A pilot analysis of gut contents in termites from the Mbalmayo Forest Reserve,Cameroon

Abstract.

• 1 Gut content analysis was carried out on eight species of higher termites representing the four included subfamilies and notional soil-feeding and wood-feeding forms. A lower termite species feeding on wood was also examined.
• 2 Pooled homogenates equivalent in volume to twenty hindguts of Thoracotermes macrothorax were diluted, stained and scored present/absent in 500 haemacytometer fields for ten content item categories: macerated organic material, lignified tissue, plant tissue fragments, fungal mycelium, arthropod parts, plant roots, safranin +ve, gentian violet +ve, humus and silica. For interspecific comparisons, the occurrence of each category was expressed as a proportion of the total haemacytometer cells examined.
• 3 A hierarchical classification of the species, based on gut contents, was prepared using a two-way indicator species analysis, and suggested the following rank order of species along a hypothetical humification gradient (soil to sound wood): Thoracotermes macrothorax, Astalotermes quietus (both soil-feeders), Termes hospes, Amalotermes phaecocephalus, Pseudacanthotermes militaris, Microtermes congoensis, Nasutitermes lujae, Microcerotermes parvus, Schedorhinotermes putorius (all notional wood-feeders). Arthropod parts, silica and humus were identified as indicator factors.
• 4 It is proposed that wood-feeding forms can be subdivided into a group consuming some silica and humus (five species: humified wood-feeders) and a second group of sound wood-feeders (two species).
• 5 Pianka's equations for diet breadth and diet overlap were also applied to the data. These identified Microtermes congoensis, Schedorhinotermes putorius and Pseudacanthotermes militaris as the most specialized feeders, i.e. that they can extract their nutrients from the least heterogenous substrates.

     

Vertical stratification of the termite assemblage in a neotropical rainforest

The importance of termites as decomposers in tropical forests has long been recognized. Studies on the richness and diversity of termite species and their ecological function have flourished in more recent times, but these have been mostly conducted in a thin stratum within a standing man’s reach. Our aims were to evaluate the specific richness and composition of the termite assemblage in the canopy of a tropical rainforest and to determine its originality with respect to the sympatric ground-level fauna. We conducted systematic searches for canopy termites, together with conventional sampling of the sympatric ground-level fauna, in the San Lorenzo forest, Panama. We hypothesized that (1) the canopy accommodates two categories of wood-feeding termites (long-distance foragers and small-colony “one-piece” species) and possibly soil-feeders in suspended soil-like habitats; (2) due to the abundance of soil-feeders, the overall diversity of the ground fauna is higher than that of the canopy; (3) differences in microclimate and resource accessibility favour vertical stratification among wood-feeders. Sixty-three canopy samples yielded ten species of termites, all wood-feeders. Five of these were not found at ground level, although a total of 243 ground samples were collected, representing 29 species. In addition to long-distance foragers (Microcerotermes and Nasutitermes spp.) and small-colony termites (mostly Kalotermitidae), the canopy fauna included Termes hispaniolae, a wood-feeding Termitidae from an allegedly soil-feeding genus, living in large dead branches. Soil-feeders were absent from the canopy, probably because large epiphytes were scarce. As predicted, the ground fauna was much richer than that of the canopy, but the species richness of both habitats was similar when only wood-feeders were considered. Vertical stratification was strongly marked among wood-feeders, as all common species, apart from the arboreal-nesting Microcerotermes arboreus, could unequivocally be assigned to either a ground or a canopy group. The canopy, therefore, contributes significantly to the total species richness of the termite assemblage, and the diversity, abundance and ecological importance of canopy termites in tropical rainforests may be higher than previously recognized.Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at .     

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I_K values were between 18 and 53 μmol m^?2 s^?1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I_K values between 70 and 74 μmol m^?2 s^?1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m^?2 s^?1. Values of α were high: between 0.4 and 1.1 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the brown and red algae and between 2.1 and 4.9 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the green algal species. At 0°C P_max values of the brown and red algae ranged from 6.8 to 19.1 μmol O₂ g^?1 FW h^?1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q₁₀ values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.     

