不同土壤类型下AM 真菌分布多样性及与土壤因子的关系

以禾本科植物群落为研究对象, 研究了宁夏六盘山林地、银川农耕地、暖泉农耕地、固原农耕地、盐池沙地、灵武沙地6 个采样地点5 种土壤类型(黑垆土、灌淤土、黄绵土、灰钙土、风沙土)下AM 真菌物种多样性及其与土壤因子的关系。结果表明: 5 种土壤类型采样点的植被根际土壤中共鉴定出5 属48 种AM真菌, 其中, 无梗囊霉属(Acaulospora)1 种, 巨孢囊霉属(Gigaspora)3 种, 球囊霉属(Glomus)37 种, 类球囊霉属(Paraglomus)1 种, 盾巨孢囊霉属(Scutellospora)6 种, 各采样点土壤均以球囊霉属为优势属。地球囊霉(G.geosporum)和木薯球囊霉(G. manihotis)是6 个采样地点中的优势种。不同土壤类型各采样点AM 真菌各属的频度存在明显差异, 球囊霉属在各点均有出现, 频度值最高。具有较高植被多样性的暖泉样点, AM 真菌的种属数量较多。土壤环境因子对AM 真菌孢子密度的影响因所处土壤、植被类型不同而异。pH、全盐、速效钾、速效磷等土壤肥力因子, 在PCA 轴上能最大程度地解释AM 真菌孢子密度与土壤环境因子之间相互关系的大部分信息。宁夏不同土壤类型区域中AM 真菌种类及分布一定程度上与该采样点的植被类型、植物多样性和土壤肥力特征相对应。     

Genetic diversity and gene flow in six accessions of Meso-America teosintes

The genus Zea (teosinte) has a native distribution from Mexico to Nicaragua (Meso-America region) and studies on teosinte species may help improve our understanding of maize genetics, population genetics, genome evolution and crop evolution. Moreover, since F1 hybrids between teosinte and maize are fertile, all teosinte species can potentially contribute to maize breeding in the form of traits such as resistance or tolerance to heavy metals in the soil and other adverse environmental conditions. Gene flow between maize and teosinte occurs in Mexico and Central America. This study analysed the genetic diversity of teosintes by using the microsatellite technique on a total of 120 individuals from six different species and 21 Simple Sequence Repeats (SSR). A total of 109 alleles were found and the number of alleles per locus ranged from 2 to 7. The genetic diversity varied between all species from 0.514 to 0.572, with a mean value of 0.548 (Nei index). Rare and unique alleles were detected in all species, with the highest frequencies found in Zea diploperennis Iltis, Doebley et Guzman, Zea perennis (Hitchc.) Reeves et Mangelsdorf and Zea nicaraguensis Iltis et Benz, which had more than seven rare alleles each. Analysis of molecular variance revealed that 19.87% of the variation between species was statistically significant (P < 0.001). When the different species were compared with the Wright (Fst) value, genetic variation between species was confirmed. The data also revealed a moderate rate gene flow between the species. Genetic diversity was found to be somewhat higher in Central America than in Mexico.     

Phylogenetic position of the disjunct species <Emphasis Type="Italic">Musa ornata</Emphasis> (Musaceae): first approach to understand its distribution

Musa L. commonly known as the banana group is one of the most important and oldest food crops of humankind. Among the wild relatives with ornamental interest in the genus, Musa ornata Roxb. shows a disjunct distribution between Asia and North America (Mexico). The wild occurrence of this species in Mexico has led to speculation about the evolutionary relationships with its Asian relatives. This study examined the phylogenetic relationships between intercontinental specimens of this species and, based on registered evidence, explored the more likely hypothesis about the origins of its distribution. The phylogeny of intercontinental specimens, along with other representatives of the same genus, was carried out using three molecular markers (ITS, trnL-F, and atpB-rbcL) and applying three phylogenetic reconstruction methods: maximum parsimony, maximum likelihood, and Bayesian inference. The genetic analysis of the combined dataset grouped together all the Mexican and most Asian specimens, but the monophyly of the species was not supported. The relationships suggest that Mexican populations may have originated from an Asian invasion. However, several studies and historical documents suggest the presence of Musa in America long before the arrival of Europeans. Based on its current distribution, phylogenetic evidence, and fossil record, this species’ disjunct distribution could be explained in terms of an ancestral distribution range that encompassed America and Asia, followed by its subsequent restriction to the Old World and a secondary dispersal by humans. However, further studies are necessary to shed more light on the origins of this disjunct distribution.     

