Effects of biological soil crusts on soil nematode communities following dune stabilization in the Tengger Desert,Northern China

Biological soil crusts (BSCs) play an important role in the dune fixation and maintaining soil biota in arid desert systems. Free-living soil nematode communities could be used as significant bioindicators to reflect soil recover regime after sand burial. However, the relationship between BSCs and nematodes is rarely known. To examine the effects of BSCs on soil nematodes, 72 soil samples under cyanobacteria–lichen and moss crusts were collected to analyse nematode communities in the different aged vegetated areas at the southeastern edge of the Tengger Desert. Our results showed the colonization and development of BSCs significantly enhanced nematode diversity. Nematode abundances, generic richness, H′, MI, EI and SI were greater under crusts than those under noncrust. In particular, nematode abundances, generic richness, H′, MI, EI and SI were positively correlated with crust ages. The differences in nematode communities were also dependent upon crust types. Nematode abundances and generic richness under moss crusts were higher than those under cyanobacteria–lichen crusts. This can be contributed to the present and succession of BSCs that increased thickness of topsoil after dunes have been stabilized, namely, creating suitable habitats and providing an essential food source for nematodes.     

Biodiversity of micro-eukaryotes in Antarctic Dry Valley soils with <5% soil moisture

Soils in the Dry Valleys of Antarctica are considered to be among the world's most extreme environments. These soils are old, cold and dry with low contents of organic carbon and nitrogen. Habitats adjacent to water (lakes and ice melts) have significant biological activity as demonstrated by the presence of algal mats, lichens and small invertebrates, particularly nematodes, tardigrades and rotifers. In contrast, there are extensive areas in the Dry Valleys that are extremely dry with less than 5% moisture content. These soils are often salty and appear to be barren of life as they have a coarse texture due to their lack of plant organic material. In contrast, molecular techniques (DNA extraction from soils, cloning and rDNA sequence analysis) demonstrated the presence of a complex micro-eukaryotic food web whose structure and composition varied with moisture content and location. Micro-eukaryotic communities in soils with 0.2-1.3% moisture were represented by species of the yeast genus Trichosporon and an unidentified clade of micro-eukaryotes, whereas levels from 3.1% to 4.9% contained complex food webs including primary producers (chlorophytes and stramenopiles), symbionts (lichen associated fungi), saprophytes (fungi), predators (alveolates and cercozoans) and fungal nematode parasite/pathogens. The soils had a diversity of species (80 species from 15 sites) with a restricted number (3-21 species) at each site. The sensitive and measurable community structure of the low moisture Dry Valley soils provides an unparalleled opportunity to examine local and global environmental effects on micro-eukaryotic community dynamics with multiple trophic levels.     

Soil erosion and hydrological response to land abandonment in a central inland area of Portugal

This paper analyses the effects of land abandonment on runoff and sediment yield in a central inland area of Portugal. Rainfall simulation experiments were performed in areas of traditional land use (land cultivated with cereals) with various types of soil plant cover associated with the period of abandonment (4–5 years, 15–20 years and 30–40 years) in two different seasons, namely under very dry conditions and after a long wet period. Statistical analysis showed a notable difference between the cultivated soils and those abandoned for a long period of time, which included appreciable vegetation recovery, higher organic matter content and negligible overland flow and soil loss. Cereal cultivation, in particular ploughing, is a very negative land management practice, due to the high runoff and soil loss. Within 4–5 years a crust develops over abandoned soils with sparse herbaceous plant cover, particularly after a dry season, which enhances runoff and sediment yield. In scrubland and oak plots, although marked water repellency was registered at the end of a dry, warm season, its influence seems to be irrelevant in terms of overland flow and erosion yield. The major factor in controlling overland flow and reducing soil erosion rates appears to be the role played by vegetation in protecting the soil surface and supplying organic carbon to the top layer. Copyright © 2010 John Wiley & Sons, Ltd.     

