Plankton metabolism and physical forcing in a productive embayment of a large oligotrophic lake: insights from stable oxygen isotopes

1. The metabolic balance of plankton communities, commonly assessed by the photosynthesis‐to‐respiration ratio (P : R), has received much attention recently in connection with allochthonous organic subsidies to lakes, while the role of physical, climate‐related forces has received less attention. 2. Here we evaluated the effects of wind and upwelling events on plankton metabolism and the potential of stable oxygen isotopes to characterise P, R and P : R on the scales necessary to characterise properly physical forcing effects in large lakes. 3. We measured the ¹⁸O/¹⁶O ratio of dissolved oxygen and water in a large productive embayment of Lake Ontario (Hamilton Harbour, Canada) and estimated P, R and P : R from the steady state solutions of a widely accepted mass balance model, together with estimates of wind‐driven gas exchange, and compared the results with those from experimental incubations of plankton samples. 4. Estimates of P, but not R, from the isotope model were significantly correlated with bottle estimates while average P : R was similar by both methods. Closer examination of physical forcing events led to a model of how wind events induce mixing, upwelling, exchange and consequent changes in P and R. These physical forcing events were captured more by the isotope model than by the bottle estimates, as episodes of immediately increased R and decreased P : R, with a subsequent stimulation of P. 5. The oxygen isotope approach provided valuable measures of plankton metabolism and helped to characterise more effectively the substantial effects on P : R of physical forcing and, in particular, mixing and exchange events.     

Effects of Calcium and Abscisic Acid on Volume Changes of Guard Cell Protoplasts of Commelina

Calcium ions contracted guard cell protoplasts (GCP) of Commelinacommunis L., being particularly effective within the concentrationrange of 0 to 0.2 mol m^–3. Abscisic acid (ABA) in thepresence of EGTA, which chelates free Ca²⁺ in the medium, contractedGCP to a similar extent to Ca²⁺ alone or Ca²⁺ and ABA together.Similarly, ABA in the absence of free Ca²⁺ (i.e. an ABA/EGTAtreatment) inhibited K⁺-induced swelling of contracted GCP,as did Ca²⁺ alone or ABA and Ca²⁺ together. Lanthanum, a Ca²⁺channel blocker, prevented the contraction of GCP by Ca²⁺ buthad no effect if ABA was also present with Ca²⁺. The inhibitionof swelling of GCP by Ca²⁺ was also prevented by the presenceof lanthanum or verapamil (another Ca²⁺ channel blocker). These results indicate that Ca²⁺ and ABA can act independentlyof each other in contracting swollen GCP and in preventing K⁺-inducedswelling of contracted GCP of C. communis. If swelling and contractionof GCP are equivalent to stomatal opening and closure, respectively,the results do not support the hypothesis that ABA opens Ca²⁺channels in the plasma membrane of guard cells allowing Ca²⁺to enter the cells and, as a second messenger, to set in motionclosing processes. Key words: Abscisic acid, calcium, guard cell protoplasts, stomata     

Brood size manipulations in Great Horned Owls Bubo virginianus: are predators food limited at the peak of prey cycles?

The reproduction of raptors strongly depends on food resources. It is unclear whether predators experience superabundant food during cyclic peaks of prey populations. In order to test this hypothesis, four pairs of Great Horned Owls Bubo virginianus with two young were subjected to brood size manipulations during high densities of cyclic Snowshoe Hare Lepus americanus populations in southwestern Yukon, Canada. Broods older than 35 days were temporarily enlarged by one, and then by two, young. No effects were observed when one owlet was added, but the addition of two young resulted in significant weight losses in manipulated broods. Females with enlarged broods moved farther from their nest sites at night, presumably reflecting increased hunting effort, and also spent less time near the nest during the day. Food additions to enlarged broods returned the parental behaviour to normal. We conclude that these large predators did not experience superabundant food at this stage of the breeding season during a peak in cyclic prey.     

Intracellular pH Regulation in the Giant-Celled Marine Alga Chaetomorpha darwinii

