Effects of the herbicides fluometuron and prometryn of Rhizoctonia solani in soil cultures.

Responses of Rhizoctonia solani to herbicides in soil cultures were assessed by measuring soil enzyme activity and other growth-related factors. Both beta-galactosidase (EC 3.2.1.23) and phosphatase (EC 3.1.3.1.3.1.3.2) activities were highly correlated with amounts of mycelium in soil. Both enzyme activities were reduced significantly by either fluometuron or prometryn at 40 microgram/g of soil; the pathogen was more distinctly suppressed by fluometron and showed a stronger tendency to overcome the effects of prometryn with time. Inhibition was also reflected in reduced ultilization of glucose and less CO2-C evolved. Except for an increase in beta-galactosidase activity in the presence of 1 microgram fluometuron, low levels of either herbicide had little effect on the pathogen.     

Effects of interactions between algae and grazing gastropods on the structure of a low-shore intertidal algal community

Summary At low levels on shores in New South Wales, foliose algae are abundant and often occupy all substrata; microalgal grazing gastropods are rare or absent. At higher levels, foliose algae are sparse or absent and grazing gastropods are abundant. Hypotheses for the causes of the lower vertical limits of distribution of these grazers include the effects of increased predation or the deleterious physiological effects of increased period of submergence at lower levels on the shore. Alternatively, the presence of the algae, because they occupy space and deprive the grazers of substratum for feeding, may prevent the downward movement, or survival of the grazers at low levels. Under the first two of these hypotheses, algae are able to colonize and grow in low-shore areas as an indirect result of factors which remove grazers. Under the third hypothesis, the algae are directly responsible for the lack of grazers.Experimental clearings of the low-shore algae and introductions of the mid-shore limpets Cellana tramoserica and Siphonaria denticulata were used to test these hypotheses. C. tramoserica grazes microalgae and removes them from the substratum, preventing colonization. S. denticulata, in contrust, crops the algae, leaving a visible cover of algae on the substratum, which can grow rapidly. Because of its method of feeding, S. denticulata had no measurable impact on the rates of colonization, nor on the dry weights of algae, compared with those of ungrazed areas. C. tramoserica could keep cleared areas tree from foliose algae, but only when the limpets were mainfained in great density (10 per 900 cm²). They were less effective where wave-action was greater.Neither species of limpets could survive when placed onto beds of mature algae, because they had no substratum on which to cling and were swept away by the waves. C. tramoserica did not invade clearings below their lower limit of distribution where they had to move over a bed of foliose algae. Few C. tramoserica moved directly downshore into cleared areas. When placed on bare rock within low-shore beds of algae of different ages, S. denticulata remained amongst the algae and maintained their tissue-weights. Few C. tramoserica remained in areas with well-developed algae, compared with areas having sparse algal growth. Those Cellana which remained amongst well-developed algae lost weight, whereas limpets in areas with less algal growth mammtained their weights. In experimental cages in low-shore beds of algae, where the limpets were inaccessible to potential predators, C. tramoserica lost weight and died. On cleared areas they survived for many weeks, but lost weight and died as algae grew and covered the substratum. In the absence of predation, the micro-algal grazer C. tramoserica could not survive in lowshore areas because algae grew too fast and occupied the substratum, making it inaccessible for the limpets to graze; the algae, once grown beyond small sporelings, are not a suitable food-source for C. tramoserica, and the loss of weight and death of these limpets is attributable to starvation.The lower limit of distribution of C. tramoserica is not due to the direct effects of physical factors associated with prolonged submersion, nor to the impact of predators, but is apparently determined by the presence of rapidly growing, extensive beds of foliose algae at low levels on the shore. The cause of the limit of distribution of S. denticulata is not yet known and predation may prove to be important. Removal of S. denticulata from low-shore algal beds would not, however, affect the domination of substrata by algae. Grazing by S. denticulata at very great density had no effect on algal cover nor weight. In the intertidal community studied, the persistence of a low-shore algal zone, bounded above by abundant grazers is not influenced by the activities of predators, but is a direct result of interactions between the grazers and the algae.     

