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Linda L Handley

Publications and source records attributed to Linda L Handley.

5 recordsLinked to original sources
PubMed2003

Global aspects of C/N interactions determining plant-environment interactions.

The atomic C:N ratio in photolithotrophs is a function of their content of nucleic acids, proteins, lipids, polysaccharides, and other organic materials, and varies from about 5 in some protein-rich microalgae to much higher values in macroalgae and in higher plants with relatively more structural and energy storage materials. These differences in C:N ratios among organisms means that there is more N assimilation by photosynthetic organisms in the oceans than on land despite the near equality of global photosynthetic C assimilation rates in the two environments. Aquatic organisms obtain inorganic C and inorganic N from the surrounding water. Terrestrial photolithotrophs obtain inorganic C, dinitrogen (by diazotrophy) and some combined N from the atmosphere, with the remaining combined N coming from the soil. The nitrogen cost of growth (biomass production rate per unit plant N) varies with the C:N ratio and specific growth rate of the organism. The C:N ratio of plants can be increased with no, or minimal, decrease in growth rate by switching from N-containing to N-free solutes involved in, for example, UV-B screening or by reducing the content of particular proteins. The water cost of growth (water lost per unit biomass gain) in terrestrial plants is a function of N supply and of C supply; water cost is lower with higher N and C availability. Water supply is also important in determining denitrification rates on land and on N (and C) fluxes from terrestrial to aquatic systems.

Carbon↗
PubMed2003

Isolation of ammonium-N as 1-sulfonato-iso-indole for measurement of delta15N.

The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil.

Amino Acids↗
PubMed2002

Seaweeds in cold seas: evolution and carbon acquisition.

Much evidence suggests that life originated in hydrothermal habitats, and for much of the time since the origin of cyanobacteria (at least 2.5 Ga ago) and of eukaryotic algae (at least 2.1 Ga ago) the average sea surface and land surface temperatures were higher than they are today. However, there have been at least four significant glacial episodes prior to the Pleistocene glaciations. Two of these (approx. 2.1 and 0.7 Ga ago) may have involved a 'Snowball Earth' with a very great impact on the algae (sensu lato) of the time (cyanobacteria, Chlorophyta and Rhodophyta) and especially those that were adapted to warm habitats. By contrast, it is possible that heterokont, dinophyte and haptophyte phototrophs only evolved after the Carboniferous-Permian ice age (approx. 250 Ma ago) and so did not encounter low (</=5 degrees C) sea surface temperatures until the Antarctic cooled some 15 Ma ago. Despite this, many of the dominant macroalgae in cooler seas today are (heterokont) brown algae, and many laminarians cannot reproduce at temperatures above 18-25 degrees C. By contrast to plants in the aerial environment, photosynthetic structures in water are at essentially the same temperature as the fluid medium. The impact of low temperatures on photosynthesis by marine macrophytes is predicted to favour diffusive CO(2) entry rather than a CO(2)-concentrating mechanism. Some evidence favours this suggestion, but more data are needed.

Antarctic Regions↗
PubMed2002

Azoarcus grass endophytes contribute fixed nitrogen to the plant in an unculturable state.

The extent to which the N2-fixing bacterial endophyte Azoarcus sp. strain BH72 in the rhizosphere of Kallar grass can provide fixed nitrogen to the plant was assessed by evaluating inoculated plants grown in the greenhouse and uninoculated plants taken from the natural environment. The inoculum consisted of either wild-type bacteria or nifK- mutant strain BHNKD4. In N2-deficient conditions, plants inoculated with strain BH72 (N2-fixing test plants) grew better and accumulated more nitrogen with a lower delta15N signature after 8 months than did plants inoculated with the mutant strain (non-N2-fixing control plants). Polyadenylated or polymerase chain reaction-amplified BH72 nifH transcripts were retrieved from test but not from control plants. BH72 nifH transcripts were abundant. The inocula could not be reisolated. These results indicate that Azoarcus sp. BH72 can contribute combined N2 to the plant in an unculturable state. Abundant BH72 nifH transcripts were detected also in uninoculated plants taken from the natural environment, from which Azoarcus sp. BH72 also could not be isolated. Quantification of nitrogenase gene transcription indicated a high potential of strain BH72 for biological N2 fixation in association with roots. Phylogenetic analysis of nitrogenase sequences predicted that uncultured grass endophytes including Azoarcus spp. are ecologically dominant and play an important role in N2-fixation in natural grass ecosystems.

Azoarcus↗