Growth kinetic parameters of two planktonic desmid species under fluctuating phosphorus conditions in continuous-flow culture

Two planktonic desmid taxa, Staurastrum chaetoceras and Cosmariumabbreviatum var. planctonicum, were examined under pulsed phosphorus(P)-limited conditions in continuous culture. Two pulse regimeswere applied, i.e. 2.5 µM P twice a week and 10 µMP once every 2 weeks. Under both pulse regimes, S.chaetocerasshowed a higher maximum P uptake rate (V^max) and affinity forP uptake (V^max/affinity constant K^m) than C.abbreviatum. Affinityfor P uptake in S.chaetoceras just before pulsing was higherthan shortly after pulsing, whereas C.abbreviatum did not showany significant difference. Cell densities and cellular P quotain S.chaetoceras and C.abbreviatum fluctuated in a comparableway, but fluctuations in C.abbreviatum were less pronouncedthan in S.chaetoceras. The mean cell volume of both specieswas greater under the bimonthly than under the biweekly pulseregime, and the lowest under continuous P-limited conditions.Competition between S.chaetoceras and C.abbreviatum under thebimonthly pulse regime was won by S.chaetoceras, but displacementwas less fast than under more frequent pulsing (equalling thesame total P supply). The above-mentioned results are discussedin relation to possible ecological strategies.     

Light-limited growth and photosynthetic characteristics of two planktonic desmid species

1. Staurastrum chaetoceras, originating from a eutrophic environment, and Cosmarium abbreviatum var. planctonicum, from an oligo-mesotrophic one, were grown at 20°C in continuous-flow culture under varied light conditions. 2. Maximum growth rate in S. chaetoceras was approximately 50% higher than in C. abbreviatum, corresponding to a higher photosynthetic capacity. 3. Higher dry weight values and dark respiration rates in C. abbreviatum (compared with S. chaetoceras) support the suggestion from growth-irradiance curves that C. abbreviatum has to invest a greater part of its photosynthetic energy in the construction and maintenance of specific cell components. 4. The differences in growth and photosynthetic parameters might be related to the presence of a copious mucilaginous cell envelope in C. abbreviatum; such an envelope is lacking in S. chaetoceras. 5. The possible ecological significance of these species-specific differences is discussed.     

Alkaline phosphatase activity in two planktonic desmid species and the possible role of an extracellular envelope

1. Cosmarium abbreviatum var. planctonicum , a desmid from oligo‐mesotrophic lakes, had a higher maximum alkaline phosphatase activity (APA) and affinity constant under both continuous and pulsed inorganic phosphorus (P_i) limitation than Staurastrum chaetoceras , a desmid predominantly encountered in eutrophic lakes.
2. APA of both species increased when measured in starved cells subjected to pulsed P_i conditions when compared to continuous P_i limitation.
3. The portion of extracellular relative to cellular APA was higher in S. chaetoceras than in C. abbreviatum , indicating that S. chaetoceras secreted the enzymes more readily into its environment.
4. The difference in APA could explain the dominance of C. abbreviatum during competition between these two species under conditions of continuous organic P (P_o) limitation, but not the outcome under a pulsed P_o shortage. The dominance of S. chaetoceras in the latter experiment can, however, be explained by species‐specific P_i‐uptake characteristics.
5. After a saturating pulse of P_i, no increase in P_i in the extracellular mucus layer of C. abbreviatum was found and it was therefore concluded that the mucilage sheath does not store P. However, the sheath could have a main function as an accumulation site of cellular APA, providing the cell with P_i.     