Controls of infiltration–runoff processes in Mediterranean karst rangelands in SE Spain

Semiarid karst landscapes represent an important ecosystem surrounding the Mediterranean Basin for which little is known on runoff generation. Knowledge of the sources and patterns of variation in infiltration–runoff processes and their controls is important for understanding and modelling the hydrological functions of such ecosystems. The objectives of this paper are to determine the infiltration rates and their controls in a representative mountain karst area (Sierra de Gádor, SE Spain) at micro-plots and to investigate the integrated response of rainfall on a typical hillslope. Rainfall simulations in micro-plots and natural rainfall-runoff monitoring on a hillslope were carried out complementarily. We investigated the role of soil surface components (vegetation, rock outcrop, fracture, and soil crust), topographic position, antecedent soil moisture, and rainfall characteristics in regulating infiltration–runoff processes. Results of rainfall simulation revealed the importance of vegetation cover and the presence of rock fractures in promoting the infiltration in the limestone karst landscape, while bare patches and rock outcrops acted as sources for runoff. All plots with > 50% vegetation cover had no runoff with up to 55 mm h^− 1 of simulated rain. In contrast, nearly all bare plots had runoff under the same simulated rain, with runoff coefficients ranging from 3.1 to 20.6% on dry soil surface conditions, and from 2.0 to 65.4% on wet soil surfaces. Runoff coefficients amounted to 59.0–79.5% for rock outcrops without cracks, but were drastically reduced by the presence of cracks. The surfaces with rock fragments resting on the soil (generally located in the middle of the slopes) prevented more effectively the runoff generation than those surfaces where rock fragments were embedded in the top soil. Antecedent soil moisture had significant impact on runoff generation, with wet soil having doubled runoff coefficient, shortened time to runoff, and increased runoff rate compared to the same but dry soil. Linear regressions indicated that the main controls for constant infiltration rate were the cover percentages of vegetation and litter, plus rainfall intensity; while the major controls for runoff coefficient were the bare soil and vegetation coverage, plus rainfall intensity. High infiltration rates measured at the micro-plots agreed with low intra-event runoff coefficients (mostly below 1%) observed under natural rainfalls at the hillslope. Runoff depth and coefficient at the hillslope was significantly correlated with rainfall depth, maximum hourly rainfall intensity and antecedent precipitation over 20 days (AP₂₀). During the 1.5-year monitoring period from Sep-2003 to Mar-2005, the overall infiltration was 41% of the total rainfall amount and the maximum infiltration rate was almost 94% of the largest single rainfall event. The results from this study contribute to improved understanding of the magnitude and controls of the surface runoff in semiarid karst mountain areas.     

中国西南喀斯特土壤水分特征研究进展

喀斯特土壤水分是岩溶植被的生命线、岩溶作用的驱动力和土壤流失的重要影响因子,关系岩溶区生态地质环境安全和社会经济发展。现有研究表明:中国西南喀斯特土壤水分含量差异大,土壤水分含量森林>灌丛>草地,阔叶林>针叶林,天然林>人工林;土壤水分含量空间分布呈斑块状,具有变异性和相关性,坡面分布复杂;含水量随土壤深度增加而增加,随季节演替呈低—升—高—降变化,干湿季差异大,日变化表现为从早到晚先降后升;土石相间分布、土下裂隙发育的小生境差异是喀斯特土壤水分空间差异大、坡位变化异常的重要原因。今后的研究重点是:喀斯特土壤水分的理化性质,土壤储水库的动态特征、适度水分、干季保水补水工程技术和湿季土壤无流失排水工程技术,对全球变化的响应,滇东高原喀斯特区土壤水分的相关研究等。     

Biological soil crust and surface soil properties in different vegetation types of Horqin Sand Land,China

