免耕覆盖及有机肥施用对土壤真菌群落组成及多样性的影响

为揭示土壤真菌群落对免耕、覆盖及有机肥施用的响应机制,在宁夏南部山区冬小麦农田连续3年采用免耕覆盖+施有机肥(NF)、免耕覆盖+不施有机肥(NC)、传统耕作不覆盖+施有机肥(TF)和传统耕作不覆盖+不施有机肥(TC)4个处理,依托Illumina MiSeq 高通量测序平台,研究了土壤真菌群落组成、多样性及其与土壤环境因子间的关系。结果表明: 4个处理共获得3490个可操作分类单元(OTUs),其中含有一些未知真菌。在已知的真菌群落中,子囊菌门和担子菌门为优势菌门,其相对丰度占总丰度的82.1%～94.2%,且TF处理下子囊菌门座囊菌纲的相对丰度最高,NF处理下担子菌门银耳菌纲的相对丰度最高。4个处理真菌群落多样性指数(Shannon和Simpson指数)依次为NC>TC>NF>TF。多元分析结果表明,微生物生物量碳是影响担子菌门和接合菌门相对丰度的主要因素,而土壤全磷、速效钾和速效磷含量高低是驱动子囊菌门真菌相对丰度变化的关键因素。在宁夏南部山区推广以免耕覆盖并施用有机肥的保护性耕作措施有利于提高土壤真菌群落多样性。     

围封对退化高寒草甸土壤微生物群落多样性及土壤化学计量特征的影响

围封对植被处于近自然恢复状态的退化草地有一定的修复作用,开展轻度退化草地围封过程中生物与非生物因素的协同互作研究是完整地认识草地生态系统结构和功能的基础.本试验对围栏封育10年的轻度退化草地的土壤化学计量特征进行了研究,同时采用高通量基因测序技术并结合Biolog-Eco方法,调查了土壤微生物多样性和功能的变化.结果表明:轻度退化草地实施围封后,土壤铵态氮含量显著升高,全钾含量显著降低,土壤有机碳、全氮、全磷、硝态氮、速效磷和速效钾则无明显变化.高寒草甸土壤微生物碳和氮在轻度退化和围栏封育草地间差异不显著;围栏封育后草地土壤微生物碳氮比显著高于轻度退化草地.随培养时间的延长,高寒草甸不同土层土壤微生物碳代谢强度均显著升高,土壤微生物碳代谢指数在轻度退化和围栏封育草地间差异不显著.高寒草甸土壤细菌OTUs显著高于真菌,轻度退化与围栏封育草地土壤微生物相似度为27.0%～32.7%.围封后,土壤真菌子囊菌门、接合菌门和球壶菌门相对丰富度显著升高,担子菌门显著降低,土壤细菌酸杆菌门显著低于轻度退化草地.土壤真菌和细菌群落组成在不同土层间差异较大,在轻度退化和围栏封育草地间仅有表层土壤真菌群落组成表现出较大差异.土壤细菌多样性受土壤全氮和速效钾影响较大,真菌多样性受地上生物量影响较大.土壤微生物对碳源利用能力主要受土壤速效钾影响.综上,长期围封禁牧对轻度退化草地土壤养分和土壤微生物无明显影响,且会造成牧草资源浪费,适度放牧可以保持草地资源的可持续利用.     

