Annual net production and life span of floating leaves in Nymphaea tetragona Georgi: a comparison with other floating-leaved macrophytes

Fredericella sultana (Blumenbach, 1779) has long been considered one of the few freshwater bryozoan species with a truly cosmopolitan distribution. However, chromosome spreads from European material show 2n = 16 compared to 2n = 14 in North American specimens. In laboratory rearing the two forms are morphologically indistinguishable except for the surface texture of their statoblasts. Smooth statoblasts of European colonies match early illustrations of the species, while the densely pitted statoblasts of the North American form resemble those of F. indica Annandale 1909. On the basis of these observations we tentatively designate the North American F. sultana as F. indica. The only known American species with smooth statoblasts is F. australiensis Goddard 1909, in which the 2n = 16 karyotype is similar or identical to European F. sultana; however, despite this karyotypic similarity the two species retain their distinguishing morphology when reared together in the laboratory. Two enzymes from a single specimen of European F. sultana were electrophoretically distinct from the corresponding enzymes present in samples of both F. australiensis and North American F. sultana. Four phosphoglucose isomerase alleles were present in North American F. aultana from four geographically separated collection sites, although only one genotype for this locus was observed in material from any one site. These genetic findings are consistent with a relatively short-range dispersal potential in this species as compared to Plumatella species.     

Freshwater bryozoans (Bryozoa) of Norway III: distribution and ecology of Plumatella fruticosa

Bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of Plumatella fruticosawas evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance, and absence. According to our material P. fruticosais one of the most common bryozoan species in Norwegian fresh water, represented in samples from 251 localities. This species occurred frequently all over the country, north to 71° 06 N (the northernmost record globally). Maximum elevation above sea level was 1179 m (maximum for Northern Europe).In most studies of freshwater bryozoans from the holarctic region, Plumatella fruticosahas been reported as widely distributed, but locally rare. In Norway, however, P. fruticosa is frequently found all over the country, even far to the north. The species apparently finds an optimal climate in the cold temperate and cold regions of Norway. Plumatella fruticosapreferred lakes, avoided slow-flowing rivers and ponds, and was absent in smaller water bodies. The species preferred somewhat higher elevation (400–900 m above sea level), but avoided lakes with the lowest summer temperatures (below 11 °C). P. fruticosa also preferred oligotrophic conditions with poor aquatic vegetation, stony shores, lakes poor in calcium and magnesium (sometimes almost comparable with distilled water), where the water was clear and colourless, and slightly acidic to neutral. The species also preferred lakes surrounded by Sphagnum bogs and was absent when pH was below 5.2. P. fruticosa avoided eutrophic conditions with rich aquatic vegetation, alkaline water (pH above 7.0), lakes with a higher content of calcium and magnesium and those with strongly coloured water (above 100 mg Pt l^–1). In spite of its preference for ion-poor conditions, it was also found in a brackish water lake. For most environmental variables, the species had a wider tolerance range than reported from elsewhere.     

Freshwater bryozoans (Bryozoa) of Norway IV: Distribution and ecology of four species of Plumatella with notes on Hyalinella punctata

Bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of Plumatella repens was evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance and absence. P. repens is one of the most common bryozoan species in Norway. It is represented at 227 localities in our material and by 29 additional records. The species occurred frequently all over the country, north to 71°09N (the northernmost record on the European mainland). Maximum elevation above sea level was 1052 m (maximum for Northern Europe). P. repens preferred lakes, avoided rivers, and was absent from the smallest water bodies. The species preferred (1) low elevation (2–200 m above sea level), (2) medium water temperature, (3) rich aquatic vegetation (eutrophic conditions), (4) small wave action, (5) high content of calcium and magnesium, (6) pH 6.4–9.6, and (7) rather high water colour. Otherwise P. repens avoided (1) habitats above 500 m but occurred up to 1052 m, (2) the lowest water temperature intervals, (3) sites with poor aquatic vegetation and stony shores, (4) medium wave action, (5) sites with a low calcium and magnesium content, (6) lakes of low water colour, and (7) lakes with pH below 6.6: it was absent from lakes with pH below 5.2. For many environmental variables, the species had a wider tolerance range than reported from elsewhere. P. fungosa, P. casmiana, and P. emarginata are all rare in Norway. The total numbers of known localities, with our records in (), are 18 (11), 7 (7), and 7 (5), respectively. These sites are all from lowland areas up to 133 m above sea level. Environmental variables in the habitats are described. P. fungosa was represented by a single floatoblast in each of the four northernmost lakes where it was recorded. One of these lakes was in North Norway some 1000 km away from the nearest known sites with living colonies. The presence of large colonies of P. fungosa in some parts of southern Norway and only `single floatoblast lakes' further north is discussed in relation to the equilibrium theory of island biogeography: birds facilitate immigration by carrying floatoblasts and environmental conditions prevent their germination and the development of living colonies. All records of P. casmiana and P. emarginata were from South Norway. Results for P. fruticosa have been published previously. Notes are given on an old and now missing sample from ca. 1900, identified by Lacourt (1968) as Hyalinella punctata – the only record of this species from Norway.     

Freshwater bryozoans (Bryozoa) of Norway V: review and comparative discussion of the distribution and ecology of the 10 species recorded

The paper is based on material presented in five contributions [Hydrobiologia 421:1–24, 2000; 459: 103–123, 2001; 479: 11–22, 2002; 501: 179–198, 2003; Archives de lInstitut grand-ducal de Luxembourg. Section des Sciences naturelles, physiques et mathématiques, Nouvelle Série 44: 127–143, 2002]. Nine species of Bryozoa were collected during field studies of 601 lakes and other surface water types in Norway. Five of the species occur throughout Norway (Plumatella fruticosa, P. repens, Paludicella articulata, Cristatella mucedo and Fredericella sultana) and one has a northerly range (Fredericella indica). With the exception of Plumatella repens, the northernmost records of these species globally are in Norway. All six species have been found at elevations of more than 1000m in South Norway, which is also their maximum elevation above sea level in Northern Europe. Three species (Plumatella fungosa, P. emarginata and P. casmiana) are rare and present only in lowland areas in South Norway. Lacourt [A Monograph of the Freshwater Bryozoa–Phylactolaemata. Zoologische Verhandelingen, Leiden 93: 1–159, 1968] considered an old and now mislaid sample from the same area to be Hyalinella punctata. Up to six species and an average of two were found in lakes. The mean numbers of species in ponds, and slow-flowing and rapid-flowing rivers were 0.6, 0.8 and 1.0, respectively. Co-occurrence of pairs of species in lakes was investigated. For 10pairs, the number of cases of co-occurrence was significantly higher than expected on the basis of random distribution. This was ascribed to some shared ecological requirements. Only one pair (Paludicella articulata–Plumatella fungosa) showed fewer cases of co-occurrence than expected. This was explained by differences in their geographical distribution and tolerance to ecological factors. Tolerance and other ecological responses were described for the six frequent species using two statistical methods. Method 1: frequency deviations, is based on the null hypothesis of random distribution. Ten environmental variables were studied (type of surface water, elevation above sea level, water temperature, aquatic vegetation, sediment, wave action, Ca, Mg, pH and water colour).The concepts absence, avoidance (frequency lower than expected), preference (frequency higher than expected) and presence (no significant deviation from expected frequency) were used. The degree of response of a particular species to a specific environmental variable was measured by the sum of the numerical values of the significant frequency deviations divided by the number of categories with significant deviations. The results can be used as adaptability indices or tolerance indices: the lower the index, the better a species is adapted for surviving with respect to the environmental variable in question. Diagrams showed (1) the relative strength of the response of the six frequent species, (2) the average index for each species for all variables and (3) the effect of each of the 10 environmental variables on the Bryozoa (the species treated as a unit: an ecological guild). Method 2: logistic regression, treated the presence or absence of each of the six frequent species as dependent variables using nine independent environmental variables. Comparison of the results of method 1 and 2, indicated that method 1, which gives details of how a species responds to different categories of a variable, was particularly useful.     

