Comparison of contemporary and fossil diatom assemblages from the western Antarctic Peninsula shelf

During the past ten years, the Antarctic Peninsula has been identified as the most rapidly warming region of the Southern Hemisphere and it is important to place this warming in the context of the natural climate and oceanographic variability of the recent geological past. Many biological proxies, such as marine diatom assemblages, have been used to determine Southern Ocean palaeoceanographic conditions during the Late Quaternary, however, few investigations have attempted to link observations of modern floras with the fossil record. In this study we examine a suite of modern austral spring (December 2003) and summer (February 2002) surface water samples from along the western Antarctic Peninsula (WAP) continental shelf and compare these to core-top, surface sediment samples. Using detrended correspondence analysis (DCA) and principal component analysis (PCA) of diatom abundance data we investigate the relationship of contemporary diatom floras with the fossil record. This multivariate analysis reveals that our modern assemblages can be divided into three groups: summer southern WAP sites, summer northern WAP sites, and spring WAP sites. Sea surface temperature (SST) is an important environmental variable for explaining seasonal differences in diatom assemblages between spring and summer, but sea surface salinity (SSS) is more important for understanding temporally-equivalent regional variations in assemblage. Our summer diatom samples are more reminiscent of early season assemblages, reflecting the unusually late sea ice retreat from the region that year. When the modern assemblages are compared to the fossil record, it is clear that most of the important diatoms from the summer assemblage are not preserved into the sediments, and that the fossil record more closely reflects spring assemblages. This observation is important for any future attempts to quantitatively reconstruct palaeoceanographic conditions along the WAP during the Late Quaternary and highlights the need for many more such studies in order to address longer timescales, such as interannual variability, in the context of the fossil record.     

Size scaling of whole‐body metabolic activity in the noble crayfish (Astacus astacus) estimated from measurements on a single leg

1. Use of electron transport system (ETS) activity in a single leg for estimating whole‐body ETS activity was explored in the noble crayfish Astacus astacus. Oxygen consumption and ETS activity of the whole body and of a walking leg were measured in different‐sized animals at 10 °C to compare the size scaling of oxygen consumption, whole‐body ETS activity and the ratio of whole‐body ETS activity to oxygen consumption (ETS/R). 2. Electron transport system activity of a leg and the ratio of ETS activity of a whole crayfish to that of a leg were correlated with wet mass of animals. Therefore, metabolic potential in whole noble crayfish can be estimated on the basis of the measured ETS activity in a single leg and crayfish mass. This approach provides a valuable tool for determining metabolic characteristics of crayfish without killing them. 3. Mass‐specific oxygen consumption decreased with increasing wet mass, while ETS activity of whole crayfish showed no significant correlation with wet mass. Both oxygen consumption and ETS activity correlated significantly with protein mass. 4. The increase in ETS/R with increasing wet mass of the noble crayfish indicates that small organisms exploit a greater proportion of their metabolic potential for standard metabolism than larger ones. This is the first report on ETS/R in crayfish.     

Coordination between water transport capacity,biomass growth,metabolic scaling and species stature in co‐occurring shrub and tree species

The significance of xylem function and metabolic scaling theory begins from the idea that water transport is strongly coupled to growth rate. At the same time, coordination of water transport and growth seemingly should differ between plant functional types. We evaluated the relationships between water transport, growth and species stature in six species of co‐occurring trees and shrubs. Within species, a strong proportionality between plant hydraulic conductance (K), sap flow (Q) and shoot biomass growth (G) was generally supported. Across species, however, trees grew more for a given K or Q than shrubs, indicating greater growth‐based water‐use efficiency (WUE) in trees. Trees also showed slower decline in relative growth rate (RGR) than shrubs, equivalent to a steeper G by mass (M) scaling exponent in trees (0.77–0.98). The K and Q by M scaling exponents were common across all species (0.80, 0.82), suggesting that the steeper G scaling in trees reflects a size‐dependent increase in their growth‐based WUE. The common K and Q by M exponents were statistically consistent with the 0.75 of ideal scaling theory. A model based upon xylem anatomy and branching architecture consistently predicted the observed K by M scaling exponents but only when deviations from ideal symmetric branching were incorporated.     

The role of functional traits and trade-offs in structuring phytoplankton communities: scaling from cellular to ecosystem level

Trait-based approaches to community structure are increasingly used in terrestrial ecology. We show that such an approach, augmented by a mechanistic analysis of trade-offs among functional traits, can be successfully used to explain community composition of marine phytoplankton along environmental gradients. Our analysis of literature on major functional traits in phytoplankton, such as parameters of nutrient-dependent growth and uptake, reveals physiological trade-offs in species abilities to acquire and utilize resources. These trade-offs, arising from fundamental relations such as cellular scaling laws and enzyme kinetics, define contrasting ecological strategies of nutrient acquisition. Major groups of marine eukaryotic phytoplankton have adopted distinct strategies with associated traits. These diverse strategies of nutrient utilization can explain the distribution patterns of major functional groups and size classes along nutrient availability gradients.     