Fungal-feeding habits of six nematode isolates in the genus Filenchus

The family Tylenchidae is a large group of soil nematodes but their feeding habits are not fully known. We studied the fungal-feeding abilities of nematodes in the genus Filenchus. We measured population growth rates (PGRs) of six nematode isolates, representing three Filenchus species, when feeding on seven fungal species on two types of culture media. On Potato Dextrose Agar (PDA) Filenchus misellus, Filenchus discrepans and an unidentified Filenchus sp. generally showed moderate to large PGRs on saprophytic fungi (Rhizoctonia solani, Chaetomium globosum, Coprinus cinereus, Flammulina velutipes) and low PGRs on plant-pathogenic fungi (Fusarium oxysporum, Pythium ultimum). In soil medium amended with chopped soybean plant material or wheat bran, the status of most of the fungi as food for the nematodes was similar to that on PDA, although PGRs tended to be lower in the soil medium. However, C. globosum, a good food on PDA, only supported low PGR in soil for each of the three nematodes. The PGRs of F. misellus on C. globosum in soil were still low even when types and amounts of organic matter amendments were varied. A nematophagous fungus, Pleurotus ostreatus (oyster mushroom), was determined to be a food for Filenchus on PDA or in soil, based on PGR measurements corrected for extraction efficiency. To determine whether fungal species and culture media affected nematode extraction efficiencies and, consequently, the apparent PGRs, we compared efficiencies between R. solani, C. globosum and C. cinereus, and between PDA and soil. The relatively low extraction efficiencies across fungal species in soil seemed responsible for the lower nematode PGRs in soil than on PDA. On PDA generally, fungal species did not affect the assessment. In soil, effects of fungal species on extraction were significant, but not consistent, across nematode species. Nevertheless, the extraction efficiency differences in soil were considered not to affect assessment of the three fungi as food for the nematodes. The confirmation that three Filenchus species reproduce by feeding on fungi in soil suggests that fungal-feeding is not an unusual habit in the field, in this genus. We believe that in community studies, nematodes in the genus Filenchus should be considered fungal feeders or root and fungal feeders, rather than only plant feeders. Our confirmation of fungal-feeding habits in the genus Filenchus supports the hypotheses that plant-feeding nematodes evolved from those feeding on fungi.     

Bacterial diversity and community structure along different peat soils in boreal forest

Bacteria in peat forest soil play important role in global carbon cycling. The distribution of bacteria population in different peat soils as a whole and how forest management practices alter the bacterial populations are still poorly known. Using pyrosequencing analysis of 16S rRNA gene, we quantified the diversity and community structure of bacteria in eight peat forest soils (pristine and drained) and two mineral forest soils from Lakkasuo, Finland with either spruce-dominant or pine-dominant tree species. In total, 191,229 sequences which ranged from 15,710 to 22,730 per sample were obtained and affiliated to 13 phyla, 30 classes and 155 genera. The peat forest soils showed high bacterial diversity and species richness. The tree species seems to have more strong impact on the bacterial diversity than the type of peat soil, which drives the changes in bacterial community structure. The dominant taxonomic groups across all soils (>1% of all sequences) were Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Planctomycetes and Verrucomicrobia. The relative abundance of bacteria phylum and genus differed between soil types and between vegetation. Significant differences in relative abundance of bacteria phyla were only found for Gemmatimonadetes and Cyanobacteria between the pristine and the drained peat forest soils. At genus level, the relative abundance of several genera differed significantly between the peat soils with same or different tree species, including Burkholderia, Caulobacter, Opitutus, Mucilanginibacter, Acidocella, Mycobacterium, Bradyrhizobium, Dyella and Rhodanobacter.     