Transoceanic ships as vectors for nonindigenous freshwater bryozoans

Aim The transport of organisms in ships’ ballast tanks is a dominant vector for aquatic invasions worldwide. Until recently, efforts to manage this vector have overlooked the potential transport of invertebrate resting stages in the residual waters and sediments within emptied ballast tanks, i.e. NOBOB (‘No Ballast On Board’) tanks. The resting stages (statoblasts) of freshwater bryozoans are often buoyant and locally abundant and thus can be taken up easily during ballasting operations. They are also resistant to extreme environmental conditions and can generate new colonies after being dormant for decades; as such, they would likely remain viable propagules after lengthy transport in ship ballast tanks. This study quantified the occurrence of freshwater bryozoan statoblasts in ballast tank sediments of transoceanic ships. Location North American Great Lakes. Methods We quantified the frequency of occurrence, abundance and diversity of bryozoans (as statoblasts) in residual sediment samples taken from 51 NOBOB tanks of 33 transoceanic ships visiting the Great Lakes from 2000 to 2002. Results Our study identified 11 species, comprising nearly 12% of the total number of freshwater bryozoans known worldwide. These include two exotic species unrecorded in the Great Lakes (Fredericella sultana and Lophopus crystallinus), an exotic species already established in the region (Lophopodella carteri) and three cosmopolitan species (Plumatella casmiana, P. fungosa and P. repens). Our estimates suggest that a ship with NOBOB tanks may carry up to 10⁶ statoblasts. Main conclusions The discovery of species unrecorded in the Great Lakes and the potentially large numbers of statoblasts being transported in ship ballast tanks indicate a significant risk of new species introductions. Furthermore, the presence of cosmopolitan species and an exotic species already established in the Great Lakes suggests the strong possibility of cryptic invasions via the introduction of exotic genotypes.     

NOR-Chromosome morphology and evidence for rDNA selection in phylactolaemates

Silver-stained chromosome spreads from the phylactolaemate ectoprocts Fredericella indica, Fredericella browni, Plumatella repens, Pectinatella magnifica and Asajirella gelatinosa show that each of these species has a single pair of NORs. In the first four species each NOR is immediately adjacent to the centromere of a large metacentric chromosome. Giemsa-stained preparations from Cristatella mucedo show centromeric gapping in a similar large metacentric, indicating the same type of NOR-chromosome. In Asajirella gelatinosa the two NORs are on a pair of smaller chromosomes, and are not immediately adjacent to a centromere. A close NOR-centromere association would inhibit meiotic crossing over in the NOR region. Since in phylactolaemates reproduction is primarily asexual, often by formation of statoblasts, there is potential intraclonal selection for favorable ribosomal DNA (rDNA) mutations, including from simultaneous germination of otherwise genetically identical statoblasts within a limited area and competition between cell lines within statoblasts. Inhibition of meiotic crossing over within the NOR would maintain its integrity during periods when intraclonal selection would not be occurring. This suggests that a more rapid rate of rDNA evolution is possible in phylactolaemates than in most other organisms, and is consistent with a derivation of this group from the morphologically similar phoronids, despite phylogenetic interpretations of rDNA sequence data that suggest the two groups are not closely related.     