Variation in growth rate,carbon assimilation,and photosynthetic efficiency in response to nitrogen source and concentration in phytoplankton isolated from upper San Francisco Bay

Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH₄⁺), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (F_v/F_m) was a sensitive indicator of NH₄⁺ toxicity, manifested by a suppression of F_v/F_m in a dose‐dependent manner. Two chlorophytes were the least sensitive to NH₄⁺ inhibition, at concentrations of >3,000 μmoles NH₄⁺ · L^?1, followed by two estuarine diatoms that were sensitive at concentrations >1,000 μmoles NH₄⁺ · L^?1, followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 μmoles NH₄⁺ · L^?1. At non‐inhibiting concentrations of NH₄⁺, the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO₃^?), whereas the other grew significantly faster on NH₄⁺. All four diatoms tested grew faster on NH₄⁺ compared with NO₃^?. We showed that in cases where growth rates were faster on NH₄⁺ than they were on NO₃^?, the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH₄⁺ dominates the total N pool and they will also not have a growth advantage when NO₃^? is dominant, as long as N concentrations are sufficient.     

Three species of fishes from an eutrophic, seasonally alkaline lake are not more tolerant to acute exposure to high pH in the laboratory

A number of different freshwater fish species (perch Perca fluviatilis , roach Rutilus rutilus and rudd Scardinius erythrophthalamus ) from either eutrophic (Slapton Ley, a seasonally alkaline lake) or non-eutrophic waters were compared with respect to their sodium uptake kinetics and tolerance to acute (1 h) exposure to pH 9·5. Further comparisons were made with rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta . The influence of fish size was also investigated in rainbow trout. Exposure to pH 9·5 was found to disrupt sodium balance and inhibit ammonia excretion in all species and sizes of fishes. The origin of fishes did not have a significant effect on the sodium uptake kinetics or the physiological responses to high pH water. The fishes from the eutrophic lake therefore did not appear to have any increased tolerance to acute exposure to alkaline water. In contrast to previous studies there was no inhibition of Na⁺ uptake during exposure to high pH. Indeed in some groups of fish Na⁺ uptake was actually stimulated, as was Na⁺ efflux. These differences are attributed to experimental water composition and interspecific differences in physiology. It was not always possible to size-match fishes of the different species, so rainbow trout were used to assess the effect of body mass (from 2 to 40 g), on Na⁺ uptake kinetics and Na⁺ or ammonia fluxes during alkaline water exposure in rainbow trout. Size had no significant effect on these measurements within this narrow range, which helps validate the comparison between species in this study.     

Effect of ouabain,amiloride, and antidiuretic hormone on the sodium-transport pool in isolated epithelia from frog skin (Rana temporaria)

Summary When tracer Na⁺ is added to the solution bathing the apical side of isolated epithelia the observed transepithelial tracer influx increases with time until a steady state is reached. The build-up of the tracer flux follows a single exponential course. The halftime for this build-up under control conditions was 0.92 ±0.06 min, and in the presence of ouabain 4.51±0.7 min. It is shown that the calculated Na⁺-transport pool is located in the cells. The Na⁺-transport pool under control conditions was 35.6 ±3.4 nmol/cm², which corresponds to an intracellular Na⁺ concentration of 7.9mm. Activation of the active Na⁺ transport by addition of antidiuretic hormone resulted in a highly significant increase in the Na⁺ transport pool, and inhibition of the transcellular Na⁺ transport with amiloride resulted in a decrease in the Na⁺-transport pool.Furthermore, the active Na⁺ transport increased along anS-shaped curve with increasing intracellular Na⁺ concentration (Na⁺-transport pool). The Na⁺ pump was found to be half saturated at an intracellular Na⁺ concentration of 12.5mm.     