青藏高原高寒草地AM真菌分布及其对近自然恢复的生态作用

超载过牧以及全球气候变化等导致大部分青藏高原高寒草地呈现持续退化态势。青藏高原高寒草地退化致使地上植物群落逐渐发生更替,地下土壤微生物群落多样性和丰富度发生改变。本文旨在探析青藏高原高寒草地丛枝菌根（arbuscular mycorrhizal,AM）真菌的分布特征、对近自然恢复的生理生态效应及其作用机制。青藏高原高寒草地中已报道4目14属61种AM真菌,约占已知AM真菌物种的20%。高寒草地禾本科植物根围AM真菌物种丰度最高,而莎草科植物根围AM真菌孢子密度最高。3种高寒草地植被类型中,高寒草原AM真菌丰度最高（33种）,山地灌丛草原次之（32种）,高寒草甸最低（22种）。高寒草原以光壁无梗囊霉Acaulospora laevis和闪亮和平囊霉Pacispora scintillans为优势种,山地灌丛草原以摩西斗管囊霉Funneliformis mosseae为优势种,高寒草甸以光壁无梗囊霉A. laevis、近明球囊霉Claroideoglomus claroideum和闪亮和平囊霉P. scintillans为优势种。高寒草地土著AM真菌与植物构建的菌根网络可以通过调节营养元素吸收、分配,促进植物建植和生长;但是毒杂草入侵可以改变土著AM真菌物种多样性和菌根网络,限制本地植被的实际生态位扩张。退化高寒草地中,AM真菌群落具有高的环境适应性和恢复力,其不仅调控地上植物群落建植和多样性,同时AM真菌建植也增加了代谢产物-球囊霉素相关土壤蛋白产生,进而协同改善地下土壤微生态系统,为退化高寒草地早期植被恢复塑造土壤生境。因此,AM真菌在退化高寒草地近自然恢复中具有较大的应用潜力。     

覆盖模式对旱作农田土壤微生物多样性及群落结构的影响

土壤微生物是表征土壤质量的敏感指标，采用Illumina HiSep技术分析不同覆盖方式对半湿润易旱区农田土壤微生物群落结构及多样性的影响，以期从微生物的角度评价农田不同覆盖措施对土壤质量的影响。设3种覆盖模式：平作塑料薄膜覆盖（P）、平作秸秆覆盖（S）和垄膜沟播覆盖（R），以平作不覆盖为对照（CK），研究不同覆盖模式下土壤微生物群落变化，分析各土壤理化因子与微生物群落之间的关系。研究结果表明各覆盖处理显著改变了土壤微生物的群落结构和多样性。所有土壤样品中，细菌群落的优势菌门是变形菌门（Proteobacteria）、酸杆菌门（Acidobacteria）、放线菌门（Actinobacteria），丰度分别为29.69%、28.28%和20.76%，CK处理下较高的土壤pH和低NO₃-N含量抑制了土壤中酸杆菌门（Acidobacteria）的生长繁殖，而放线菌门（Actinobacteria）相对丰度为所有处理中最高。真菌群落的优势菌门是子囊菌门（Ascomycota）、担子菌门（Basidiomycota），丰度分别为59.65%和20.96%，S处理下过低的土壤温度抑制了担子菌门（Basidiomycota）生长和繁殖，其相对丰度为所有处理中最低。与CK相比，P和R处理显著提高土壤细菌的多样性和丰富度；S和R处理下土壤真菌多样性和丰富度显著增加，而P处理的土壤真菌多样性和丰富度均无显著差异。斯皮尔曼相关分析表明土壤细菌多样性主要受土壤含水量（SM）和硝态氮含量（NO₃-N）影响，而土壤真菌多样性主要受土壤温度（ST）、全氮（TN）和硝态氮含量（NO₃-N）影响；RDA分析表明微生物群落结构的变化主要受SM、ST、NO₃-N和TN含量的影响。总的来说，R处理下土壤细菌和真菌的多样性和丰富度较CK处理显著提高，该处理下土壤中担子菌门（Basidiomycota）和球囊菌（Glomeromycota）相对丰度为所有处理中最高，两者分别形成的外生菌根和从生菌根不但促进了根部养分的吸收，而且提高了作物的抗逆性，且结果证明该处理的作物产量为最高，因此在半湿润旱作区推荐采用垄膜沟播覆盖种植方式。     

