Patterns and sources of variation in Daphnia phosphorus content in nature

It has recently been shown that Daphnia can vary in the phosphorus (P)-content of their body tissues, but the relative importance of genetic versus environmental causes for this variation is unexplored. We measured variation in P-content (as % body mass) of Daphnia from eight lakes and conducted experiments to contrast three sources of variation: interspecific variation, clonal variation and phenotypic plasticity. Daphnia P-content decreased with increasing seston C:P ratio across lakes. This relationship reflected both inter- and intraspecific variation. Daphnia parvula and D. dubia exhibited high P-content and were found in shallow lakes with low C:P seston, whereas D. pulicaria had low P-content and was found in deep, stratified lakes having high C:P seston. Populations of D. dentifera spanned this lake gradient and exhibited P-content that was negatively related to seston C:P. Evidence for phenotypic plasticity came from experiments with D. pulicaria and D. dentifera collected from a lake with P-deficient seston and fed a P-sufficient diet in the laboratory. In addition, populations of D. dentifera differed in P-content even after 7 d of feeding on P-sufficient resources, suggesting within-species clonal variation. However, mesocosm experiments revealed broad and surprisingly continuous variation in the P-content of individual clones of D. pulex (range 1.54–1.05%) and D. mendotae (1.51–1.07%) over a gradient in dietary C:P. The broad range in P-content exhibited by individual clones, acclimated for generations, suggests that variation in Daphnia P-content from laboratory experiments needs to be interpreted with caution. These results also show that phenotypic variation in response to environment can be a larger source of variation in P-content than genetic differences within or among species.     

Development of three copper metalloenzymes in clover leaves

Subterranean clover (Trifolium subterraneum L. cv Seaton Park) was grown in solution cultures containing adequate nitrogen both with and without Cu. After Cu deficiency had developed, Cu²⁺ was added to some deficient plants and Cu content, protein content, and activities of three Cu metalloenzymes (diamine oxidase [EC1.4.3.6], ascorbate oxidase [EC1.10.3.3] and o-diphenol oxidase [EC1.10.3.1]) were assayed in young and recently matured leaf blades over 11 days during the development of the next three leaves.

Copper deficiency had little effect on protein concentrations, but markedly depressed enzyme activities and Cu concentration in all leaf blades assayed. Within 4 d of adding Cu²⁺ to Cu-deficient plants, Cu concentrations of all the leaf blades increased to adequate values. Enzyme activities only increased to control levels in leaves which had not yet emerged at the time that Cu²⁺ was added.

The results suggest that active holoenzymes of diamine oxidase, ascorbate oxidase, and o-diphenol oxidase can only be synthesized in leaf blades during very early stages of their development.

     

Alkaline Sucrose Gradient Sedimentation of Chromosomal Deoxyribonucleic Acid from Escherichia coli PolA+ and PolA− Strains During Thymine Starvation

Single-strand breaks were not detected in the deoxyribonucleic acid of Escherichia coli after thymine starvation for up to 180 min, even in a sensitive PolA(-) strain.     

Climate–ecosystem modelling made easy: The Land Sites Platform

Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines.     

Implications of Seedling Emergence to Site Restoration following Bauxite Mining in Western Australia

Seedling emergence of 12 selected northern jarrah (Eucalyptus marginata Donn ex Smith) forest species were investigated to assist Alcoa of Australia Ltd. in maximizing the establishment of topsoil species in rehabilitated bauxite mining sites. The species, which encompassed a range of seed weights (0.024 mg to 87 mg), plant families, seed-storage types, life forms, and germination requirements, were placed on the soil surface and at depths of 1, 2, 5, 10, and 15 cm under controlled conditions in a glasshouse. Ability to emerge from deep burial was found to depend on seed size for species that annually release their seed to the topsoil but not for species that store their seed on the plant. All selected species were capable of emerging from 2 cm depth of burial, but eight of the 12 species were either unable to emerge from 5 cm or showed a significant reduction in emergence from 5 cm depth of burial compared to optimally buried seed. This group included two small-seeded species, Stylidium calcaratum and Chamaescilla corymbosa; the major forest dominant, Eucalyptus marginata; the serotinous canopy-borne seed of Hakea amplexicaulis; and the wind-dispersed seed of Xanthorrhoea gracilis. A few seeds of the legume species Kennedia coccinea, Acacia pulchella, and Bossiaea aquifolium established seedlings from depths of 15 cm. Currently, Alcoa removes the upper 15 cm of topsoil separately from the underlying soil prior to the commencement of mining. This topsoil is respread at a similar depth following mining as part of the rehabilitation procedure. It is recommended that Alcoa continue to strip topsoil to a depth of 15 cm but investigate the option of re-spreading topsoil onto rehabilitated pits at a shallower depth to maximize establishment via the soil seed bank.