Growth responses of 15 rain-forest tree species to a light gradient: the relative importance of morphological and physiological traits

1. Growth of seedlings of 15 rain-forest tree species was compared under controlled conditions, at six different light levels (3, 6, 12, 25, 50 and 100% daylight).
2. Most plant variables showed strong ontogenetic changes; they were highly dependent on the biomass of the plant.
3. Growth rate was highest at intermediate light levels (25–50%) above which it declined. Most plant variables showed a curvilinear response to irradiance, with the largest changes at the lowest light levels.
4. There was a consistent ranking in growth between species; species that were fast growing in a low-light environment were also fast growing in a high-light environment.
5. At low light, interspecific variation in relative growth rate was determined mainly by differences in a morphological trait, the leaf area ratio (LAR), whereas at high light it was determined mainly by differences in a physiological trait, the net assimilation rate (NAR).
6. NAR became a stronger determinant of growth than LAR in more than 10–15% daylight. As light availability in the forest is generally much lower than this threshold level, it follows that interspecific variation in growth in a forest environment is mainly owing to variation in morphology.     

Functional responses of five cyprinid species to planktonic prey

Synopsis The functional responses of five species of cyprinids (Chalcalburnus chalcoides, Vimba vimba, Abramis brama, Rutilus rutilus, and Scardinius erythrophthalmus) feeding on four planktonic prey types were measured in the laboratory. Although no alternative prey types were present, the response curves were sigmoid in most cases, because attack rates were not independent of prey density. The findings are explained as being the overt expression of the fishes& foraging tactics. The chief way of maximizing food uptake, according to our interpretation, is accelerating attack rates with increasing prey density. The ability of prey to escape or relative prey size may interfere with this strategy. C. chalcoides, the only obligatory planktivore among the species studied, attacks at higher rates and responds most markedly to changes in prey density.     

Plant species responses along a grazing disturbance gradient in Australian grassland

Abstract. Floristic data from paired roadside-paddock analyses from grassland in central Queensland, Australia, were ordinated. The mean direction of the vectors between these pairs was almost perfectly aligned with the indirect gradient represented by the first axis of Non-metric Multi-dimensional Scaling. It confirms anecdotal evidence of a trend from infrequently grazed roadsides to constantly grazed paddocks. The increasing abundance of annual herbs and grasses along this putative gradient is consistent with documented trends from elsewhere in the world. The response patterns of individual species along the disturbance gradient is consistent with ecological theory predicting unimodal peaks in abundance along physical environmental gradients. The ancestral perennial dominants of the grasslands, Dichanthium sericeum and D. queenslandicum, exhibited a declining response to grazing disturbance. Even the generally unpalatable perennial grass Aristida leptopoda declined considerably in the upper segments of the grazing disturbance gradient. A suite of herbaceous trailing legumes had peaks in their abundance near the middle of the grazing disturbance gradient, trends that can be readily explained by the combination of their palatability and intolerance to competition from tall perennial grasses. Several species including the noxious exotic herb Parthenium hysterophorus showed increasing abundance along the grazing disturbance gradient. The methodology may have application as a rapid method of assessing disturbance impacts elsewhere, and is most suited where a management differential between paired plots can be reliably generalized and where the physical environment is relatively monotonous.     

Ammonium dependency in Closterium aciculare T.West, a planktonic desmid from alkaline, eutrophic waters

One Japanese and some Dutch clones of the planktonic desmidspecies Closterium actculare were unable to grow on nitrateas the nitrogen source whereas they did grow well on ammoniumLack of nitrate reductase activity in the absence of ammoniumsuggests a structural shortage in the synthesis of this enzyme.Distributional patterns of C aciculare in space and time, ie. in eutrophic lakes, with abundance peaks in periods of circulationof the water column, may be well explained from the above-mentionedphysiological characteristic     

Lycopodium annotinum and light quality: Growth responses under canopies of twoVaccinium species

Lycopodium annotinum, a clonal pteridophyte, was grown under canopies formed by various combinations of deciduousVaccinium myrtillus and evergreenV. vitis-idaea. The canopies differed in red:far-red ratio, withV. myrtillus giving the lowest ratio. The current year's horizontal segments ofL. annotinum had the same specific weight in all treatments, but the lengths of the segments were significantly increased when grown under the canopy ofV. myrtillus compared withV. vitis-idaea. The number of vertical apices was also increased. Both these responses increased the amount of assimilating structures ofL. annotinum when growing under aV. myrtillus canopy. This might be beneficial for the evergreenL. annotinum, since it can then utilize spring and autumn periods when the deciduousV. myrtillus has no leaves.     