Bryozoan populations reflect nutrient enrichment and productivity gradients in rivers

1. The hypothesis that nutrient enrichment will affect bryozoan abundance was tested using two complementary investigations; a field‐based method determining bryozoan abundance in 20 rivers of different nutrient concentrations by deploying statoblast (dormant propagule) traps and an experimental laboratory microcosm study measuring bryozoan growth and mortality. These two methods confirmed independently that increased nutrient concentrations in water promote increases in the biomass of freshwater bryozoans. 2. Statoblasts of the genus Plumatella were recorded in all rivers, regardless of nutrient concentrations, demonstrating that freshwater bryozoans are widespread. Concentrations of Plumatella statoblasts were high in rivers with high nutrient concentrations relative to those with low to moderate nutrient concentrations. Regression analyses indicated that phosphorus concentrations, in particular, significantly influenced statoblast concentrations. 3. Concentrations of Lophopus crystallinus statoblasts were also higher in sites characterised by high nutrient concentrations. Logistic regression analysis revealed that the presence of L. crystallinus statoblasts was significantly associated with decreasing altitude and increasing phosphorus concentrations. This apparently rare species was found in nine rivers (out of 20), seven of which were new sites for L. crystallinus. 4. Growth rates of Fredericella sultana in laboratory microcosms increased with increasing nutrient concentration and high mortality rates were associated with low nutrient concentrations. 5. Our results indicate that bryozoans respond to increasing nutrient concentrations by increased growth, resulting in higher biomasses in enriched waters. We also found that an important component of bryozoan diets can derive from food items lacking chlorophyll a. Finally, bryozoans may be used as independent proxies for inferring trophic conditions, a feature that may be especially valuable in reconstructing historical environments by assessing the abundance of statoblasts in sediment cores.     

Population dynamics of oxiclinal species in lake Arcas-2 (Spain)

Oxiclinal rotifer species show high concentrations just above the oxic-anoxic interface in the hypolimnion of some lakes. The stratification of their populations is best shown by sampling at close depth intervals and quantifying their densities by the Utermöhl technique. With this technique we were able to count males which otherwise pass through filters and more accurately count egg production. We evaluated female, male and egg numbers of the two main oxiclinal species of lake Arcas-2: Filinia hofmanni and Anuraeopsis fissa, during two annual cycles (1990–91). F. hofmanni was an exclusive oxiclinal species. It had an exponential growth phase at the onset of stratification giving a distinct spring peak. The population then maintained a high density during summer, but was almost absent the rest of the year. This cycle is repeated annually but population density can vary among years, depending on winter-spring circulation. Sexuality was always observed when the animal was present in the samples, with a maximum of males and resting eggs at the peak of the population. Resting eggs were always inside females. The annual cycle of A. fissa is displaced with respect to that of F. hofmanni: A. fissa attained greatest densities during summer, until the autumn overturn. Mixis in A. fissa was restricted to the end of the stratification period. Moreover, A. fissa occured throughout the vertical profile and secondarily occupied the oxicline.     

Kinetics of ammonium, nitrate and phosphorus uptake by Canna indica and Schoenoplectus validus

Canna indica L. is an upright perennial rhizomatous herb, and Schoenoplectus validus (Vahl) A. Löve and D. Löve is a tall, perennial, herbaceous sedge. The nutrient uptake kinetics of C. indica and S. validus were investigated using the modified depletion method after plants were grown for 4 weeks in simulated secondary-treated wastewater. The maximum uptake rate (I_max) and Michaelis–Menten constant (K_m) were estimated by iterative curve fitting. The I_max for NH₄N (623 μmol g⁻¹ dry root weight h⁻¹) was significantly higher than that for NO₃N (338 μmol g⁻¹ dry root weight h⁻¹) in S. validus. In contrast, no difference was observed in C. indica. The I_max values for NO₃N and NH₄N were higher in S. validus than in C. indica. A significantly lower K_m was detected for NO₃N uptake in C. indica (385 μmol L⁻¹) compared to that in S. validus (1908 μmol L⁻¹). The I_max for PO₄P did not differ between the plant species. The K_m for PO₄P was significantly higher in C. indica (157 μmol L⁻¹) than in S. validus (60 μmol L⁻¹). In conclusion, we found that S. validus preferred NH₄N over NO₃N, had greater capacity for N uptake and higher affinity for PO₄P, but C. indica had greater affinity for NO₃N. Nutrient uptake capacity is likely related to habitat preference, and is influenced by the structure of roots and rhizomes.     

