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1.
1. Although many studies have focussed on the effects of catchment land use on lotic systems, the importance of broad (catchment) and fine (segment/reach) scale effects on stream assemblages remain poorly understood. 2. Nine biological metrics for macrophytes (498 sites), benthic macroinvertebrates (491) and fish (478) of lowland and mountain streams in four ecoregions of France and Germany were related to catchment and riparian buffer land use using partial Redundancy Analysis and Boosted Regression Trees (BRTs). 3. Lotic fauna was better correlated (mean max., r = 0.450) than flora (r = 0.277) to both scales of land use: the strongest correlations were noted for mountain streams. BRTs revealed strong non‐linear relationships between mountain assemblage metrics and land use. Correlations increased with increasing buffer lengths, suggesting the importance of near‐stream land use on biotic assemblages. 4. Several metrics changed markedly between 10–20% (mountain ecoregions) and 40–45% (lowland) of arable land use, irrespective of the buffer size. At mountain sites with >10% catchment arable land use, metric values differed between sites with <30% and sites with >30% forest in the near‐stream riparian area. 5. These findings support the role of riparian land use in catchment management; however, differences between mountain and lowland ecoregions support the need for ecoregion‐specific management.  相似文献   
2.
Abstract Bruchidius atrolineatus (Pic) is a common pest infesting cowpea seeds ( Vigna unguiculata Walp) in Africa. In the Sahelian zone, the adults are in reproductive diapause during the dry season. Diapause induction depends on the climatic conditions during embryonic and post-embryonic development. A strain of B. atrolineatus originating from the Niamey (13oN) was reared in different thermoperiodic and photoperiodic conditions. In the thermoperiodic regime 40:25oC, in continuous darkness, induction of diapause was dependent on the duration of the thermophase. Photoperiod could also influence diapause induction but the response depended on the temperature. When the beetles were reared in conditions of LD 12:12 h, 40:25oC, for seven generations, the proportion of diapausing adults decreased and their sensitivity to photoperiod increased. In LD 14:10 h, 40:25CC, the proportion of diapausing adults remained high regardless of the photoperiod. In these conditions, the first emerging adults were sexually active and were used for selection of a strain with a low incidence of diapause. After twelve generations, the proportion of diapausing beetles was lower than 5%. The responses of this selected strain to photo- and thermoperiods were reduced. The sensitivity of B. atrolineatus to photoperiod and thermoperiod could be controlled by genetic systems as observed in other insect species.  相似文献   
3.
The paralabial organelle of the rumen ciliate Ophryoscolex purkinjei , located on the ventral side of the ciliophor, is a highly specialized part of the somatic cortex. It consists of alternating rows of short modified cilia and thin pellicular folds which form a ridge-like structure. The central "top kinety" is composed of monokinetids which bear cilia with 9 + 2 axonemes and 2 μm in length. The top kinety is accompanied by a comb-shaped fold on its distal side and by a broad wedge-shaped fold on its proximal side. To both sides there follow two or three lateral kineties made of dikinetids. The anterior kinetosome of each pair bears a clavate cilium, only 0.5–0.7 μm in length and with a 9 + 0 axoneme while the cilium of the posterior kinetosome is even shorter. Lateral folds with numerous microtubules cover these lateral kineties and rows of barren basal bodies. The fine structure of this supposed sensory organelle show a basic pattern in four other ophryoscolecids, and its increasing complexity parallels the suggested phylogenetic line of evolution of these ciliates.  相似文献   
4.
Daily routine 3 p.m. meteorological data for Melbourne, Victoria, were processed to provide estimates of maximum forest fire danger index (including soil-water deficit), potential number of days for failure of fire suppression for given quantities of fuel, and potential number of days for optimal prescribed fuel reduction burning in eucalypt forests given the same quantities of fuel. Although two models for estimating soil dryness gave widely different results, the effect of these differences on the value of the McArthur forest fire danger index (FFDI) was relatively small overall. However, over the 28 years of record, the number of ‘extreme’ days given using the Mount dryness index was 50% greater than that given by the Keetch-Byram index. The number of forest fires in Victoria (as a whole) was found to be related to 3 p.m. FFDI (for Melbourne) and to the incidence of weekends or public holidays. Potentially, bushfires near Melbourne would be ‘uncontrollable’; that is, with an intensity greater than 4000 kW m-1 on level ground, on an average of about 100 days per year (at 3 p.m.) if ignition were to occur where litter fuel weights were about 301 ha-1. However, if fuel weights were less than 81 ha-1, the potential number of ‘uncontrollable’ fires would be near zero. Using equations to predict conditions ideally suited to safe fuel reduction burning at 3 p.m. the average number of appropriate days per year increased from zero at a fuel weight of near 71 ha-1 to a maximum of 14 at 15 t ha-1. The extent to which the models used in this study are accurate is arguable so further work is needed.  相似文献   
5.