Physical and chemical properties (including coverage, thickness, hardness, moisture, particle size distribution, organic matter and nutrient contents etc.) of biological soil crust and 0–5.0 cm surface soil under the crust in three types of vegetation (semi-shrub Artemisia frigida, shrub Salix gordejevii and tree Populus simonii) were surveyed in 2005 and 2006 in Horqin Sand Land to understand the effects of different vegetation types on development of soil crust and surface soil properties under crust. The results showed that 1) no physical soil crust or biological soil crust (BSC) formed on mobile dunes without vegetation, though most ground surface in originally mobile dunes had been covered by BSC fifteen years after planted vegetation was established; 2) BSC development was best in shrub S. gordejevii sites, second in semi-shrub A. frigida sites, and weakest in tree P. simonii sites; 3) development of BSC was better in moss crust distributed mainly beneath or near plant canopies than in lichen crust distributed mainly between plant canopies in all three vegetation types; 4) surface soil properties 0–5.0 cm under BSC were improved significantly in all three vegetation types compared to those in mobile sand land. The magnitude of improvement was greater in S. gordejevii sites than in A. frigida and P. simonii sites, and greater in moss crust sites than lichen crust sites, but the magnitude of improvement decreased significantly with increasing surface soil depth; 5) based on the above-mentioned results, we suggest that S. gordejevii should be favored in future planting in Horqin Sand Land.     

Soil nematode communities are ecologically more mature beneath late- than early-successional stage biological soil crusts

Biological soil crusts are key mediators of carbon and nitrogen inputs for arid land soils and often represent a dominant portion of the soil surface cover in arid lands. Free-living soil nematode communities reflect their environment and have been used as biological indicators of soil condition. In this study, we test the hypothesis that nematode communities are successionally more mature beneath well-developed, late-successional stage crusts than immature, early-successional stage crusts. We identified and enumerated nematodes by genus from beneath early- and late-stage crusts from both the Colorado Plateau, Utah (cool, winter rain desert) and Chihuahuan Desert, New Mexico (hot, summer rain desert) at 0–10 and 10–30 cm depths. As hypothesized, nematode abundance, richness, diversity, and successional maturity were greater beneath well-developed crusts than immature crusts. The mechanism of this aboveground–belowground link between biological soil crusts and nematode community composition is likely the increased food, habitat, nutrient inputs, moisture retention, and/or environmental stability provided by late-successional crusts. Canonical correspondence analysis of nematode genera demonstrated that nematode community composition differed greatly between geographic locations that contrast in temperature, precipitation, and soil texture. We found unique assemblages of genera among combinations of location and crust type that reveal a gap in scientific knowledge regarding empirically derived characterization of dominant nematode genera in deserts soils and their functional role in a crust-associated food web.     

Characteristics of bacteria in the forest soils under natural vegetation

Characteristics of the predominant bacteria isolated in November and May from the forest soils of both dry and wet types under natural vegetation were studied.

Although Gram-negative rods were the most abundant bacteria in both soil types and in both seasons, their contents were less and other bacteria especially spore-forming ones increased in May.

Among Gram-negative rods in the soil of the dry type in November, the most predominant was those with nonchromogenic rods motile with polar flagella which grew in a simple synthetic media containing glucose or p-hydroxybenzoate and ammonium as the sole carbon and nitrogen sources. In May, the ratio of the bacteria which require amino nitrogen or those with more chomplex nutritional requirement increased. In the soil of moderately wet type, the difference in kinds of bacteria between the two seasons was not so clear as that in the dry type.

Most of Bacillus species obtained in these soils were those requiring amino acids or other growth factors among which B. cereus was most abundant.     

How different or similar are nematode communities between a paddy and an upland rice fields across a flooding-drainage cycle?