玉米秸秆还田对土壤丛枝菌根真菌群落的影响

为揭示农业管理活动对土壤丛枝菌根(AM)真菌的影响机制,基于Illumina Miseq高通量测序平台以及脂肪酸指纹图谱方法,研究了连续4年玉米秸秆还田后,AM真菌群落组成、AM真菌生物量及其与土壤环境因子间的相互关系.结果表明:所获得的2430个AM真菌OTUs从门到种依次分类,共分为1门、3纲、4目、8科、10属、143种,但不同处理间AM真菌群落丰富度(Chao1指数和ACE指数)、多样性(Shannon、Simpson多样性指数)没有显著差异.AM真菌中类球囊霉属、球囊霉属为优势属.随秸秆还田量的增加,球囊霉属丰度降低;3000、9000 kg·hm^-2秸秆还田量下,类球囊霉属、无梗囊霉属的丰度与对照(0 kg·hm^-2)间差异达极显著水平;原囊霉属、类球囊霉属、球囊霉属在3000 kg·hm^-2秸秆还田量下与对照间差异显著,非度量多维尺度(NMDS)分析表明,9000、12000 kg·hm^-2的秸秆还田量下土壤AM真菌β多样性与对照间聚集度较其他处理相差较远,秸秆还田量对AM真菌β多样性的影响显著.多元分析结果能在累积变量82.8%上揭示土壤主要理化性状与AM真菌丰富度、多样性的空间变化关系.土壤全氮、碱解氮是影响以磷脂脂肪酸表征的土壤主要微生物类群生物量以及以中性脂肪酸表征的AM真菌生物量的主要因子.持续玉米秸秆还田改变了AM真菌属水平上的分类学组成;随秸秆还田量的增加,AM真菌特有的微生物种类减少,AM真菌群落组成间的相似度下降;秸秆还田增加了土壤AM真菌生物量及其占土壤微生物总生物量的比例.     

不同施肥模式对雷竹林土壤真菌群落特征的影响

为探明施肥处理对雷竹林土壤真菌群落特征的影响,采用末端限制性片段长度多态性(T-RFLP)和荧光定量PCR技术,分析有机肥(M)、化肥(CF)、化肥配施有机肥(CFM)、化肥配施有机肥加覆盖(CFMM)及不施肥(CK)处理土壤真菌群落结构和数量特征.结果表明:施肥显著影响真菌群落结构与多样性,表层(0～20 cm)土壤中M、CFMM处理与CK,亚表层(20～40 cm)土壤中CF、CFMM处理与CK之间真菌群落结构均存在明显差异;且表层土壤中CF、CFMM处理真菌Shannon指数和均匀度指数显著低于CK.M、CFM处理表层土壤真菌数量显著高于CK.土壤有机质、全氮、铵态氮和速效钾含量显著影响了真菌群落结构的变异;全氮、铵态氮、硝态氮含量与真菌数量均呈显著正相关.表明雷竹林表层和亚表层土壤中真菌群落对施肥处理的响应存在明显差异,表层土壤真菌群落明显受有机质添加的影响,而亚表层则对化肥投入较为敏感;施肥对真菌群落多样性的影响主要集中在表层土壤.     

Grassland plant and invertebrate species richness increases from mowing are mediated by impacts on soil chemistry

Pasture and improved grasslands are commonly managed by a combination of artificial fertilisation and biomass removal, but a deeper understanding of how management options interact over the long-term are required to improve sustainability. Studies of multi-trophic responses to these options can provide important insights for biodiversity and soil management, particularly when they cover long time periods. In this study, we provide a novel perspective on long-term experimental field studies of grassland management by examining the direct and indirect effects of N fertilisation and mowing (with biomass retention and removal) on above-ground biodiversity, below-ground soil chemistry and their interactions. Our experimental treatments were applied annually from 1994 in medium to high soil fertility conditions on a non-native pastoral farm in New Zealand, and analysis of data to 2013 show that in general, plants and soil properties did not respond to N fertiliser treatments. In response to mowing regimes, soil properties exhibited subtle, but annually varying changes mostly related to biomass retention or removal, and plant richness was consistently higher under all mowing treatments. The management regime with the greatest gains in diversity also depended on year of study. We further analysed the indirect effects of mowing treatments on plant and arthropod richness via soil properties using structural equation modelling, and found that the impact of mowing is likely to be mediated by soil chemistry changes. In particular, the direct positive impact of mowing on plant richness may be offset by changes to soil properties, depending on whether biomass is retained or removed. We suggest that management regime effects on soil chemistry may limit plant composition changes to those species able to take advantage of altered conditions. These findings suggest that management to improve grassland diversity and soil conditions should consider the abiotic history and conditions of the site.     