Temperature affects the response of heterotrophic bacteria and mixotrophic algae to enhanced concentrations of soil extract

To investigate the consequences of increased temperature and enhanced input of dissolved organic matter (DOM) into lakes for heterotrophicic bacteria and for mixotrophic algae which use DOM in addition to photosynthesis, the hypotheses were tested whether (1) both bacteria and mixotrophic algae benefit from increased input of DOM, or (2) increased DOM input enhances bacterial biomass and thereby decreases algal biomass. Growth experiments in batch cultures, exudation measurements, and competition experiments in chemostats were performed at two temperature levels. Increased temperature stimulated the autotrophic growth rate of Chlorella protothecoides. Bacteria and Chlorella increased their heterotrophic growth rates at higher DOM concentration at lower temperature whereas enhanced DOM concentration hardly stimulated their growth at higher temperature. In chemostats, enhanced input of soil extract increased both bacterial and algal biomass at lower temperature whereas bacterial biomass increased only slightly and algal biomass decreased at higher temperature. Thus, the temperature determines the response of microorganisms to enhanced DOM concentration.     

Photosynthetic acclimation to different light levels in the brown marine macroalga, <Emphasis Type="Italic">Hizikia fusiformis</Emphasis> (Sargassaceae,Phaeophyta)

Hizikia fusiformis thalli experience dynamic incident light conditions during the period of growth. The present study was designed to examine how changing photon irradiance affects the photosynthesis both in the short and long terms by culturing H. fusiformis under three different light levels: 35 μmol photons m^-2 s^-1 (low light, LL), 85 μmol photons m^-2 s^-1 (intermediate light, IL), and 165 μmol photons m^-2 s^-1 (high light, HL). A similar relative growth rate was observed between IL- and HL-grown algae, but the growth rate was significantly reduced in LL-grown algae. The photosynthetic rates (P _n) measured at their respective growth light levels were found to be lowest in the thalli grown at LL and highest at HL. However, LL-grown algae exhibited much higher P _n in comparison with IL- and the HL-grown thalli at the same measuring photosynthetic photon flux density, indicating the photosynthetic acclimation to low growth light in H. fusiformis. The photosynthesis–light curves showed that LL-grown algae had a highest light-saturating maximum P _n (P _max) in comparison with IL- or HL-grown algae when the photosynthetic rates were expressed on the biomass basis. However, P _max was highest in HL-grown algae compared to IL- or LL-grown algae when the rates were normalized to chlorophyll a. The photosynthesis–inorganic carbon (Ci) response curves were also significantly affected by the growth light conditions. The highest value of apparent photosynthetic conductance occurred in LL-grown algae while the lowest value in HL-grown algae. Additionally, the activity of external carbonic anhydrase (CA) tended to increase while the total CA activity inclined to decrease in H. fusiformis thalli when the growth light level altered from 35 to 165 μmol photons per square meter per second. The external CA inhibitors showed a higher inhibition in HL-grown algae compared with LL-grown algae. It was proposed that photosynthetic acclimation to low light condition in H. fusiformis was achieved through an increase in the number of reaction centers and increased capacities of electron transport and of Ci transport within cells. The ability of photosynthetic acclimation to low light confers H. fusiformis thalli to overcome the environmental low light condition as a result of the attenuation of seawater or self-shading through enhancing its photosynthetic performance and carbon assimilation necessary for growth.     

A metabolomics approach to assessing phytotoxic effects on the green alga Scenedesmus vacuolatus

The potential of metabolomics for toxicity analysis with synchronized algal populations during growth was explored in a proof of principle study. Low molecular weight compounds from hydrophilic and lipophilic extracts of algal populations of the unicellular green alga Scenedesmus vacuolatus were analyzed using gas chromatography-mass spectrometry (GC-MS) and subsequent multivariate analysis to identify time-related patterns. Algal metabolite responses were studied under control and exposure conditions for the photosystem II-inhibiting herbicide prometryn. To define the typical metabolic profile of control S. vacuolatus cultures seven time points over a growth period of 14 h were evaluated. The results show a clear time-related trend in metabolite levels and a distinct separation of exposed and reference algal populations. The results suggest an impairment of the energy metabolism associated with an activation of catabolic processes and a retardation of carbohydrate biosynthesis in treated algae. Metabolite results were compared to observation parameters, currently used in phytotoxicity assessment, showing that metabolites respond faster to exposure than algal growth. The potential of metabolomics for toxicity evaluation, especially to identify physiological markers and to detect effects at an early state of exposure, are discussed. Therefore, we suggest a metabolomics approach utilizing synchronous algal cultures to be a suitable future tool in ecotoxicology.     

