Bacterial Communities Associated with <Emphasis Type="Italic">Chenopodium album</Emphasis> and <Emphasis Type="Italic">Stellaria media</Emphasis> Seeds from Arable Soils

The bacterial community compositions in Chenopodium album and Stellaria media seeds recovered from soil (soil weed seedbank), from bulk soil, and from seeds harvested from plants grown in the same soils were compared. It was hypothesized that bacterial communities in soil weed seedbanks are distinct from the ones present in bulk soils. For that purpose, bacterial polymerase chain reaction denaturing gradient gel electrophoresis (PCR–DGGE) fingerprints, made from DNA extracts of different soils and seed fractions, were analyzed by principal component analysis. Bacterial fingerprints from C. album and S. media seeds differed from each other and from soil. Further, it revealed that bacterial fingerprints from soil-recovered and plant-harvested seeds from the same species clustered together. Hence, it was concluded that microbial communities associated with seeds in soil mostly originated from the mother plant and not from soil. In addition, the results indicated that the presence of a weed seedbank in arable soils can increase soil microbial diversity. Thus, a change in species composition or size of the soil weed seedbank, for instance, as a result of a change in crop management, could affect soil microbial diversity. The consequence of increased diversity is yet unknown, but by virtue of identification of dominant bands in PCR–DGGE fingerprints as Lysobacter oryzae (among four other species), it became clear that bacteria potentially antagonizing phytopathogens dominate in C. album seeds in soil. The role of these potential antagonists on weed and crop plant growth was discussed.     

Small-scale shifting mosaics of two dominant grassland species: the possible role of soil-borne pathogens

We analyzed the dynamics of dominant plant species in a grazed grassland over 17 years, and investigated whether local shifts in these dominant species, leading to vegetation mosaics, could be attributed to interactions between plants and soil-borne pathogens. We found that Festuca rubra and Carex arenaria locally alternated in abundance, with different sites close together behaving out of phase, resulting in a shifting mosaic. The net effect of killing all soil biota on the growth of these two species was investigated in a greenhouse experiment using gamma radiation, controlling for possible effects of sterilization on soil chemistry. Both plant species showed a strong net positive response to soil sterilization, indicating that pathogens (e.g., nematodes, pathogenic fungi) outweighed the effect of mutualists (e.g., mycorrhizae). This positive growth response towards soil sterilization appeared not be due to effects of sterilization on soil chemistry. Growth of Carex was strongly reduced by soil-borne pathogens (86% reduction relative to its growth on sterilized soil) on soil from a site where this species decreased during the last decade (and Festuca increased), while it was reduced much less (50%) on soil from a nearby site where it increased in abundance during the last decade. Similarly, Festuca was reduced more (67%) on soil from the site where it decreased (and Carex increased) than on soil from the site where it increased (55%, the site where Carex decreased). Plant-feeding nematodes showed high small-scale variation in densities, and we related this variation to the observed growth reductions in both plant species. Carex growth on unsterilized soil was significantly more reduced at higher densities of plant-feeding nematodes, while the growth reduction in Festuca was independent of plant-feeding nematode densities. At high plant-feeding nematode densities, growth of Carex was reduced more than Festuca, while at low nematode densities the opposite was found. Each plant species thus seems to be affected by different (groups of) soil-borne pathogens. The resulting interaction web of plants and soil-borne pathogens is discussed. We hypothesize that soil disturbances by digging ants and rabbits may explain the small-scale variation in nematode densities, by locally providing “fresh” sand. We conclude that soil-borne pathogens may contribute to plant diversity and spatial mosaics of plants in grasslands. Received: 19 January 2000 / Accepted: 11 April 2000     

The bryophyte diaspore bank and its role after small-scale disturbance in a boreal forest

Abstract. The composition of the bryophyte diaspore bank in an old-growth Picea abies forest was studied before and after experimental disturbance of forest-floor patches. 40 species, both hepatics and mosses, emerged from spores, and probably also from gemmae and moss fragments, in greenhouse cultivations of soil samples. The three most abundant taxa were Pohlia nutans, Sphagnum spp. and Polytrichum commune/longisetum. Initially, the number of species from the diaspore bank in mineral soil, 9.9 species/sample, was higher than that in humus, 6.6. Four years after the disturbance took place, the reverse was found. Several species that are typical colonisers of disturbed soil were very common in the diaspore bank. By contrast, some of the most abundant forest floor species appeared to be absent. The diaspore bank of bryophytes appears to play a role similar to that of the seed bank in vascular plants: (1) it allows species to survive unfavourable periods (temporal dispersal); (2) it facilitates rapid colonisation after disturbance; (3) it influences the post-disturbance species composition and diversity. The results emphasise that the understanding of vegetation succession patterns is, to a large extent, dependent on quantitative data on the relative importance of spatial and temporal dispersal.     