Exceptional Visible‐Light‐Driven Cocatalyst‐Free Photocatalytic Activity of g‐C3N4 by Well Designed Nanocomposites with Plasmonic Au and SnO2

In this work, plasmonic Au/SnO₂/g‐C₃N₄ (Au/SO/CN) nanocomposites have been successfully synthesized and applied in the H₂ evolution as photocatalysts, which exhibit superior photocatalytic activities and favorable stability without any cocatalyst under visible‐light irradiation. The amount‐optimized 2Au/6SO/CN nanocomposite capable of producing approximately 770 μmol g^?1 h^?1 H₂ gas under λ > 400 nm light illumination far surpasses the H₂ gas output of SO/CN (130 μmol g^?1), Au/CN (112 μmol g^?1 h^?1), and CN (11 μmol g^?1 h^?1) as a contrast. In addition, the photocatalytic activity of 2Au/6SO/CN maintains unchanged for 5 runs in 5 h. The enhanced photoactivity for H₂ evolution is attributed to the prominently promoted photogenerated charge separation via the excited electron transfer from plasmonic Au (≈520 nm) and CN (470 nm > λ > 400 nm) to SO, as indicated by the surface photovoltage spectra, photoelectrochemical I–V curves, electrochemical impedance spectra, examination of formed hydroxyl radicals, and photocurrent action spectra. Moreover, the Kelvin probe test indicates that the newly aligned conduction band of SO in the fabricated 2Au/6SO/CN is indispensable to assist developing a proper energy platform for the photocatalytic H₂ evolution. This work distinctly provides a feasible strategy to synthesize highly efficient plasmonic‐assisted CN‐based photocatalysts utilized for solar fuel production.     

Seasonal variation of leaf glutamine synthetase isoforms in temperate deciduous trees strongly suggests different functions for the enzymes

Changes in the activities of leaf glutamine synthetase (GS) isoforms were followed in four temperate deciduous trees from full leaf expansion to senescence (May to November). In the early part of the season, total GS activity was high in all species, with values ranging from 90 to 200 μmol h⁻¹ g⁻¹ fw. During this early period this activity comprised only the activity of the chloroplastic (GS₂) isoform in all species. These high GS₂ activities are consistent with the role of GS₂ in the re-assimilation of photorespired ammonia. The early high values also coincided with high nitrate reductase activity in one of the species, the highly nitrophilous species Sambucus nigra, with values of up to 16μmol h⁻¹ g⁻¹ fw. This indicates that GS₂ is also important in the assimilation of ammonia produced from nitrate reduction. From mid- to late-season, the cytosolic isoform (GS₁) was detected in all four species and became increasingly more active in comparison to GS₂. By the time of senescence it was the dominant enzyme of the two forms in both S. nigra and Carpinus betulus. The results provide strong support for recent findings that GS₁ is an important enzyme for the mobilization of nitrogen for translocation or storage.     

PHOTOSYNTHESIS AND RESPIRATION OF THE CONCHOCELIS STAGE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES IN RESPONSE TO ENVIRONMENTAL VARIABLES1

Photosynthesis and respiration of three Alaskan Porphyra species, P. abbottiae V. Krishnam., P. pseudolinearis Ueda species complex (identified as P. “pseudolinearis” below), and P. torta V. Krishnam., were investigated under a range of environmental parameters. Photosynthesis versus irradiance (P–I) curves revealed that maximal photosynthesis (P_max), irradiance at maximal photosynthesis (I_max), and compensation irradiance (I_c) varied with salinity, temperature, and species. The P_max of Porphyra abbottiae conchocelis varied between 83 and 240 μmol O₂ · g dwt^?1 · h^?1 (where dwt indicates dry weight) at 30–140 μmol photons · m^?2 · s^?1 (I_max) depending on temperature. Higher irradiances resulted in photoinhibition. Maximal photosynthesis of the conchocelis of P. abbottiae occurred at 11°C, 60 μmol photons · m^?2·s^?1, and 30 psu (practical salinity units). The conchocelis of P. “pseudolinearis” and P. torta had similar P_max values but higher I_max values than those of P. abbottiae. The P_max of P. “pseudolinearis” conchocelis was 200–240 μmol O₂ · g dwt^?1 · h^?1 and for P. torta was 90–240 μmol O₂ · g dwt^?1 · h^?1. Maximal photosynthesis for P. “pseudolinearis” occurred at 7°C and 250 μmol photons · m^?2 · s^?1 at 30 psu, but P_max did not change much with temperature. Maximal photosynthesis for P. torta occurred at 15°C, 200 μmol photons · m^?2 · s^?1, and 30 psu. Photosynthesis rates for all species declined at salinities <25 or >35 psu. Estimated compensation irradiances (I_c) were relatively low (3–5 μmol · photons · m^?2 · s^?1) for intertidal macrophytes. Porphyra conchocelis had lower respiration rates at 7°C than at 11°C or 15°C. All three species exhibited minimal respiration rates at salinities between 25 and 35 psu.     