Photosynthetic responses to light variation in rainforest species

Summary The dependence of net carbon gain during lightflecks (artificial sunflecks) on leaf induction state, lightfleck duration, lightfleck photosynthetic photon flux density (PFD), and the previous light environment were investigated in A. macrorrhiza and T. australis, two Australian rainforest species. The photosynthetic efficiency during lightflecks was also investigated by comparing observed values of carbon gain with predicted values based on steady-state CO₂ assimilation rates. In both species, carbon gain and photosynthetic efficiency increased during a series of five 30-or 60-s lightflecks that followed a long period of low light; efficiency was linearly related to leaf induction state.In fully-induced leaves of both species, efficiency decreased and carbon gain increased with lightfleck duration. Low-light grown A. macrorrhiza had greater efficiency than predicted based on steady-state rates (above 100%) for lightflecks less than 40 s long, whereas leaves grown in high light had efficiencies exceeding 100% only during 5-s lightflecks. The efficiency of leaves of T. australis ranged from 58% for 40-s lightflecks to 96% for 5-s lightflecks.In low-light grown leaves of A. macrorrhiza, photosynthetic responses to lightflecks below 120 mol m^-2 s^-1 were not affected significantly by the previous light level. However, during lightflecks at 530 mol m^-2 s^-1, net carbon gain and photosynthetic efficiency of leaves previously exposed to low light levels were significantly reduced relative to those of leaves previously exposed to 120 and 530 mol m^-2 s^-1.These results indicate that, in shade-tolerant species, net carbon gain during sunflecks can be enhanced over values predicted from steady-state CO₂ assimilation rates. The degree of enhancement, if any, will depend on sunfleck duration, previous light environment, and sunfleck PFD. In forest understory environments, the temporal pattern of light distribution may have far greater consequences for leaf carbon gain than the total integrated PFD.Supported by National Science Foundation Grant BSR 8217071 and USDA Grant 85-CRCR-1-1620     

Photosynthetic responses to dynamic light under field conditions in six tropical rainforest shrubs occuring along a light gradient

 We examined in the field the photosynthetic utilization of fluctuating light by six neotropical rainforest shrubs of the family Rubiaceae. They were growing in three different light environments: forest understory, small gaps, and clearings. Gas exchange techniques were used to analyse photosynthetic induction response, induction maintenance during low-light periods, and lightfleck (simulated sunfleck) use efficiency (LUE). Total daily photon flux density (PFD) reaching the plants during the wet season was 37 times higher in clearings than in the understory, with small gaps exhibiting intermediate values. Sunflecks were more frequent, but shorter and of lower intensity in the understory than in clearings. However, sunflecks contributed one-third of the daily PFD in the understory. Maximum rates of net photosynthesis, carboxylation capacity, electron transport, and maximum stomatal conductance were lower in understory species than in species growing in small gaps or clearings, while the reverse was true for the curvature factor of the light response of photosynthesis. No significant differences were found in the apparent quantum yield. The rise of net photosynthesis during induction after transfer from low to high light varied from a hyperbolic shape to a sigmoidal increase. Rates of photosynthetic induction exhibited a negative exponential relationship with stomatal conductance in the shade prior to the increase in PFD. Leaves of understory species showed the most rapid induction and remained induced longer once transferred to the shade than did leaves of medium- or high-light species. LUE decreased rapidly with increasing lightfleck duration and was affected by the induction state of the leaf. Fully induced leaves exhibited LUEs up to 300% for 1-s lightflecks, while LUE was below 100% for 1–80 s lightflecks in uninduced leaves. Both induced and uninduced leaves of understory species exhibited higher LUE than those of species growing in small gaps or clearings. However, most differences disappeared for lightflecks 10 s long or longer. Thus, understory species, which grew in a highly dynamic light environment, had better capacities for utilization of rapidly fluctuating light than species from habitats with higher light availability. Received: 4 January 1997 / Accepted: 28 April 1997     