Modelling bryophyte distribution based on ecological information for extent of occurrence assessment

For some groups such as bryophytes, the IUCN distribution criteria are of critical importance to evaluate threat status, since other parameters cannot be determined readily. In this study, we propose the use of ecological niche modelling methods to estimate the extent of occurrence (EOO) of species. Herbarium (LISU) collection data are used to estimate the potential distribution of bryophytes based on three different methods: GARP, MAXENT and ENFA. The records of bibliographic references were projected against model predictions, and used for validation purposes using the receiver operating characteristic (ROC) method, as well as knowledge about ecological and geographic affinities.Four species (Antitrichia californica, Riccia sommieri, Cryphaea heteromalla and Racomitrium hespericum) were chosen as case studies; they were selected to represent taxa with contrasting ecological requirements, biogeographic importance and conservation value. The main difference between the two approaches (topological and ecological) for determining EOO is that the former only consider species distribution in space, whereas ecological methods may include both spatial distribution as well as environmental ranges. The methodological advance presented here explores the links between population distribution and environmental data, filling the gaps between distribution and administrative borders.     

Effects of land use on soil erosion in a tropical dry forest ecosystem,Chamela watershed,Mexico

During the past few decades, Mexico has been converting tropical dry forest (TDF) into cropland and pasture, with land degradation expressed as soil erosion being the main environmental consequence. The factors and processes influencing soil erosion are related to scale. At a microscale, the stability of soil aggregates has a significant impact on soil erodibility and strongly influences other soil properties. However, at plot and watershed scales, these relationships are less well known. The relationships between the distribution of soil aggregate size, soil properties and soil erosion were examined for two soil geomorphological units (hillslopes over granite and hillslopes over tuffs) and three land uses (TDF, unburned pasture and burned pasture) within the Chamela watershed of west–central Mexico. To evaluate soil aggregation as a parameter for upscaling soil erosion, the researchers measured microtopographic features at plot scales and interpreted 1:35,000 panchromatic aerial photographs at a watershed scale. Analysis of variance indicated significant differences in soil organic carbon (P < 0.05) and soil moisture (P < 0.01) contents between the two soil geomorphological units, and field tests showed differences in soil texture and structure.     

Earthworm distribution and abundance predicted by a process-based model

Earthworms are significant ecosystem engineers and are an important component of the diet of many vertebrates and invertebrates, so the ability to predict their distribution and abundance would have wide application in ecology, conservation and land management. Earthworm viability is known to be affected by the availability and quality of food resources, soil water conditions and temperature, but has not yet been modelled mechanistically to link effects on individuals to field population responses. Here we present a novel model capable of predicting the effects of land management and environmental conditions on the distribution and abundance of Aporrectodea caliginosa, the dominant earthworm species in agroecosystems. Our process-based approach uses individual based modelling (IBM), in which each individual has its own energy budget. Individual earthworm energy budgets follow established principles of physiological ecology and are parameterised for A. caliginosa from experimental measurements under optimal conditions. Under suboptimal conditions (e.g. food limitation, low soil temperatures and water contents) reproduction is prioritised over growth. Good model agreement to independent laboratory data on individual cocoon production and growth of body mass, under variable feeding and temperature conditions support our representation of A. caliginosa physiology through energy budgets. Our mechanistic model is able to accurately predict A. caliginosa distribution and abundance in spatially heterogeneous soil profiles representative of field study conditions. Essential here is the explicit modelling of earthworm behaviour in the soil profile. Local earthworm movement responds to a trade-off between food availability and soil water conditions, and this determines the spatiotemporal distribution of the population in the soil profile. Importantly, multiple environmental variables can be manipulated simultaneously in the model to explore earthworm population exposure and effects to combinations of stressors. Potential applications include prediction of the population-level effects of pesticides and changes in soil management e.g. conservation tillage and climate change.     

河西走廊中段荒漠草地地上生物量分布特征及其与环境因子的关系

[目的]揭示河西走廊中段荒漠草地地上生物量的空间分布特征及其与环境因子的关系,为区域草地生态系统碳库及其变化评估提供基础资料。[方法]利用从52个样点获得的样方调查数据,进行统计分析。[结果](1)河西走廊中段荒漠草地单位面积地上生物量的范围为11.17~523.76g/m2,平均值为149.67g/m2,大致表现为西北高,东南低的分布特征;(2)调查中共出现15种优势植物群落地,地上部生物量黑果枸杞群落最小,为49.88±7.42g/m2,叉枝鸦葱群落最大,为201.69±98.48g/m2;(3)地上生物量与经度呈显著的负相关关系,与海拔呈显著的正相关关系;(4)土壤环境因子能够解释地上生物量39.8%的空间变异,其中土壤类型、土壤容重和土壤有机质的影响较显著,而土壤含水量的影响相对较弱。[结论]河西走廊荒漠草地地上生物量趋势为由西北至东南逐渐降低;海拔和土壤环境因子是影响分布格局的关键因子。     

