John A. Raven

Phosphorus limitation of nitrogen fixation by Trichodesmium in the central Atlantic Ocean

Marine fixation of atmospheric nitrogen is believed to be an important source of biologically useful nitrogen to ocean surface waters, stimulating productivity of phytoplankton and so influencing the global carbon cycle. The majority of nitrogen fixation in tropical waters is carried out by the marine cyanobacterium Trichodesmium, which supplies more than half of the new nitrogen used for primary production. Although the factors controlling marine nitrogen fixation remain poorly understood, it has been thought that nitrogen fixation is limited by iron availability in the ocean. This was inferred from the high iron requirement estimated for growth of nitrogen fixing organisms and the higher apparent densities of Trichodesmium where aeolian iron inputs are plentiful. Here we report that nitrogen fixation rates in the central Atlantic appear to be independent of both dissolved iron levels in sea water and iron content in Trichodesmium colonies. Nitrogen fixation was, instead, highly correlated to the phosphorus content of Trichodesmium and was enhanced at higher irradiance. Furthermore, our calculations suggest that the structural iron requirement for the growth of nitrogen-fixing organisms is much lower than previously calculated. Although iron deficiency could still potentially limit growth of nitrogen-fixing organisms in regions of low iron availability—for example, in the subtropical North Pacific Ocean—our observations suggest that marine nitrogen fixation is not solely regulated by iron supply.

The role of trace metals in photosynthetic electron transport in O2-evolving organisms

Iron is the quantitatively most important trace metal involved in thylakoid reactions of all oxygenic organisms since linear (= non-cyclic) electron flow from H2O to NADP+ involves PS II (2–3 Fe), cytochrome b6-f (5 Fe), PS I (12 Fe), and ferredoxin (2 Fe); (replaceable by metal-free flavodoxin in certain cyanobacteria and algae under iron deficiency). Cytochrome c6 (1 Fe) is the only redox catalyst linking the cytochrome b6-f complex to PS I in most algae; in many cyanobacteria and Chlorophyta cytochrome c6 and the copper-containing plastocyanin are alternatives, with the availability of iron and copper regulating their relative expression, while higher plants only have plastocyanin. Iron, copper and zinc occur in enzymes that remove active oxygen species and that are in part bound to the thylakoid membrane. These enzymes are ascorbate peroxidase (Fe) and iron-(cyanobacteria, and most al gae) and copper-zinc- (some algae; higher plants) superoxide dismutase. Iron-containing NAD(P)H-PQ oxidoreductase in thylakoids of cyanobacteria and many eukaryotes may be involved in cyclic electron transport around PS I and in chlororespiration. Manganese is second to iron in its quantitative role in the thylakoids, with four Mn (and 1 Ca) per PS II involved in O2 evolution. The roles of the transition metals in redox catalysts can in broad terms be related to their redox chemistry and to their availability to organisms at the time when the pathways evolved. The quantitative roles of these trace metals varies genotypically (e.g. the greater need for iron in thylakoid reactions of cyanobacteria and rhodophytes than in other O2-evolvers as a result of their lower PS II:PS I ratio) and phenotypically (e.g. as a result of variations in PS II:PS I ratio with the spectral quality of incident radiation).

THE TRANSPORT AND FUNCTION OF SILICON IN PLANTS

A number of lines of evidence (Mr, number of ‐OH groups, measured fluxes at inner mitochondrial membranes) suggest the intrinsic PSi(OH)4 of about 10‐10 m s‐1 in the plant cell plasmalemma. While relatively low, such a PSi(OH)4 could maintain the intracellular concentration of Si(OH)4 equal to that in the medium for a phytoplankton cell of 5 μm radius growing with a generation time of 24 h. Such passive entry could not account for SiO, precipitation such as is required for scale (Chrysophyceae) or wall (Bacillariophyceae) production in terms of either the generation of a super‐saturated solution or the quantity of SiO2 required; active transport occurs at the plasmalemma (and possibly at an internal membrane) of such cells. The energy required for silicification, even in a diatom with an Si/C ratio of 0.25, is only some 2% of the total energy (as NADPH and ATP) needed for growth; the energy cost of leakage of Si(OH)4 due to the intrinsic permeability of lipid bilayers to Si(OH)4 is never more than 10% of the cost of silicification.

