Impact of clear-cutting and prescribed burning on microbial diversity and community structure in a Jack pine (Pinus banksiana Lamb.) clear-cut using Biolog Gram-negative microplates

The impacts of clear-cutting and clear-cutting followed by prescribed burning on soil microbial diversity and community structure were assessed using sole-carbon-source utilization. Microorganisms were washed from organic and mineral soil samples and used to inoculate Biolog Gram-negative microplates. Patterns of colour development were analysed using principal component analyses and calculation of Shannon diversity indices. No differences between treatments were detected when individual samples were used. However, both organic and mineral soil samples from the burned plot showed lower microbial diversity when pooled samples were examined.     

Responses of soil microbial communities to prescribed burning in two paired vegetation sites in southern China

Prescribed burning is a common site preparation practice for forest plantation in southern China. However, the effects of prescribed burning on soil microbial communities are poorly understood. This study examined changes in microbial community structure, measured by phospholipid fatty acids (PLFAs), after a single prescribed burning in two paired vegetation sites in southern China. The results showed that the total amount of PLFA (totPLFA) was similar under two vegetation types in the wet season but differed among vegetation type in the dry season, and was affected significantly by burning treatment only in the wet season. Bacterial PLFA (bactPLFA) and fungal PLFA (fungPLFA) in burned plots all decreased compared to the unburned plots in both seasons (P = 0.059). Fungi appeared more sensitive to prescribed burning than bacteria. Both G⁺ bacterial PLFA and G⁻ bacterial PLFA were decreased by the burning treatment in both dry and wet seasons. Principal component analysis of PLFAs showed that the burning treatment induced a shift in soil microbial community structure. The variation in soil microbial community structure was correlated significantly to soil organic carbon, total nitrogen, available phosphorus and exchangeable potassium. Our results suggest that prescribed burning results in short-term changes in soil microbial communities but the long-term effects of prescribed burning on soil microbial community remain unknown and merit further investigation.     

Basidiomycete fungal communities in Australian sclerophyll forest soil are altered by repeated prescribed burning

Soil basidiomycetes play key roles in forest nutrient and carbon cycling processes, yet the diversity and structure of below ground basidiomycete communities remain poorly understood. Prescribed burning is a commonly used forest management practice and there is evidence that single fire events can have an impact on soil fungal communities but little is known about the effects of repeated prescribed burning. We have used internal transcribed spacer (ITS) terminal restriction fragment length polymorphism (T-RFLP) analysis to investigate the impacts of repeated prescribed burning every two or four years over a period of 30 years on soil basidiomycete communities in an Australian wet sclerophyll forest. Detrended correspondence analysis of ITS T-RFLP profiles separated basidiomycete communities in unburned control plots from those in burned plots, with those burned every two years being the most different from controls. Burning had no effect on basidiomycete species richness, thus these differences appear to be due to changes in community structure. Basidiomycete communities in the unburned control plots were vertically stratified in the upper 20 cm of soil, but no evidence was found for stratification in the burned plots, suggesting that repeated prescribed burning results in more uniform basidiomycete communities. Overall, the results demonstrate that repeated prescribed burning alters soil basidiomycete communities, with the effect being greater with more frequent burning.     

Determinants of Soil Microbial Communities: Effects of Agricultural Management, Season, and Soil Type on Phospholipid Fatty Acid Profiles