几种生态环境中AM真菌多样性比较研究

对渤海湾的海岛林地(IFL),黄河三角洲盐碱地(SAS)、鲁西南煤矿(CMS)和内蒙古退化草原(DGL)等几种生态环境中丛枝菌根(Arbuscular mycorrhiza,AM)真菌的多样性进行了调查。结果表明,在所调查的样点中,AM真菌的物种多样性不同,IFL中的最高,其次是SAS,CMS和DGL的最低。各地AM真菌种的丰度、孢子密度、频度、相对多度等也差异较大。这与各生态环境中的生态因子的差异相关。在总体上,Glomus属在各采样点出现的频度和相对多度最高,其次是Acaulospora属。但不同生态环境之问又存在差异,例如CMS中Acaulospora属的频度和相对多度比Glomus属的高。在IFL中,Gigaspora属的相对多度比Acaulospora属的高。各生态环境中的生态优势种不同,如在CMS中是A．mellea,在IFL和SAS土壤中却分别是G．margarita和G．caledonium,而DGL中各个种的分布却较均衡。     

A preliminary survey of the arbuscular mycorrhizal status of grassland plants in southern Tibet

We report for the first time the arbuscular mycorrhizal (AM) status of native plant species and AM fungal diversity in the grasslands of southern Tibet. A total of 51 soil samples were collected from the rhizospheres of the dominant plant species, and AM fungal structures were observed in 18 (82%) of 22 plant species examined. Vesicles and aseptate hyphae were the structures most frequently observed in the plant roots. After trap culture for 5 months, 25 AM fungal taxa were identified in the soil samples collected, of which nine belonged to Glomus, ten to Acaulospora, one to Entrophospora and five to Scutellospora. The frequency of occurrence of different genera and species varied greatly. Glomus was the dominant genus, and the most frequent and abundant species was Glomus mosseae. Over the whole sampling area, spore density in the rhizosphere soil of different host plant species ranged from 2 to 66 per 20 g air-dried soil. Overall AM fungal species richness was 2.10 and species diversity was 2.35. AM fungal diversity was also compared among the four different land use types (farmland and normal, disturbed and highly disturbed montane scrub grassland). Spore densities in the farmland and normal grassland were much higher than in the grasslands that had been degraded to varying degrees. The species richness in normal grassland was the highest of the four land use types examined. Species diversity varied from 1.99 to 0.94 and was highest in normal grassland, intermediate in degraded grassland and farmland, and lowest in the highly disturbed grassland.     

Illumina高通量测序揭示艾比湖湿地6种盐生植物根际土壤真菌群落组成及多样性

[目的] 通过研究新疆艾比湖湿地不同盐生植物根际土壤真菌的多样性和群落结构,为艾比湖湿地退化恢复工作和真菌深入研究提供理论支持。[方法] 利用高通量测序技术对真菌扩增子ITS1区进行测定,从而分析艾比湖湿地6种盐生植物根际土壤真菌群落多样性,并结合相关土壤理化因子分析环境与真菌群落多样性和丰富度的关联。[结果] 艾比湖湿地6种盐生植物根际土壤真菌群落多样性及丰富度存在差异,碱蓬根际土壤真菌多样性最高,芦苇根际土壤真菌群落丰富度最高。真菌群落组成分析表明,土壤样品中真菌菌落主要隶属于子囊菌门（Ascomycota）和担子菌门（Basidiomycota）,其中子囊菌门为主要优势菌门;链格孢霉属（Alternaria）是6种植物共有的优势菌属,但是其在不同植物之间的丰度存在差异,在戟叶鹅绒藤中的丰度最高,在准噶尔大戟中的丰度最低。pH与真菌多样性呈显著负相关,全磷（TP）与真菌群落丰富度呈显著正相关,pH、电导率（EC）和有机质（OM）对优势菌属的影响最大。[结论] 艾比湖湿地6种盐生植物根际土壤真菌群落组成及多样性具有显著差异,碱蓬和芦苇根际土壤真菌的多样性和丰度高于其他植物,子囊菌门和链格孢霉属是艾比湖湿地的主要土壤真菌门属。研究结果可为艾比湖湿地的生态修复提供理论指导。     

Assessing the impact of land abandonment, nitrogen enrichment and fairy-ring fungi on plant diversity of Mediterranean grasslands