The paddy field is being recognised as a biodiversity hotspot fostering a variety of organisms. However, there are few studies on the ecology of paddy field nematodes. We characterised nematode communities in rice paddy fields by comparing them with upland fields of rice or soybean. We examined nematode communities of the top (0-15 mm) and second (15-50 mm) soil layers before flooding (March or April), during flooding (June or July) and during the draining period (October) 2007-2009. We found that the nematode community in the paddy was different than that in the upland fields during all periods. Rhabdolaimus, Tobrilus, Mesodorylaims and Monhysteridae characterised the top of the paddy and Hirschmanniella characterised the second layer of the paddy. Total nematode density was generally lower in the paddy than in the upland field. However, the density in the paddy top layer increased with time from the flooding period to the draining period, during which time it was about the same as (or even greater than) the peak density in the upland fields. The density in the second layer of the paddy remained lower than that in the top layer of the paddy throughout the time course. Community diversity values were generally greater in the paddy top layer than in the paddy second layer across the six sampling periods, but periodic differences between the paddy and upland fields or between soil layers were not significant. During the flooding period, the F/(F + B) (13-37) and Enrichment Index (17-38) values were lower in the paddy than in the upland fields (32-47, 37-74, respectively) to reflect that bacteria dominate over fungi with slow decomposition due to anaerobic conditions in the flooded paddy field. In addition, particularly in the top layer, the Maturity (2.0-2.4) and Structure Index (23-72) values were greater in the paddy than in the upland fields (1.7-2.1, 9-15, respectively), indicating a well-developed ecosystem under water. These unique nematode communities persisted during the draining period, but there was a rapid increase in opportunistic bacterivores, which increased the EI values. We suggest that bactivorous nematodes in the families Cephalobidae and Chronogasteridae, herbivores in the genus Hirschmanniella, and fungivores in the genus Filenchus may be specific to paddy field soil rather than to pond and lake sediments.     

藏北高寒草甸植物群落对土壤线虫群落的影响

2011年5月—11月,对西藏北部高寒草甸3种典型植物群落下0～30 cm范围内不同深度土层的土壤线虫群落进行调查,浅盆法收集土壤线虫,应用个体密度、多样性指数等特征值来分析高寒环境下土壤线虫群落的组成、分布特征与多样性。调查共分离得到33 038条土壤线虫,隶属于2纲6目51科93属;线虫个体密度平均为847条100 g-1干土;表聚性明显。研究结果表明,不同植物群落间的土壤线虫群落组成存在一定差异,土壤线虫数量的大小顺序为委陵菜植物群落<藏北嵩草植物群落<高山嵩草植物群落,土壤线虫数量差异显著(p<0.05);土壤线虫数量随生长季变化发生明显波动,返青期最多,盛长期次之,枯草期最低;不同植物群落的优势属种类不同。生物多样性为委陵菜植物群落>高山嵩草植物群落>藏北嵩草植物群落,这可能是放牧干扰强度不同,以及植物群落影响下的土壤性质分异所导致的结果。总之,不同植物群落下土壤线虫群落特征的分异初步显示出线虫指示环境因子影响土壤生态系统的潜力。     

Design and evaluation of nematode 18S rDNA primers for PCR and denaturing gradient gel electrophoresis (DGGE) of soil community DNA

Consensus nematode 18S ribosomal DNA primers were designed by aligning available 18S sequences and identifying a variable region flanked by highly conserved regions. These primers were then used to amplify nematode 18S rDNA from whole soil community DNA extracted from a range of European grassland types. Cloning of the PCR amplicons (778 bp) followed by restriction digest analysis (RFLP) resulted in the recovery of 34 unique nematode sequences from the four grasslands studied. Comparison of these data with the limited number of 18S rDNA nematode sequences currently held in on-line databases revealed that all of the sequences could be assigned to known nematode taxa albeit tentatively in some cases. Two of the sequences recovered from the site in the Netherlands (wet, hay-grassland) were recovered in a clade that included a sequence of the genus Trichodorus whilst other sequences from this site showed similarity with 18S rDNA sequences of the genus Prismatolaimus (five sequences), Xiphinema (one sequence) and Enoplus (one sequence). Of the remaining sequences, two showed some affinity with Mylonchulus (UK, upland peat), four with Steinernema (UK) and one sequence with Mesorhabditis (Hungary, east European Steppe). Three sequences from the Netherlands and one from Hungary were recovered in a clade that included a sequence of the genus Pratylenchoides whilst three further sequences from the Netherlands and two from Hungary were recovered in a clade encompassing the genus Globodera. Of the remaining nine sequences, two (NL6, NL62) formed a distinct lineage within the Adenophorea with 90% bootstrap recovery in a paraphyletic clade that included sequences of Prismatolaimus and Trichodorus. Seven sequences (three from the Netherlands, three from the UK and one from Greece) were left unassigned though the tree topology suggested some relationship (58% bootstrap recovery) with the genus Cephalobus. To assess whether primers used to amplify 18S rDNA might be used to fingerprint genetic diversity in nematode communities in soil, the environmental sequence data were used to design a second set of primers carrying a GC-clamp. These primers amplified a 469 bp fragment internal to the region flanked by the primer set used to derive the nematode trees and were used to amplify 18S rDNA for subsequent analysis using denaturing gradient gel electrophoresis (DGGE). DGGE analysis of six major European grassland types revealed considerable genetic diversity between sites. However, the relationships seen with the DGGE data were inconsistent with previous studies where the same soils had been characterized with respect to functional and morphological diversity. To confirm that this second set of primers was amplifying nematode sequences, selected bands on the DGGE gels were extracted, PCR amplified and sequenced. The final alignment was 337 bases. These analyses revealed the presence of sequence signatures from the genera Paratrichodorus, Plectus, Steinernema, Globodera, Cephalobus and Pratylenchoides.     