Seasonal Growth and Photosynthetic Performance of the Antarctic Macroalga Desmarestia menziesii (Phaeophyceae) Cultivated under Fluctuating Antarctic Daylengths

Growth, photosynthesis, dark respiration and pigment contents were monitored in adult sporophytes of the Antarctic brown alga Desmarestia menziesii J. Agardh grown under fluctuating Antarctic daylength conditions. Growth rates were closely coupled to daylength variations with values varying from 0.05% d^?1 in winter condition (July-August) to 0.5% d^?1 in early summer (December). Photosynthetic pigments had maximum values of 1.8 mg g^?1 FW (chlorophyll a), 0.4 mg g^?1 FW (chlorophyll c) and 0.9 mg g^?1 FW (fucoxanthin) in summer. These changes were also closely related to individual size and biomass of the plants. Net photosynthesis (P_max), on a fresh weight basis, showed a clear seasonal pattern with highest rates of 25μmol O₂ g^?1 FW h^?1 in October and minima close to 9μmol O₂ g^?1 FW h^?1 in April. Dark respiration was high in spring (13μmol O₂ g^?1 FW h^?1) approximately coinciding with growth peaks. Likewise, photosynthetic efficiency (α) and the initial saturating light point of photosynthesis (l_k) increased significantly in spring [1.3 μimol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 and 26μmol photons m^?2 s^?1, respectively]. In the case of α, no significant differences between fresh weight and Chl a based rates were found. The results of the present study are the first that demonstrate seasonality of physiological parameters in D. menziesii sporophytes and confirm also that phenology and physiology of macroalgae can be simulated in the laboratory. On the other hand this study adds new elements to the explanation of the life strategy of D. menziesii, in particular that algal growth and photosynthesis occur under a programmed seasonal pattern.     

Use of carbon and nitrogen isotope ratios in termite research

In this paper, I review carbon and nitrogen isotopic (natural abundance levels) studies of termites. The carbon isotope ratio of CH₄ emitted from termites, together with the emission rates of CO₂, CH₄ and H₂, showed several trends corresponding to the kinds of symbiotic microbes and feeding habits. The fraction of methane oxidized in the nest structure was estimated by comparing carbon isotope ratio of CH₄ emitted from the nest with that produced by termites in the nest. Symbiotic nitrogen fixation in the gut of termites has been shown to have a significant contribution to the nitrogen economy in some wood-feeding termites. The carbon isotope ratio distinguishes between C4 from C3 plants, and the fractional contribution of grass in the diet can thereby be estimated. The carbon and nitrogen isotope ratios in termites are discernible among soil-feeders, fungus cultivators and wood-feeders. Wood/soil-interface feeders have intermediate values between wood- and soil-feeders, and thus carbon and nitrogen stable isotope ratios are assumed to characterize the degree of humification of the material consumed by termites. It is suggested that carbon and nitrogen isotope ratios are useful indicators of the functional position of termites in the decomposition process. A similar isotope pattern has been obtained in earthworms, suggesting that isotope signatures might be useful parameters in investigating detritivorous animals in general.     