Abstract Phospholipid fatty acid (PLFA) profiles were measured in soils from organic, low-input, and conventional farming systems that are part of the long term Sustainable Agriculture Farming Systems (SAFS) Project. The farming systems differ in whether their source of fertilizer is mineral or organic, and in whether a winter cover crop is grown. Sustained increases in microbial biomass resulting from high organic matter inputs have been observed in the organic and low-input systems. PLFA profiles were compared to ascertain whether previously observed changes in biomass were accompanied by a change in the composition of the microbial community. In addition, the relative importance of environmental variables on PLFA profiles was determined. Redundancy analysis ordination showed that PLFA profiles from organic and conventional systems were significantly different from April to July. On ordination plots, PLFA profiles from the low-input system fell between organic and conventional systems on most sample dates. A group of fatty acids (i14:0, a15:0, 16:1ω7c, 16:1ω5c, 14:0, and 18:2ω6c) was enriched in the organic plots throughout the sampling period, and another group (10Me16:0, 2OH 16:1 and 10Me17:0) was consistently lower in relative abundance in the organic system. In addition, another group (15:0, a17:0, i16:0, 17:0, and 10Me18:0) was enriched over the short term in the organic plots after compost incorporation. The relative importance of various environmental variables in governing the composition of microbial communities could be ranked in the order: soil type > time > specific farming operation (e.g., cover crop incorporation or sidedressing with mineral fertilizer) > management system > spatial variation in the field. Measures of the microbial community and soil properties (including microbial biomass carbon and nitrogen, substrate induced respiration, basal respiration, potentially mineralizable nitrogen, soil nitrate and ammonium, and soil moisture) were seldom associated with the variation in the PLFA profiles. Received: 3 February 1997; Accepted: 7 August 1997     

不同森林恢复类型对土壤微生物群落的影响

为了评价不同森林恢复类型与方式对南方红壤丘陵区退化生态系统土壤微生物群落的影响,借助氯仿熏蒸法、平板涂抹法和BIOLOG检测法,比较研究了4种森林恢复类型土壤微生物的群落特征．结果表明,4种森林恢复类型土壤微生物生物量碳、细菌数量差异显著,2项指标均以天然次生林土壤最高,人工林次之,荒地最差;碳源平均颜色变化率(AWCD法)和微生物代谢多样性指数(丰富度和多样性)在5种植被类型的土壤中也有明显差异,其趋势与微生物量碳、细菌数量基本相同;天然次生林土壤微生物群落利用碳源的整体能力和功能多样性比人工林和荒地强．相关分析表明,0～20和20～40cm土壤微生物的代谢多样性与根系生物量紧密相关(r=0．933,P<0．05;r=0．925,P<0．05)．自然恢复更有利于改善土壤微生物的结构和功能．     

Soil microbial diversity, community structure and denitrification in a temperate riparian zone

Nitrate (NO ₃ ^– ) removal in riparian zones bordering agricultural areas occurs via plant uptake, microbial immobilisation and bacterial denitrification. Denitrification is a desirable mechanism for removal because the bacterial conversion of NO ₃ ^– to N gases permanently removes NO ₃ ^– from the watershed. A field and laboratory study was conducted in riparian soils adjacent to Carroll Creek, Ontario, Canada, to assess the spatial distribution of denitrification relative to microbial community structure and microbial functional diversity. Soil samples were collected in March, June, and August 1997 at varying soil depths and distances from the stream. Denitrification measurements made using the acetylene block technique on intact soil cores were highly variable and did not show any trends with riparian zone location. Microbial community composition and functional diversity were determined using sole carbon source utilization (SCSU) on Biolog® GN microplates. Substrate richness, evenness and diversity (Shannon index) were greatest within the riparian zone and may also have been influenced by a rhizosphere effect. A threshold relationship between denitrification and measures of microbial community structure implied minimum levels of richness, evenness and diversity were required for denitrification.     