Annual and long-term fluctuations of the nematode fauna in a Swedish Scots pine forest soil

Samples from an old Scots pine forest at Ivantjärnsheden in the middle of Sweden were used to study predictability and patterns of variation of soil nematode communities. There were two annual sampling series (1974–75 and 1977–78) and one long-term series sampled in September ten times over a period of 25 years. The abundance and the composition of the fauna fluctuated rather considerably in both the annual and long-term series. In the annual series abundance and species composition varied in a way which can partly be explained by changes in temperature and moisture. Total nematode abundance was influenced by soil water contents as indicated by co-variations with precipitation. Although the variations in abundance and fauna composition were large no systematic changes could be detected during 25 years. The differences in faunal structure between the two annual series were greater than between the annual and the long-term series.In all series there was a distinct vertical stratification of the fauna. In the superficial moss and litter layers species belonging to Adenophorea (Plectus) dominated. In deeper layers members of Rhabditida (Acrobeloides) contributed a greater proportion of the fauna. Variations of the annual series indicate that coexistence of different nematode species is facilitated by differences in response to temperature and moisture. The abundance of fungal and bacterial feeders changed in a regular way. During the summer the proportions of fungal and bacterial feeders were almost equal, but during the wet and cold winter the proportion of bacterial feeders increased. Rapidly growing bacterial feeding species belonging to Rhabditida were common in late summer and early autumn, whereas the more slowly growing bacterial feeders belonging to Adenophorea were most abundant during the winter. Although the community fluctuated rather much the average values indicated a rather high degree of predictability and also a high similarity with nematode faunas of other pine forest soils.     

气候变化和人类活动对西南喀斯特地貌区植被NDVI变化相对作用

定量厘定气候变化和人类活动对西南喀斯特地貌区植被NDVI变化的相对作用,可为揭示喀斯特地貌区植被NDVI时空演变特征及其驱动机制提供依据。以MODIS NDVI、SRTM DEM、基于站点的气象数据为数据源,建立Theil-Sen Median斜率估计、残差分析、相对作用分析等多数学模型,分析了2001—2019年西南喀斯特地貌区气候变化和人类活动对植被NDVI变化的相对作用,揭示植被NDVI与降水、气温、相对湿度和日照时数的相关性。结果表明:研究时段内西南喀斯特地貌区植被NDVI总体上呈上升态势,植被NDVI变化趋势呈现明显的空间异质性,植被NDVI增加的区域面积远大于减少的区域面积; 研究区植被改善和植被退化均受人类活动的主导。研究时段内西南喀斯特地貌区植被NDVI与降水、气温以及相对湿度整体呈正相关,相关程度依次递减,与日照时数呈负相关。综上可知,研究时段内西南喀斯特地貌区植被覆盖呈改善态势,人类活动可被认为是影响西南喀斯特地貌区植被NDVI变化的主要驱动力,植被NDVI与降水、气温、相对湿度和日照时数的相关系数在空间上呈现明显的异质性。     