Effects of Gibberellic Acid and N,N-Dimethyl Piperidinium Chloride on the Dose of and Physiological Responses to Prometryn in Black Nightshade (Solanum nigrum L.)

The use of gibberellic acid (GA₃) and N, N-dimethyl piperidinium chloride (DPC) in combination with prometryn would likely increase the control of black nightshade in cotton fields. Experiments were designed to investigate the physiological and biochemical responses of black nightshade at the three- to four-leaf stage to prometryn applied at different rates, either alone or in combination with GA₃ or DPC, in a greenhouse environment. These studies demonstrated that prometryn applied in combination with DPC at low rates (7.2 g ai ha⁻¹) led to increased fresh weight and visible injury of black nightshade compared with prometryn applied alone or in combination with GA₃; however, at rates of 36, 180, and 900 g ai ha⁻¹, prometryn in combination with DPC caused the least visible injury among all treatments and prometryn in combination with GA₃ caused the greatest visible injury. These results suggest that black nightshade suffered more severe damage when prometryn was applied in combination with GA₃, which is supported by the reduced soluble protein content, lower antioxidant enzyme activities, and higher malondialdehyde (MDA) content in the plants treated with prometryn plus GA₃. These results indicate that the application of GA₃ in combination with prometryn to black nightshade may have the potential to lower the levels of prometryn tolerance in these plants.     

The role of rhizosphere bacteria in herbicide-mediated increase in Rhizoctonia solani-induced cotton seedling damping-off

A study was carried out to determine the role of rhizosphere-residing bacteria in the observed pendimethalin- and prometryn-mediated increase in cotton seedling damping-off incidence caused by Rhizoctonia solani. Judging from the results, pendimethalin-mediated increase in disease incidence may be due to a decrease in the populations of indigenous cotton root colonizing bacteria in the presence of pendimethalin. Prometryn-mediated increase in disease may be due to a decrease in the populations of indigenous root colonizing bacteria as well as increased susceptibility of cotton seedlings to R. solani infection in the presence of prometryn. Pendimethalin and prometryn neither affected the growth of R. solani nor caused any visible change in seedling physical characteristics.     

Stress responses and metal tolerance of <Emphasis Type="Italic">Chlamydomonas acidophila</Emphasis> in metal-enriched lake water and artificial medium

Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake-water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium-grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations.     

Effects of snow removal and algal photoacclimation on growth and export of ice algae

Net growth of ice algae in response to changes in overlying snow cover was studied after manipulating snow thickness on land-fast, Arctic sea ice. Parallel laboratory experiments measured the effect of changing irradiance on growth rate of the ice diatom, Nitzschia frigida. After complete removal of thick snow (≥9 cm), in situ ice algae biomass declined (over 7–12 days), while removal of thin snow layers (4–5 cm), or partial snow removal, increased net algal growth. Ice bottom ablation sometimes followed snow removal, but did not always result in net loss of algae. Similarly, in laboratory experiments, small increases in irradiance increased algal growth rate, while greater light shifts suppressed growth for 3–6 days. However, N. frigida could acclimate to relatively high irradiance (110 μmol photons m² s⁻¹). The results suggest that algal loss following removal of a thick snow layer was due to the combination of photoinhibition and bottom ablation. The smaller relative increase in irradiance after removal of thin or partial snow layers allowed algae to maintain high specific-growth rates that compensated for loss from physical mechanisms. Thus, the response of ice algae to snow loss depends both on the amount of change in snow depth and algal photophysiology. The complex response of ice algae growth and export loss to frequently changing snow fields may contribute to horizontal and temporal patchiness of ecologically and biogeochemically important variables in sea ice and should be considered in predictions of how climate change will affect Arctic marine ecosystems.     

Physiological response of 10 phytoplankton species exposed to macondo oil and the dispersant,Corexit

