Gypsum and halite associated with the cyanobacterium Entophysalis

A study has been made on stalactite‐like structures formed by the cyanobacterium (blue‐green alga) En‐tophysalis major, growing on the roof of an undercut cliff facing the lagoon of Aldabra Atoll. The cyanobacterial cells grow in a rubbery, brown, gelatinous mucilage that contains some crystals; this mucilage surrounds a central region filled partly with gas and partly with further crystals. Halite is the predominant mineral in the mucilage, and gypsum the only mineral in the inner region. There is no evidence for a direct causal relationship between cyanobacterial metabolism and mineral crystallization, but the organic mucilage may have exerted an indirect physical control. A theory is suggested to explain the deposition of gypsum and halite, which depends on loss of water from the surface of the mucilage layer, and the layer as a whole acting as a semipermeable membrane. As the water volume decreases, gypsum will be deposited first, but subsequently, with increasing evaporation, there will be a mixture of gypsum and halite and finally halite only.     

Predominance of Methanolobus spp. and Methanoculleus spp. in the Archaeal Communities of Saline Gas Field Formation Fluids

The microbial communities in sulfate-rich, saline formation fluids of a natural gas reservoir in Lower Saxony, Germany were investigated to enhance the knowledge about microbial communities in potential carbon dioxide sequestration sites. This investigation of the initial state of the deep subsurface microbiota is necessary to predict their influence on the long-term stability and storage capacity of such sites. While the bacterial 16S rDNA gene library was comprised of sequences affiliating with the Firmicutes, the Alphaproteobacteria, the Gammaproteobacteria and the Thermotogales, the archaeal 16S rDNA libraries were simply dominated by two phylotypes related to the genera Methanolobus and Methanoculleus. The monitoring of the archaeal communities in different formation fluid samples by T-RFLP and Real-Time-PCR indicated that these two methanogenic genera dominated at all, whereas the proportion of the two groups varied. Thus, methylotrophic and autotrophic methanogenesis seems to be of importance in the reservoir fluids, dependent on the provided reduction equivalents and substrates and it also may influence the fate of CO₂ in the subsurface.     

Ultrastructural and Biogeochemical Features of Microbiotic Soil Crusts and their Implications in a Semi-Arid Habitat

This investigation was designed to explore the relationships between lichen symbionts (phycobiont and mycobiont) and the substrate on which they grow by examining the chemical and ultrastructural features of the lichen-soil interface. These lichens form an integral part of microbiotic soil crusts. Fragments of three different lichen biotypes growing over gypsum crystals and marls were fixed and embedded in resin. The lichen-substratum interface was then examined by scanning electron microscopy with backscattered electron imaging. In situ observation, microanalytical (EDS), and FT-Raman plus infrared spectroscopy of the lichen-substratum interface indicated that different ultrastructural features of the mycobiont were related to biogeochemical processes and Ca 2+ distribution in the soil crust. Phycobionts were observed to make direct contact with the substratum and to be surrounded by a nondifferentiated thallus structure. These observations suggest that they can grow outside the thallus in the early stages of lichen development in the semi-arid conditions of their habitat. The particular ultrastructural features of the lichen thallus and of the lichen-substratum interface appear to have marked effects on runoff phenomena and ponding generation of the surface.     

深海热液区微生物矿化过程的功能群和分子机制

深海热液区富含铁、锌、铜等含金属矿物(硫化物、氧化物、碳酸盐等)和无机小分子气体(H_2S、H_2、CO_2、CH_4等),具有独特的生态系统。微生物是深海热液生态系统的主要生产者和重要组成,并以控制矿化和诱导矿化两种途径参与了深海热液区的生物地球化学循环。在深海热液区存在着不同类型的微生物参与了生物矿化过程,如硫氧化菌、金属氧化菌、硫还原菌和金属还原菌等。本文详述了这些微生物参与的生物矿化现象、菌群多样性和矿化过程的分子机制,并对研究微生物矿化的研究工作进行了展望。     

Human influences on mobility of nitrogen in the environment: Needs for research and management

Nitrogen (N) cycles through air, water and soil and plays an important role in the synthesis of complex N compounds in all forms of life on the planet earth by combining with carbon, hydrogen and oxygen (O). Besides, natural fixation of N by microorganisms, advertent and inadvertent fixation of N by human activities (e.g. landscape transformations, fossil fuel burning and use of N in agricultural fields) are altering the global cycle of N. As a result of human activities, N enters in water bodies (e.g. streams, estuaries and coastal regions) making them hostile for aquatic life and contaminates ground water (used for drinking) through nitrate (NO₃^-) leaching which causes a number of health problems to human beings and animals. Hence, reduction in level of NO₃^- in water bodies and ground water is a prerequisite that can be met through sustainable management of natural and modified ecosystems. More specifically, agricultural management practices need to be better designed to synchronize the availability of NO₃^- with that of the crop N demand. These management goals can be achieved by thorough understanding of the origin and fate of N, by using isotopic analysis of N and O in NO₃^-, which can provide the best management options for N in the environment. Overall, an integrated approach would be required to limit N production/use and release to prevent critical environmental limit being exceeded.     

