Geomicrobiology of a Weathering Crust from an Impact Crater and a Hypothesis for its Formation

Understanding the role of microbe-mineral interactions in rock weathering is vital to an understanding of nutrient availability to the biosphere and, in so far as weathering influences carbon dioxide drawdown, climate control. We studied a weathering crust on a resurge tsunami deposit (Loftarstone) from the ～ 455 Ma old Lockne impact crater, central Sweden with an integrated approach using XRD, electron microprobe analysis, SEM-EDS and GCMS analysis of organics. The lichens and fungal hyphae network preferentially weather the chlorite in the Loftarstone compared to feldspars and quartz. We demonstrate, using a fungal isolate (identified by ITS sequencing), that biologically induced dissolution of the calcite component produces cavities which increase the surface area of interaction between the biota and the rock substrate. The weathering crust exfoliates from the rock surface in sheets, which we attribute to the dissolution of the calcite matrix. We present a hypothesis for the crust development. As well as providing insights into weathering on substrates derived from a diversity of high-energy geological disturbances, such as impact events and tsunamis, the weathering crust provides a model system to understand weathering processes in other common lithologies with mixed mineralogies at small spatial scales, including many sedimentary rocks. This work reveals how each different clast plays a unique part in the weathering process, leading to a well-defined weathering sequence.     

Symbiosis research at the end of the millenium

The development of symbiosis research over the closing 50 years of the last millenium is reviewed. At the beginning of this period, there had been very little previous research into aquatic microbial symbiosis. The advent of new experimental techniques, combined with the developing acceptance of the symbiotic origin of eukaryotic cell structure (and especially that chloroplasts evolved from a symbiosis involving photosynthetic aquatic microbes) brought symbiosis research into much greater prominence for a time in the 1970s and 1980s. Nevertheless, at the end of the millenuim, symbiosis as a subject still lacks a clear and strong identity amongst biologists in general. Three reasons are identified for this: continuing absence of a generally accepted definition of the term; little or no representation in the academic structure of biology; and the current adverse climate of research funding in many countries. However, the growing importance of symbiosis in biotechnology and in conserving biodiversity makes future prospects much brighter.     

An assessment of lichenometry as a method for dating recent stone movements in two stone circles in Cumbria and Oxfordshire

WINCHESTER, V., 1988. An assessment of lichenometry as a method for dating recent stone movements in two stone circles in Cumbria and Oxfordshire. Lichenometry uses the size/age relationship of lichens to date stone surfaces. A study of neolithic stone circles at Rollright in Oxfordshire and Castlerigg in Cumbria showed that stone movements in the recent past may be deduced from the varying sizes of lichen populations on different surfaces and approximate dates may be suggested for periods of change. Thalli of Aspicilia calcarea dating to around 1366 and of Rhizocarpon geographicum to 1523 are reported. Problems in past work have mainly concerned the effects on growth of environmental variation, anomalous growth, colonization rates, aspect preferences, variable lifespans and an inconsistent methodology. Where a consistent methodology can be applied the technique shows considerable potential not only for dating in glacial environments, its major use to date, but also for assessing the detailed treatment over the recent centuries of historic or prehistoric structures.     

Mycobiont-cyanobiont interactions during dark nitrogen fixation by the lichen Peltigera aphthosa

Acetylene reduction (nitrogenase activity) by excised cephalodia of Peltigera aphthosa Willd. slowly declined on transfer of the cephalodia from light to darkness. The decline was more rapid in the absence of CO₂ or when phosphoenolpyruvate carboxylase activity was inhibited by adding maleic acid or malonic acid. When glutamine synthetase (GS) activity was totally inhibited by adding l -methionine- dl -sulphoximine (MSX) the decline in nitrogenase activity in the absence of CO₂ still occurred. However, this loss of activity did not occur when the mycobiont was disrupted using digitonin (0.01 % w/v) and the fixed NH₄⁺ was released into the medium. The data suggest that dark CO₂ fixation by the fungus supplies carbon skeletons which remove newly fixed NH₄⁺ produced by the cyanobacterium. When such carbon skeletons are not available MH₄⁺ accumulates and inhibits nitrogenase activity even in the absence of GS activity. It is probable that NH₄⁺ and a product of GS exert independent inhibitory effects on nitrogenase activity.     

The most ancient terrestrial lichen <Emphasis Type="Italic">Winfrenatia reticulata</Emphasis>: A new find and new interpretation

Silicified fossils from Rhynie cherts in Scotland are studied. A lichen belonging to the genus Winfrenatia is detected and studied. This oldest terrestrial lichen is dated to the Pragian (=Siegenian) of the Early Devonian. New characters of the lichen are described, and their new interpretation is given. The main component of the lichen thallus is a filamentous cyanobacterium (Nostocales). Structures which were interpreted as fungal hyphae are probably hollow sheaths of this cyanobacterium. Mycobiont hyphae develop at the base of the thallus and symbiose with a coccoid cyanobacterium. Thus, Winfrenatia reticulata is a three-parted organism, constituted of a mycobiont and filamentous and coccoid cyanobacteria.     