From plant traits to invasion success: Impacts of the alien Fallopia japonica (Houtt.) Ronse Decraene on two native grassland species

Alien invasive plants threaten biodiversity, productivity and ecosystem functioning throughout the world. We examined the effect of Fallopia japonica on two native grassland species (Trifolium repens, Lolium perenne). We hypothesized that its negative effects on the native species are dependent on three mechanisms: (i) allelochemicals released and accumulated in soil with a history of invasion, (ii) altered soil biota and (iii) direct resource competition. We measured the response of the native species as the difference in their functional traits when grown under the three conditions. Our results demonstrate that neither allelochemicals nor soil biota from soil with history of F. japonica invasion had measurable effects on either species. Competition with the invader strongly reduced height, biomass and specific leaf area (SLA) of T. repens, while it had a lower effect on L. perenne. Furthermore, our results reveal that F. japonica took advantage of a positive plant–soil and plant–plant interaction. The results show that the prominent mechanism underpinning the invasion success of F. japonica in the grassland was the direct resource competition. This prominent role is also confirmed by the significant interactions between competition, allelochemicals and soil biota from soils with history of invasion of F. japonica on SLA of the native species.     

The effects of oxalates produced by Salsola tragus on the phosphorus nutrition of Stipa pulchra

Oxalic acid is produced by some species of plants and mycorrhizal fungi and it may solubilize unavailable soil phosphorus (P) bound by cations (Ca⁺⁺, Al⁺⁺, Fe⁺⁺⁺). Field and greenhouse experiments were conducted to show whether oxalate produced by the annual Salsola tragus or added oxalic acid would solubilize P from the inorganic-bound soil P pool, making it available for uptake by Stipa pulchra. Oxalate could be leached in the laboratory from the senescent canopy of Salsola, and leaching by rainfall was hypothesized to be a source of potential increased soil P under the Salsola canopy. Both oxalate leached from the canopy of Salsola and added oxalic acid increased the availability of soil P in greenhouse experiments. The source of the increase in available soil P in the greenhouse experiment was shown to be the inorganic-bound P pool, as the total P concentration of the soil decreased with increasing oxalate. There were significant increases in Stipa shoot P in response to Salsola leachates and in response to added oxalate in the greenhouse studies. These results suggest an important role for oxalate in P cycling. On disturbed sites where Salsola invades it may act to facilitate the establishment of later seral species like Stipa by creating a nutrient island of available P.     

辽宁碱蓬根际土壤真菌多样性的季节变化及其耐盐性

采用稀释平板法和形态学鉴定法进行了辽宁碱蓬(Suaeda liaotungensis)根际土壤真菌的分离鉴定及季节、盐度对真菌多样性的影响分析。结果表明:春、夏、秋、冬四季辽宁碱蓬根际土壤中的真菌菌落数分别为6410、4180、5730和3340,种类分别为6属13种、9属16种、11属31种、6属12种,共分离鉴定出13属42种真菌;其根际土壤真菌的多样性指数、丰富度指数和均匀度指数,从大到小的次序均为秋夏春冬,3种指数均在秋季达到峰值;多样性指数和丰富度指数差异较大,均匀度指数波动较小,春季和冬季的均匀度指数相近。辽宁碱蓬根际土壤真菌种类明显多于无植被土壤,是无植被土壤的7倍,多样性指数和均匀度指数分别是无植被土壤的4—8倍和1—1.2倍;其根际土壤真菌优势种群包括青霉属(Penicillium)、葡萄穗霉属(Stachybotrys)、枝孢属(Cladosporium)、木霉属(Trichoderma)、曲霉属(Aspergillus)和镰孢属(Fusarium);4个季节的优势菌不尽相同,但均有一个共同的优势菌属青霉属。以Na Cl浓度梯度法制造盐胁迫生境,检测辽宁碱蓬根际土壤真菌对盐胁迫的响应,结果表明:60%左右的菌种能耐受5%以下盐度、15%左右的菌种能耐10%—20%盐度;筛选出了6株高度耐盐菌:细交链孢霉、草酸青霉、产黄青霉、烟曲霉、细极链格孢和赭曲霉,其中最高耐盐菌种赭曲霉可耐20%盐度。创新之处在于以盐度和季节为变量检测辽宁碱蓬根际土壤真菌的种群构成,为其深入研究奠定了理论基础。     

10. Snow algae of the Windmill Islands region, Antarctica

A list of the 24 species of snow algae identified from the region, a resume of what is currently known about the major species, and avenues for further research are provided. New species discovered include 2 Desmotetra spp., one Chlorosarcina sp., 2 Chloromonas spp. and a Palmellopsis sp. Several of these are from genera whose members have previously been found only in the soil flora. Not only was it necessary to elucidate the life cycle of these species, but it was also essential to examine them ultrastructurally to determine their taxonomic positions.     