Semi-natural calcareous grasslands are of great conservation interest because of their high species richness, but they are threatened by land abandonment and nitrogen eutrophication. These plant communities evolved as a result of a long history of human activity, which generated and maintained these habitats by extensive grazing and mowing. Calcareous grasslands are listed as a priority for conservation in the EC Habitats Directive. However, the effects of different management regimes, nitrogen enrichment, and soil-borne pathogens on plant species diversity are less clear for grasslands of the Mediterranean Basin, compared to meadows in Northern and Central Europe. In this study, we assessed the impact of land abandonment, nitrogen enrichment, and fairy-ring fungi on species diversity in semi-natural grasslands found in the Mediterranean Basin by comparing the available literature with findings from recent studies carried out in Central Italy. In a series of field experiments, the cutting of abandoned grassland consistently reduced the living biomass of the dominant perennial grasses, such as Brachypodium rupestre and Bromus erectus, and promoted a rapid increase in species richness and diversity by allowing the establishment of rare species. There was a similar, but less effective, restoration of species diversity and composition in mowed grassland after litter removal. We also show that nitrogen enrichment at levels comparable to atmospheric deposition depresses species diversity, which also hampers the positive effects of litter removal. Our findings are consistent with previous results achieved in Northern and Central Europe, which however, mainly focused on grasslands with intermediate to high primary productivity levels. The limited availability of data from low-productivity, drought-prone Mediterranean grasslands requires further studies to assess the impact of land abandonment and nitrogen eutrophication in such ecosystems. Finally, we discuss the role of fairy-ring fungi in the maintenance of plant diversity in species-rich grassland. We show that fairy-ring fungi (e.g. Agaricus campestris) critically affect the spatial distribution and diversity of coexisting plant species. By killing the dominant perennial herbs, these radially growing plant pathogens produce empty niches for rare, short-lived species, thus affecting the vegetation pattern. Overall, our results are of interest for environmental managers, as they provide guidelines for the restoration of abandoned areas and the conservation of these species-rich habitats.     

Inner Mongolian steppe arbuscular mycorrhizal fungal communities respond more strongly to water availability than to nitrogen fertilization

Plant community productivity and species composition are primarily constrained by water followed by nitrogen (N) availability in the degraded semi‐arid grasslands of Inner Mongolia. However, there is a lack of knowledge on how long‐term N addition and water availability interact to influence the community structure of arbuscular mycorrhizal (AM) fungi, and whether AM fungi contribute to the recovery of degraded grasslands. Soils and roots of the dominant plant species Stipa grandis and Agropyron cristatum were sampled under two water levels and N) rates after 8 years. The abundance and diversity of AM fungi remained relatively resilient after the long‐term addition of water and N. Variation in the AM fungal communities in soils and roots were affected primarily by watering. AM fungal abundance and operational taxonomic unit (OTU) richness were significantly correlated with average aboveground net primary productivity and biomass of plant functional groups. Hyphal length density was significantly correlated with plant richness, the average biomass of S. grandis and perennial forbs. Both water and plant biomass had a considerable influence on the AM fungal assemblages. The tight linkages between AM fungi with aboveground plant productivity highlight the importance of plant–microbe interactions in the productivity and sustainability of these semi‐arid grassland ecosystems.     

Flower resource and land management drives hoverfly communities and bee abundance in seminatural and agricultural grasslands