Growth and light absorption of some planktonic cyanobacteria, diatoms and Chlorophyceae under simulated natural light fluctuations

Specific growth rates of Limnozhrix redekei, Planktothrix agardhii(cyanobacteria), Synedraacus, Stephanodiscus minutulus (diatoms),Scenedesmus acuminatus and Scenedesmus armatus (Chlorophyceae)were compared under different time structures of illumination,but the same daily light exposure, at 20C. Fluctuating irradiancesimulating a uniform rapid transport of the algal cells acrossthe aquatic light field on a cloudless day with Z^eu/Z^mix=1 wascompared with constant irradiance throughout the same photoperiodof 12 h length as well as a photoperiod of 6 h length. Fluctuatinglight (30 min for a cycle) resulted in a decrease in specificgrowth rates as compared with constant irradiance at the samephotoperiod length. This decrease amounts to 15–20% fordiatoms, 20–25% for Chlorophyceae and 35–40% forcyanobacteria, respectively. The decrease is somewhat lowerif the fluctuations simulating mixing are slower (60 min fora cycle). The specific growth rate is also decreased by a shorterphotoperiod, but this effect is more species specific. Regardingthe in vivo absorption spectra, fluctuating light or a shorterphotoperiod has little or no effect on the Chlorophyceae anddiatoms studied, whereas cyanobacteria show an increase in lightabsorption by chlorophyll a and phycobilins.     

Ecological traits of planktonic viruses and prokaryotes along a full-salinity gradient

Virus-prokaryote interactions were investigated in four natural sites in Senegal (West Africa) covering a salinity gradient ranging from brackish (10‰) to near salt saturation (360‰). Both the viral and the prokaryote communities exhibited remarkable differences in their physiological, ecological and morphological traits along the gradient. Above 240‰ salinity, viral and prokaryotic abundance increased considerably with the emergence of (1) highly active square haloarchaea and of (2) viral particles with pleiomorphic morphologies (predominantly spindle, spherical and linear shaped). Viral life strategies also showed some salinity-driven dependence, switching from a prevalence of lytic to lysogenic modes of infection at the highest salinities. Interestingly, the fraction of lysogenized cells was positively correlated with the proportion of square cells. Overall, the extraordinary abundance of viruses in hypersaline systems (up to 6.8 × 10(8) virus-like particles per milliliter) appears to be partly explained by their high stability and specific ability to persist and proliferate in these apparently restrictive habitats.     

Growth responses of a woody species to clipping and goat saliva

Studies on the role of mammalian herbivore saliva in plant–animal interactions have mostly focused on graminoid species and bovine saliva. A trial was performed in Botswana with clipping treatments to simulate browsing of shoots and the application of goat saliva on the woody species Combretum apiculatum Sonder (Combretaceae). Treatments were performed during early growing season while shoot growth was rapid, and responses of trees were recorded later in the same season. Clipped shoots with saliva had significantly enhanced shoot growth (tripled in length) and leaf production (2.7 times more leaves) compared to clipped shoots without saliva. However, unclipped shoots still grew more than clipped shoots, with or without saliva treatment.     