Culture experiments were conducted on ten phytoplankton species to examine their biological and physiological responses during exposure to oil and a combination of oil and dispersant. The species tested included a range of taxa typically found in the Gulf of Mexico such as cyanobacteria, chlorophytes, and diatoms. Cultures were exposed to Macondo surrogate oil using the water accommodated fraction (WAF), and dispersed oil using a chemically enhanced WAF (CEWAF) and diluted CEWAF, to replicate conditions following the Deepwater Horizon spill in the Gulf of Mexico. A range of responses were observed, that could broadly class the algae as either “robust” or “sensitive” to oil and/or dispersant exposure. Robust algae were identified as Synechococcus elongatus, Dunaliella tertiolecta, two pennate diatoms Phaeodactylum tricornutum and Navicula sp., and Skeletonema grethae CCMP775, and were largely unaffected by any of the treatments (no changes to growth rate or time spent in lag phase relative to controls). The rest of the phytoplankton, all centric diatoms, exhibited at least some combination of reduced growth rates or increased lag time in response to oil and/or dispersant exposure. Photophysiology did not have a strong treatment effect, with significant inhibition of photosynthetic efficiency (F_v/F_m) only observed in the CEWAF, if at all. We found that the effects of oil and dispersants on phytoplankton physiology were species‐dependent, and not always detrimental. This has significant implications on how oil spills might impact phytoplankton community structure and bloom dynamics in the Gulf of Mexico, which in turn impacts higher trophic levels.     

SHORT‐ AND LONG‐TERM EFFECTS OF ELEVATED CO2 ON PHOTOSYNTHESIS AND RESPIRATION IN THE MARINE MACROALGA HIZIKIA FUSIFORMIS (SARGASSACEAE,PHAEOPHYTA) GROWN AT LOW AND HIGH N SUPPLIES1

The short‐term and long‐term effects of elevated CO₂ on photosynthesis and respiration were examined in cultures of the marine brown macroalga Hizikia fusiformis (Harv.) Okamura grown under ambient (375 μL · L^?1) and elevated (700 μL · L^?1) CO₂ concentrations and at low and high N availability. Short‐term exposure to CO₂ enrichment stimulated photosynthesis, and this stimulation was maintained with prolonged growth at elevated CO₂, regardless of the N levels in culture, indicating no down‐regulation of photosynthesis with prolonged growth at elevated CO₂. However, the photosynthetic rate of low‐N‐grown H. fusiformis was more responsive to CO₂ enrichment than that of high‐N‐grown algae. Elevation of CO₂ concentration increased the value of K_1/2(Ci) (the half‐saturation constant) for photosynthesis, whereas high N supply lowered it. Neither short‐term nor long‐term CO₂ enrichment had inhibitory effects on respiration rate, irrespective of the N supply, under which the algae were grown. Under high‐N growth, the Q₁₀ value of respiration was higher in the elevated‐CO₂‐grown algae than the ambient‐CO₂‐grown algae. Either short‐ or long‐term exposure to CO₂ enrichment decreased respiration as a proportion of gross photosynthesis (Pg) in low‐N‐grown H. fusiformis. It was proposed that in a future world of higher atmospheric CO₂ concentration and simultaneous coastal eutrophication, the respiratory carbon flux would be more sensitive to changing temperature.     

Toxicity and biodegradation of fluometuron by selected cyanobacterial species

The Biodegradation capabilities of six selected cyanobacterial species for fluometuron, a phenylurea herbicide, as well as its inhibitory effect on chlorophyll a content were investigated. The selected species (three strains of Microcystis aeruginosa, Anabaena cylindrica, A. flos-aquae and A. spiroides) were subjected to three elevated concentrations of fluometuron (0.14, 0.7 and 1.4 mg/ml) for different exposure times (1–5 days). Results revealed that biodegradation of fluometuron is species-dependent and positively correlated with the exposure time, reaching maximum efficiency after 5 days at all the investigated concentrations. All the species tested showed generally great ability to degrade the compound even at the highest concentration with specific variations among them. Biodegradation efficiencies of fluometuron by the selected species were in the following ranges; 39.2–99.9; 87.5–100; and 93.2–100 at 0.14; 0.7 and 1.4 mg fluometuron/ml respectively. It was noticed that the gradual increase in the pesticide concentration enhances its biodegradability by the selected algal species. Variations according to species as well as exposure time were discussed. The highest fluometuron concentration (1.4 mg/l) showed the highest inhibition of chlorophyll a content in the tested species and toxicity was also species- and time-dependent.     

Size-dependent growth rates in eukaryotic and prokaryotic algae exemplified by green algae and cyanobacteria: comparisons between unicells and colonial growth forms

The size dependency of maximum growth rates was investigatedin cyanobacteria and in green algae (Chlorophyta). Both unicellularand colony-forming species were included in the study. Significantallometric relationships were found between size and maximumgrowth rate for both cyanobacteria and green algae. The size-dependentgrowth could be described by the same scaling exponent in bothcyanobacteria and green algae, but in both cyanobacteria andgreen algae only unicells evinced size-dependent growth rates—therewas no relationship between colony size and growth rate in colonialforms of cyanobacteria and green algae. It is concluded thatthe colonial growth form represents an evolutionary adaptationto escape the negative effects of size-dependent growth, whileretaining the positive effects of increased size, e.g. a decreasedgrazing pressure.     