Myoanatomy and serotonergic nervous system of plumatellid and fredericellid phylactolaemata (lophotrochozoa,ectoprocta)

The phylogenetic position of the Ectoprocta within the Lophotrochozoa is discussed controversially. For gaining more insight into ectoproct relationships and comparing it with other potentially related phyla, we analysed the myoanatomy and serotonergic nervous system of adult representatives of the Phylactolaemata (Plumatella emarginata, Plumatellavaihiriae, Plumatella fungosa, Fredericella sultana). The bodywall contains a mesh of circular and longitudinal muscles. On its distal end, the orifice possesses a prominent sphincter and continues into the vestibular wall, which has longitudinal and circular musculature. The tentacle sheath carries mostly longitudinal muscle fibres in Plumatella sp., whereas F. sultana also possesses regular circular muscle fibres. Three groups of muscles are associated with the lophophore: 1) Lophophoral arm muscles (missing in Fredericella), 2) epistome musculature and 3) tentacle musculature. The epistome flap is encompassed by smooth muscle fibres. A few fibres extend medially over the ganglion to its proximal floor. Abfrontal tentacle muscles have diagonally arranged muscle fibres in their proximal region, whereas the distal region is formed by a stack of muscles that resemble an inverted ‘V’. Frontal tentacle muscles show more variation and either possess one or two bases. The digestive tract possesses circular musculature which is striated except at the intestine where it is composed of smooth muscle fibres. The serotonergic nervous system is concentrated in the cerebral ganglion. From the latter a serotonergic nerve extends to each tentacle base. In Plumatella the inner row of tentacles at the lophophoral concavity lacks serotonergic nerves. Bodywall musculature is a common feature in many lophotrochozoan phyla, but among other filter feeders like the Ectoprocta is only present in the ‘lophophorate’ Phoronida. The longitudinal tentacle musculature is reminiscent of the condition found in phoronids and brachiopods, but differs to entoproct tentacles. Although this study shows some support for the ‘Lophophorata’, more comparative analyses of possibly related phyla are required. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.     

Age and growth,reproduction and diet of a sublittoral population of the rock goby Gobius paganellus (Teleostei,Gobiidae)

Colonisation of extremely acidic waters (pH 3) by aquatic angiosperms occurs widely, but is poorly documented. Unlike acid rain affected and other naturally acidic aquatic ecosystems, waters with pH 3 usually have a high conductivity, with high concentrations of SO₄ ^2- and often high concentrations of Fe³⁺, other heavy metal ions and Al³⁺. Where Fe³⁺ concentration is high, as in many mine waters, it provides a strong buffering system. In such waters, the biogeochemical Fe cycle exerts over water chemistry and the availability of nutrients and carbon for organisms. Biological activity is limited by low concentrations of phosphorus and inorganic carbon (DIC), which in this pH range is essentially all in the form of dissolved CO₂. A number of angiosperms grow in such waters including Phragmites australis, Typha spp. and Juncus bulbosus, though the last is the only one reported to grow totally submerged in waters with pH 3 . J. bulbosus occurs in many lignite mining lakes in Lusatia (north eastern Germany) with pH 3. The characteristics and possible survival strategies for this and other species are discussed.     

Tubulin-isotype analysis of two grass species-resistant to dinitroaniline herbicides