Evaluating the effects of terrestrial ecosystems, climate and carbon dioxide on weathering over geological time: a global-scale process-based approach

Global weathering of calcium and magnesium silicate rocks provides the long-term sink for atmospheric carbon dioxide (CO(2)) on a timescale of millions of years by causing precipitation of calcium carbonates on the seafloor. Catchment-scale field studies consistently indicate that vegetation increases silicate rock weathering, but incorporating the effects of trees and fungal symbionts into geochemical carbon cycle models has relied upon simple empirical scaling functions. Here, we describe the development and application of a process-based approach to deriving quantitative estimates of weathering by plant roots, associated symbiotic mycorrhizal fungi and climate. Our approach accounts for the influence of terrestrial primary productivity via nutrient uptake on soil chemistry and mineral weathering, driven by simulations using a dynamic global vegetation model coupled to an ocean-atmosphere general circulation model of the Earth's climate. The strategy is successfully validated against observations of weathering in watersheds around the world, indicating that it may have some utility when extrapolated into the past. When applied to a suite of six global simulations from 215 to 50 Ma, we find significantly larger effects over the past 220 Myr relative to the present day. Vegetation and mycorrhizal fungi enhanced climate-driven weathering by a factor of up to 2. Overall, we demonstrate a more realistic process-based treatment of plant fungal-geosphere interactions at the global scale, which constitutes a first step towards developing 'next-generation' geochemical models.     

Molecular analysis of lichen-associated bacterial communities

The bacterial communities associated with 11 different lichen samples (belonging to eight different species) from different habitats were investigated. The culturable aerobic-heterotrophic fraction of the bacterial communities was isolated from nine lichen samples on protein-rich and sugar-rich/N-free media. Thirty-four bacterial isolates were purified and pooled into groups (phylotypes) by analysis of the ribosomal internal transcribed spacer polymorphism. Twenty five phylotypes were identified, each comprising between one and three isolates. One isolate of each phylotype was partially sequenced and the resulting 16S rRNA gene sequences were compared in a phylogenetic analysis. Three genera of Firmicutes, four of Actinobacteria and three of Proteobacteria were identified. Two phylotypes, belonging to the phyla Actinobacteria and Proteobacteria, respectively, were not identified at genus level. Some bacterial taxa were retrieved frequently in different lichen species sampled in the same or different sites. Paenibacillus and Burkholderia phylotypes seem to be common in lichens. Luteibactor rhizovicina was found in three different lichens of two different regions. In a cultivation-independent approach, total DNA was extracted from 11 lichen samples. Molecular fingerprints of the bacterial communities were obtained by PCR-amplification of the internal transcribed spacer region, and sequencing of selected bands indicated the presence of additional bacteria.     

Defoliation and mycorrhizal symbiosis: a functional balance between carbon sources and below-ground sinks

Herbivory is generally assumed to negatively influence mycorrhizal fungi because of reduced photosynthate to support mycorrhizae following defoliation. We examined effects of 60% and 100% defoliation (excluding current year needles) on tree growth and ectomycorrhizal associations of 10–15 year old Scots pines ( Pinus sylvestris ). Over 98% of short roots were colonized by mycorrhizal fungi, and contrary to expectation, defoliation did not decrease the proportion of living fungi in fine roots. Furthermore, defoliation did not alter the ratios of produced needle biomass to the biomass of fine roots or living fungi in fine roots. The composition of mycorrhizal morphotypes was changed, however, which suggests competition among different mycorrhizal growth forms owing to their carbon demands. We propose that these outcomes are a consequence of a functional balance between carbon sources in plant foliage and below-ground sinks, i.e. growing roots and mycorrhizal associates.     

Ecological aspects of mycorrhizal symbiosis: with special emphasis on the functional diversity of interactions involving the extraradical mycelium