Effects of UVB radiation on the carragenophyte <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> (Rhodophyta,Gigartinales): changes in ultrastructure,growth, and photosynthetic pigments

Damage to the ozone layer has led to increased levels of ultraviolet radiation at the earth’s surface. Increased ultraviolet radiation can affect macroalgae in many important ways, including reduced growth rate, changes in cell biology and ultrastructure. Kappaphycus alvarezii is a red macroalga of economic interest due to its production of kappa carrageenan. In this study, we examined two strains of K. alvarezii (green and red) exposed to ultraviolet B radiation (UVBR) for 3 h per day during 28 days of cultivation in vitro. UVBR caused changes in the ultrastructure of cortical and subcortical cells, which included increased thickness of the cell wall and plastoglobuli, reduced intracellular spaces, changes in the cell contour, and destruction of chloroplast internal organization. While the green strain exposed to photosynthetically active radiation (PAR) showed growth rates of 6.75% day⁻¹, the red strain grew only 6.35% day⁻¹. Upon exposure to PAR + UV-B, a decreasing trend in growth rates was observed for both strains, with the green strain growing 3.0% day⁻¹ and the red strain growing 2.77% day⁻¹. Significant differences in growth rates between control and UV-B-exposed algae were also found in both strains. Furthermore, compared with control algae, phycobiliprotein contents (phycoerythrin, phycocyanin, and allophycocyanin) were observed to decrease in both strains after PAR + UV-B exposure. However, while the chlorophyll a levels increased in both strains, the green strain showed no significant differences in chlorophyll a levels. Taken together, these findings strongly suggested that UVBR negatively affects the ultrastructure, growth rates, and photosynthetic pigments of intertidal macroalgae and, in the long term, their economic viability.     

Effects of pH on toxicity of As,Cr, Cu,Ni and Zn to Selenastrum capricornutum Printz

Acute toxicity tests were conducted to establish the response of Selenastrum capricornutum Printz to sublethal concentrations of As, Cr, Cu, Ni and Zn at a broad range of pH levels. Cultures were incubated for a period of seven days at pH 4 in standard algal assay media containing sublethal concentrations of metals. At this low pH, growth was depressed for all metals tested. The adjustment of pH to higher levels resulted in increased growth when cultures were treated with As, Cu, or Ni and incubated for an additional 7 days. Toxicity was least at the optimum pH range for growth of the alga.The observation that the toxicity of As, Cu, and Ni to S. capricornutum decreases markedly at pH values above 4.0 may be of ecological importance in the control of acid mine pollution. If a high percentage of algae show a similar response to decreasing toxicity with increasing pH, it clearly would be of value to adopt measures which control pH as well as the levels of metals present. It was suggested that algae with a broad pH growth range, such as S. capricornutum, could benefit from the addition of highly alkaline materials to waters where certain metals are present.     

Degradation of long chain n-alkanes by Chlorococcales

Summary Four out of thirty-one algae strains belonging to the order Chlorococcales exhibited good growth on solid media containing n-alkanes. Chlorella vulgaris (397) was able to degrade n-tridecane in cooxidation. The corresponding secondary alcohols and ketones in C₂-to C₇-position could be identified in the culture broth. The same oxidation products could be found in the media of cultures grown in darkness with the addition of glucose. This demonstrates a subterminal degradation pathway of C. vulgaris.There was no indication for a mono-or diterminal oxidation of alkanes by algae.The fatty acid pattern of lipids exhibited an incease in long chain acids and a decrease in shorter chain acids. The growth rate of cells grown on alkanes increased after 72 h, but the release of autospores was retarded.     