Direct and acclimatory responses of stomatal conductance to elevated carbon dioxide in four herbaceous crop species in the field

In order to separate the net effect of growth at elevated [CO₂] on stomatal conductance (g_s) into direct and acclimatory responses, mid‐day values of g_s were measured for plants grown in field plots in open‐topped chambers at the current ambient [CO₂], which averaged 350 μmol mol^?1 in the daytime, and at ambient + 350 μmol mol^?1[CO₂] for winter wheat, winter barley, potato and sorghum. The acclimatory response was determined by comparing g_s measured at 700 μmol mol^?1[CO₂] for plants grown at the two [CO₂]. The direct effect of increasing [CO₂] from 350 to 700 μmol mol^?1 was determined for plants grown at the lower concentration. Photosynthetic rates were measured concurrently with g_s. For all species, growth at the higher [CO₂] significantly reduced g_s measured at 700 μmol mol^?1[CO₂]. The reduction in g_s caused by growth at the higher [CO₂] was larger for all species on days with low leaf to air water vapour pressure difference for a given temperature, which coincided with highest conductances and also the smallest direct effects of increased [CO₂] on conductance. For barley, there was no other evidence for stomatal acclimation, despite consistent down‐regulation of photosynthetic rate in plants grown at the higher [CO₂]. In wheat and potato, in addition to the vapour pressure difference interaction, the magnitude of stomatal acclimation varied directly in proportion to the magnitude of down‐regulation of photosynthetic rate through the season. In sorghum, g_s consistently exhibited acclimation, but there was no down‐regulation of photosynthetic rate. In none of the species except barley was the direct effect the larger component of the net reduction in g_s when averaged over measurement dates. The net effect of growth at elevated [CO₂] on mid‐day g_s resulted from unique combinations of direct and acclimatory responses in the various species.     

Studies on nitrate reductase activity in Laminariadigitata (Huds.) Lamour. I. Longitudinal and transverse profiles of nitrate reductase activity within the thallus

The distribution of the enzyme nitrate reductase (NR) within the thallus of the brown alga Laminaria digitata (Huds.) Lamour is described for plants sampled from the east coast of Scotland in May and June when growth rates are at a maximum. Highest NR activities (≈ 0.2 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the mature blade. NR activities declined towards the basal meristematic region of the blade. Activities in the stipe and holdfast were also low, being between 0.05 and 0.07 μmol NO₃^? reduced·g^?1 wet wt·h^?1. The activities of the enzyme glutamine synthetase (GS), which is important in the assimilation of NH₄⁺, showed a similar distribution within the blade to those of NR.The transverse profile of NR activity in the stipe exhibited a decline from the outer to the inner tissues. Maximum activities (0.13 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the meristoderm, while those of the cortex and medulla were 0.04 and 0.01 μmol NO₃^? reduced·g^?1 wet wt·h^?1 respectively.These data indicate that most of the NO₃^? assimilation occurs in the mature blade rather than in the meristematic tissue where there is a high nitrogen demand for growth. The data are consistent with the maintenance of meristematic growth by the internal transport of organic nitrogen from the mature blade.     

A community of submerged aquatic CAM plants in Lake Kalgaard,Denmark

The CO₂ exchange pattern of leaves of dominant Isoetes lacustris L., Littorella uniflora (L.) Aschers. and Lobelia dortmanna L. from oligotrophic, carbon-poor Lake Kalgaard, Denmark was examined by gas-exchange experiments and by following the diurnal acidity rhythm. Both variables suggest Crassulacean Acid Metabolism (CAM) in Littorella and Isoetes. During the dark, both species had a continuous, but declining CO₂ uptake. The maximum uptake in Littorella was 28 μmol CO₂ g^?1 DW h^?1 or about 36% of the light CO₂ assimilation rate. In Isoetes, corresponding figures were 19 μmol CO₂ g^?1 DW h^?1 and 22%.A peak of 49.5 μEq g^?1 FW titratable acidity (Littorella) and 41.9 μEq g^?1 FW (Isoetes) was found at the end of the dark period, reflecting an increase of 11.6 μEq g^?1 FW (9 h)^?1 (Littorella) and 16.3 μEq g^?1 FW (9 h)^?1 (Isoetes). These results agreed with the cumulative CO₂ assimilation during the dark.The assimilation of CO₂ in the dark is important, apparently, for growth of Littorella and Isoetes in Lake Kalgaard. Lobelia, which exhibits little dark CO₂ assimilation, is also the least abundant species, at less than 1% of the total cover.     

