Experimental manipulations of the phytoplankton periodicity in large limnetic enclosures in Blelham Tarn,English Lake District

This paper reviews the results of experimental manipulations, carried out during the period 1977–1983, on the phytoplankton maintained in the limnetic enclosures at Blelham Tarn, English Lake District. Three categories of manipulations are considered.The effects of variation in the scale and frequency of phosphorus loading (range: 0.3 to 2.5 g P m^–2 a^–1) upon the mean phytoplankton biomass, its seasonal distribution and specific dominance are shown to conform to well-established patterns and relationships observed in natural lakes. Much of the seasonal variability in species dominance occurred independently of nutrient ratios, though carbon availability has been critical at times. Attempts to manipulate the rates of removal of phytoplankton by grazing have confirmed that they act selectively against certain smaller species only, that they alter the rate of successional change, rather than its direction, and that they have little lasting influence upon the total phytoplankton standing crop. Attempts to manipulate rates of sinking loss through artificial enlargement of the epilimnetic circulation also regulated the light-conditions experienced by suspended phytoplankton.Growth-rate relationships to an index of light exposure and to temperature fluctuation are also derived for several species and are related to morphological and physiological characters of the organisms concerned. These interpretations are briefly reviewed in relation to periodic cycles in natural lakes.     

Biphasic Cell-Size and Growth-Rate Homeostasis by Single Bacillus subtilis Cells

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Growth rate and relative otolith size in populations of adult Müller's pearlside Maurolicus muelleri

Within populations of adult Müller's pearlside Maurolicus muelleri the otolith radius tended to increase with age at a given fish length, which indicated the presence of a growth-rate effect. Among populations the relative otolith size was negatively correlated to growth-rate estimates, which again indicated a growth-rate effect. There were only minor differences in temperature conditions among the locations, and birth-date differences did not appear to account for variation in otolith radius relative to fish length in older age groups. The presence of a growth-rate effect may be useful, as the relative otolith size may be used for evaluation of age and growth estimates, although there are several limitations to its usefulness.     

A Garden Experiment on Susceptibility to Rabbit-Grazing, Sapling Growth Rates, and Age at First Reproduction for Eleven European Woody Species

Abstract: Eleven European shrub and tree species have been grown for 13 years in a randomized array (with 2 or 3 provenances for 5 of 11 species) in an experimental garden in southern England. A plague of rabbits in the second year damaged a greater proportion of plants in species with faster height growth, including those that are the commonest colonizers of pastures; most plants recovered rapidly. Apparently, resilience rather than resistance enables these plants to be invaders of abandoned grasslands. Among the shrubs there was little evidence of a trade-off between initial rate of height growth and final height. The small tree Crataegus monogyna overtook the tallest shrub ( Cornus sanguinea ) in the 12th year. Among the shrubs, after 12 years, there was a trend for basal area to be greater in taller species; the trees had notably low basal area for their height. Most individuals of the shrub species reproduced before those of Crataegus and Sorbus aria (in 3–6 years rather than 5–13). Among the shrubs, the earliest to reproduce were fast-growing ( Rosa canina , then Ligustrum vuigare, Prunus spinosa and Rhamnus catharticus ), but then species with a wide range of growth rates all reproduced at the same time ( Euony-mus europaeus, Juniperus communis and Viburnum opulus slow-growing, Cornus sanguinea and V. lantana fast-growing). The results are discussed in relation to theories of resource allocation, and the behaviour of the particular species in the field.     

Plant allometry, stoichiometry and the temperature-dependence of primary productivity

Aim While physical constraints influence terrestrial primary productivity, the extent to which geographical variation in productivity is influenced by physiological adaptations and changes in vegetation structure is unclear. Further, quantifying the effect of variability in species traits on ecosystems remains a critical research challenge. Here, we take a macroecological approach and ask if variation in the stoichiometric traits (C: N: P ratios) of plants and primary productivity across global‐scale temperature gradients is consistent with a scaling model that integrates recent insights from the theories of metabolic scaling and ecological stoichiometry. Location This study is global in scope, encompassing a wide variety of terrestrial plant communities. Methods We first develop a scaling model that incorporates potentially adaptive variation in leaf and whole‐plant nutrient content, kinetic aspects of photosynthesis and plant respiration, and the allometry of biomass partitioning and allocation. We then examine extensive data sets concerning the stoichiometry and productivity of diverse plant communities in light of the model. Results Across diverse ecosystems, both foliar stoichiometry (N : P) and ‘nitrogen productivity’ (which depends on both community size structure and plant nutrient content) vary systematically across global scale temperature gradients. Primary productivity shows no relationship to temperature. Main conclusions The model predicts that the observed patterns of variation in plant stoichiometry and nutrient productivity may offset the temperature dependence of primary production expected from the kinetics of photosynthesis alone. Our approach provides a quantitative framework for treating potentially adaptive functional variation across communities as a continuum and may thus inform studies of global change. More generally, our approach represents one of the first explicit combinations of ecological stoichiometry and metabolic scaling theories in the analysis of macroecological patterns.     