Influence of outbreak of macroalgal blooms on phosphorus release from the sediments in Swan Lake Wetland,China

Macroalgal blooms have occurred worldwide frequently in coastal areas in recent decades, which dramatically modify phosphorus (P) cycle in water column and the sediments. Rongcheng Swan Lake Wetland, a coastal wetland in China, is suffering from extensive macroalgal blooms. In order to verify the influence of macroalgal growth on sediment P release, the sediments and filamentous Chaetomorpha spp. were incubated in the laboratory to investigate the changes of water quality parameters, P levels in overlying water, and sediments during the growth period. In addition, algal biomass and tissue P concentration were determined. In general, Chaetomorpha biomasses were much higher in high P treatments than in low P treatments. Compared with algae+low P water treatment, the addition of sediments increased the algal growth rate and P accumulation amount. During the algal growth, water pH increased greatly, which showed significant correlation with algal biomass in treatments with high P (P < 0.05). P fractions in the sediments showed that Fe/Al–P and organic P concentrations declined during the algal growth, and great changes were observed in algae+low P water+sediment treatment for both. As a whole, the sediments can supply P for Chaetomorpha growth when water P level was low, and the probable mechanism was the release of Fe/Al–P at high pH condition induced by intensive Chaetomorpha blooms.     

Seasonal variation in biomass and photosynthetic activity of epilithic algae on a rock at the upper littoral area in the north basin of Lake Biwa, Japan

Vertical distributions of biomass and the photosynthetic activity of epilithic algae were observed seasonally with regard to their physical and chemical parameters along a rocky shoreline of the upper littoral area in the north basin of Lake Biwa. Chlorophyll a amounts in epilithic algae showed a marked change with depth from spring to early summer. The algal biomass showed higher values on the lower part of a large rock in early spring, and gradually increased on the upper part as a result of the growth of Spirogyra sp., a filamentous Chlorophyceae. This growth seems to be associated with a rise in water temperature, with the biomass at the upper depths seeming to be affected by a hydraulic disturbance. The standing crop of epilithic algae showed a maximum value in June and declined to a minimum in August because of the corresponding proliferation or disappearance of Spirogyra as well as changes in the water level. The maximum value of the assimilation number calculated from the potential photosynthetic rate of epilithic algae was obtained at the lower depths in June when Spirogyra grew vigorously. Appreciably high assimilation numbers were also observed in summer and fall, although chlorophyll a amounts were low. The present study is the first in a series to clarify the contribution of epilithic algae on rocky areas to productivity throughout the entire littoral ecosystem.     

EXTRACTIVE AND ENZYMATIC ANALYSES FOR LIMITING OR SURPLUS PHOSPHORUS IN ALGAE

An extractive procedure for detection of surplus-stored phosphorus (luxury consumption) in algae and an enzymatic analysis for conditions of P-limited growth in algae have been evaluated. A simple 60-min boiling water extraction of algae known to contain surplus P separates essential P compounds and surplus-stored P compounds. Surplus P compounds can be measured in the extract as orthophosphate. Extracts of algae limited in their growth by the amount of available P contain little or no orthophosphate. Limitation of algal growth by P supply induces the enzyme alkaline phosphatase. The activity of this enzyme can be measured at pH 9 using p-nitro-phenylphosphate as substrate. Algae which were P-limited and contained no extractable orthophosphate have as much as 25 times more alkaline phosphatase activity than algae with surplus available P.     

Studies on life history characteristics of <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> O. F. Müller (Rotifera) in relation to temperature,salinity and food algae

Effects of temperature (18, 24, and 30°C), salinity (5–40 ppt, five intervals) and algal foods (Synechococcus sp., Chlorella pyrenoidosa, Isochrysis zhanjiangensis, Dunaliella salina and Tetraselmis cordiformis) on the life table demography of six geographical Brachionus plicatilis sensu stricto clones, which had been identified according to the prevalent taxonomy and biometric analysis of B. plicatilis sensu lato, were studied. The results showed that temperature, salinity and temperature × salinity significantly influenced the life history parameters. Genotype (clone) had no effect on the population growth rate but did influence the net reproductive rate, generation time and lifespan. All rotifer clones showed the expected increase in population growth rate with increasing temperature. B. plicatilis s. s. attained a higher population growth rate at low–medium salinities (5–20 ppt) than at high salinities (25–40 ppt). The equivalent spherical diameter (ESD) of food algae, salinity and ESD × salinity had significant effects on the life history parameters. In this case, genotype had no effect on population growth rate, net reproductive rate and generation time but did influence lifespan. The population growth rate of B. plicatilis s. s. evaluated against particle retention spectrum of algae at two salinities resulted in bell-shaped curves. Dunaliella salina with an ESD = 7.7 μm was considered to be the best food for B. plicatilis s. s. while Synechococcus appeared to be an inadequate food algae.