衡阳紫色土丘陵坡地植被恢复对土壤微生物功能多样性的影响

以典型湖南省衡阳紫色土丘陵坡地不同植被恢复阶段为研究对象,采用空间代替时间序列的方法,选用立地条件基本相似的草本(狗尾草,GS)、灌草(紫薇-狗尾草,FG)、灌丛(牡荆+剌槐,FX)和乔灌(枫香+苦楝-牡荆,AF)群落阶段,运用Biolog-ECO微平板技术,对4个不同恢复阶段0～10和10～20 cm土层的土壤微生物功能多样性进行研究,探讨植被恢复对土壤微生物功能多样性的影响.结果表明: 植被恢复后土壤微生物群落代谢活性显著升高,同一土层不同恢复阶段AWCD值的大小顺序为乔灌群落＞灌丛群落＞灌草群落＞草本群落,相同恢复阶段不同土层的AWCD值的大小顺序为0～10 cm＞10～20 cm;主成分分析(PCA)表明,灌草群落与灌丛群落具有相似的土壤微生物C源利用方式及代谢功能,而草本群落、乔灌群落具有不同的C源利用方式及代谢功能,在主成分分离中起主要贡献作用的C源是糖类、氨基酸类以及代谢中间产物和次生代谢物;土壤微生物的Shannon物种丰富度指数(H)、Shannon均匀度指数(E)、Simpson优势度指数(D)和McIntosh指数(U)均以乔灌群落最高,灌草群落和灌丛群落次之,草本群落最低;相关分析表明,土壤含水量(SWC)、土壤总有机碳(STOC)、全氮(TN)、全磷(TP)和速效磷(AP)对土壤微生物代谢功能及功能多样性指数有重要影响,脲酶(URE)、磷酸酶(APE)、蔗糖酶(INV)和过氧化氢酶(CAT)活性与土壤微生物代谢功能及功能多样性指数存在显著相关关系.表明植被恢复可使土壤微生物代谢功能增强,土壤微生物繁殖加快、数量增大,从而促进土壤微生物对土壤C源的利用强度.     

The Influence of Tropical Plant Diversity and Composition on Soil Microbial Communities

There is growing interest in understanding the linkages between above- and belowground communities, and very little is known about these linkages in tropical systems. Using an experimental site at La Selva Biological Station, Costa Rica, we examined whether plant diversity, plant community composition, and season influenced microbial communities. We also determined whether soil characteristics were related to differences in microbial communities. Phospholipid fatty acid (PLFA) composition revealed that microbial community composition differed across a plant diversity gradient (plots contained 1, 3, 5, or over 25 species). Plant species identity also was a factor influencing microbial community composition; PLFA composition significantly varied among monocultures, and among three-species combinations that differed in plant species composition. Differences among treatments within each of these comparisons were apparent in all four sampling dates of the study. There was no consistent shift in microbial community composition between wet and dry seasons, although we did see significant changes over time. Of all measured soil characteristics, soil C/N was most often associated with changes in microbial community composition across treatment groups. Our findings provide evidence for human alteration of soil microbial communities via the alteration of plant community composition and diversity and that such changes are mediated in part by changes in soil carbon quality.     

Microbial Biomass and Community Structure in a Sequence of Soils with Increasing Fertility and Changing Land Use

Abstract The microbial biomass and community structure of eight Chinese red soils with different fertility and land use history was investigated. Two community based microbiological measurements, namely, community level physiological profiling (CLPP) using Biolog sole C source utilization tests and phospholipid fatty acid (PLFA) profiles, were used to investigate the microbial ecology of these soils and to determine how land use alters microbial community structure. Microbial biomass-C and total PLFAs were closely correlated to organic carbon and total nitrogen, indicating that these soil microbial measures are potentially good indices of soil fertility in these highly weathered soils. Metabolic quotients and C source utilization were not correlated with organic carbon or microbial biomass. Multivariate analysis of sole carbon source utilization patterns and PLFAs demonstrated that land use history and plant cover type had a significant impact on microbial community structure. PLFAs showed these differences more than CLPP methods. Consequently, PLFA analysis was a better method for assessing broad-spectrum community differences and at the same time attempting to correlate changes with soil fertility. Soils from tea orchards were particularly distinctive in their CLPP. A modified CLPP method, using absorbance readings at 405 nm and different culture media at pH values of 4.7 and 7.0, showed that the discrimination obtained can be influenced by the culture conditions. This method was used to show that the distinctive microbial community structure in tea orchard soils was not, however, due to differences in pH alone. Received: 1 December 1999; Accepted: 6 June 2000; Online Publication: 28 August 2000     