<Emphasis Type="Italic">Acer rubrum</Emphasis> (red maple) growth is negatively affected by soil from forest stands dominated by its invasive congener (<Emphasis Type="Italic">Acer platanoides</Emphasis>, Norway maple)

Invasive species continue to alter the plant communities of the eastern United States. To better understand the mechanisms and characteristics associated with invasive success, we studied competition between two Acer species. In a greenhouse, we tested (1) the effect of forest soil type (beneath an invasive and native stand) on seedling growth of the invasive Acer platanoides (Norway maple) and native A. rubrum (red maple), and the (2) effects of full (above- and below-ground) and partial inter-specific competition on species growth. We found A. rubrum growth was negatively affected by soil from the invaded stand, as it had lower above-ground (32%) and below-ground (26%) biomass, and number of leaves (20%) than in the native soil. The root:shoot resource allocations of A. platanoides depended on soil type, as it had 14% greater root:shoot mass allocation in the native soil; this ability to change root:shoot allocation may be contributing to the ecological success of the species. Widely published as having a large ecological amplitude, A. rubrum may be a useful species for ecological restoration where A. platanoides has been present, but the impacts of A. platanoides on soil functioning and subsequent plant interactions must be addressed before protocols for native reintroductions are improved and implemented.     

May Rare Metallophytes Benefit from Disturbed Soils Following Mining Activity? The Case of the Crepidorhopalon tenuis in Katanga (D. R. Congo)

Cuprophytes are plants that mostly occur on Cu‐rich soil. In South Central Africa, these species are threatened by intensive mining exploitation destroying their habitats. Crepidorhopalon tenuis (Scrophulariaceae) is a tiny annual cuprophyte endemic to the Zambesian center of endemism and is particularly abundant in the Lubumbashi area. We investigate here the ecological niche of C. tenuis through the analyses of its abundance and distribution in relation to soil factors, plant community composition, and anthropogenic perturbations. Soil and vegetation data were collected in seven sites (five metalliferous and two nonmetalliferous). The current study shows that C. tenuis has its ecological optimum on copper‐rich soil and can be referred to as an elective pseudometallophyte. This species is rare in primary steppic savanna on natural metalliferous soil. Its frequency and abundance peak in pioneer communities on bare soil. In particular, the species showed a surprising ecological plasticity as it was able to benefit from anthropogenic disturbance and to colonize the large areas of bare, contaminated soil left over by mining activities. Our results strongly suggest that C. tenuis was a very rare species in natural metalliferous communities, restricted to patchy areas of open soil in steppic savanna. Recent anthropogenic habitats may have conservation value for some rare metallophytes with colonizing traits and low competitive ability.     

Hypericum scruglii sp. nov. (Guttiferae) from Sardinia

A new species of Hypericum (Guttiferae) from Sardinia, H. scruglii, is described and illustrated. It occurs on damp soil, near springs or streams with freshwater, where it grows with numerous hygrophytes. This diploid species (2n=16) belongs to the sect. Adenosepalum and is closely related to H. tomentosum, a species widespread in the west Mediterranean region.     

Reduced risk for positive soil-feedback on seedling regeneration by invasive trees on a very nutrient-poor soil in Seychelles

Invasive plants sometimes alter habitat conditions so as to promote further invasion, either by the same or by other non-native species. Such positive feedbacks often occur because the non-native species increases soil fertility, thereby favouring recruitment of non-native seedlings. This has been demonstrated in nitrogen-poor habitats invaded by nitrogen-fixing species, but it is unclear whether similar processes operate in habitats limited by phosphorus and other nutrients. I compared the growth of seedlings of Cinnamomum verum, an abundant invasive tree on phosphorus-poor soils in the Seychelles, in soils taken from beneath different tree species. I expected that soil phosphorus availability would be higher beneath stands of C. verum than beneath stands of either the native Northea hornei or the non-native nitrogen-fixing species, Falcataria moluccana. I therefore predicted that C. verum seedlings would grow faster in soil taken from beneath C. verum trees than in soil taken from beneath either of the other two species. To test this hypothesis, I performed a bioassay experiment with seedlings of C. verum grown in soils from stands of C. verum, F. moluccana and N. hornei. Different nutrient treatments (control, plus phosphorus (P), plus nitrogen (N), plus N and P, and plus complete fertilizer) were applied to investigate how nutrient availabilities modulate the effects of the trees. In the control treatment without added nutrients, there was a weak tendency for seedlings to perform better in the soils from beneath invasive than native trees. However, seedling growth in soils from beneath invasive species was markedly higher following the addition of phosphorus in the case of the F. moluccana soil, and complete fertilizer in the case of the C. verum soil. These results indicate that on very nutrient-poor soils, a low supply of nutrients other than N may reduce the risk of a soil-feedback by invasive trees on seedling regeneration.     

