Biodiversity amongst microorganisms and its relevance

Concluding remarks from the joint IUBS/IUMS workshop on Biodiversity amongst microorganisms and its relevance held in Amsterdam on 7–8 September 1991. An international microbial ecology programme can be justified in its own right now that appropriate investigative tools have been developed. Microorganisms influence global change, and indicate global health and environmental quality. At the same time, an inventory of the world's microbial species and their properties is required, together with associated culture collections and genomes. Sampling methods need to be standardized, both for species and functions. Extreme environments are a particularly rich source of microbial genomes, and endangered habitats should be sampled as a matter of priority. Cataloguing and conserving the world's microbial biodiversity is justifiable and scientifically important.     

Antarctic terrestrial ecosystems: The Vestfold Hills in context

Antarctic terrestrial ecosystems are briefly described, with emphasis on Signy Island in the maritime antarctic region, and the McMurdo oasis, southern Victoria Land, and Vestfold Hills in the continental antarctic region.As the largest and best known coastal ice-free oasis, the Vestfold Hills contain excellent examples of terrestrial sublithic, epilithic, chasmoendolithic, epiphytic and terricolous algal communities, as well as epilithic, endolithic, and epiphytic lichen communities, and moss communities. Many of the numerous lakes support dense communities of aquatic algae.     

Factors affecting the survival of E. coli in a river

The relationships between physical, chemical and microbial characteristics of an aquatic ecosystem and the survival of E. coli have been studied. Two conditions of the ecosystem (warm and cold) are considered. T₉₀ (time necessary for 90% of a bacterial population to die) in the warm situation shows an inverse exponential relationship with water temperature. Besides the direct relationship temperature-T₉₀, there is an indirect effect of temperature upon T₉₀ through the natural microflora of the water. The relationships between temperature and the heterotrophic population, and between the heterotrophic population and the bacterial consumers (P.F.U.), are exponential and linear, respectively.     

Steady state terrestrial ecosystems and the global carbon cycle

The assumption that landscapes dominated by mature vegetation are presently in carbon steady state with the atmosphere is challenged. Evidence suggests that the vegetation and soils of these landscapes are frequently disturbed and over short time periods (<300 yr) slowly sequester atmospheric carbon. The critical consideration in this argument is the time interval used to evaluate a steady state. Current models of carbon flux through the terrestrial biota limit their time considerations to 120 yr, a short and inadequate time interval for realistic assumptions about steady state in the carbon cycle of vegetation.Research performed under subcontract 19B-07762C with S. Brown and 19X-43326C with the Center for Energy and Environment Research of the University of Puerto Rico (A. E. Lugo) under Martin Marietta Energy Systems, Inc., contract DE-AC05-840R21400 with the U.S. Department of Energy.     

The cumulative effect of wetlands on stream water quality and quantity. A landscape approach

A method was developed to evaluate the cumulative effect of wetland mosaics in the landscape on stream water quality and quantity in the nine-county region surrounding Minneapolis—St. Paul, Minnesota. A Geographic Information System (GIS) was used to record and measure 33 watershed variables derived from historical aerial photos. These watershed variables were then reduced to eight principal components which explained 86% of the variance. Relationships between stream water quality variables and the three wetland-related principal components were explored through stepwise multiple regression analysis. The proximity of wetlands to the sampling station was related to principal component two, which was associated with decreased annual concentrations of inorganic suspended solids, fecal coliform, nitrates, specific conductivity, flow-weighted NH₄ flow-weighted total P, and a decreased proportion of phosphorus in dissolved form(p < 0.05). Wetland extent was related to decreased specific conductivity, chloride, and lead concentrations. The wetland-related principal components were also associated with the seasonal export of organic matter, organic nitrogen, and orthophosphate. Relationships between water quality and wetlands components were different for time-weighted averages as compared to flow-weighted averages. This suggests that wetlands were more effective in removing suspended solids, total phosphorus, and ammonia during high flow periods but were more effective in removing nitrates during low flow periods.     