Trifluralin-resistant biotypes of Eleusine indica (L.) Gaertn. (goosegrass) and Setaria viridis (L.) Beauv. (green foxtail) exhibit cross-resistance to other dinitroaniline herbicides. Since microtubules are considered the primary target site for dinitroaniline herbicides we investigated whether the differential sensitivity of resistant and susceptible biotypes of these species results from modified tubulin polypeptides. One-dimensional and two-dimensional polyacrylamide gel electrophoresis combined with immunoblotting using well-characterised anti-tubulin monoclonal antibodies were used to display the family of tubulin isotypes in each species. Seedlings of E. indica exhibited four -tubulin isotypes and one -tubulin isotype, whereas those of S. viridis exhibited two -tubulin and two -tubulin isotypes. Comparison of the susceptible and resistant biotypes within each species revealed no differences in electrophoretic properties of the multiple tubulin isotypes. These results provide no evidence that resistance to dinitroaniline herbicides is associated with a modified tubulin polypeptide in these biotypes of E. indica or S. viridis.Abbreviations 1-D, 2-D one-, two-dimensional - ID₅₀ dose causing 50% inhibition - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate - S susceptible - R resistant We gratefully acknowledge Professor B.J. Gossett (Clemson University, South Carolina, USA) and Professor I.N. Morrison (University of Manitoba, Winnipeg, Canada) for providing seed stocks of Eleusine indica and Setaria viridis, respectively. Antibodies TAT-1 and KMX-1 were a kind gift from Professor K. Gull (University of Manchester, UK). Technical assistance with seed germination was provided by Ms. K.E. Cronin. We acknowledge financial support from the Science and Engineering Research Council for a studentship to T.R.W.     

Identification of specific proteins from seed embryos by two-dimensional gel electrophoresis for the discrimination between indica and japonica rice

Summary Proteins extracted from seed embryos of 29 different cultivated rice (Oryza sativa L.) and one wild rice (O. rufipogon Griff.) were compared by two-dimensional gel electrophoresis analysis. Among more than 300 protein spots on the gel we found some interesting variations in ten spots which were individually designated as proteins A-J. Protein E was observed in all indica cultivars but was not found in those of the subspecies japonica. In contrast, protein F was only detected in japonica cultivars. Protein A existed in all japonica cultivars but, with the exception of IR-36, could not be found in other indica cultivars. Therefore, proteins A, E and F can be used as markers for the identification of indica and japonica. Some so-called Javanica cultivars showed the characteristics of japonica subspecies with regard to proteins A and F, while one other cultivar of Javanica expressed a type intermediate between indica and japonica interms of proteins A and E. One feature discriminating between Javanica and japonica cultivars was found in the D, G, and J proteins which were expressed strongly in Javanica cultivars but were scarcely expressed in those of japonica. Expression of subspecies-specific proteins E and F in f₁ hybrids was also investigated.     

Does the impact of nutrients on the biological structure and function of brackish and freshwater lakes differ?

The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P l^-1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5 and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. l^-1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2 and N. integer in lakes with a salinity above 0.5. Above 2 the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwater state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5.     

Response of effective quantum yield of photosystem 2 to in situ temperature in three alpine plants

The response of effective quantum yield of photosystem 2 (F/F_m) to temperature was investigated under field conditions (1 950 m a.s.l.) in three alpine plant species with contrasting leaf temperature climates. The in situ temperature response did not follow an optimum curve but under saturating irradiances [PPFD >800 µìmol(photon) m^–2s^–1] highest F/F_m occurred at leaf temperatures below 10°C. This was comparable to the temperature response of antarctic vascular plants. Leaf temperatures between 0 and 15°C were the most frequently (41 to 56%) experienced by the investigated species. At these temperatures, F/F_m was highest in all species (data from all irradiation classes included) but the species differed in the temperature at which F/F_m dropped below 50% (Soldanella pusilla >20°C, Loiseleuria procumbens >25°C, and Saxifraga paniculata >40°C). The in situ response of F/F_m showed significantly higher F/F_m values at saturating PPFD for the species growing in full sunlight (S. paniculata and L. procumbens) than for S. pusilla growing under more moderate PPFD. The effect of increasing PPFD on F/F_m, for a given leaf temperature, was most pronounced in S. pusilla. Despite the broad diurnal leaf temperature amplitude of alpine environments, only in S. paniculata did saturating PPFD occur over a broad range of leaf temperatures (43 K). In the other two species it was half of that (around 20 K). This indicates that the setting of environmental scenarios (leaf temperature×PPFD) in laboratory experiments often likely exceeds the actual environmental demand in the field.This revised version was published online in March 2005 with corrections to the page numbers.     