人为干扰对栲树次生林群落物种多样性和土壤理化性质的影响

为探究人为干扰对栲树群落的影响,采用典型样地法研究不同程度人为干扰对碧峰峡栲树(Castanopsis fargesii)次生林群落的物种多样性和土壤理化性质的影响。结果表明,碧峰峡栲树群落共有维管植物148种,隶属60科106属。乔木层和草本层物种多样性指数随干扰强度的加强先增加后减小,灌木层物种多样性水平最高。乔木层优势种以栲树、杉木(Cunninghamia lanceolata)等为主,灌木层物种丰富,优势种较多,草本层优势种数量为中度干扰轻度干扰重度干扰。土壤有机碳、钾含量和含水量与群落物种多样性水平显著相关(P0.05)。中度干扰在一定程度上能够促进碧峰峡栲树群落物种多样性并改善土壤性质,土壤有机碳、钾含量和含水量对物种多样性有显著影响。     

<Emphasis Type="Italic">Aspicilia tibetica</Emphasis>, a new terricolous species of the Himalayas and adjacent regions

A new species, Aspicilia tibetica Sohrabi & Owe-Larss., is described from Tibet, where it grows on soil and plant debris at altitudes between 4,600 and 5,400 m, and where it seems to be rather commonly distributed. It is characterized by a crustose, white thallus, 8-spored asci with small, globose to ellipsoid ascospores, a brown epihymenium, and non-moniliform to submoniliform paraphyses. It lacks secondary substances. The new species is compared with other terricolous Aspicilia species. Morphological, chemical, and phytogeographical differences between the non-vagrant terricolous species are summarized.     

川西不同树种人工林对土壤涵水能力的影响

为评价青藏高原东缘不同树种造林对土壤涵水能力的影响,选择立地条件与营林方式相同的4种人工林(连香树(Cercidiphyllum japonicum)、油松(Pinus tabulaeformis)、落叶松(Larix kaempferi)和华山松(Pinus armandii))为研究对象,以落叶阔叶灌丛为对照,比较造林恢复28 a后不同人工林土壤孔隙度及持水性的变化,结合林地凋落物贮量及细根生物量等参数,试图揭示造成不同人工林地土壤涵水能力及潜力差异化的因素。结果显示:营造油松和华山松纯林不仅没能有效改善土壤孔隙状况,反而加剧了土壤涵水功能的退化。相反,连香树和落叶松在代替次生落叶灌丛造林后,土壤容重显著下降,孔隙度增加且小孔隙比例升高,持蓄水能力提高。凋落物及细根特性是不同林地土壤持水性能差异的重要因素。综合分析表明,在对退化生态系统进行造林恢复时,应尽量避免营造高密度针叶纯林,应结合种植有助于土壤结构改良的落叶或阔叶树种。     

Edaphic correlates of feedstock‐associated diazotroph communities

Miscanthus × giganteus and Panicum virgatum are potential promising bioenergy feedstock crops suitable for the temperate zone. The energy efficiency and sustainability of bioenergy production could be improved by reducing their fertilizer inputs – particularly energy intensive nitrogen fertilizers. Miscanthus is known to benefit from nitrogen fixation by associative diazotrophs. However, because the effects of edaphic‐, management‐, and plant‐related factors on feedstock‐associated diazotroph communities have not yet been characterized, it is not currently possible to optimize the nitrogen contribution to feedstock crops from associated diazotroph communities. To address this critical knowledge gap, we characterized the bacterial and diazotroph communities in the rhizosphere and endophytic compartments of both species at eight research sites across Illinois. We also quantified the nifH gene abundance in the rhizosphere soil as well as a range of soil chemistry parameters at these sites. Multivariate statistical analyses revealed that diazotroph and bacterial communities in the rhizosphere varied primarily among sites, with very small differences between host species. Conversely, diazotroph and bacterial communities in the endophytic compartments differed significantly between plant species, but did not vary substantially among sites. Finally, nifH gene abundance in the rhizospheres of both species varied substantially from site to site and was positively correlated with soil iron concentration as well as soil ammonium concentration, and negatively correlated with abundance of other soil nutrients including calcium, total nitrogen, and nitrates. These results indicate the potential edaphic drivers of associative diazotroph communities in feedstock rhizospheres and suggest that manipulating bioavailable iron content in the soil is a potential direction for investigating the optimization of these communities to improve their nitrogen contribution to crops.     