Rao-Blackwellisation of sampling schemes   总被引:15,自引:0,他引:15  
  相似文献   
6.
Active roles of cell-cell interaction between melanocytes and neighboring keratinocytes for the regulation of melanocyte functions in the skin have been suggested. We examined substantial regulatory mechanisms of keratinocyte extracellular matrix (kECMs) for normal human melanocyte functions without direct cell-cell contact. We specially devised kECMs from proliferating or differentiating keratinocytes and further treated them with environmental stimulus ultraviolet B (UVB) for skin pigmentary system. Normal human melanocytes (NHM) were cultured on the various keratinocyte ECMs and initially the effects of the kECMs upon melanocyte morphology (dendrite formation and extension), growth, melanin production and expressions of pigmentation-associated protein (MEL-5) and proliferation-associated protein (proliferating cell nuclear antigen; PCNA/cyclin) were studied. Then we compared the effects of these cell-matrix interactions with those of direct melanocyte-keratinocyte, cell-cell contact in co-culture on melanocyte functions. Melanocytes cultured on any types of the kECMs that were tested significantly extended dendrites more than that on plastic cell culture dish without kECM (control). Melanocytes cultured on the kECM prepared from UVB irradiated differentiating keratinocytes resulted in 219% increase in the number of dendrites. The growth of melanocytes on kECMs was also stimulated up to 280% of control. The kECM produced by proliferating keratinocytes had a more significant effect on the growth than kECM from differentiating keratinocytes. This melanocyte growth stimulating effect was decreased with kECM from UVB treated differentiating keratinocytes. The melanin content per melanocyte was constant on any of the kECMs. Expression of pigmentation-associated protein detected by monoclonal antibody, MEL-5, was not changed on the kECM, while it was increased in melanocytes in co-culture with keratinocytes. Expression of PCNA/cyclin in melanocytes cultured on kECMs was generally downregulated on kECM and in co-culture compared to that in a control culture. We demonstrated that the kECMs play important roles in the melanocyte morphology and proliferation. These observations suggest that environmental (UVB) and physiological (Ca++) stimuli can regulate melanocyte functions through the keratinocyte extracellular matrix in vivo.  相似文献   
7.
Comparative Study of Microsporidian Spores by Flow Cytometric Analysis   总被引:2,自引:0,他引:2  
ABSTRACT. Spore suspensions of microsporidian parasites of fish (Microsporidium ovoideum, Glugea stephani, Glugea atherinae and Spraguea lophii ) have been analyzed by flow cytometry. Spore nuclei were dyed either by propidium iodide or bis-benzimide (Hoechst 33342). By observation of forward light scatter and fluorescence the four species could be distinguished and the mono- and diplokaryotic populations of S. lophii identified. Staining of DNA by bis-benzimide was better and easier than propidium iodide. Forward light scatter and fluorescence values were characteristic of each species and remained unchanged throughout the year, so flow cytometry can be used for distinction of spores of some microsporidian parasites once their flow cytometric parameters are known. However, special care has to be taken in tool calibration and material preparation for analysis because of the high precision of the technique.  相似文献   
8.
System-level adjustments to elevated CO2 in model spruce ecosystems   总被引:6,自引:0,他引:6  
Atmospheric carbon dioxide enrichment and increasing nitrogen deposition are often predicted to increase forest productivity based on currently available data for isolated forest tree seedlings or their leaves. However, it is highly uncertain whether such seedling responses will scale to the stand level. Therefore, we studied the effects of increasing CO2 (280, 420 and 560 μL L-1) and increasing rates of wet N deposition (0, 30 and 90 kg ha-1 y-1) on whole stands of 4-year-old spruce trees (Picea abies). One tree from each of six clones, together with two herbaceous understory species, were established in each of nine 0.7 m2 model ecosystems in nutrient poor forest soil and grown in a simulated montane climate for two years. Shoot level light-saturated net photosynthesis measured at growth CO2 concentrations increased with increasing CO2, as well as with increasing N deposition. However, predawn shoot respiration was unaffected by treatments. When measured at a common CO2 concentration of 420 μL L-1 37% down-regulation of photosynthesis was observed in plants grown at 560 μL CO2 L-1. Length growth of shoots and stem diameter were not affected by CO2 or N deposition. Bud burst was delayed, leaf area index (LAI) was lower, needle litter fall increased and soil CO2 efflux increased with increasing CO2. N deposition had no effect on these traits. At the ecosystem level the rate of net CO2 exchange was not significantly different between CO2 and N treatments. Most of the responses to CO2 studied here were nonlinear with the most significant differences between 280 and 420 μL CO2 L-1 and relatively small changes between 420 and 560 μL CO2 L-1. Our results suggest that the lack of above-ground growth responses to elevated CO2 is due to the combined effects of physiological down-regulation of photosynthesis at the leaf level, allometric adjustment at the canopy level (reduced LAI), and increasing strength of below-ground carbon sinks. The non-linearity of treatment effects further suggests that major responses of coniferous forests to atmospheric CO2 enrichment might already be under way and that future responses may be comparatively smaller.  相似文献   
9.