The N-15 natural abundance (delta N-15) of ecosystem samples reflects measures of water availability

We assembled a globally-derived data set for site-averaged foliar delta(15)N, the delta(15)N of whole surface mineral soil and corresponding site factors (mean annual rainfall and temperature, latitude, altitude and soil pH). The delta(15)N of whole soil was related to all of the site variables (including foliar delta(15)N) except altitude and, when regressed on latitude and rainfall, provided the best model of these data, accounting for 49% of the variation in whole soil delta(15)N. As single linear regressions, site-averaged foliar delta(15)N was more strongly related to rainfall than was whole soil delta(15)N. A smaller data set showed similar, negative correlations between whole soil delta(15)N, site-averaged foliar delta(15)N and soil moisture variations during a single growing season. The negative correlation between water availability (measured here by rainfall and temperature) and soil or plant delta(15)N fails at the landscape scale, where wet spots are delta(15)N-enriched relative to their drier surroundings. Here we present global and seasonal data, postulate a proximate mechanism for the overall relationship between water availability and ecosystem delta(15)N and, newly, a mechanism accounting for the highly delta(15)N-depleted values found in the foliage and soils of many wet/cold ecosystems. These hypotheses are complemented by documentation of the present gaps in knowledge, suggesting lines of research which will provide new insights into terrestrial N-cycling. Our conclusions are consistent with those of Austin and Vitousek (1998) that foliar (and soil) delta(15)N appear to be related to the residence time of whole ecosystem N.

Opportunities for improving phosphorus‐use efficiency in crop plants

Limitation of grain crop productivity by phosphorus (P) is widespread and will probably increase in the future. Enhanced P efficiency can be achieved by improved uptake of phosphate from soil (P-acquisition efficiency) and by improved productivity per unit P taken up (P-use efficiency). This review focuses on improved P-use efficiency, which can be achieved by plants that have overall lower P concentrations, and by optimal distribution and redistribution of P in the plant allowing maximum growth and biomass allocation to harvestable plant parts. Significant decreases in plant P pools may be possible, for example, through reductions of superfluous ribosomal RNA and replacement of phospholipids by sulfolipids and galactolipids. Improvements in P distribution within the plant may be possible by increased remobilization from tissues that no longer need it (e.g. senescing leaves) and reduced partitioning of P to developing grains. Such changes would prolong and enhance the productive use of P in photosynthesis and have nutritional and environmental benefits. Research considering physiological, metabolic, molecular biological, genetic and phylogenetic aspects of P-use efficiency is urgently needed to allow significant progress to be made in our understanding of this complex trait.

Plant mineral nutrition in ancient landscapes: high plant species diversity on infertile soils is linked to functional diversity for nutritional strategies

Ancient landscapes, which have not been glaciated in recent times or disturbed by other major catastrophic events such as volcanic eruptions, are dominated by nutrient-impoverished soils. If these parts of the world have had a relatively stable climate, due to buffering by oceans, their floras tend to be very biodiverse. This review compares the functional ecophysiological plant traits that dominate in old, climatically buffered, infertile landscapes (OCBILS) with those commonly found in young, frequently disturbed, fertile landscapes (YODFELs). We show that, within the OCBILs of Western Australia, non-mycorrhizal species with specialised root clusters predominantly occur on the most phosphate-impoverished soils, where they co-occur with mycorrhizal species without such specialised root clusters. In global comparisons, we show that plants in OCBILs, especially in Western Australia, are characterised by very low leaf phosphorus (P) concentrations, very high N:P ratios, and very high LMA values (LMA = leaf mass per unit leaf area). In addition, we show that species in OCBILs are far more likely to show P-toxicity symptoms when exposed to slightly elevated soil P levels when compared with plants in YODFELs. In addition, some species in OCBILs exhibit a remarkable P-resorption proficiency, with some plants in Western Australia achieving leaf P concentrations in recently shed leaves that are lower than ever reported before. We discuss how this knowledge on functional traits can guide us towards sustainable management of ancient landscapes.