Growth responses to arbuscular mycorrhizae by rain forest seedlings vary with light intensity and tree species

Light intensity and root colonization by arbuscular mycorrhizal (AM) fungi are considered important factors affecting the performance of rain forest plants, yet few studies have examined how these two factors interact. Whether AM colonization promoted growth or caused shifts in biomass allocation in seedlings of four species of Australian rain forest tree (Flindersia brayleana, Acmena resa, Cryptocarya mackinnoniana and Cryptocarya angulata), grown in a glasshouse under light conditions that mimicked the shaded understory (3% PAR) and small light gaps (10% PAR), was examined. Seedlings were grown in sterilized field soil and either inoculated with AM fungi or provided sterile inoculum. Four major findings emerged. First, in all species, seedlings grown in small gap light intensities were larger than seedlings grown in understory light intensities. Second, when seedling biomass was included as a covariate, variation in light intensity was associated with significant shifts in biomass allocation. In all species, leaf area ratio was lower at 10% PAR than at 3% PAR, while root-to-shoot ratio showed the opposite pattern in one of the four species (C. mackinonniana). Third, although percentage root length colonized by AM fungi was greater at 10% PAR than 3% PAR in all species, this difference could be accounted for by variation in seedling size in all species except C. angulata. Fourth, growth and biomass allocation responses to AM colonization varied with light intensity and plant species. AM colonization promoted growth in both light regimes only in F. brayleana, while it had no effect on growth in C. mackinnoniana and C. angulata in either light regime and promoted growth only under high light in A. resa. AM colonization had no effect on leaf area ratio or root-to-shoot ratio in any of the species, and significantly altered specific root length in only one of the four species (C. mackinnoniana). These findings suggest that rain forest seedlings are highly variable in their growth responses to AM colonization and that some of this variability is related to the light intensity of the environment. Given that seedlings may spend many years in the shaded understory, these differences among species could have important effects on long-term seedling performance and seedling community dynamics.     

Growth limitation of planktonic bacteria in a large mesotrophic lake

We studied nutrient-limitation of bacterioplankton growth in Lake Constance, a mesotrophic lake, between February and August in 1992. We amended 1-m filtrates with a single nutrient or nutrient combinations at 5 or 10 m final concentration, and the limiting nutrient or nutrient combination was inferred from the assay in which bacterial growth was most stimulated. The following nutrients were added individually or in combination: glucose, amino acids, peptone, and ammonium as C and N sources, and inorganic phosphate. From January until the beginning of the phytoplankton spring bloom in mid-April, C alone was growth-limiting. During the spring bloom a complex growth-limitation pattern occurred; first P was limiting, then for only 1 week C + N together, and thereafter P + C. During the clear-water phase with very low chlorophyll concentrations, P + C together limited bacterial growth again, interrupted by a period when C + N + P shortage caused a triple limitation. Later in the season, P + C were growth-limiting again. The growth efficiency (bacterial biomass produced/substrates used) on the basis of amino acid and carbohydrate used varied between 17 and 35%. The addition of various C and N sources indicated that the growth efficiency strongly depended on the quality of the substrates and the adaptation of the bacterial assemblages, for example, whether C and N originated from amino acids or glucose and ammonium.     

不同蒿属植物对光强的适应性差异研究

对中国四种蒿属植物(毛莲蒿、蒙古蒿、牡蒿和灰苞蒿)的光合响应曲线进行了研究。结果表明:牡蒿具有高光饱点(411.0μmol·m-2·s-1)和最大光合速率(18.627μmol·m-2·s-1),以及较低的光补偿点(17.867μmol·m-2·s-1),对高光的适应能力最强;灰苞蒿的暗呼吸速率(0.353μmol·m-2·s-1)和表观量子效率(0.038)最低,说明该种对弱光的适应能力较差,且在弱光条件下只能维持较低的生长速率;灰苞蒿水分利用效率随光强的变化趋势与其他三种蒿属植物一致,但总体上维持在一个较高的水平,可能与其对干旱生境的适应有关。光合响应曲线各个拟合指标在种间呈现出了较大的变异,其中光补偿点(L cpμmol·m-2·s-1)和暗呼吸速率(R dayμmol·m-2·s-1)差异达到了显著水平。说明植物功能性状与植物对环境长期适应密切相关,并且这种适应性是稳定可遗传的。     