Biotic and abiotic preferences of the cladoceran invader Limnosida frontosa

During the late 1980s and early 1990s, the cladoceran Limnosida frontosa invaded several lakes within its natural range in southeastern Norway. In this project, we wanted to study the types of lakes preferred by Limnosida. We also wanted to evaluate the potential competitive effects on other zooplankton species. In a survey of 65 Norwegian lakes, Limnosida showed preference for lakes of low Ca concentrations and low productivity. This is probably due to decreased competition from species with higher Ca requirements and a lower fish predation on zooplankton in these lakes compared to more productive lakes. Particle size preferences of Limnosida were studied and compared with those of the microfiltrator Daphnia magna, as there was no published information on the food preference of Limnosida.When fed monodisperse fluorescent latex beads (0.5, 1.0, 6.0 m), Limnosida strongly selected the largest beads, while D. magna had a more nonselective feeding behaviour. Mesh sizes of Limnosida's filtering appendages were 0.4–1.2 m depending on the animal size, and the particle selection was correlated with the filter mesh sizes. Limnosida should thus be considered a low efficiency grazer on bacteria and -algae. Hence, this species probably does not interfere significantly with microfiltrators like Diaphanosoma brachyurumand most daphnids. This was supported by community analysis of lakes with and without Limnosida. In general, Limnosida commonly co-occurred with a number of filter-feeding cladocerans, and we found no sign of competitive exclusion in lakes where the species has become established.     

Recent changes in the seaweed community of Western Prince Edward Island: implications for the seaweed industry

Prior to 1980, seaweed beds of western Prince Edward Island, Canada, were dominated by Chondrus crispus Stackhouse, associated with 37 other species of common algae. Furcellaria lumbricalis (Huds.) Lamour. occurred in 4.6% of the samples from the Pleasant View bed but never reached measurable levels of cover. By 1991 F. lumbricalis was reported in 67% of the samples from this bed. Furcellaria lumbricalis biomass was negatively correlated with C. crispus biomass and positively correlated with Phyllophora Grev. spp. biomass. F. lumbricalis biomass and cover peaked in subtidal areas below 4 m at 359 ± 299 SD fresh g 0.25 m^–2. Harvesters avoid concentrations of F. lumbricalis, resulting in a 5% content of this species in the commercial harvest. Systematic harvesting located concentrations of F. lumbricalis in seven of 10 commercial beds. Proposed causes for change in species dominance from C. crispus to F. lumbricalis range from general environmental change, natural succession to excessive human perturbation.     

Comparative effects of growth irradiance on photosynthesis and leaf anatomy of Flaveria brownii (C4-like), Flaveria linearis (C3–C4) and their F1 hybrid