Distribution and cycling of C, N, Ca, Mg, K and P in three pristine, old-growth forests in the Cordillera de Piuchué, Chile

We assessed a number of biomass and soil parameters in order to examinerelationships among nutrient availability, forest productivity and vegetationpatterns in two old-growth forested watersheds in a pristine montane landscapeon Isla de Chiloé, Chile. We selected watersheds in both gymnosperm- andangiosperm-dominated forests and determined tree species, d.b.h. and health forall trees < 2 cm d.b.h. in plots established at 50m intervals. Soils were sampled at two depths in each plot andanalyzed for total C and N, and for exchangeable Ca, K, Mg andresin-extractableP. Allometric relationships and vegetation nutrient concentrations were used todetermine above-ground pools from the vegetation survey data. Growth rates werederived from increment core measures. Soil pools of most elements measuredappear adequate to support forest growth indefinitely. Mineralized nitrogen,which is similar in quantity to the annual demand for nitrogen from the soil isthe exception, consistent with the possibility of N limitation in two of theforest types studied. A third type, an evergreen broadleaved forest, appears torequire substantially more nitrogen than would appear to be available from netmineralization measurements. Productivity per unit of nitrogen required fromthesoil is quite high, largely as a consequence of the evergreen habit of thespecies in these forests. Compared to other temperate montane forests in theNorthern Hemisphere, nutrient pools and cycling characteristics were found tobemostly similar across forest types, in spite of considerable variation invegetation and soils.     

Microbial responses to a changing environment: implications for the future functioning of terrestrial ecosystems

In this review, we present a conceptual model which links plant communities and saprotrophic microbial communities through the reciprocal exchange of growth-limiting resources. We discuss the numerous ways human-induced environmental change has directly and indirectly impacted this relationship, and review microbial responses that have occurred to date. We argue that compositional shifts in saprotrophic microbial communities underlie functional responses to environmental change that have ecosystem-level implications. Drawing on a long-term, large-scale, field experiment, we illustrate how and why chronic atmospheric N deposition can alter saprotrophic communities in the soil of a wide-spread sugar maple (Acer saccharum) ecosystem in northeastern North America, resulting in the slowing of plant litter decay, the rapid accumulation of soil organic matter, and the accelerated production and loss of dissolved organic carbon (DOC). Compositional shifts in soil microbial communities, mediated by ecological interactions among soil saprotrophs, appear to lie at the biogeochemical heart of ecosystem response to environmental change.     

陆地生物地球化学模型的应用和发展

以TEM和DNDC模型为例,在分析国外生物地球化学模型发展基础上,按照模拟方法,应用目的,元素类型,生态系统类型和空间尺度等对现有的生物地球化学模型进行了分类,对生物地球化学模型的基本框架（植物,大气和土壤3个组分及植物－大气,植物－土壤和土壤－大气界面等3个界面）,以及内部基本过程（物理的,化学的和生物的过程）进行了总结分析,对目前生物地球化学模型建立中的几个问题（如跨尺度问题,地理信息系统（GIS）和遥感技术结合,考虑人类活动的影响和生物地球化学模型的比较研究）的研究动态进行了评价。     

Selenium in sediment and food webs of the Tapajós River basin (Brazilian Amazon) and its relation to mercury

BackgroundWe investigated Se levels along the Tapajós River basin - which is an important tributary of the Amazon River - and the possible antagonistic effect of Se in Hg availability. This is the first study to investigate Se transfer from abiotic to biotic compartments and along the food chain in aquatic ecosystems of the Amazon basin.MethodsSe concentrations were measured in superficial sediment (n = 29), plankton (n = 28) and fishes (n = 121) along two stretches of the Tapajós River basin (Tap_up/mi and Tap_low), comprising approximately 500 km with different hydrological characteristics.ResultsSe concentrations in sediment were significantly higher in the Tap_low (345−664 μg kg⁻¹) than in the Tap_up/mi (60−424 μg kg⁻¹). The seasonal flooding of the Amazon River probably helps to carry selenium-rich sediment to the Tapajós mouth (Tap_low stretch). We suggest that Se in sediment could decrease the bioavailability of Hg resulting in lower MeHg concentrations in fish, as observed in the Tap_low (45−934 μg kg⁻¹). Sediment and plankton were positively correlated in relation to their Se concentrations (r = 0.62; p = 0.001) suggesting that sediment can possibly be the main source of Se to plankton. Our data indicate Se uptake by primary consumers, as noted in phytoplankton levels. The decrease of Se concentrations along the food chain was also noteworthy.ConclusionThis work elucidates some aspects of Se biogeochemistry in the Amazon basin and shows its importance regarding Hg cycles in aquatic ecosystems.     

Nutrient dynamics on a precipitation gradient in Hawai'i

We evaluated soil and foliar nutrients in five native forests in Hawai'i with annual rainfall ranging from 500 mm to 5500 mm. All of the sites were at the same elevation and of the same substrate age; all were native-dominated forests containing Metrosiderospolymorpha Gaud. Soil concentrations of extractable NO₃-N and PO₄-P, as well as major cations (Ca, Mg, and K), decreased with increasing annual precipitation, and δ¹⁵N values became more depleted in both soils and vegetation. For M.polymorpha leaves, leaf mass per area (LMA) and lignin concentrations increased significantly, while δ¹³C values became more depleted with increasing precipitation. Foliar phosphorus, and major cation (Ca, Mg, and K) concentrations for M.polymorpha all decreased significantly with increasing precipitation. For other native forest species, patterns of LMA, δ¹³C, and δ¹⁵N generally mirrored the pattern observed for M. polymorpha. Decreasing concentrations of available rock-derived nutrients in soil suggest that the effect of increased rainfall on leaching outweighs the effect of increasing precipitation on weathering. The pattern of decreased foliar nutrient concentrations per unit leaf area and of increased lignin indicates a shift from relatively high nutrient availability to relatively high carbon gain by producers as annual precipitation increases. For nitrogen cycling, the pattern of higher inorganic soil nitrogen concentrations in the drier sites, together with the progressively depleted δ¹⁵N signature in both soils and vegetation, suggests that nitrogen cycling is more open at the drier sites, with smaller losses relative to turnover as annual precipitation increases. Received: 24 March 1997 / Accepted: 19 September 1997