The vacuolar pH (pH_v) and the cytoplasmic pH (pH_c) of the marinegiant-celled green alga Chaetomorpha darwinii were measuredby pH microelectrode techniques on extracted vacuolar sap, andby the [^I4C]DMO distribution method respectively. Equilibrationof DMO occurred with a half-time of about 2 h, with an apparentP_DMO of 3.6 x 10^–5 cm s^–1, but the vacuolar concentrationof free, undissociated DMO was always less than the externalconcentration. The explanation offered for freshwater giant-celledalgae of net DMO^– leakage across the plasmalemma cannotapply to Chaetomorpha darwinii, since electrically-driven DMO^–exit from the cytoplasm should be similar across the plasmalemmaand the tonoplast in these cells with large, vacuole-positivepotential differences across the tonoplast. pHc was accordinglycomputed assuming either tonoplast or plasmalemma equilibrationof DMO, with correction for DMO metabolism within the cell.pH_c was 8.0–8.3 in the light in artificial seawater (pH_oabout 8.0), was some 0.5 units lower in the dark, and was slightlylower with an external pH of 7. Vacuolar pH was 6.5–6.9,without consistent effects of illumination or of external pHof 7 rather than 8. While µ_H+ at the tonoplast was similarto that in giant-celled freshwater algae (although with a greatercontribution from relative to pH), µ_H+ at the plasmalemmawas less than 8 kJ mol^–1, i.e. less than one-third ofthe value in freshwater green algae. µ_Na+ was some 13kJ mol^–1 at the plasmalemma. The possibility that theprimary active transport process at the plasmalemma of Chaetomorphadarwinii (and certain other marine algae) is Na⁺ efflux ratherthan H⁺ efflux is discussed.     

Nuclear Division in the Ameboflagellate Adelphamoeba galeacystis

Nuclear division in synchronized cultures of the ameboflagellate Adelphamoeba galeacystis has been described. Division in this organism is typically promitotic. It occurs within an intact nuclear membrane and is characterized by the persistence of the nucleolus and its transformation into 2 polar masses. The nucleolus is stained with pyronin-Y by the methyl green pyronin-Y technic, and with Heidenhain's hematoxylin, but is unstained by the Feulgen reaction. The reaction with these stains is removed after digestion of the nucleolus by ribonuclease. During mitosis the nucleolus undergoes an orderly series of vacuolizations before forming the polar masses. The chromatin is Feulgen positive, stains with methyl green by the methyl green pyronin-Y technic and undergoes a series of characteristic changes during the division process. Synchronization of amebae grown on coverglasses was accomplished by transfer of cells from 30 to 38.5 C for a period of 100 min. A temporal sequence of nucleolar and chromatin participation in the nuclear division of this organism is suggested.     

Future energy potential of Miscanthus in Europe

European field experiments have demonstrated Miscanthus can produce some of the highest energy yields per hectare of all potential energy crops. Previous modelling studies using MISCANMOD have calculated the potential energy yield for the EU27 from mean historical climate data (1960–1990). In this paper, we have built on the previous studies by further developing a new Miscanthus crop growth model MISCANFOR in order to analyse (i) interannual variation in yields for past and future climates, (ii) genotype-specific parameters on yield in Europe. Under recent climatic conditions (1960–1990) we show that 10% of arable land could produce 1709 PJ and mitigate 30 Tg of carbon dioxide-carbon (CO₂-C) equivalent greenhouse gasses (GHGs) compared with EU27 primary energy consumption of 65 598 PJ, emitting 1048 Tg of CO₂-C equivalent GHGs in 2005. If we continue to use the clone Miscanthus × giganteus , MISCANFOR shows that, as climate change reduces in-season water availability, energy production and carbon mitigation could fall 80% by 2080 for the Intergovernmental Panel on Climate Change A2 scenario. However, because Miscanthus is found in a huge range of climates in Asia, we propose that new hybrids will incorporate genes conferring superior drought and frost tolerance. Using parameters from characterized germplasm, we calculate energy production could increase from present levels by 88% (to 2360 PJ) and mitigate 42 Tg of CO₂-C equivalent using 10% arable land for the 2080 mid-range A2 scenario. This is equivalent to 3.6% of 2005 EU27 primary energy consumption and 4.0% of total CO₂ equivalent C GHG emissions.     

Trophic level asynchrony in rates of phenological change for marine,freshwater and terrestrial environments

Recent changes in the seasonal timing (phenology) of familiar biological events have been one of the most conspicuous signs of climate change. However, the lack of a standardized approach to analysing change has hampered assessment of consistency in such changes among different taxa and trophic levels and across freshwater, terrestrial and marine environments. We present a standardized assessment of 25 532 rates of phenological change for 726 UK terrestrial, freshwater and marine taxa. The majority of spring and summer events have advanced, and more rapidly than previously documented. Such consistency is indicative of shared large scale drivers. Furthermore, average rates of change have accelerated in a way that is consistent with observed warming trends. Less coherent patterns in some groups of organisms point to the agency of more local scale processes and multiple drivers. For the first time we show a broad scale signal of differential phenological change among trophic levels; across environments advances in timing were slowest for secondary consumers, thus heightening the potential risk of temporal mismatch in key trophic interactions. If current patterns and rates of phenological change are indicative of future trends, future climate warming may exacerbate trophic mismatching, further disrupting the functioning, persistence and resilience of many ecosystems and having a major impact on ecosystem services.