The effects of temperature and nutrient concentrations on nitrate and phosphate uptake in different species of Porphyra from Long Island Sound (USA)

Uptake rates of nitrate and phosphate were measured for four species and one variety of Porphyra from Long Island Sound (USA) at two temperatures and two nutrient medium concentrations at increasing intervals over a 24- or 48-h period. Maximum uptake rates found were: V_{30 μM}^{0-1 h}=73.8 μmol NO₃ g⁻¹ DW h⁻¹ and V_{3 μM}^{0-1 h}=16.7 μmol PO₄ g⁻¹ DW h⁻¹, in the two thinnest Porphyra. We found that the nitrate uptake rates were significantly greater at 30 μM than 3 μM NO₃ concentration, and that the uptake rates decreased with time of exposure. Temperature (5, 15, and 25 °C) did not have as strong an effect on nitrate uptake rates as did nutrient concentration. Q₁₀ values and uptake rates at four different nitrate concentrations indicated that nutrient uptake at 5 °C was initially an active process. After 24 h, the processes involved appeared passive as Q₁₀ values were between 1.0 and 1.3 and nitrate uptake curves were linear. Nitrate uptake rates correlated positively with the surface area/volume (SA/V) ratio. No coherent trends were found for uptake of phosphate, except that the uptake rates were significantly higher in 30 μM NO₃ medium as opposed to 3 μM NO₃. We did not find any significant difference in uptake rate and pattern between the summer species Porphyra purpurea (Roth.) C. Agardh, the eurythermic Porphyra suborbiculata Kjellm., the winter species Porphyra rosengurttii J. Coll and J. Cox, and the two varieties of Porphyra leucosticta Thur. Le Jol. (both winter species).     

Standard metabolic rate models for Carmine Shiner (Notropis percobromus) and Common Shiner (Luxilus cornutus) across different temperature regimes

Standard metabolic rates (SMR) were measured empirically for carmine shiner Notropis percobromus and common shiner Luxilus cornutus to develop SMR models that predict metabolic responses of each species under thermal conditions observed in the wild. SMR increased significantly with body mass and rising water temperature, ranging from 0.05 mg O₂ h⁻¹ at 10°C to 0.89 mg O₂ h⁻¹ at 20°C for N. percobromus weighing 0.6–2.5 g and from 0.11 mg O₂ h⁻¹ at 10°C to 0.98 mg O₂ h⁻¹ at 20°C for L. cornutus weighing 0.8–6.6 g. SMR models significantly differed between sympatric species on account of differences in model intercepts (RA) and temperature coefficients (RQ), however, the allometric relationships between mass and SMR did not significantly differ between species. Known distribution of N. percobromus and L. cornutus includes the Birch River located in Manitoba, Canada, where N. percobromus is listed as Endangered. Little is known about the physiology of N. percobromus or the species' ability to acclimate or adapt to different environmental conditions. While size differences between species contributed, in part, to differences in SMR predictions for Birch River populations, SMR trends (< 2 mg O₂ h⁻¹) for individuals weighing 1 g were similar for both species across daily temperatures. Respirometry experiments contributed to developing species-specific SMR models and inform on the effect of natural and anthropogenic stressors, namely water temperature, on the conservation of N. percobromus in this ecosystem.     

Field studies of ammonia excretion in Aphanius iberus (Pisces; Cyprinodontidae): body size and habitat effects

The effects of body size and habitat variability on ammonia excretion rates (R_AMs) of Aphanius iberus were analyzed in situ for the first time. At hourly intervals during a 5‐h field experiment, ammonia excretion was measured in 75 mature specimens from three sampling sites (small creek, marine salt‐mine, and salt‐marsh) established in a gradient of water salinity (0–5; 35–40; 65–70‰). Our results showed a specific size dependence pattern of R_AMs in the reproduction period, which might reflect an effect of the reproductive effort. In addition, the results point to a significant decrease in mean R_AM values of each population from freshwater aquatic systems (3.81 ± 0.58 μmol g⁻¹ h⁻¹ in fish of 2.8 ± 0.3 mm total length, TL) to salt aquatic systems with significantly higher alkalinity (2.52 ± 0.35 μmol g⁻¹ h⁻¹ in fish of 3.1 ± 0.5 mm TL in marine salt‐mine; 1.98 ± 0.55 μmol g⁻¹ h⁻¹ in fish of 3.1 ± 0.4 mm TL in salt‐marsh). Due to the size‐dependent pattern, R_AM in different habitats cannot be compared directly; ancova , followed by residual compared analysis (regression‐related techniques), is seen as a valid method for this purpose. This work presents the first field data on ammonia excretion in the Aphanius genus and the flexible physiologic response characteristic of Cyprinodontids has been demonstrated.     