Interspecific interactions affect N and P uptake rather than N:P ratios of plant species: evidence from intercropping

种间相互作用影响植物氮和磷的吸收量而不是氮磷比 量化不同农艺措施下作物氮和磷吸收量(即从农田中移除的量)的化学计量特征对理解农田生态系统中的养分收支和优化氮、磷肥施用至关重要。目前还不清楚在不同的氮肥和覆膜措施下,单作和间作体系作物氮和磷吸收量以及氮磷化学计量特征随整个生长季的变化。本研究探讨了植物种间养分竞争如何对(1) 5种种植模式(小麦、玉米和大麦单作、小麦/玉米和大麦/玉米间作),(2)两种施氮水平(0和225 kg N ha⁻¹)和(3)两种玉米覆膜处理(覆膜和不覆膜)下的作物氮、磷吸收量(以及氮磷比)时间动态的影响。研究结果表明,小麦和大麦的氮、磷竞争能力强于玉米,导致间作体系共生期的小麦和大麦氮、磷吸收量相比于单作增加,而玉米氮、磷吸收量相比于单作减少。3种作物植株氮磷比随作物生长而降低。作物氮磷比不受间作的影响,也不随施氮呈现一致的变化,覆膜降低了玉米的氮磷比。两种间作体系群落水平的氮磷比在成熟期与相应单作不同。由于(1)间作从土壤移除的氮和磷的比例不同于单作,以及(2)作物对氮和磷的吸收在施氮和覆膜下均是不耦合的,这些发现可能对间作系统的养分收支有启示意义。     

The Use of Chemostats in Microbial Systems Biology

Cells regulate their rate of growth in response to signals from the external world. As the cell grows, diverse cellular processes must be coordinated including macromolecular synthesis, metabolism and ultimately, commitment to the cell division cycle. The chemostat, a method of experimentally controlling cell growth rate, provides a powerful means of systematically studying how growth rate impacts cellular processes - including gene expression and metabolism - and the regulatory networks that control the rate of cell growth. When maintained for hundreds of generations chemostats can be used to study adaptive evolution of microbes in environmental conditions that limit cell growth. We describe the principle of chemostat cultures, demonstrate their operation and provide examples of their various applications. Following a period of disuse after their introduction in the middle of the twentieth century, the convergence of genome-scale methodologies with a renewed interest in the regulation of cell growth and the molecular basis of adaptive evolution is stimulating a renaissance in the use of chemostats in biological research.     

The life-cycle of Apatania fimbriata Pictet in the Breitenbach

The life-cycle of Apatania fimbriata (Pictet, 1843) (Trichoptera: Limnephilidae) was studied in the Breitenbach (Hesse, Federal Republic of Germany) and in the laboratory at 6 °C, 10 °C and 14 °C at 14 h day length. Embryogenesis was mainly temperature dependent in the 4 °C–18 °C range. At a constant 22 °C embryos developed to well-differentiated larvae which did not hatch. In the laboratory experiments, developmental rates increased with increasing temperature (6 °C, 10 °C and 14 °C); larvae went through a dormancy in the third and fourth larval instars; in the field this occurred between November and February. The dormancy synchronized the larval development. Laboratory studies led to the conclusion that the dormancy was not temperature dependent but endogenously determined. The emergence pattern of adults showed a clear diurnal pattern, with a maximum emergence approximately two hours after sunset. A comparison of several years emergence studies showed a decreasing number of females with increasing distance from the spring. A comparison of the dry weight of females between two traps at the stream showed a significantly higher weight from the downstream site. For males no between-site differences were observed.     

Growth of Acanthamoeba castellanii and Hartmannella vermiformis on live, heat-killed and DTAF-stained bacterial prey

The growth responses of two species of amoeba were evaluated in the presence of live, heat-killed and heat-killed/5-(4,6-dichlorotriazin-2-yl) aminofluorescein (DTAF)-stained cells of Escherichia coli, Pseudomonas aeruginosa, Klebsiella aerogenes, Klebsiella ozaenae and Staphylococcus aureus. The specific growth rates of both species were significantly higher with live bacterial prey, the only exception being Hartmannella vermiformis feeding on S. aureus, for which growth rates were equivalent on all prey states. There was no significant difference between growth rates, yield or ingestion rates of amoebae feeding on heat-killed or heat-killed/stained bacterial cells, suggesting that it was the heat-killing process that influenced the amoeba-bacteria interaction. Pretreatment of prey cells had a greater influence on amoebic processing of Gram-negative bacteria compared with the Gram-positive bacterium, which appeared to be as a result of the former cells being more difficult to digest and/or losing their ability to deter amoebic ingestion. These antipredatory mechanisms included microcolony formation in P. aeruginosa, toxin production in K. ozaenae, and the presence of an intact capsule in K. aerogenes. E. coli and S. aureus did not appear to possess an antipredator mechanism, although intact cells of the S. aureus were observed in faecal pellets, suggesting that any antipredatory mechanism was occurring at the digestion stage.