Pollination is a key ecosystem service, and appropriate management, particularly in agricultural systems, is essential to maintain a diversity of pollinator guilds. However, management recommendations frequently focus on maintaining plant communities, with the assumption that associated invertebrate populations will be sustained. We tested whether plant community, flower resources, and soil moisture would influence hoverfly (Syrphidae) abundance and species richness in floristically‐rich seminatural and floristically impoverished agricultural grassland communities in Wales (U.K.) and compared these to two Hymenoptera genera, Bombus, and Lasioglossum. Interactions between environmental variables were tested using generalized linear modeling, and hoverfly community composition examined using canonical correspondence analysis. There was no difference in hoverfly abundance, species richness, or bee abundance, between grassland types. There was a positive association between hoverfly abundance, species richness, and flower abundance in unimproved grasslands. However, this was not evident in agriculturally improved grassland, possibly reflecting intrinsically low flower resource in these habitats, or the presence of plant species with low or relatively inaccessible nectar resources. There was no association between soil moisture content and hoverfly abundance or species richness. Hoverfly community composition was influenced by agricultural improvement and the amount of flower resource. Hoverfly species with semiaquatic larvae were associated with both seminatural and agricultural wet grasslands, possibly because of localized larval habitat. Despite the absence of differences in hoverfly abundance and species richness, distinct hoverfly communities are associated with marshy grasslands, agriculturally improved marshy grasslands, and unimproved dry grasslands, but not with improved dry grasslands. Grassland plant community cannot be used as a proxy for pollinator community. Management of grasslands should aim to maximize the pollinator feeding resource, as well as maintain plant communities. Retaining waterlogged ground may enhance the number of hoverflies with semiaquatic larvae.     

Drought consistently alters the composition of soil fungal and bacterial communities in grasslands from two continents

The effects of short‐term drought on soil microbial communities remain largely unexplored, particularly at large scales and under field conditions. We used seven experimental sites from two continents (North America and Australia) to evaluate the impacts of imposed extreme drought on the abundance, community composition, richness, and function of soil bacterial and fungal communities. The sites encompassed different grassland ecosystems spanning a wide range of climatic and soil properties. Drought significantly altered the community composition of soil bacteria and, to a lesser extent, fungi in grasslands from two continents. The magnitude of the fungal community change was directly proportional to the precipitation gradient. This greater fungal sensitivity to drought at more mesic sites contrasts with the generally observed pattern of greater drought sensitivity of plant communities in more arid grasslands, suggesting that plant and microbial communities may respond differently along precipitation gradients. Actinobateria, and Chloroflexi, bacterial phyla typically dominant in dry environments, increased their relative abundance in response to drought, whereas Glomeromycetes, a fungal class regarded as widely symbiotic, decreased in relative abundance. The response of Chlamydiae and Tenericutes, two phyla of mostly pathogenic species, decreased and increased along the precipitation gradient, respectively. Soil enzyme activity consistently increased under drought, a response that was attributed to drought‐induced changes in microbial community structure rather than to changes in abundance and diversity. Our results provide evidence that drought has a widespread effect on the assembly of microbial communities, one of the major drivers of soil function in terrestrial ecosystems. Such responses may have important implications for the provision of key ecosystem services, including nutrient cycling, and may result in the weakening of plant–microbial interactions and a greater incidence of certain soil‐borne diseases.     

After the hotspots are gone: Land use history and grassland plant species diversity in a strongly transformed agricultural landscape

Question: We asked how landscape configuration and present management influence plant species richness and abundance of habitat specialists in grasslands in a ‘modern’(much exploited and transformed) agricultural Swedish landscape. Location: Selaön, south‐eastern Sweden (59°24’ N, 17°10’ E). Methods: Present and past (150 and 50 years ago) landscape pattern was analysed in a 25 km² area. Species richness was investigated in 63 different grassland patches; grazed and abandoned semi‐natural grasslands, and grazed ex‐arable fields. Influence of landscape variables; area, past and present grassland connectivity, present management on total species richness, density and abundance of 25 grassland specialists was analysed. Results: Semi‐natural grasslands (permanent unfertilised pastures or meadows formed by traditional agricultural methods) had declined from 60% 150 years ago to 5% today. There was a significant decline in species richness and density in abandoned semi‐natural grasslands. Total species richness was influenced by present management, size and connectivity to present and past grassland pattern. Landscape variables did not influence species density in grazed semi‐natural grassland suggesting that maintained grazing management makes grassland patches independent of landscape context. The abundance of 16 grassland specialists was mainly influenced by management and to some extent also by landscape variables. Conclusion: Although species richness pattern reflect management and to some extent landscape variables, the response of individual species may be idiosyncratic. The historical signal from past landscapes is weak on present‐day species richness in highly transformed, agricultural landscapes. Generalizations of historical legacies on species diversity in grasslands should consider also highly transformed landscapes and not only landscapes with a high amount of diversity hotspots left.     