Photosynthetic rates and related anatomical characteristics of leaves developed at three levels of irradiance (1200, 300 and 80 umol · m^–2 · s^–1) were determined in the C₄-like species Flaveria brownii A.M. Powell, the C₃–C₄-intermediate species F. linearis Lag., and the F₁ hybrid between them (F. brownii × F. linearis). In the C₃–C₄ and F₁ plants, increases in photosynthetic capacity per unit leaf area were strongly correlated with changes in mesophyll area per unit leaf area. The C₄-like plant F. brownii, however, showed a much lower correlation between photosynthetic capacity and mesophyll area per unit leaf area. Plants of F. brownii developed at high irradiance showed photosynthetic rates per unit of mesophyll cell area 50% higher than those plants developed at medium irradiance. These results along with an increase in water-use efficiency are consistent with an increase of C₄ photosynthesis in high-irradiance-grown F. brownii plants, whereas in the other two genotypes such plasticity seems to be absent. Photosynthetic discrimination against ¹³C in the three genotypes was less at high than at low irradiance, with the greatest change occurring in F. brownii. Discrimination against ¹³C expressed as ¹³C was linearly correlated (r ² = 0.81; P<0.001) with the ratio of bundle-sheath volume to mesophyll cell area when all samples from the three genotypes were combined. This tissue ratio increased for F. brownii and the F₁ hybrid as growth irradiance increased, indicating a greater tendency towards Kranz anatomy. The results indicated that F. brownii had plasticity in its C₄-related anatomical and physiological characteristics as a function of growth irradiance, whereas plasticity was less evident in the F₁ hybrid and absent in F. linearis.Abbreviations A leaf surface area - A_ma, A_mn, A_lm total ma, mn or lm cell surface area - bs vascular bundle sheath - lm large spongy-mesophyll cells - ma mesophyll cells adjacent to bundle sheath - mn mesophyll cells not adjacent to bundle sheath - P_n net photosynthesis - (H, M, L) PPFD (high, medium, low) photosynthetic photon flux density - SLDW specific leaf dry wight - V_bs bs volume - V_{(ma + mn + bs)} total photosynthetic tissue volume - ¹³C ¹³C discrimination We thank Mrs. Lisa Smith for technical assistance in light microscopy and Dr. Ned Friedman (Department of Botany, University of Georgia, Athens, GA, USA) for the use of digitizing equipment. Participation of Dr. J.L. Araus in this work was supported by a grant Beca de Especialización para Doctores y Tecnólogos en el Extranjero, from Ministerio de Educatión y Ciencia, Spain.     

The effects of phosphorus nutrition and soil pH on the growth of some ancient woodland indicator plants and their interaction with competitor species

The forest under-storey herbs Anemone nemorosa, Lamiastrum galeobdolon and Veronica montana are generally considered indicator species of old, broadleaved woodland sites where the soil fertility is often low. In a glasshouse bioassay, however, all three species not only showed large positive growth responses to supplied P concentrations (0–10mgL ^–1) solutions, but also tolerated high P concentrations (20–40mgL ^–1), well above those normally found in their natural habitat. Plants responded by raising the concentrations of P in their shoot and root tissues and increasing their biomass, resulting in an increased P uptake. A shade-tolerant competitor species, Urtica dioica, also grew vigorously across the full range of P concentrations, restricting the growth of the woodland species. This emphasises the difficulty of establishing semi-natural woodland vegetation in the presence of competitor species, for example in situations where new woodlands are planted on fertile ex-agricultural soils containing large residual concentrations of P. The influence of soil pH on the growth and nutrient relations of A. nemorosa, L. galeobdolon, V. montana, Poa trivialisandU. dioicawas determined in a separate experiment using an ex-arable soil as the growing medium with pH levels adjusted from 7.4 to 5.8 and 4.3 respectively. Acidifying the soil enhanced growth, but reduced the concentrations of N, P and K in the leaves of all three woodland species, probably due to dilution of these minerals in the increased dry matter production. The competitor species (P. trivialis and U. dioica) responded in similar manner to the woodland indicator species. These results suggest that manipulating soil pH as a means of facilitating the establishment of woodland indicator species in new farm woods is unlikely, in the short term, to be effective where competitor species are present.     

Current state of seaweed resources in Spain

Commercial seaweeds in Spain are harvested on the north and northwest coasts. They are mainly agarophytes and carrageenophytes (Gelidium spp. and some Irish moss-like species, respectively), although some Phaeophyceae species (Fucus spp. and Laminaria spp.) are also exploited for alginates. No industrial seaweed cultivation is carried out in Spain at present. Spain's total commercial seaweed harvest can be estimated at 6,528 ± 2,076 t dry wt year^–1. Gelidium spp. are by far the most harvested, attaining 5,135 ± 1,761 t dry wt y^–1. To date, Spain's commercial seaweed harvest is low compared with that of other countries, but data on field standing crops and productivities of commercial taxa suggest that harvesting could be increased greatly.