Low growth temperatures modify the efficiency of light use by photosystem II for CO2 assimilation in leaves of two chilling-tolerant C4 species, Cyperus longus L. and Miscanthus x giganteus

Two C4 plants, Miscanthus x giganteus and Cyperus longus L., were grown at suboptimal growth temperatures and the relationships between the quantum efficiencies of photosynthetic electron transport through photosystem II (PSII) (PSII operating efficiency; Fq'/Fm') and CO2 assimilation (phiCO2) in leaves were examined. When M. x giganteus was grown at 10 degrees C, the ratio of the PSII operating efficiency to phiCO2 increased relative to that found in leaves grown at 14 and 25 degrees C. Similar increases in the Fq'/Fm': phiCO2 occurred in the leaves of two C. longus ecotypes when the plants were grown at 17 degrees C, compared to 25 degrees C. These elevations of Fq'/Fm': phiCO2 at low growth temperatures were not attributable to the development of anthocyanins, as has been suggested for maize, and were indicative of the operation of an alternative sink to CO2 assimilation for photosynthetic reducing equivalents, possibly oxygen reduction via a Mehler reaction, which would act as a mechanism for protection of PSII from photoinactivation and damage. Furthermore, in M. x giganteus grown at 10 degrees C, further protection of PSII was effected by a 20-fold increase in zeaxanthin content in dark-adapted leaves, which was associated with much higher levels of non-photochemical quenching of excitation energy, compared to that observed in leaves grown at 14 and 25 degrees C. These differences may explain the long growing season and remarkable productivity of this C4 plant in cool climates, even in comparison to other C4 species such as C. longus, which occur naturally in such climates.     

Effect of external pH on the growth, photosynthesis and photosynthetic electron transport of Chlamydomonas acidophila Negoro, isolated from an extremely acidic lake (pH 2.6)

In extremely acidic lakes, low primary production rates have been measured. We assumed that proton stress might explain these observations and therefore investigated the photosynthetic behaviour of a Chlamydomonas species, a main primary producer in acidic lakes, over a range of pH values. Identified as C. acidophila using small subunit rDNA analysis, this species is identical to other isolates from acidic environments in Europe and South America, suggesting a worldwide distribution. Laboratory experiments with C. acidophila , revealed a broad pH-tolerance for growth and photosynthesis, the lower pH limit lying at pH 1.5 and the upper limit at pH 7. Growth rates at optimum pH conditions (pH 3 and 5) were equal to those of the mesophilic Chlamydomonas reinhardtii . In contrast, photosynthetic rates were significantly higher, suggesting that higher photosynthetic rates compensated for higher dark respiration rates, as confirmed experimentally. Electron transport capacities of PSI and PSII, P700⁺ re-reduction times and measurements of PSII fluorescence revealed the induction of alternative electron transport mechanisms, such as chlororespiration, state transitions and cyclic electron transport, only at suboptimal pH values (pH 1.5; 4 and 6–7). The results indicate, that C. acidophila is well adapted to low pH and that the relatively low primary production rates are not a result of pH stress.     

Effects of agronomic application of olive mill wastewater in a field of olive trees on carbohydrate profiles, chlorophyll a fluorescence and mineral nutrient content

Olive mill wastewater (OMW) management is a serious environmental issue for the Mediterranean area where there is the most production of olive oil. OMW contains a high organic load, substantial amounts of plant nutrients but also several compounds with recognized toxicity towards living organisms. Moreover, OMW may represent a low cost source of water. We studied the influence of irrigation with OMW (amounts applied: 30, 60, 100 and 150 m³ h⁻¹) in a field of olive trees on root colonization, photosynthesis, chlorophyll fluorescence, leaf nutrient concentration and soluble carbohydrate. The soil fatty acid methyl ester (FAME) 16:1ω5 was used to quantify biomass of arbuscular mycorrhizal (AM) fungi and the root FAME 16:1ω5 analysis was used as index for the development of colonization in the roots. Agronomic application of OMW decreased significantly the abundance of the soil FAME 16:1ω5 and the root FAME 16:1ω5 in the soil amended with 60, 100 and 150 m³ ha⁻¹ OMW. Decreased root FAME 16:1ω5 due to OMW amendment was associated with a significant reduction of tissue nutrient concentrations in the olive trees. The highest application of OMW to the soil reduced significantly the olive trees uptake of N, P, K, Ca, Mg, Fe, Cu, Mn and Zn. Land spreading of OMW increased concentration of soluble carbohydrate in the olive leaves, mostly due to decreased sink demand for carbon by the root. In the olive trees amended with 150 m³ ha⁻¹ OMW, net CO₂ uptake rate (A), quantum yield of photosystem II electron transport (Φ_PSII), maximal photochemical efficiency of photosystem II (Fv/Fm), photochemical quenching (q_p) and the electron transport rate (ETR) were significantly depressed, whereas non-photochemical quenching (NPQ) was found to increase. Taken with data from experiments in field conditions, our results suggest that agronomic application of OMW alters the functioning of arbuscular mycorrhizas and can even disrupt the relationship between AM fungi and olive trees.