Diversity and distribution of soil fungal communities in a semiarid grassland

The fungal loop model of semiarid ecosystems integrates microtopographic structures and pulse dynamics with key microbial processes. However limited data exist about the composition and structure of fungal communities in these ecosystems. The goal of this study was to characterize diversity and structure of soil fungal communities in a semiarid grassland. The effect of long-term nitrogen fertilization on fungi also was evaluated. Samples of rhizosphere (soil surrounding plant roots) and biological soil crust (BSC) were collected in central New Mexico, USA. DNA was amplified from the samples with fungal specific primers. Twelve clone libraries were generated with a total of 307 (78 operational taxonomic units, OTUs) and 324 sequences (67 OTUs) for BSC and rhizosphere respectively. Approximately 40% of soil OTUs were considered novel (less than 97% identity when compared to other sequences in NCBI using BLAST). The dominant organisms were dark-septate (melanized fungi) ascomycetes belonging to Pleosporales. Effects of N enrichment on fungi were not evident at the community level; however the abundance of unique sequences, sampling intensity and temporal variations may be uncovering the effect of N in composition and diversity of fungal communities. The fungal communities of rhizosphere soil and BSC overlapped substantially in composition, with a Jaccard abundance similarity index of 0.75. Further analyses are required to explore possible functions of the dominant species colonizing zones of semiarid grassland soils.     

Soil arthropod composition differs between old-fields dominated by exotic plant species and remnant native grasslands

Secondary succession after agriculture abandonment (old-fields) is mostly dominated by exotic grass species. Non-native plant invasions may alter soil fauna, potentially inducing plant-soil feedbacks. Despite their importance in nutrient cycling and plant-soil interactions, meso and macrofauna received less attention than bacteria or fungi. Here we compared the composition of the soil arthropod community in native remnants and plant exotic-dominated old-fields grasslands in the Inland Pampa, Argentina. We sampled independent remnants and old-field grassland plots within a 100 km² agricultural landscape to test the hypothesis that the abundance of soil arthropod organisms is related to the quality of the plant biomass, whereas the diversity of the soil biota is related to plant species richness, resulting in a different soil biota composition because of differing plant communities. When compared to non-invaded remnant grasslands, soil activity and soil food-web characteristics of the old-fields sites included: 1. Higher total arthropod abundance, particularly of Isopoda, Pseudoescorpionida and Blattaria; 2. Lower abundance of Hymenoptera and Enthomobryomorpha (Collembola); 3. Lower diversity, and evenness, but similar richness of soil organisms orders; 4. Higher soil respiration rates and soil temperature; and 5. Higher total soil N and K⁺content, but lower soil P content. These results illustrate that soil arthropod composition can vary widely within grasslands patches depending on plant species composition. Also, the more diverse plant community of remnant grasslands supports a more diverse soil biota, although soil activity is slower. Our results support the strong linkage between plant community and soil arthropod composition and suggest that changes in soil biota composition might promote plant-soil feedback interactions inducing the persistence of these alternative grassland states in new agricultural human-modified landscapes.     