Biogeographical variation in community response to root allelochemistry: novel weapons and exotic invasion

Centaurea diffusa is one of the most destructive invasive weeds in the western USA and allelopathy appears to contribute to its invasiveness ( Callaway & Aschehoug 2000 ). Here we identify a chemical from the root exudates of C. diffusa, 8‐hydroxyquinoline, not previously reported as a natural product, and find that it varies biogeographically in its natural concentration and its effect as an allelochemical. 8‐Hydroxyquinoline is at least three times more concentrated in C. diffusa‐invaded North American soils than in this weed's native Eurasian soils and has stronger phytotoxic effects on grass species from North America than on grass species from Eurasia. Furthermore, experimental communities built from North American plant species are far more susceptible to invasion by C. diffusa than communities built from Eurasian species, regardless of the biogeographical origin of the soil biota. Sterilization of North American soils suppressed C. diffusa more than sterilization of Eurasian soils, indicating that North American soil biota may also promote invasion by C. diffusa. Eurasian plants and soil microbes may have evolved natural resistance to 8‐hydroxyquinoline while North American plants have not, suggesting a remarkable potential for evolutionary compatibility and homeostasis among plants within natural communities and a mechanism by which exotic weeds destroy these communities.     

Torulopsis navarrensis sp. nov. A new species of yeast isolated from an acid washed brown soil in the province of Navarra,Spain

A new species of Torulopsis Berlese (4) was recovered in 1973 from an acid washed brown forest soil in the province of Navarra. It could not be identified with any hitherto described species of yeast, but on the basis of its both morphological and physiological characteristics it was assigned to the genus Torulopsis Berlese as representative of a new species for which the name of Torulopsis navarrensis is proposed.     

Temperature resistant Nocardia biovarieties in Tucumán,Argentina?

Eighty-six regional strains of the pathogenic Nocardia species isolated from soil and human mycetoma were tested for their response to different incubation temperatures and for their tolerance to different temperatures. The aim was to assess whether growth temperature and tolerance to elevated temperatures are valuable criteria for the differentiation of pathogenic species of local strains based on the results obtained from a large number of strains. The results showed that 75.34% of all N. brasiliensis isolates from both sources grew at a temperature higher than 37 °C. 20% of the mycetoma strains and 11.32% of those from soil grew at 45 °C. 98.1% of N. brasiliensis from soil and 55.0% of the mycetoma strains tolerated 50 °C for 8 h and many isolates from both sources endured this temperature for an even longer time and tolerated yet higher temperatures. Both properties (growth temperature and temperature tolerance) are used to identify N. asteroides complex (N. farcinica) and N. otitidiscaviarum, and according to our results they are not suitable to differentiate regional strains of this species. The N. asteroides strains assayed showed an ability to grow at and tolerate elevated temperatures superior to those belonging to the other species. Although adaptation of local N. asteroides and N. otitidiscaviarum strains to temperature is important, it is more significant for N. brasiliensis, because this species is predominant in the Tucumán soil and responsible for the major number of diseases in the area.This revised version was published online in October 2005 with corrections to the Cover Date.     

A new species of Penicillium isolated from soil at the Kruger National Park in South Africa

A new species of Penicillium Link ex Fries is described and illustrated. It is represented by twenty six isolates recovered from soil at twenty six different locations at the southern part of the Paul Kruger National Park in South Africa. It clearly differs from all species of the genus described so far among the Biverticillata-Symmetrica Section, and it is therefore described and proposed as a new taxon: Penicillium krugerii sp. nov.     

Soil mycoflora from trufflè native areas of Saudi Arabia

Soil fungi of areas in the North-Eastern region of Saudi Arabia where truffles are native were surveyed. Forty-three species of fungi belonging to twenty genera were isolated. Most were recovered from soils underneath or around truffle ascocarps: thirty species from soil under the surface of Tirmania nivea ascocarps, twenty-four from Terfezia boudieri soil and twenty species each from Tirmania pinoyi and Terfezia claveryi soils. Rhizosphere soil of Helianthemum lippi, on the other hand, yielded twenty-four fungal species while only fourteen fungal species were found in soil without vegetation. The total counts of fungi/g soil were highest in soils from the under surface of truffles, followed by rhizosphere soil, with the lowest in soils without vegetation.