Different symbiotic mycorrhizal associations between plantsand fungi occur, almost ubiquitously, in a wide range of terrestrialecosystems. Historically, these have mainly been consideredwithin the rather narrow perspective of their effects on theuptake of dissolved mineral nutrients by individual plants.More recent research has placed emphasis on a wider, multifunctionalperspective, including the effects of mycorrhizal symbiosison plant and microbial communities, and on ecosystem processes.This includes mobilization of N and P from organic polymers,release of nutrients from mineral particles or rock surfacesvia weathering, effects on carbon cycling, interactions withmyco-heterotrophic plants, mediation of plant responses to stressfactors such as drought, soil acidification, toxic metals, andplant pathogens, as well as a range of possible interactionswith groups of other soil micro-organisms. Mycorrhizal fungiconnect their plant hosts to the heterogeneously distributednutrients required for their growth, enabling the flow of energy-richcompounds required for nutrient mobilization whilst simultaneouslyproviding conduits for the translocation of mobilized productsback to their hosts. In addition to increasing the nutrientabsorptive surface area of their host plant root systems, theextraradical mycelium of mycorrhizal fungi provides a directpathway for translocation of photosynthetically derived carbonto microsites in the soil and a large surface area for interactionwith other micro-organisms. The detailed functioning and regulationof these mycorrhizosphere processes is still poorly understoodbut recent progress is reviewed and potential benefits of improvedunderstanding of mycorrhizosphere interactions are discussed. Key words: Arbuscular mycorrhiza, biotic interactions, carbon flow, ectomycorrhiza, ericoid mycorrhiza, mycelium, nutrient uptake, symbiosis, weathering Received 22 January 2008; Revised 7 February 2008 Accepted 7 February 2008     

Nitrogen fixation in lichens is important for improved rock weathering

It is known that cyanobacteria in cyanolichens fix nitrogen for their nutrition. However, specific uses of the fixed nitrogen have not been examined. The present study shows experimentally that a mutualistic interaction between a heterotrophic N₂ fixer and lichen fungi in the presence of a carbon source can contribute to enhanced release of organic acids, leading to improved solubilization of the mineral substrate. Three lichen fungi were isolated fromXanthoparmelia mexicana, a foliose lichen, and they were cultured separately or with a heterotrophic N₂ fixer in nutrient broth media in the presence of a mineral substrate. Cells of the N₂-fixing bacteria attached to the mycelial mats of all fungi, forming biofilms. All biofilms showed higher solubilizations of the substrate than cultures of their fungi alone. This finding has bearing on the significance of the origin and existence of N₂-fixing activity in the evolution of lichen symbiosis. Further, our results may explain why there are N₂-fixing photobionts even in the presence of non-fixing photobionts (green algae) in some remarkable lichens such asPlacopsis gelida. Our study sheds doubt on the idea that the establishment of terrestrial eukaryotes was possible only through the association between a fungus and a phototroph.     

The Pleiomorphic Plant MTOC： An Evolutionary Perspective

γ-Tubulin is an essential component of the microtubule organizing center （MTOC） responsible for nucleating microtubules in both plants and animals. Whereas γ-tubulin is tightly associated with centrosomes that are inheritable organelles in cells of animals and most algae, it appears at different times and places to organize the myriad specialized microtubule systems that characterize plant cells. We have traced the distribution of γ-tubulin through the cell cycle in representative land plants （embryophytes） and herein present data that have led to a concept of the pleiomorphic and migratory MTOC. The many forms of the plant MTOC at spindle organization constitute pleiomorphism, and stage-specific “migration” is suggested by the consistent pattern of redistribution of γ-tubulin during mitosis. Mitotic spindles may be organized at centriolar centrosomes （only in final divisions of spermatogenesis）, polar organizers （POs）, plastid MTOCs, or nuclear envelope MTOCs （NE-MTOCs）. In all cases, with the possible exception of centrosomes in spermatogenesis, the γ-tubulin migrates to broad polar regions and along the spindle fibers, even when it is initially a discrete polar entity. At anaphase it moves poleward, and subsequently migrates from polar regions （distal nuclear surfaces） into the interzone （proximal nuclear surfaces） where interzonal microtubule arrays and phragmoplasts are organized. Following cytokinesis, γ-tubulin becomes associated with nuclear envelopes and organizes radial microtubule systems （RMSs）. These may exist only briefly, before establishment of hoop-like cortical arrays in vegetative tissues, or they may be characteristic of interphase in syncytial systems where they serve to organize the common cytoplasm into nuclear cytoplasmic domains （NCDs）.     

生命周期方法在产业共生系统环境效益评价中的应用——研究进展及问题分析

近年来,产业共生作为产业生态学最具特征的领域引起了相关研究者的广泛关注。当前的研究逐渐从产业共生系统的定性描述分析转向定量的系统评价上。传统的产业共生系统环境效益评价仅仅关注共生系统本身,而忽视了占环境影响20%—50%的上、下游过程及替代过程的环境影响,为了得到客观的、系统的环境影响评价,将生命周期分析方法引入产业共生效益评价显得尤为重要。首先回顾了生命周期分析方法在产业共生研究中的发展过程,接着评述了3种生命周期分析方法在产业生态研究中的优劣势。并重点分析了将生命周期思想引入产业共生效益评价方法存在的功能单位设定问题及系统边界的选择问题。最后,呼吁为避免隐形污染的转移,必须尽快将生命周期分析的方法和管理理念引入我国生态工业园设计、规划、评价和管理的全过程中。