冬小麦免耕覆盖与生物有机肥施用对土壤细菌群落的影响

为揭示保护性耕作措施对土壤细菌群落结构及多样性的影响规律,选取免耕覆盖＋施生物有机肥（NF）、免耕覆盖＋不施生物有机肥（NC）、传统耕作不覆盖＋施生物有机肥（TF）和传统耕作不覆盖＋不施生物有机肥（TC）4个处理,以农田土壤生态系统为研究对象,利用16S rDNA基因Illumina MiSeq高通量测序技术,研究了冬小麦免耕覆盖与生物有机肥施用对土壤细菌群落结构及多样性的影响。结果表明：1）与TC处理相比,NF处理显著降低了土壤pH （P=0.03^*）,增加了土壤全氮（P=0.002^**）、总碳含量（P=0.0001^**,P=0.007^**）,影响了土壤碳/氮比分配（P=0.003^**）。2）从16个土壤样本中共获得细菌27门、86纲、125目、213科和315属,其中放线菌门（Actinobacteria）、酸杆菌门（Acidobacteria）、绿弯菌门（Chloroflexi）和变形菌门（Proteobacteria）为优势菌门,其相对丰度约占总丰度的82.40%。3）与传统耕作施生物有机肥处理相比,免耕覆盖施生物有机肥增加了土壤细菌的多样性指数（Simpson指数和Shannon指数）,降低了ACE丰富度指数。4）NMDS及多元分析结果表明：土壤细菌群落丰富度指数、多样性指数均与土壤pH、速效磷和土壤碳/氮比成正相关,与土壤微生物生物量碳（SMBC）和土壤总碳成负相关;其中,土壤pH和SMBC分别是影响酸杆菌门和放线菌门的主要驱动因子。施生物有机肥和耕作措施两种因素均对土壤细菌群落结构组成产生了影响,但以施用生物有机肥对土壤细菌群落多样性的影响较明显;此外,施用生物有机肥在传统耕作和免耕覆盖两种情况下均增加了冬小麦产量,但以传统耕作施生物有机肥处理最明显。因此,传统耕作配施生物有机肥是宁夏南部山区改善土壤理化性质、增加土壤细菌群落丰富度和多样性的重要途径。     

Plant functional diversity enhances associations of soil fungal diversity with vegetation and soil in the restoration of semiarid sandy grassland

The trait‐based approach shows that plant functional diversity strongly affects ecosystem properties. However, few empirical studies show the relationship between soil fungal diversity and plant functional diversity in natural ecosystems. We investigated soil fungal diversity along a restoration gradient of sandy grassland (mobile dune, semifixed dune, fixed dune, and grassland) in Horqin Sand Land, northern China, using the denaturing gradient gel electrophoresis of 18S rRNA and gene sequencing. We also examined associations of soil fungal diversity with plant functional diversity reflected by the dominant species' traits in community (community‐weighted mean, CWM) and the dispersion of functional trait values (FD_is). We further used the structure equation model (SEM) to evaluate how plant richness, biomass, functional diversity, and soil properties affect soil fungal diversity in sandy grassland restoration. Soil fungal richness in mobile dune and semifixed dune was markedly lower than those of fixed dune and grassland (P < 0.05). Soil fungal richness was positively associated with plant richness, biomass, CWM plant height, and soil gradient aggregated from the principal component analysis, but SEM results showed that plant richness and CWM plant height determined by soil properties were the main factors exerting direct effects. Soil gradient increased fungal richness through indirect effect on vegetation rather than direct effect. The negative indirect effect of FDis on soil fungal richness was through its effect on plant biomass. Our final SEM model based on plant functional diversity explained nearly 70% variances of soil fungal richness. Strong association of soil fungal richness with the dominant species in the community supported the mass ratio hypothesis. Our results clearly highlight the role of plant functional diversity in enhancing associations of soil fungal diversity with community structure and soil properties in sandy grassland ecosystems.     

Floristic diversity and the richness of locally endangered plant species of semi-natural grasslands under different management practices,southern Kyushu,Japan

Background: The rapid decline of semi-natural grasslands in Japan threatens many relic and endemic plant species. There is insufficient knowledge on how the impacts of land-use changes and management of grasslands have been affecting grassland ecosystems and what conservation measures may be taken to conserve as much of the existing plant diversity as possible.

Aim: We assessed the existing management regimes for their suitability for conserving Red Data Book (RDB) species.

Methods: We conducted our study in four districts of Kushima, Kyushu, south-west Japan, with different land-use histories. We compared species richness, plant density and abundance in six grassland types: regularly burnt, regularly mown, paddy levee, roadside, landslip and wetland communities in a total of 289 1 m x 1 m quadrats, recorded in172 grassland patches. Species richness plant density and abundance were analysed with special reference to RDB species under different land use history.

Results: Species richness of grasslands did not differ across different land use histories, yet our analysis showed that the reduced area of grasslands markedly affected the density of RDB species. Grassland types differed in their ability to support RDB species: regularly burnt grasslands were the richest in RDB species and poorest in alien species, followed by regularly mown grasslands, paddy levees, landslip, wetland and roadside communities.

Conclusions: Traditional management regimes, such as regular burning or mowing of grasslands have the best potential for conserving RDB species, and thus should be part of conservation management practices of semi-natural grasslands.