干旱区典型盐生植物群落下土壤微生物群落特征

运用Biolog技术,对干旱区玛纳斯河流域扇缘带的6种典型盐生植物群落下土壤微生物群落特征差异性进行了研究,探讨不同植物群落对土壤微生物群落的影响。结果表明:不同盐生植物群落土壤平均颜色变化率(AWCD)随培养时间的延长而逐渐增加,大小顺序依次为:梭梭花花柴白刺绢蒿柽柳雾冰藜,且差异显著。不同植物群落土壤微生物对6类碳源利用差异显著(P0.05),其中梭梭群落利用率最高,雾冰藜群落利用率最低。碳水化合物类和氨基酸类是主要碳源,胺类的利用率最低。主成分分析(PCA)表明,在31种因子中提取的2个主成分因子,分别可以解释所有变量方差的41.51%和25.35%,对PC1和PC2起分异作用的主要碳源分别为碳水化合物类和氨基酸类。土壤微生物群落Shannon指数、Simpson指数上,除雾冰藜群落较低,其他群落之间均差异不显著(P0.05)。植物群落Margalef指数,Shannon指数和Simpson指数上,均为绢蒿,梭梭和柽柳群落较为优势。相关性分析表明,植物群落多样性指数与土壤微生物多样性指数呈显著正相关关系(P0.05),说明了植物多样性越丰富,土壤微生物越丰富。总体来说,干旱区不同盐生植物群落对土壤微生物群落多样性具有重要影响。其中,梭梭群落的土壤微生物群落具有较强的微生物总体活性和功能多样性。     

长期人为干扰对桂西北喀斯特草地土壤微生物多样性及群落结构的影响

人为干扰是喀斯特草地正向演替的主要障碍因素, 从土壤微生物角度探讨草地对干扰的响应可为喀斯特生态恢复与科学利用提供依据。该研究依托中国科学院环江喀斯特生态系统观测站长期干扰监测样地, 通过高通量测序测定3个干扰模式(火烧、刈割、刈割除根)和1个对照(封育)处理的土壤细菌、真菌α多样性和群落结构, 并分析它们与环境因子(坡位、土壤理化性质)的关系, 揭示人为干扰对桂西北喀斯特草地土壤微生物的影响及机制。结果显示: 1)对于α多样性, 在中坡和下坡, 火烧均显著降低了真菌Chao1指数, 刈割均显著降低了细菌的香农指数和谱系多样性指数; 刈割除根在中、下坡分别显著降低了真菌Chao1指数和细菌香农指数。2)对于群落结构, 火烧、刈割和刈割除根在中、下坡均显著降低了酸杆菌门细菌相对丰度, 火烧在下坡使子囊菌门真菌相对丰度从74.49%显著降低至34.72%。3)冗余分析显示, 微生物生物量碳含量解释细菌和真菌α多样性变化的29.8%和26.8%以及细菌群落结构变化的31.7%; 细根生物量解释细菌α多样性和真菌群落结构变化的13.9%和10.3%。可见, 长期人为干扰对土壤微生物α多样性产生负面影响, 并显著改变微生物群落结构, 影响程度因干扰方式、微生物种类不同而异, 且受坡位调控。土壤微生物生物量碳含量和细根生物量的减少是人为干扰影响土壤微生物多样性和群落结构的重要因素。α多样性及子囊菌的减少将不利于土壤生态系统稳定性的维持, 酸杆菌的减少将不利于土壤有机质降解和铁循环。因此, 长期火烧、刈割等人为干扰将导致喀斯特草地生态系统功能发生退化。     