Effects of edaphic factors on the tree stand diversity in a tropical forest of Sierra Madre del Sur, Mexico

Two sites with similar environmental parameters, except for the edaphic factor, were selected in the mountainous tropical forest of southern Mexico. Site 1 was established on an Alisol; site 2, on a Phaeozem. Representative soil profiles were examined on each of the sites, and topsoil was sampled on a regular grid pattern. The soil of site 2 was richer in organic matter and major nutrients and had a less acid reaction than the soil of site 1. The species diversity of the trees at site 2 (30 species) was higher than that at site 1 (17 species). The species compositions of the trees were different on the two soils: there were only six species in common for both sites. The coefficients of species similarity on the sites were low. We concluded that the presence of different soils within the same type of forest ecosystem increases its ??-diversity. The examination of edaphic preferences of the species showed that Alstonia longifolia and Thouinidium decandrum preferred rich soils, Inga punctata and Ocotea sinuata preferred poor soils, and Cupania dentata and Hamelia patens did not display preferences in the studied range of soil properties. Thus, the spatial variability of the soil properties affect the spatial pattern of tree species in the studied tropical forest ecosystems.     

Investigation and evaluation of the genus Lilium resources native to China

China is known as an important distribution center for the genus Lilium, with 55 species having been reported in the country thus far. This study was conducted to provide the first comprehensive evaluation of Lilium distribution in China. A total of 27 species of Lilium and 3 varieties were found to exist in the main centers of Lilium distribution in China; these species were identified and classified based on their morphological characteristics. The distribution and botanical characteristics of the various species are reviewed in this study. We also describe differences, mainly in flower color within the same species, which may be representative of new natural varieties or ecotypes. An analytical hierarchy process (AHP) utilizing 16 indicator characteristics was used to evaluate the collected Lilium resources based on their ornamental value, utilization potential, and ecological adaptability. L. dauricum received the highest AHP scores, indicating that it was the species best suited for sustained exploitation. In addition, L. henryi, L. rosthornii, L. tsingtauense, L. concolor var. pulchellum, L. lancifolium, and species with trumpet–shaped flowers also showed better potential for exploitation than other species. This study also provides references regarding the effective exploitation and use of wild Lilium resources.     

Population genetics and ethnobotany of cultivated Diospyros riojae Gómez Pompa (Ebenaceae), an endangered fruit crop from Mexico

The traditional cultivation of an endangered species, Diospyros riojae, in North-Central Mexico, and the sale of its fruit, is described for the first time. This is complemented by the first examination of genetic structure in New World Ebenaceae. Genetic comparisons are made among 27 accessions of D. riojae from across its known range of cultivation, and individuals of Diospyros conzattii, Diospyros digyna, Diospyros californica, Diospyros rosei, Diospyros rekoi and an unknown species of Diospyros from Oaxaca, Mexico. Morphological comparisons are made between D. conzattii, D. riojae, and the unknown species of Diospyros from Oaxaca. D. riojae is cultivated in two markedly different climates: arid and semi-arid localities west of the Sierra Gorda, especially near Tecozautla, Hidalgo, and humid areas of the Huasteca Region, east of the Sierra Gorda. Much lower levels of genetic diversity were detected in western populations, where populations are larger, and management intensity is the greatest. Neither the results of our genetic analysis, nor our morphological analysis of recent collections of D. riojae, D. conzattii, and an unknown species from Oaxaca, are consistent with the most recent revision of Neotropical Diospyros. Taxon-level divergence, rather than cultivar-level divergence, is suggested for D. riojae and D. conzattii.     