Physiological and DNA fingerprinting of the bacterial community of Meloidogyne fallax egg masses

Bacterial communities associated with the plant-parasitic nematode Meloidogyne fallax egg masses were compared with those present in the rhizoplane. Two agricultural soils with different nematode population dynamics were used in a glasshouse study, with either potato or tomato as host plant for the nematode. DNA fingerprints and bacterial community level physiological profiles (CLPP) were studied using PCR-DGGE of 16S rRNA genes and Biolog Eco MicroPlates. CLPP and DNA fingerprinting both showed differences between egg mass and rhizoplane bacterial communities. PCR-DGGE showed some bands specific to the egg mass samples. These bands were present in egg masses from both soils. This study shows that egg masses of M. fallax have a distinct bacterial community from that of the adjacent rhizoplane. Soil and host plant factors interactively influence the bacterial egg mass community. Differences in nematode population dynamics between the sample sites cannot be clearly related to the observed differences in the egg mass microbial communities.     

1999-2019年西南喀斯特地区NDVI时空变化及其气候驱动

[目的]西南喀斯特地区生态环境脆弱,对其植被覆盖变化及气候驱动机制进行研究具有重要意义。[方法]基于1999—2019年SPOT NDVI数据和同期209个气象站点的气温和降水数据,采用Theil-Sen+Mann-Kendall趋势分析法、偏相关分析和复相关分析法,探讨西南喀斯特地区NDVI时空变化及其气候驱动。[结果]1999—2019年西南喀斯特地区NDVI呈显著上升趋势,整体植被覆盖较好;NDVI变化主要以极显著上升趋势为主,仅5.73%的地区呈退化趋势。NDVI与气温和降水整体上均呈正偏相关关系,气温对NDVI的影响强于降水,且存在空间差异性。NDVI与气温和降水的复相关显著性通过0.05,0.01水平的面积分别占15.12%,5.68%;NDVI主要受气温驱动,占研究区面积的13.90%,其他气候因子驱动类型占比均未超过3%。[结论]揭示了西南喀斯特地区植被覆盖的时空变化特征,明确了气候因子对植被覆盖变化的驱动机制。     

Altitudinal terrestrial isopod diversity

We have assessed the diversity of terrestrial isopods across an elevational and habitat gradient on Mt. Panachaiko (NW Peloponnisos, Greece). Previous knowledge on the biodiversity of this mountain was restricted to very few records of individual species, and no systematic sampling had ever been applied for any animal taxon. We selected the most representative habitat types within an altitudinal range from 750 to 1700 m a.s.l., where we applied qualitative and quantitative monthly sampling using hand collecting and pitfall traps for 6 months during the snow-free period (June–November). We sampled three sites with maquis vegetation, one site with fir forest, one with sparse hawthorn vegetation and two at a highland meadow, and we compared the distribution and abundance patterns of isopod species among these habitat types. Overall, 13 isopod species were found, seven of which were also captured in pitfall traps. One species, Armadillidium lobocurvum, was extremely abundant at the most elevated sites, resulting in very uneven patterns of abundance. The habitat types with higher diversity of isopod species were the sparse hawthorns and the open maquis, and the richest month was July. We also discuss the phenology of the most abundant species at the highland meadows.     

The influence of <Emphasis Type="Italic">Aster x salignus</Emphasis> Willd. Invasion on the diversity of soil yeast communities

The annual dynamics of yeast communities were studied in the soddy-podzolic soil under the thickets of Aster x salignus Willd., one of the widespread invasive plant species in central Russia. Yeast groups in the soils under continuous aster thickets were found to differ greatly from the yeast communities in the soils under the adjacent indigenous meadow vegetation. In both biotopes the same species (Candida vartiovaarae, Candida sake, and Cryptococcus terreus) are dominants. However, in the soils under indigenous grasses, eurybiontic yeasts Rhodotorula mucilaginosa, which almost never occur in the soil under aster, are widespread. In the soil under aster, the shares of other typical epiphytic and pedobiontic yeast fungi (ascomycetic species Wickerhamomyces aniomalus, Barnettozyma californica and basidiomycetic species Cystofilobasidium macerans, Guehomyces pullulans) significantly increase. Thus, the invasion of Aster x salignus has a clear effect on soil yeast complexes reducing their taxonomic and ecological diversity.     