长期施肥对农田黑土微生物群落功能多样性的影响

为了研究长期不同施肥对农田黑土微生物群落功能多样性的影响,采用Biolog ECO微平板培养法,对已经连续施肥35年的农业部哈尔滨黑土生态环境重点野外科学观测试验站4种处理(CK、NPK、M、MNPK)的两个土层(0～20、20～40 cm)微生物群落功能多样性进行研究.结果表明: 在0～20 cm土层,有机无机肥(MNPK)配施能够显著提高土壤微生物对碳源的利用能力以及群落代谢功能的丰富度、多样性和优势度,而在20～40 cm土层则低于单施化肥(NPK)处理,两个土层单施化肥均降低土壤微生物群落代谢均匀度.不同施肥处理土壤微生物对6种碳源的利用率在0～20和20～40 cm两个土层间存在差异,而在每个土层的处理间差异显著(P<0.05),但各处理间的变化规律在两个土层中不一致.典范对应分析(CCA)结果表明,各处理土壤微生物群落代谢功能在0～20和20～40 cm土层间存在差异,且在两个土层的处理间也存在差异,而土壤养分含量对各处理土壤微生物群落代谢功能的影响规律在两个土层中较为相似.长期不同施肥会对耕层及以下土壤微生物群落功能多样性产生影响,在20～40 cm土层中单施化肥对微生物群落功能多样性的影响较大.     

Impact of Carbon and Flooding on the Metabolic Diversity of Microbial Communities in Soils

The assumption that carbon and soil water content are major determinants of microbial community structure and function is rarely questioned because of substantial evidence of the impacts of these variables on specific populations and functions. The significance of carbon and water for metabolic diversity at the microbial community level was tested on the field scale in agricultural plots varying in carbon inputs and in whether they were flooded. Surface soils in which rice straw was incorporated or burned and which were flooded or unflooded were sampled at monthly intervals three times during the flooded winter period (January to March) and again 1 month postdraining. Biomass carbon and nitrogen were not affected by treatments, active bacterial counts showed slight increases, and respiration rates were increased by carbon inputs and flooding. Biolog microplates were inoculated with soil extracts to quantify the metabolic diversity of the soil microbial community. Canonical correspondence analysis and the Monte Carlo permutation testing showed that differences in substrate utilization patterns were significantly related (P < 0.001) to carbon and flooding treatments. Biolog substrates whose metabolism was altered by the treatments were consistent across dates and tended to be positively related (utilization enhancement) to carbon inputs and negatively related to winter flooding. The importance of carbon as an environmental variable increased over time after straw treatment, whereas the importance of water became evident after flooding and decreased after drainage. The effect of long-term rice straw incorporation on substrate utilization patterns at another field site was consistent with these results despite the dissimilarities of the two soils.     

Organic Layer Serves as a Hotspot of Microbial Activity and Abundance in Arctic Tundra Soils

Tundra ecosystem is of importance for its high accumulation of organic carbon and vulnerability to future climate change. Microorganisms play a key role in carbon dynamics of the tundra ecosystem by mineralizing organic carbon. We assessed both ecosystem process rates and community structure of Bacteria, Archaea, and Fungi in different soil layers (surface organic layer and subsurface mineral soil) in an Arctic soil ecosystem located at Spitsbergen, Svalbard during the summer of 2008 by using biochemical and molecular analyses, such as enzymatic assay, terminal restriction fragment length polymorphism (T-RFLP), quantitative polymerase chain reaction (qPCR), and pyrosequencing. Activity of hydrolytic enzymes showed difference according to soil type. For all three microbial communities, the average gene copy number did not significantly differ between soil types. However, archaeal diversities appeared to differ according to soil type, whereas bacterial and fungal diversity indices did not show any variation. Correlation analysis between biogeochemical and microbial parameters exhibited a discriminating pattern according to microbial or soil types. Analysis of the microbial community structure showed that bacterial and archaeal communities have different profiles with unique phylotypes in terms of soil types. Water content and hydrolytic enzymes were found to be related with the structure of bacterial and archaeal communities, whereas soil organic matter (SOM) and total organic carbon (TOC) were related with bacterial communities. The overall results of this study indicate that microbial enzyme activity were generally higher in the organic layer than in mineral soils and that bacterial and archaeal communities differed between the organic layer and mineral soils in the Arctic region. Compared to mineral soil, peat-covered organic layer may represent a hotspot for secondary productivity and nutrient cycling in this ecosystem.     