Abstract. A conceptual framework is presented for modelling short-term processes in the plant and its environment as an integrated system. Flows of water, water vapour, heat, momentum, CO2, soluble carbohydrate and phosphorus are all described by equations of the same general type, i.e. in terms of diffusivity-type parameters, capacities and potential gradients. A representative volume of the crop is divided horizontally into layers and vertically between crop and environment for treatment by a finite-difference method. Vertical flow occurs in the atmosphere, soil, stems and larger roots, andilateral flow between leaves and air, and between finer roots and soil. The interception of direct sunlight and the flux densities of downward and upward diffuse radiation within layers are calculated by a step-wise procedure.
The conversions of materials within the plant are treated as functions of appropriate state variables. Schemes for carbon and phosphorus provide for flow to and from the translocation system, and for photosynthesis, respiration and growth.
A model of a fully-established lucerne crop is described and the sensitivity of model performance to changes in a number of parameter values explored. Simulation runs under varying conditions indicate realistic prediction of diurnal trends.  相似文献   
10.
FLUXNET and modelling the global carbon cycle   总被引:3,自引:0,他引:3  
Measurements of the net CO2 flux between terrestrial ecosystems and the atmosphere using the eddy covariance technique have the potential to underpin our interpretation of regional CO2 source–sink patterns, CO2 flux responses to forcings, and predictions of the future terrestrial C balance. Information contained in FLUXNET eddy covariance data has multiple uses for the development and application of global carbon models, including evaluation/validation, calibration, process parameterization, and data assimilation. This paper reviews examples of these uses, compares global estimates of the dynamics of the global carbon cycle, and suggests ways of improving the utility of such data for global carbon modelling. Net ecosystem exchange of CO2 (NEE) predicted by different terrestrial biosphere models compares favourably with FLUXNET observations at diurnal and seasonal timescales. However, complete model validation, particularly over the full annual cycle, requires information on the balance between assimilation and decomposition processes, information not readily available for most FLUXNET sites. Site history, when known, can greatly help constrain the model‐data comparison. Flux measurements made over four vegetation types were used to calibrate the land‐surface scheme of the Goddard Institute for Space Studies global climate model, significantly improving simulated climate and demonstrating the utility of diurnal FLUXNET data for climate modelling. Land‐surface temperatures in many regions cool due to higher canopy conductances and latent heat fluxes, and the spatial distribution of CO2 uptake provides a significant additional constraint on the realism of simulated surface fluxes. FLUXNET data are used to calibrate a global production efficiency model (PEM). This model is forced by satellite‐measured absorbed radiation and suggests that global net primary production (NPP) increased 6.2% over 1982–1999. Good agreement is found between global trends in NPP estimated by the PEM and a dynamic global vegetation model (DGVM), and between the DGVM and estimates of global NEE derived from a global inversion of atmospheric CO2 measurements. Combining the PEM, DGVM, and inversion results suggests that CO2 fertilization is playing a major role in current increases in NPP, with lesser impacts from increasing N deposition and growing season length. Both the PEM and the inversion identify the Amazon basin as a key region for the current net terrestrial CO2 uptake (i.e. 33% of global NEE), as well as its interannual variability. The inversion's global NEE estimate of −1.2 Pg [C] yr−1 for 1982–1995 is compatible with the PEM‐ and DGVM‐predicted trends in NPP. There is, thus, a convergence in understanding derived from process‐based models, remote‐sensing‐based observations, and inversion of atmospheric data. Future advances in field measurement techniques, including eddy covariance (particularly concerning the problem of night‐time fluxes in dense canopies and of advection or flow distortion over complex terrain), will result in improved constraints on land‐atmosphere CO2 fluxes and the rigorous attribution of mechanisms to the current terrestrial net CO2 uptake and its spatial and temporal heterogeneity. Global ecosystem models play a fundamental role in linking information derived from FLUXNET measurements to atmospheric CO2 variability. A number of recommendations concerning FLUXNET data are made, including a request for more comprehensive site data (particularly historical information), more measurements in undisturbed ecosystems, and the systematic provision of error estimates. The greatest value of current FLUXNET data for global carbon cycle modelling is in evaluating process representations, rather than in providing an unbiased estimate of net CO2 exchange.  相似文献   
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