or by extrinsic environmental factors that varied with harvest timing. These results in combination show that soil microbial resistance and resilience was affected by plant community composition, and the time of measurement, but was largely unrelated to plant species richness.     

石油污染土壤中不同人工林木根际丛枝菌根真菌与球囊霉素的研究

以陕西延长县石油污染区常见的13种人工种植林木为材料,测定了各人工种植林木根际丛枝菌根(AM)真菌发育状况、污染土壤的理化性质、土壤酶活性和球囊霉素含量,探讨AM真菌在石油污染土壤生态修复中的作用。结果表明,13种林木均能形成AM,其定殖率平均为63.2%,孢子密度平均为1.93个.g-1干土,其中受污染程度最低的柠条AM真菌定殖率和孢子密度最高,分别为91.6%和4.73个.g-1干土;毛白杨、狼牙刺和刺槐的根际土壤养分(有机碳、碱解氮、速效磷)含量相对较高;各种人工种植林木的根际土壤球囊霉素含量、多酚氧化酶和过氧化氢酶活性随根际土壤石油烃污染浓度的增加而明显升高,其中刺槐、狼牙刺和酸枣根际土壤的过氧化氢酶和多酚氧化酶活性都较高,同时这3种林木的球囊霉素含量也较高。因此,林木根际土壤球囊霉素含量、多酚氧化酶和过氧化氢酶活性可以作为石油污染的敏感指标。     

中亚热带原生和次生湿性常绿阔叶林种子植物区系多样性比较

对瓦屋山的湿性常绿阔叶林破坏后自然恢复的次生群落及其与原生湿性常绿阔叶林的比较研究表明,中山湿性常绿阔叶林砍伐破坏后在封山条件下经过４２年的自然恢复形成的植被,已经形成常绿阔叶外貌,其物种多样性丰富,区系组成已经与破坏前相似;湿性常绿阔叶林的典型珍稀濒危和樗种已经随森林环境的恢复而迅速回归或就地保存;虽然自然恢复产次生林乔木层尚存在较多落叶伴生种,但优势种已与破坏前相似。有力地说明了中山湿性常绿阔     

Soil Bacterial Community Shift Correlated with Change from Forest to Pasture Vegetation in a Tropical Soil

The change in vegetative cover of a Hawaiian soil from forest to pasture led to significant changes in the composition of the soil bacterial community. DNAs were extracted from both soil habitats and compared for the abundance of guanine-plus-cytosine (G+C) content, by analysis of abundance of phylotypes of small-subunit ribosomal DNA (SSU rDNA) amplified from fractions with 63 and 35% G+C contents, and by phylogenetic analysis of the dominant rDNA clones in the 63% G+C content fraction. All three methods showed differences between the forest and pasture habitats, providing evidence that vegetation had a strong influence on microbial community composition at three levels of taxon resolution. The forest soil DNA had a peak in G+C content of 61%, while the DNA of the pasture soil had a peak in G+C content of 67%. None of the dominant phylotypes found in the forest soil were detected in the pasture soil. For the 63% G+C fraction SSU rDNA sequence analysis of the three most dominant members revealed that their phyla changed from Fibrobacter and Syntrophomonas assemblages in the forest soil to Burkholderia and Rhizobium–Agrobacterium assemblages in the pasture soil.