Inorganic Carbon Acquisition by Marine Autotrophs

Publisher Summary This chapter discusses inorganic carbon (C) acquisition by marine autotrophs. This chapter discusses the characteristics of inorganic C acquisition process responsible for major biogeochemical process. The chapter discusses the transport of inorganic C species from seawater to the site of carboxylation; the interconversions of inorganic C species that occur en route ; and the mechanism of the carboxylations, which occur in parallel to yielding carboxylic acids usable in biosynthesis leading to the production of all organic C in the organism, including any “photorespiratory” decarboxylation processes. There is great genetic and ecological diversity among marine autotrophs; even when chemolithotrophs and non-O 2 -evolving phototrophs are not considered, there is much more genetic diversity among marine photolithotrophic O 2 -evolvers than among terrestrial O 2 -evolvers. O 2 -evolvers bring about more than 90% of gross inorganic C assimilation in the oceans, and essentially all of this inorganic C is routed through Ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO), although in some instances some or all of this inorganic C has been subject to a prior carboxylation–decarboxylation cycle using enzymes other than RUBISCO. There have been variable results from attempts to demonstrate a higher inorganic C concentration inside the cells of marine O 2 -evolvers than in normal seawater for organisms, while gas-exchange characteristics suggest the occurrence of a CO 2 -concentrating mechanism. The evolution of inorganic C-assimilation systems in marine autotrophs will only be better understood when more is known of the present day mechanisms of inorganic C transport at the molecular genetic level.

The potential effects of global climate change on microalgal photosynthesis, growth and ecology

Abstract The global environment is currently experiencing a period of significant change in climate as a result of human activities. Although the planet has experienced very significant variations in climate in the geological past, the rate at which the present changes are occurring is extraordinary. Anthropogenic influences have resulted in an enhancement of atmospheric carbon dioxide levels which will amount to a two- to threefold increase over the next century and this has already led to a measurable rise in global temperature. At the same time, chlorofluorocarbons are reacting with ozone in the stratosphere, a process that has led to appreciable enhancement of UV-B radiation (UVBR) fluxes to the earths surface at high latitudes. This review addresses our present state of knowledge about the effects of enhanced carbon dioxide levels, elevated UVBR fluxes and higher temperatures on the ecophysiology of microalgae. We consider the potential interactions between these and other environmental factors, such as nutrient availability, and also address the ecological consequences of climate change for microalgal assemblages and the flow of materials to higher trophic levels.

Photosynthesis in algae.