Soil microbial activity and free-living nematode community in the upper soil layer of the anticline erosional cirque,Makhtesh Ramon,Israel

The physical–chemical peculiarity of soil rock formations is one of the leading factors determining diversity and abundance of soil biota. The main aim of the present research was to study soil microbial and free-living nematode abundance and diversity on different soil rock formations (basalt, sandstone, limestone, granite and gypsum) of the Makhtesh Ramon erosional cirque. The obtained results showed the strong effect of soil features of different soil formations on microbial biomass and respiration as well as on the soil free-living nematode communities and its trophic and species composition. The Sorenson-Czenkanowski similarity index indicated significant differences between soil properties as well as between soil biota in observed soil formations. The qCO₂, which is known to increase according to the level of environmental stress, reached maximal values in the sandstone soil formation. The values of ecological indices such as Simpson's dominance index, maturity index and modification and species richness pointed to a specific ecological condition in the studied soil formations dependent on low content of an essential soil matter as soil moisture, organic matter and cations.     

Inferring habitat-suitability areas with ecological modelling techniques and GIS: A contribution to assess the conservation status of Vipera latastei

Some snakes are highly vulnerable to extinction due to several life history traits. However, the elusive behavior and secretive habits of some widespread species constrain the collection of demographic and ecological data necessary for the identification of extinction-prone species. In this scenario, the enhancement of ecological modelling techniques in Geographical Information Systems (GIS) is providing researchers with robust tools to apply to such species. This study has identified the environmental factors that limit the current distribution of Vipera latastei, a species with secretive behavior, and has evaluated how human activities affect its current conservation status, identifying areas of best habitat suitability in the Iberian Peninsula. Ecological-niche factor analysis (ENFA) indicated low marginality (0.299) and high tolerance (0.887) scores, suggesting strong tendency for the species to live in average conditions throughout the study area and to inhabit any of the environmental conditions. The analysis also revealed that this viper tends to select particular Mediterranean habitats, although topographic factors (altitude and slope) were the major environmental constraints for the Iberian distribution pattern of the species. The presence of other parapatric viper species in the north of the Iberian Peninsula (V. aspis and V. seoanei) and two human-related variables (landscape transformation and human density) also had a negative relation with the occurrence of V. latastei. All factors can explain its absence in northern Iberia and its fragmented distribution as currently is found mostly in mountains and relatively undisturbed low-altitude areas. The historical destruction and alteration of natural Mediterranean habitats and several life-history traits of the species contribute to its vulnerability to extinction. The ENFA analysis proved to be an outstanding method to evaluate the factors that limit the distribution range of secretive and widespread species such as V. latastei, updating evaluation of their conservation status.     

Effect of five forage legume covers on soil quality at the Eastern plains of Venezuela

At the Eastern planes of Venezuela, large to tracts of pastureland are sustained by low fertility acid soils that often lead to overgrazing, decreased pasture production, invasion by weeds, and soil compaction and erosion. The objective of this study was to evaluate the behavior of local forage legume species and its influence on chemical and biochemical properties of soil with the ultimate goal of identifying which one of these species have the potential to be used as cover in the establishment of a “Ley farming” system. The study was conducted on an Oxisol and used five local species from the genus Centrosema (Centrosema brasilianum, Centrosema macrocarpum, Centrosema pascuorum, Centrosema rotundifolium and Centrosema molle) which were established as cover for a period of 3 years. Dry matter (DM) and soil samples were collected twice a year, during the dry season (April) and during the rainy season (October). The soil parameters evaluated were total nitrogen, organic matter, calcium, potassium, magnesium, pH, soil respiration, and enzymatic activities that include β-glucosidase, arylsulphatase, phosphatase, urease, protease, dehydrogenase and catalase. The annual average data were used to identify indicators of soil quality through principal component analysis (PCA) that led to calculate a soil quality index (SQI). The results indicated that DM production varied among the different legume covers, showing C. macrocarpum the greatest productivity (1340 kg h⁻¹). The PCA identified seven of the tested soil variables as quality indicators: total nitrogen, pH, calcium, soil respiration and arylsulfatase and β-glucosidase activities. Total nitrogen, P and β-glucosidase activity were the indicators showing the largest changes over time being able to discriminate between treatments. After the 3 year period of the trial the SQI of the soil tested raised from 0.17 (very low quality) to 0.30 (low quality) where C. brasilianun, C. pascuorum and C. molle were established and to 0.40 (moderate quality) where C. macrocarpum and C. rotundifolium were established. Thus, the legume crop covers influenced positively the soil quality. C. macrocarpum was the legume cover that showed the greatest soil improvement, having the best potential to be used as forage cover to establish a “Ley farming” system at the Eastern planes of Venezuela.     