转基因甘蔗对根际土壤微生物多样性的影响

应用Biolog法研究了转几丁质酶和β-1,3-葡聚糖酶基因甘蔗对根际土壤微生物多样性的影响。结果表明:转基因甘蔗根际土壤微生物利用单一碳源能力(AWCD)要高于非转基因甘蔗的根际土壤微生物;转基因甘蔗和非转基因甘蔗根际上壤样品的Simpson指数(1/D)、Shannon-Wiener指数(H)、Mclntosh指数(U)均存在差异,其中转基因甘蔗根际土壤微生物的Simpson指数显著高于非转基因甘蔗土壤微生物,两种土壤微生物群落优势度的差别很大,其次是Mclntosh指数(U)指数,丰富度的差别不是很大。说明转基因甘蔗根系在生长期的分泌物刺激根际土壤微生物群落的生长,可能诱导了具有某些特定生理特征的微生物群落的发展,因此转基因甘蔗对根际土壤微生态有一定的影响。     

黄土丘陵沟壑区地形变化对土壤微生物群落功能多样性的影响

研究黄土高原丘陵沟壑区破碎地形对土壤微生物功能多样性的影响,对于理解复杂地形区生态过程与系统功能的空间变化具有重要意义。选择陕西省安塞县陈家洼为研究区,依据坡面地形变化选择不同坡位土壤,采用Biolog微平板培养法探究地形变化对土壤微生物群落功能多样性的影响。实验发现,土壤微生物群落培养的平均颜色变化率(AWCD)增长曲线总的呈现出坡下部坡中部坡上部的规律,且坡下部AWCD值与坡中部、坡上部间差异显著(P0.05);坡下部土壤微生物群落功能多样性显著高于坡中部和坡上部,但不同土层深度(0—10 cm、10—20 cm)间无显著性差异(P0.05);对土壤微生物群落功能多样性差异贡献较大的碳源是糖类、羧酸类和多酚化合物类碳源;土壤含水率高低是不同坡位土壤微生物群落功能多样性差异显著的主要原因;微生物群落丰富度(H)和均一度(D)与土壤全氮含量正相关,优势度(U)反之,土壤全碳、全磷和p H对土壤微生物群落结构和功能多样性差异作用不显著。     

外来物种刺槐对土壤微生物功能多样性的影响

以延河流域不同植被区内人工刺槐(Robinia pseudoacacia)群落和乡土植物群落的土壤微生物为研究对象,利用Biolog微平板技术对土壤微生物功能多样性进行测定,分析人工引种刺槐在不同环境梯度(3个植被区)下对土壤微生物功能多样性的影响。结果表明:刺槐对不同环境梯度下的土壤微生物的影响明显不同。从草原区到森林区,刺槐林之间土壤微生物群落的平均颜色变化率(AWCD)和土壤微生物功能多样性指数均没有显著变化;但与乡土植物群落比较,草原区、森林草原区和森林区土壤AWCD分别表现为刺槐乡土植物、刺槐乡土植物、刺槐乡土植物;在草原区和森林草原区刺槐林土壤微生物群落的群落丰富度指数(S)、Shannon-Wiener指数(H)、Simpson指数(D)、Mc Intosh指数(U)均大于乡土植物,森林区刺槐林群落丰富度指数(S)、Shannon指数(H)、Simpson指数(D)均小于乡土植物;刺槐林和乡土植物群落下土壤微生物碳源利用存在差异,主要体现在对糖类、氨基酸类的利用上。PCA分析显示主成分1贡献较大的碳源有24种,在主成分分离中起主要贡献作用的是糖类、氨基酸类和羧酸类。土壤碳氮含量能影响土壤微生物功能多样性指数,土壤含水量和温湿度能够影响碳源的利用类型。刺槐对土壤微生物功能多样性的影响存在区域差异,在评价刺槐对土壤生态过程与功能的影响时必须要考虑这种空间差异性。     