Introductory Chapters.- 1 The Algae and their General Characteristics.- Summary.- I. Introduction.- II. The Algae: Their Origins and Diversity.- III. The Green, Red and Brown Algae.- IV. The Chromophytes.- V. The Chlorarachniophytes.- VI. The Euglenophytes.- VII. Algal Genomes.- VIII. Algae as Sources of Natural Products.- IX. Concluding Remarks.- Acknowledgements.- References.- 2 Algal Plastids: Their Fine Structure and Properties.- Summary.- I. Introduction.- II. Origin of Plastids.- III. Chlorophyte Plastids.- IV. Rhodophyte Plastids.- V. Cyanelles (Glaucocystophyte Plastids).- VI. Cryptophyte Plastids.- VII. Chlorarachniophyte Plastids.- VIII. Euglenophyte Plastids.- IX. Dinoflagellate Plastids.- X. Chrysophyte (Ochrophyte) Plastids.- XI. Phaeophyte, Bacillariophyte, Eustigmatophyte, Raphidophyte, Synurophyte, Pelagophyte, Silicoflagellate, Pedinellid and Xanthophyte Plastids.- XII. Haptophyte Plastids.- XIII. Apicomplexan Plastids.- XIV. Kleptoplastids.- XV. Microstructure of the Thylakoid Membrane.- Acknowledgments.- References.- 3 The Photosynthetic Apparatus of Chlorophyll b- and d-Containing Oxyphotobacteria.- Summary.- I. Introduction.- II. Advances in Photosynthesis in Chlorophyll b- and d-Containing Oxyphotobacteria.- III. Green Oxyphotobacteria and the Endosymbiotic Theory of Green Plastids Evolution.- IV. Concluding Remarks.- Acknowledgments.- References.- Molecular Genetics of Algae.- 4 Structure and Regulation of Algal Light-Harvesting Complex Genes.- Summary.- I. Introduction.- II. Higher Plant Light-Harvesting Complexes.- III. Algal Light-Harvesting Complexes.- IV. Origin and Evolution of the Light-Harvesting Antennae.- V. Concluding Remarks.- Acknowledgments.- References.- 5 Functional Analysis of Plastid Genes through Chloroplast Reverse Genetics in Chlamydomonas.- Summary.- I. Introduction.- II. Algal Chloroplast Transformation.- III. Reverse Chloroplast Genetics of Photosynthesis.- IV. Several ycfs Encode Novel Proteins Involved in Photosynthesis.- V. Chloroplast Reverse Genetics of Essential Genes of Chlamydomonas.- VI. Conclusions and Prospects.- Acknowledgments.- References.- 6 Biochemistry and Regulation of Chlorophyll Biosynthesis.- Summary.- I. Introduction.- II. An Overview of Tetrapyrroles and Their Derivatives.- III. Chlorophyll Forms and Their Distribution in Algal Species.- IV. Early Steps in Chlorophyll Biosynthesis.- V. The Pathway from ALA to Protoporphyrin IX.- VI. The Iron Branch.- VII. The Magnesium Branch-Chlorophyll a Formation.- VIII. Biosynthesis of Chlorophyll b and Other Algal Chlorophylls.- Acknowledgments.- References.- Summary.- Biochemistry and Physiology of Algae.- 7 Oxygenic Photosynthesis in Algae and Cyanobacteria: Electron Transfer in Photosystems I and II.- Summary.- I. Introduction.- II. Overview of Photosystems I and II.- III. Mutagenesis and Genetic Engineering of the Photosystems.- IV. Photosystem II function.- V. Photosystem II Structure.- VI. Photosystem I.- VII. Conclusions.- Acknowledgment.- References.- 8 Oxygen Consumption: Photorespiration and Chlororespiration.- Summary.- I. Introduction.- II. Photorespiration.- III. Chlororespiration: A Mechanism to Maintain Thylakoid Membrane Energization in the Dark?.- Acknowledgments.- References.- 9 The Water-Water Cycle in Algae.- Summary.- I. Introduction.- II. The Water-Water Cycle in Plant Chloroplasts.- III. Operation of the Water-Water Cycle in Cyanobacteria and Eukaryotic Algae.- IV. Scavenging System of O2- and H2O2 in the Algal Water-Water Cycle.- V. Physiological Functions of the Water-Water Cycle in Cyanobacteria and Eukaryotic Algae.- VI. Concluding Remarks.- Acknowledgment.- References.- 10 Carbohydrate Metabolism and Respiration in Algae.- Summary.- I. Introduction.- II. Carbohydrate Metabolism: Low M, Compounds.- III. Carbohydrate Metabolism: Storage Polysaccharides.- IV. Carbohydrate Metabolism: Structural Polysaccharides.- V. Respiration: Carbon Pathways.- VI. Respiration: Redox Reactions and Energy Conservation.- VII. Respiration: Spatial and Temporal Aspects.- VIII. Quantifying Carbohydrate Metabolism and Respiration in Relation to Growth and Maintenance.- Acknowledgments.- References.- 11 Carbon Acquisition Mechanisms of Algae: Carbon Dioxide Diffusion and Carbon Dioxide Concentrating Mechanisms.- Summary.- I. Introduction.- II. Rubisco Kinetic Properties in Relation to the CO2 and O2 Concentrations in Cyanobacterial and Algal Habitats.