The temperate-tropical gradient of planktonic Protozoa and Rotifera

Many flagellates, ciliates and rhizopods appear to be cosmopolitan, at least when considered at the morphospecies level. There are indications of tropical endemics among the ciliates and the rhizopods, but the percentage of endemics appears to be low. Among the rotifers there is a well marked latitudinal gradient, but the picture is complicated by the occurrence of warm water species during hot summers in temperate regions. A further complication has been introduced by the artificial development of heated water associated with power stations. The characteristic rotifer associations of the tropics are governed largely by temperature and salinity. A study of the altitudinal distribution of rotifers in Africa reveals an interplay between latitude and altitude in determining the similarities of the associations to those found in the temperate Old World.     

Differences in light usage among three fern species of genus <Emphasis Type="Italic">Blechnum</Emphasis> of contrasting ecological breadth in a forest light gradient

In Chilean evergreen temperate forest, fern species of the genus Blechnum occur in diverse microhabitats in a light gradient. We hypothesized that differences in the habitat preferences of three co-occurring Blechnum species would be associated with differences in the magnitude of responses of light capture [chlorophyll (Chl) content] and use (photosynthetic capacity and performance) to light availability. We measured the abundance, chlorophyll content, photosynthetic capacity (A), and photosynthetic performance (chlorophyll fluorescence of photosystems I and II) of juvenile individuals of each species growing in different light levels in the field. While Blechnum magellanicum covers a broad light environments range, B. mochaenum is restricted to shade, and B. penna-marina occupies full sun sites. Despite significant interspecific differences in average total chlorophyll content, this trait did not differ among species along the light gradient. There was significant interspecific variation in both the mean value and the plasticity of Chl a:Chl b ratio and A to light availability. While B. penna-marina showed a flatter reaction norm (lower response) of Chl a:Chl b ratio to light availability than its two congeners, B. mochaenum showed a lower response of A to light availability. B. penna-marina and B. magellanicum individuals from open sites had higher light saturation points of the electron transport rate (ETR) of both photosystems (ETR_LSP I and II) and photochemical quenching (qL and NA) than the shade restricted B. mochaenum. Additionally, non-photochemical quenching values for both photosystems (NPQ and ND) were higher in ferns species occurring in shaded sites. The adjustment of the photosynthetic capacity and performance to light availability appears to be an important mechanism of acclimation in these three Blechnum species that differ in their habitat preferences across a light gradient.     

Growth rate responses of Missouri and Lower Yellowstone River fishes to a latitudinal gradient

Growth rate coefficients estimated for channel catfish Ictalurus punctatus , emerald shiners Notropis aherinoides, freshwater drums Aplodinotus grunniens , river carpsuckers Carpiodes arpio and saugers Stizostedion canadense collected in 1996–1998 from nine river sections of the Mssouri and lower Yellowstone rivers at two life-stages (young-of-the-year and age 1+ years)were significantly different among sections. However, they showed no river-wide latitudinal trend except for age 1+ years emerald shiners that did show a weak negative relation between growth and both latitude and length of growing season. The results suggest growth rates of fishes along the Missouri River system are complex and could be of significance in the Management and conservation of fish communities in this altered system.     

Length–weight relationships of eight freshwater planktonic crustacean species in Japan

1. The relationships between body length and dry weight were examined for eight species of freshwater planktonic crustacea common in Japan: Eodiaptomus japonicus, Acanthodiaptomus pacificus, Daphnia galeata, D. similis, D. magna, Scapholeberis mucronata, Simocephalus exspinosus and Bosmina longirostris.
2. The relationships of two diaptomid species were similar and the approximate equation was ln W = 2.7 + 2.6*ln L , where L is prosome length (mm) and W is dry weight (μg). The carapace length–dry weight relationships in branchiopods were more variable, with the slope ranging from 1.9 to 2.9 and the intercept from 2.0 to 3.7.
3. The effects of food conditions on the relationship were examined in the laboratory, and the seasonal changes in the field were also studied.
4. Practical advice is presented for predicting crustacean weight from body length.