冬季覆盖作物秸秆还田对双季稻田根际土壤微生物群落功能多样性的影响

微生物群落功能多样性是土壤质量变化重要的指标,不同作物类型的秸秆还田措施对土壤微生物群落功能多样性具有明显的影响。以位于双季稻主产区不同冬季覆盖作物-双季稻种植模式大田定位试验田为研究对象,以冬闲-双季稻种植模式为对照(CK),应用Biolog-GN技术开展黑麦草-双季稻(Ry)、紫云英-双季稻(Mv)、油菜-双季稻(Ra)和马铃薯-双季稻(Po)种植模式条件下不同冬季覆盖作物秸秆还田后对双季稻田根际土壤微生物功能多样性影响的研究。研究结果表明,早稻和晚稻成熟期,与CK处理相比,冬季覆盖作物秸秆还田处理增加了稻田土壤碳源平均颜色变化率(AWCD),以Po处理AWCD均为最高,均显著高于Ry和CK处理。不同冬季覆盖作物秸秆还田处理土壤微生物代谢多样性指数表现出明显的差异,早稻成熟期,Po处理的Richness、Shannon和McIntosh指数均为最高,其次为Ry、Mv和Ra处理,CK处理最低;晚稻成熟期,各处理的Richness、Shannon和McIntosh指数大小顺序均表现为PoRaMvRyCK。土壤微生物碳源利用的主成分分析结果表明,各冬季覆盖作物秸秆还田处理根际土壤微生物利用的主要碳源为氨基酸类和糖类物质,不同处理间碳源利用类型有差异。冬季覆盖作物秸秆还田措施有利于提高双季稻田根际土壤微生物对碳源的利用能力、物种丰富度和均匀度。     

Long-term effect of re-vegetation on the microbial community of a severely eroded soil in sub-tropical China

The long-term (18 years) effects of re-vegetating eroded soil on soil microbial biomass, community structure and diversity were investigated in a forest soil derived from Quaternary clay in the Red Soil Ecological Experimental Station of the Chinese Academy of Sciences. Large areas of land in this region of China have been subjected to severe soil erosion, characterised by the removal of the fertile surface soil and even the exposure of parental rock in some areas due to a combination of deforestation and heavy rainfall. The effects of planting eroded or uneroded soil with Pinus massoniana, Cinnamomum camphora or Lespedeza bicolor on the soil microbial community and chemical properties were assessed. Total soil microbial community DNA was extracted and bacterial 16 S rRNA gene fragments were amplified by PCR and analysed by terminal restriction fragment length polymorphism (T-RFLP). Microbial biomass carbon (C_mic) was measured by chloroform fumigation-extraction. Following the restoration there were significant increases in both C_mic and bacterial diversity (Shannon index), and significant changes in bacterial community structure. Erosion factors were significant only in minor dimensions suggesting that the restoration had been largely successful in terms of bacterial community structure. Compared with uneroded soil, C_mic recovered in L. bicolor and P. massoniana restored eroded plots and was significantly greater under these tree species than C. camphora, although soils in C. camphora restored plots displayed the highest bacterial diversity. The recovery of microbial biomass and diversity in the eroded plots was, to large extent, accompanied by the development of the same bacterial community structure as in the uneroded plots with erosion having relatively little effect on bacterial community structure.     

Plant Communities, Soil Microorganisms, and Soil Carbon Cycling: Does Altering the World Belowground Matter to Ecosystem Functioning?

Soil microorganisms mediate many critical ecosystem processes. Little is known, however, about the factors that determine soil microbial community composition, and whether microbial community composition influences process rates. Here, we investigated whether aboveground plant diversity affects soil microbial community composition, and whether differences in microbial communities in turn affect ecosystem process rates. Using an experimental system at La Selva Biological Station, Costa Rica, we found that plant diversity (plots contained 1, 3, 5, or > 25 plant species) had a significant effect on microbial community composition (as determined by phospholipid fatty acid analysis). The different microbial communities had significantly different respiration responses to 24 labile carbon compounds. We then tested whether these differences in microbial composition and catabolic capabilities were indicative of the ability of distinct microbial communities to decompose different types of litter in a fully factorial laboratory litter transplant experiment. Both microbial biomass and microbial community composition appeared to play a role in litter decomposition rates. Our work suggests, however, that the more important mechanism through which changes in plant diversity affect soil microbial communities and their carbon cycling activities may be through alterations in their abundance rather than their community composition.