Diversity of arbuscular mycorrhizal fungi in red tangerine (Citrus reticulata Blanco) rootstock rhizospheric soils from hillside citrus orchards

Root colonization, abundance of spores and hyphae, as well as species diversity of arbuscular mycorrhizal (AM) fungi were analyzed in citrus orchards along an altitudinal gradient. The citrus trees were heavily colonized (50.87–77.45%) by native AM fungi. In citrus orchards located at <600 m above sea level (asl), we recorded more extensive hyphal and arbuscular colonization, and higher spore and hyphal length density. AM fungal colonization, spore density, and hyphal length density were closely correlated with edaphic factors such as available phosphorus, pH, and organic matter. A total of 18 AM fungal species belonging to 3 different orders, Archaeosporales (1 species), Diversisporales (7 species) and Glomerales (10 species), were identified on the basis of spore morphological characteristics. In orchards located at higher altitudes (≥700 m asl), we observed a significant decrease in species richness and Shannon–Wiener index values. However, in all of the surveyed orchards, Glomus aggregatum, Funneliformis mosseae and Rhizophagus intraradices were the dominant species. Isolate frequency and relative abundance of AM fungi exhibited clearly distinct distribution patterns among taxonomic families. Canonical correspondence analysis revealed that the AM fungal community structure was significantly influenced by environmental factors, especially altitude, pH, soil moisture, and available nitrogen. Our data indicated that environmental factors are important in determining AM fungal root colonization, propagule numbers, and species diversity in citrus orchards.     

Plant endemism and natural protected areas in the peninsula of Baja California, Mexico

The Peninsula of Baja California, Mexico has long been recognized as a hotspot for plant richness and endemism. However, its extraordinary diversity is not adequately protected by the existing protected areas. We analyzed the distribution of the endemic vascular flora of the peninsula, and its presence or absence in protected areas. We also identified regions with greater numbers of endemic species not currently under protected status. The families Asteraceae, Cactaceae, and Fabaceae alone contain 40% of the endemic species. All the peninsular species within the Begoniaceae, Thymeliaceae, Araliaceae and Hippocastanaceae are endemic. Of the total number of endemic taxa in the region, 76.4% are present within protected areas. The endemic genera Adenothamnus, Carterothamnus, Faxonia, and Ornithostaphylos are entirely absent from protected areas. Of the 567 endemics found in protected areas 75 represent varieties or subspecies Of the 175 not found in protected areas 21 are varieties or subspecies. A gap analysis identified that the areas with the highest number of unprotected endemic species are in the Mediterranean-type ecosystems of the north-west part of the peninsula and in the deciduous dry tropical communities of the cape region at the southernmost tip of Baja California. Our findings suggest that it is necessary to create several protected areas along the peninsula for the successful conservation of rare and endemic taxa These new areas should encompass a latitudinal gradient of biogeographical units (including Mediterranean communities and montane habitats of the Sierras) along the peninsula.     

Genetic variations and interrelationships in Vanilla planifolia and few related species as expressed by RAPD polymorphism

Vanilla is naturally distributed in Mexico and parts of Central America and the history of origin of cultivated vanilla suggests that the entire stock outside Mexico may be from a single genetic source. In the present study, RAPD polymorphism was used to estimate the level of genetic diversity and interrelationships among different collections of Vanilla planifolia Andr., and few related species, including both leafy and leafless types such as V. tahitensis J.W.Moore, V. andamanica, Rolfe, V. pilifera Holtt., and V. aphylla Blume. Studies revealed that there are very limited variation within collections of V. planifolia, indicative of its narrow genetic base, and of the related species we tested, V. tahitensis is nearest to V. planifolia. The species studied are diverse and have a similarity ranging from 1.2 to 57.3 %. Of the sampled taxa, V. andamanica is the most divergent and there is also reasonable variability within its collections, indicating the possibility of natural seed set. A total of 82 polymorphic bands expressed in the RAPD profiles were used to generate a genetic distance matrix, which was then used in cluster analysis. Specific groupings were revealed by the cluster analysis whereby the leafless forms (V. aphylla, V. pilifera and the new species) and V. andamanica formed separate clusters. This is the first report of species interrelationship studies, including both cultivated and wild vanilla species.