Characterization of the soil organic matter and plant tissues in an initial stage of the plant succession and soil development by means of curie-point pyrolysis coupled with GC-MS

The composition of the soil organic matter in soil developing under the influence of vegetation during the primary succession in the poor sandy area was investigated. The Curie-point pyrolysis method coupled with gas chromatographic separation and mass spectrometric identification of pyrolysates was applied during the investigation. A comparison of occurrence and diversity in composition of organic compounds in plant tissues and humus horizon of soils under the communities of coniferous forest series in the initial stages and phases was carried out. A large diversity of organic compounds under Algae-Cyanophyta communities, biological soil crusts and Polytrichum piliferum was noticed. A clear differentiation in the composition of the soil organic matter at different phases of succession under predominating communities with cryptogamous and vascular plants was observed. The analysis of organic compounds in plant tissues was found to facilitate the determination of origin of various groups of organic compounds in the soil. The results obtained from the Curie point pyrograms in the humus horizon (A) under grasses (Corynephorus canescens, Koeleria glauca) differed from the pyrolysates obtained under Algae-Cyanophyta communities. The polysaccharide derivates are more frequent in the pyrolysis products under algae, grasses (Corynephorus canescens, Koeleria glauca) and mosses than under Pinus sylvestris. In the beginning of the terminal stage of succession, lignin, phenols and aliphatic substances, prevailed over the polysaccharide derivates in the humus horizon.     

Soil fungal community structure along a soil health gradient in pea fields examined using deep amplicon sequencing

Soil fungi and oomycetes (syn. peronosporomycetes) are the most common causes of pea diseases, and these pathogens often occur in complexes involving several species. Information on the dynamics within this complex of pathogens, and also between the complex of pathogens and other fungi in the development of root disease is limited. In this study, next-generation sequencing of nuclear ribosomal internal transcribed spacer-1 was used to characterize fungal communities in agricultural soils from nine pea fields, in which pea roots showed different degrees of disease. Fungal species richness, diversity, and community composition were analyzed and compared among the different pea soils. After filtering for quality and excluding non-fungal sequences, 55,460 sequences clustering into 434 operational taxonomic units (OTUs), were obtained from the nine soil samples. These sequences were found to correspond to 145–200 OTUs in each soil. The fungal communities in the nine soils were strongly dominated by Ascomycota and Basidiomycota. Phoma, Podospora, Pseudaleuria, and Veronaea, at genus level, correlated to the disease severity index of pea roots; Phoma was most abundant in soils with diseased plants, whereas Podospora, Pseudaleuria, and Veronaea were most abundant in healthy soils. No correlation was found between the disease severity index and the abundance of some of the other fungi and oomycetes normally considered as root pathogens in pea.     

Size spectra of soil nematode assemblages under different land use types

Although the slopes of size spectra (plots of abundance on organism size) have been widely used to assess aquatic and terrestrial communities, size spectra have not been used to assess soil nematode communities. Two forms of size spectra (one based on the average biomass of nematode genera and another based on the average biomass of nematode size classes were used to assess the soil nematode communities in managed forage land and cropland, and in naturally developed grass-shrubland and secondary forests in a karst peak-cluster depression area. R² values were larger for size spectra based on nematode size classes than on genera. The slopes of the size spectra for total nematodes were more negative in forage land and cropland than in grass-shrubland and secondary forests, which was consistent with disturbance of the soil nematode community by agricultural management. The results suggest that size spectra analysis is applicable to soil nematodes; they can reveal different land use types and may reveal the degree to which the soil nematodes in particular and the soil community in general have been disturbed. Size spectra may be more useful if based on nematode size classes rather than on genera.