- III. Lines of Evidence Used in Distinguishing Organisms Relying on Diffusive CO2 Entry from Those Using Carbon Concentrating Mechanisms (CCMs).- IV. Occurrence and Mechanism of CCMs.- V. Evolution of CCMs.- VI. Conclusions and Prospects.- Acknowledgments.- References.- Light-Harvesting Systems in Algae.- 12 Modeling the Excitation Energy Capture inThylakoid Membranes.- Summary.- I. Introduction.- II. Structural Composition of the Thylakoid Membrane.- III. Experimental Approaches.- IV. Kinetic Modeling of the Thylakoid Membrane.- V. Concluding Remarks.- Acknowledgments.- References.- 13 Light-Harvesting Systems in Algae.- Summary.- I. Introduction.- II. Chlorophylls.- III. Light-Harvesting Proteins.- IV. Optimizing Light-Harvesting Architecture.- V. Problems with Photosystem II.- VI. Off-Loading Excess Light Energy: Xanthophyll Cycle and Reaction Center Sinks.- VII. Control of Light Harvesting.- Acknowledgments.- References.- 14 Red, Cryptomonad and Glaucocystophyte Algal Phycobiliproteins.- Summary.- I. Introduction.- II. Structure and Components of Phycobilisomes.- III. Molecular Biology of Red Algal, Glaucocystophyte and Cryptomonad Phycobiliproteins.- IV. Phycobiliprotein Structure.- V. Phycobiliprotein Types.- VI. Phycobiliprotein Crystal Structure.- VII. Bilin Chromophores.- VIII. Energy Transfer.- IX. Applications/Industrial Uses.- References.- 15 Carotenoids of Light Harvesting Systems: Energy Transfer Processes from Fucoxanthin and Peridinin to Chlorophyll.- Summary.- I. Introduction.- II. Distribution of Carotenoids in Algae.- III. Optical Properties of Carotenoids in Relation to Functions.- IV. Functions.- V. Antenna Function of Carotenoids in Algae.- VI. Electronic States and Dynamic Properties of Molecules.- VII. Energy Transfer Processes and Mechanism.- References.- General Aspects of Photosynthesis in Algae.- 16 Photoinhibition, UV-B and Algal Photosynthesis.- Summary.- I. Introduction.- II. The Algal Light Climate.- II. Photoinhibition by PAR.- III. Effects of UV Radiation.- IV. Photoinhibition and UV Stress in the Field.- V. Scope for Further Research.- Acknowledgment.- References.- 17 Adaptation, Acclimation and Regulation in Algal Photosynthesis.- Summary.- I. Introduction.- II. The Range of Resource Availabilities and Other Environmental Factors within Which Algae Can Photosynthesize.- III. Adaptation of the Photosynthetic Apparatus.- V. Adaptation of Algal Photosynthesis to Environmental Extremes.- VI. Acclimation of Algal Photosynthesis.- VII. Regulation of Algal Photosynthesis.- VIII. Rates of Regulation and Acclimation.- IX. Conclusions.- Acknowledgments.- References.- 18 Photosynthesis in Marine Macroalgae.- Summary.- I. Introduction.- II. Radiation Conditions in Coastal Waters.- III. Light Absorption by Macroalgae.- IV. Determination of Photosynthetic Rates.- V. Effects of Excessive Light on Photosynthesis.- VI. Algal Photosynthesis Under Low Light Conditions.- VII. Seasonal Photosynthetic Performance of Macroalgae.- VIII. Adaptation and Acclimation of Photosynthesis and Respiration to Temperature and Salinity.- References.- 19 Photosynthesis in Symbiotic Algae.- Summary.- I. Introduction.- II. Algal Symbiotic Associations.- III. The Host-Algal Interface.- IV. Carbon Acquisition, Fixation and Secretion.- V. Photoacclimation and Photoadaptation.- VI. Coral Bleaching and Photoinhibition.- References.

The Evolution of Vascular Land Plants in Relation to Supracellular Transport Processes

Publisher Summary This chapter describes several aspects of the significance of transport processes in the evolution of vascular land plants from their putative ancestors—the green algae. The vascular land plants have, in addition to the transport processes at the cell level, which are common to all organisms, important transport processes at the supracellular level, which involve complex anatomical features. The homoiohydric vascular land plant has three major transport systems at the supracellular level—the apoplast, the symplast, and the intercellular gas space system. The aquatic green algal ancestors of these plants use only the symplast for transport at the supracellular level. The other two transport systems, together with the elaboration of the symplast into the much more efficient phloem, are essential components of the homoiohydric land plants.