The ecophysiological significance of lung-air retention during submersion by the air-breathing crabs Cardisoma carnifex and Cardisoma hirtipes

The air-breathing crabs Cardisoma hirtipes and C. carnifex trap 18.8 and 15.5 ml of air respectively within the lumen of the lung (branchial chamber) when submerging, rather than breathe water, and suffer a hypoxic hypercapnia. The role, effect and advantage of trapping air within the lung during submergence was assessed for both species. Cardisomaretained at least 85% of the lung air during a 30-min submergence. The mass-specific O₂uptake rate (MO₂) of air-breathing C. hirtipes and C. carnifexwas reduced by at least 60% during submersion and the crabs additionally consumed 80% or more of the O₂stored in the trapped air. After 30 min of submergence the large arterial-venous difference in haemolymph partial pressure of O₂ (PO₂) and O₂ content (CO₂) of air-breathingCardisoma was completely removed, consistent with near-zero O₂ transport. Removing the air from the lung lumen did not restore MO₂ but rather deprived the crab of an O₂ store and, in C. hirtipes, promoted anaerobiosis. Submergence reduced the haemolymph CO₂ by 50% or more, regardless of the presence of trapped air in their lungs. C. hirtipes and C. carnifex with a retained air bubble lost Na at only 2.6 and 2.3 μmol g^-1 h^-1, respectively, but at 3.9 and 5.0 μmol g^-1 h^-1 without the air bubble. Unidirectional Na uptake in C. hirtipes was only 0.90 μmol g^-1 h^-1 when air was trapped in the lung but 1.74 μmol g^-1 h^-1 when the bubble was removed. In C. carnifex these rates were 1.88 and 2.79 μmol g^-1 h^-1 respectively. C. hirtipes and C. carnifex both trap air within the lung and avoid exposing exchange surfaces to water. There is no large respiratory advantage to expelling the air but there are significant ion regulation cost savings in retaining it.     

COMPARISON OF DEVELOPMENT AND PHOTOSYNTHETIC GROWTH FOR FILAMENT CLUMPS AND REGENERATED MICROPLANTLET CULTURES OF AGARDHIELLA SUBULATA (RHODOPHYTA, GIGARTINALES)

Two axenic, in vitro liquid suspension cultures were established for Agardhiella subulata (C. Agardh) Kraft et Wynne, and their growth characteristics were compared. This study illustrated how reliable routes for the development of suspension cultures of macrophytic red algae of terete thallus morphology can be achieved for biotechnology applications. Undifferentiated filament clumps of 2–8 mm diameter were established by induction of callus-like tissue from thallus explants, and lightly branched microplantlets of 2–10 mm length were established by regeneration of filament clumps. The filament clumps were susceptible to regeneration. Adventitious shoot formation was reliably induced from 40% to 70% of the filament clumps by gentle mixing at 100 rev min^?1 on an orbital shaker. The specific growth rate of the microplantlets was higher than the filament clumps in nonagitated well plate culture (4%–6% per day for microplantlets vs. 2%–3% per day for filament clumps) at 24° C and 8–36 μmol photons·m^?2·s^?1 irradiance (10:14 h LD cycle) when grown on ASP12 artificial seawater medium at pH 8.6–8.9 with 20%–25% per day medium replacement. Oxygen evolution rate vs. irradiance measurements showed that relative to the filament clumps, microplantlets had a higher maximum specific oxygen evolution rate (P_o,max= 0.181 ± 0.035 vs. 0.130 ± 0.023 mmol O₂·g^?1 dry cell mass·h^?1), but comparable respiration rate (Q_o= 0.040 ± 0.013 vs. 0.033 ± 0.017 mmol O₂·g^?1 dry cell mass·h^?1), compensation point (I_c= 3.8 ± 2.4 vs. 5.7 ± 1.2 μmol photons·m^?2·s^?1), and light intensity at 63.2% of saturation (I_k= 17.5 ± 3.9 vs. 14.9 ± 2.6 μmol photons·m^?2·s^?1). The microplantlet culture was more suitable for suspension culture development than the filament clump culture because it was morphologically stable and exhibited higher growth rates.     