湘南山区农业生态系统能量分析

一、引言由于农业系统的复杂性和存在较多的随机因素,对农业系统实行全面定量研究是比较困难的,仅从定性的描述和一些经济指标来判定系统的优劣及系统的特征是不理想的。而从能量观点对农业生态系统加以分析则是一个全面且能定量的方法,并且具有较强的客观性,能够反映农业生态系统最基本、最本质的关系。     

Epilithic bacterial and algal colonization in a stream run, riffle, and pool: a test of biomass covariation

Epilithic bacterial and algal biomass were compared among a run, riffle, and pool along an open-canopy section of a third-order, temperate stream. Epilithic biofilms were sampled after 3, 7, 14, 21, 28, and 35 days colonization on unglazed ceramic tiles that were attached to plastic trays (n = 3) placed across each of the three habitats (i.e., run, riffle, pool). The diverse habitats and sampling regime were selected to provide a range in algal biomass so that potential covariation between epilithic bacterial and algal biomass could be assessed. There were significant differences among habitats and among trays within each habitat for both chlorophyll a and AFDM. Chlorophyll a and AFDM increased in the run and pool throughout the colonization period. In the riffle, chlorophyll a and AFDM increased rapidly early in colonization, then decreased. Epilithic bacterial biomass increased rapidly with no significant differences among the three habitats throughout colonization. Further, bacterial biomass did not correlate with either chlorophyll a or AFDM in any of the three habitats or on any of the sampling days. These results suggest that epilithic algal and bacterial biomass may be regulated by independent controls in some stream environments.     

Mathematical model for the ecosystem response of Lake Ladoga to phosphorus loading

The ecosystem response model described in this paper combines an ecosystem model and a three-dimensional circulation model of Lake Ladoga developed earlier by the authors. The ecosystem model describes the process of Lake Ladoga eutrophication, and its biological submodel describes changes in the phyto- and zooplankton. In the earlier model version, lake circulation was determined using a two-dimensional hydrodynamical model which was not completely adequate. The present model allows calculation of the distributions of phyto- and zooplankton and mineral phosphorus and nitrogen. One of its main advantages is that reliable computations of the ecosystem dynamics over an extended period of time are possible. The response of the ecosystem to different levels of phosphorus pollution loading and to weather conditions is studied.     

Evaluating second year cropping on jhum fallows in Mizoram,north-eastern India—Phytomass dynamics and primary productivity

Cropping on jhum fallows in north-eartern India is predominantly done for one year in a jhum cycle. If second year cropping is done, expanse of the forest land required for slashing and burning could be reduced significantly. We tested this hypothesis in a young (6 yr) and an old (20 yr) jhum fallow. We also evaluated if the productivity during second year cropping could be alleviated by auxiliary measures such as tilling the soil or application of fertilizers (chemical or farm-yard manure or both in combination). The results demonstrate that the ecosystem productivity (total dry matter production) and economic yield (rice grain production) decline with shortening of jhum cycle. Second year cropping causes a further decline in ecosystem productivity in old jhum field, but not in young jhum field. Economic yield from second year cropping in its traditional form (without any fertilizer treatment) is not much lower than that in the first year, and can be improved further by manuring the soil. Tilling of soil improves neither ecosystem productivity nor economic yield. Different fertilization treatments respond differently; while inorganic manuring enhances ecosystem productivity, a combination of inorganic and organic manuring improves economic yield     

Base cation biogeochemistry and weathering under oak and pine: a controlled long-term experiment

Large earthen-walled lysimeters at the San Dimas Experimental Forest in southern California present a unique opportunity to assess vegetation effects on biogeochemical processes and cation release by weathering in controlled soil-vegetation systems where archived samples of soil parent material are available for comparison. The lysimeters were filled in 1937 with homogenized fine sandy loam derived on site from the weathering of diorite, and planted in 1946 with scrub oak (Quercus dumosa) and Coulter pine (Pinus coulteri). Changes in base cation contents were measured in above-ground biomass, and total and exchangeable soil pools to a depth of 1 meter. All cations in the non-exchangeable soil pool decreased relative to the initial fill material, indicating release by weathering. Sodium and K were depleted from both exchangeable and non-exchangeable pools of the soils. Plant uptake of Na was minimal, whereas K storage in vegetation exceeded the loss from the exchangeable soil pool. In both soil-vegetation systems, but especially for oak, there was an increase in exchangeable Ca and Mg. For all base cations, storage in above-ground biomass was greater for oak, whereas losses by weathering from the non-exchangeable soil pool were greater under pine. Strong evidence supports biocycling as a controlling mechanism resulting in greater Ca and Mg release by weathering under pine. In addition, decreases in non-exchangeable Ca and Mg were strongly correlated to decrease in Si under oak, whereas no correlation was observed under pine. We conclude that weathering reactions or stoichiometry differed between vegetation types.Corresponding author