Picoplankton—cells with a diameter of less than 3 µm—are the dominant contributors to both primary production and biomass in open oceanic regions1,2. However, compared with the prokaryotes3, the eukaryotic component of picoplankton is still poorly known. Recent discoveries of new eukaryotic algal taxa based on picoplankton cultures4,5 suggest the existence of many undiscovered taxa. Conventional approaches based on phenotypic criteria have limitations in depicting picoplankton composition due to their tiny size and lack of distinctive taxonomic characters6. Here we analyse, using an approach that has been very successful for prokaryotes7 but has so far seldom been applied to eukaryotes8, 35 full sequences of the small-subunit (18S) ribosomal RNA gene derived from a picoplanktonic assemblage collected at a depth of 75 m in the equatorial Pacific Ocean, and show that there is a high diversity of picoeukaryotes. Most of the sequences were previously unknown but could still be assigned to important marine phyla including prasinophytes, haptophytes, dinoflagellates, stramenopiles, choanoflagellates and acantharians. We also found a novel lineage, closely related to dinoflagellates and not previously described.

Oceanic 18S rDNA sequences from picoplankton reveal unsuspected eukaryotic diversity

The rare earth elements (REEs) form a chemically uniform group and include yttrium (Y), lanthanum (La) and the lanthanides cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) Their average abundance in the Earth’s crust range from 66µg g−1 in Ce to 05µg g−1 in Tm and «01µg g−1 in Pm Recent great improvements in more routine analytical technique, the use of REEs as fertilisers, at least in East Asian agriculture, and the importance of these elements as indicators in both pedological and physiological processes and reactions have contributed to an increased interest in these previously less considered elements in environmental sciences This review of recent and current literature deals with REEs in primary and secondary soil minerals, concentrations in surface soils, factors influencing adsorption, solubility and transport in soils, including weathering and transformations of REE minerals, and vertical distribution in soil profiles Reviewed and discussed are also concentrations, distribution and localisation of REEs in plants and plant organs, soil-plant relationships and interactions, effects on plant growth and crop production and their importance in plant physiology and biochemistry The REEs are found, usually several elements together, as phosphates, carbonates and silicate minerals finely dispersed especially in magmatic and metamorphic rocks REE concentrations in surface soils of humid climates, such as the A(E)-horizons of Podzols and Laterites, are usually lower than in the parent material, due to higher weathering and leaching rates than of the average soil constituents Some fractionation may occur due to the formation of more element-specific secondary minerals Transfer from soil to plant is usually low, but extreme accumulators are found, eg, among several species of ferns Roots have generally higher concentrations than shoots Possible uptakemechanisms of REEs are discussed Uptake is positively, though often weakly, correlated with soil acidity and easily soluble concentrations of the elements, but rarely well related to their total concentrations in the soil Under certain conditions, low concentrations of at least some REEs seem to favour plant growth and productivity, but the physiological mechanisms are still not well understood Some considerations concerning the boundary between essential and non-essential micro nutrients are discussed

Rare earth elements in soil and plant systems - A review

Aquatic surface chemistry: Edited by Werner Stumm. Wiley, New York. 1987. $69.95 (ISBN 0471822951)

Rare earth elements in pore waters of marine sediments

The solubility of iron in seawater

The influence of phosphate coprecipitation on rare earth distributions in natural waters

Sorption of yttrium and rare earth elements by amorphous ferric hydroxide: Influence of solution complexation with carbonate

Sorption of yttrium and rare earth elements by amorphous ferric hydroxide : Influence of pH and ionic strength

Distribution coefficients were obtained for yttrium and the rare earth elements (YREEs) in aqueous solutions containing freshly precipitated hydroxides of trivalent cations (Fe3+, Al3+, Ga3+, and In3+). Observed patterns of log
 i
 
K
S–, where i
 
K
S = [MS
 i
 ][M3+]−1[S
 i
 ]−1, [MS
 i
 ] is the concentration of a sorbed YREE, [M3+] is the concentration of a free hydrated YREE ion, and [S
i] is the concentration of a sorptive solid substrate (Fe(III), Al, Ga, In)– exhibited similarities to patterns of YREE solution complexation constants with hydroxide (OH
β
1) and fluoride (F
β
1), but also distinct differences. The log
 i
 
K
S pattern for YREE sorption on Al hydroxide precipitates is very similar to the pattern of YREE hydroxide stability constants (logOH
β
1) in solution. Linear free-energy relationships between log
 i
 
K
S and logOH
β
1 showed excellent correlation for YREE sorption on Al hydroxide precipitates, good correlation for YREE sorption on Ga or In hydroxide precipitates, yet poor correlation for YREE sorption on Fe(III) hydroxide precipitates. Whereas the correlation between log
 i
 
K
S and logF
β
1 was generally poor, patterns of log(
 i
 
K
S/F
β
1) displayed substantially increased smoothness compared to patterns of log
 i
 
K
S. This indicates that the conspicuous sequence of inflections along the YREE series in the patterns of log
 i
 
K
S and logF
β
1 is very similar, particularly for In and Fe(III) hydroxide precipitates. While the log
 i
 
K
S patterns obtained with Fe(III) hydroxide precipitates in this work are quite distinct from those obtained with Al, Ga, and In hydroxide precipitates, they are in good agreement with patterns of YREE sorption on ferric oxyhydroxide precipitates reported by others. Furthermore, our log
 i
 
K
S patterns for Fe(III) hydroxide precipitates bear a striking resemblance to predicted log
 i
 
K
S patterns for natural surfaces that are based on YREE solution chemistry and shale-normalized YREE concentrations in seawater. Yttrium exhibits an itinerant behavior among the REEs: sorption of Y on Fe(III) hydroxide precipitates is intermediate to that of La and Ce, while for Al hydroxide precipitates Y sorption is similar to that of Eu. This behavior of Y can be rationalized from the propensities of different YREEs for covalent vs. ionic interactions. The relatively high shale-normalized concentration of Y in seawater can be explained in terms of primarily covalent YREE interactions with scavenging particulate matter, whereby Y behaves as a light REE, and primarily ionic interactions with solution ligands, whereby Y behaves as a heavy REE.

Comparative Scavenging of Yttrium and the Rare Earth Elements in Seawater: Competitive Influences of Solution and Surface Chemistry

Determination of SO4β1 for yttrium and the rare earth elements at I = 0.66 m and t = 25°C—implications for YREE solution speciation in sulfate-rich waters

Johan Schijf

Papers

The influence of phosphate coprecipitation on rare earth distributions in natural waters

Sorption of yttrium and rare earth elements by amorphous ferric hydroxide: Influence of solution complexation with carbonate

Sorption of yttrium and rare earth elements by amorphous ferric hydroxide : Influence of pH and ionic strength

Comparative Scavenging of Yttrium and the Rare Earth Elements in Seawater: Competitive Influences of Solution and Surface Chemistry

Determination of SO4β1 for yttrium and the rare earth elements at I = 0.66 m and t = 25°C—implications for YREE solution speciation in sulfate-rich waters