A coupled model of stomatal conductance and photosynthesis for winter wheat

The model couples stomatal conductance (g _s) and net photosynthetic rate (P _N) describing not only part of the curve up to and including saturation irradiance (I _max), but also the range above the saturation irradiance. Maximum stomatal conductance (g _smax) and I _max can be calculated by the coupled model. For winter wheat (Triticum aestivum) the fitted results showed that maximum P _N (P _max) at 600 μmol mol⁻¹ was more than at 350 μmol mol⁻¹ under the same leaf temperature, which can not be explained by the stomatal closure at high CO₂ concentration because g _smax at 600 μmol mol⁻¹ was less than at 350 μmol mol⁻¹. The irradiance-response curves for winter wheat had similar tendency, e.g. at 25 °C and 350 μmol mol⁻¹ both P _N and g _s almost synchronously reached the maximum values at about 1 600 μmol m⁻² s⁻¹. At 25 °C and 600 μmol mol⁻¹ the I _max corresponding to P _max and g _smax was 2 080 and 1 575 μmol m⁻² s⁻¹, respectively.     

Biotic and abiotic controls on the ecosystem significance of consumer excretion in two contrasting tropical streams

1. Excretion of nitrogen (N) and phosphorus (P) is a direct and potentially important role for aquatic consumers in nutrient cycling that has recently garnered increased attention. The ecosystem‐level significance of excreted nutrients depends on a suite of abiotic and biotic factors, however, and few studies have coupled measurements of excretion with consideration of its likely importance for whole‐system nutrient fluxes. 2. We measured rates and ratios of N and P excretion by shrimps (Xiphocaris elongata and Atya spp.) in two tropical streams that differed strongly in shrimp biomass because a waterfall excluded predatory fish from one site. We also made measurements of shrimp and basal resource carbon (C), N and P content and estimated shrimp densities and ecosystem‐level N and P excretion and uptake. Finally, we used a 3‐year record of discharge and NH₄‐N concentration in the high‐biomass stream to estimate temporal variation in the distance required for excretion to turn over the ambient NH₄‐N pool. 3. Per cent C, N, and P body content of Xiphocaris was significantly higher than that of Atya. Only per cent P body content showed significant negative relationships with body mass. C:N of Atya increased significantly with body mass and was higher than that of Xiphocaris. N : P of Xiphocaris was significantly higher than that of Atya. 4. Excretion rates ranged from 0.16–3.80 μmol NH₄‐N shrimp^?1 h^?1, 0.23–5.76 μmol total dissolved nitrogen (TDN) shrimp^?1 h^?1 and 0.002–0.186 μmol total dissolved phosphorus (TDP) shrimp^?1 h^?1. Body size was generally a strong predictor of excretion rates in both taxa, differing between Xiphocaris and Atya for TDP but not NH₄‐N and TDN. Excretion rates showed statistically significant but weak relationships with body content stoichiometry. 5. Large between‐stream differences in shrimp biomass drove differences in total excretion by the two shrimp communities (22.3 versus 0.20 μmol NH₄‐N m^?2 h^?1, 37.5 versus 0.26 μmol TDN m^?2 h^?1 and 1.1 versus 0.015 μmol TDP m^?2 h^?1), equivalent to 21% and 0.5% of NH₄‐N uptake and 5% and <0.1% of P uptake measured in the high‐ and low‐biomass stream, respectively. Distances required for excretion to turn over the ambient NH₄‐N pool varied more than a hundredfold over the 3‐year record in the high‐shrimp stream, driven by variability in discharge and NH₄‐N concentration. 6. Our results underscore the importance of both biotic and abiotic factors in controlling consumer excretion and its significance for nutrient cycling in aquatic ecosystems. Differences in community‐level excretion rates were related to spatial patterns in shrimp biomass dictated by geomorphology and the presence of predators. Abiotic factors also had important effects through temporal patterns in discharge and nutrient concentrations. Future excretion studies that focus on nutrient cycling should consider both biotic and abiotic factors in assessing the significance of consumer excretion in aquatic ecosystems.     

ATP and Ergosterol as Indicators of Fungal Biomass during Leaf Decomposition in Streams: a Comparative Study

Ergosterol and ATP concentrations, microbial respiration and sporulation rates of aquatic hyphomycetes associated with leaves of Castanea sativa decomposing in a 5^th order stream were determined periodically over a period of 102 days in order to compare ergosterol and ATP as indicators of fungal biomass. ATP and ergosterol concentrations exhibited a significant positive correlation (F = 4.459, DF = 28, P < 0.001) during the first stages of leaf breakdown (until day 39), i.e., during periods of increasing fungal biomass. No correlation was found between ATP and ergosterol concentrations during later stages of decomposition (days 39 to 102). Respiration rates increased rapidly up to 0.525 mg O₂ h^–1 g^–1 AFDM during the first month and remained high until the end of the experiment. Sporulation rates peaked at day 9 (1069 conidia day^–1 mg^–1 AFDM) and decreased during later stages of decomposition. ATP‐to‐biomass conversion factors were determined for both fungi (0.59 μmol ATP g^–1 dry mass) and bacteria (1.30 μmol ATP g^–1 dry mass) collected from the stream and grown in the laboratory. Estimates of fungal biomass based on ATP concentrations were similar to those calculated from ergosterol concentrations during the first 39 days of breakdown. The results here presented suggest that ATP is a reliable method to quantify microbial biomass in streams and that the relative importance of bacteria increases at later stages of decomposition. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

THE ACTIVITIES OF BUTYRYLCHOLINESTERASE AND CARBONIC ANHYDRASE, THE RATE OF ANAEROBIC GLYCOLYSTS, AND THE QUESTION OF A CONSTANT DENSITY OF GLIAL CELLS IN CEREBRAL CORTICES OF VARIOUS MAMMALIAN SPECIES FROM MOUSE TO WHALE

Abstract— The question of a constant density of glial cells in mammalian cerebral cortex regardless of species was examined by surveying the cortical activities of two enzymes primarily localized to dial cells. The cortical activity of butyrylcholinesterase (EC 3.1.1.8) was essentially constant at a rate of approx. 0.1 μmol of butyrylthiocholine hydrolysed min^-1 g^-1 over the range of species from rat (brain wt., 1.6 g) to fin whale and sperm whale (brain wt., 6800 and 7800 g, respectively). Over the same range the activity of cortical acetylcholinesterase, a neuronal enzyme, decreases by a factor of 7. Thus, butyrylcholinesterase ranged from < 2 per cent (in small rodent brains) to approximately 10 per cent (in whale brain) of the cortical acetylcholinesterase activity. The cortical activity of carbonic anhydrase (EC 4.2.1.1) was constant at a rate of 6.2 (± 0.25) μmol of CO₂ evolved min^-1 g^-1 over the range of species from guinea-pig (brain wt., 4.75 g) to fin whale (brain wt., 6800 g). These data obtained by assaying the dehydration reaction were confirmed by limited assays of the esterase activity of the enzyme (with p-nitrophenylacetate as substrate) and agreed with limited, previously reported data for the hydration reaction. Thus, the circumstantial evidence strongly favoured a relative constancy of cortical glial cell density regardless of species. The rates of anaerobic glycolysis in the cerebral cortex of various species were also investigated. For six species from mouse (brain wt., 0.4 g) to beef (brain wt., 380 g) cortical anaerobic glycolysis varied only slightly in the range of 50–62 μmol of CO₂ evolved h^-1 g^-l, whereas cortical oxygen consumption for the same range of species decreased by a factor of 3. Previously frozen samples of beef cortex glycolysed at 35 per Cent of the rate of fresh (unfrozen) samples. Since identical rates were obtained for previously frozen samples of fin whale cerebral cortex, we concluded that the relative constancy of cortical anaerobic glycolysis could be extended to the range from mouse to whale and that this aspect of cortical metabolism is probably primarily glial in localization. Some implications of the latter conclusion for the proposed role of astrocytes as modulators of neuronal activity have been discussed.