Long-term nutrient trends and harmful cyanobacterial bloom potential in hypertrophic Lake Taihu,China

Rapid economic development in China’s Lake Taihu basin during the past four decades has accelerated nitrogen (N) and phosphorus (P) loadings to the lake. This has caused a shift from mesotrophic to hypertrophic conditions, symptomized by harmful cyanobacterial blooms (CyanoHABs). The relationships between phytoplankton biomass as chlorophyll a (Chla) and nutrients as total nitrogen (TN) and total phosphorus (TP) were analyzed using historical data from 1992 to 2012 to link the response of CyanoHAB potential to long-term nutrient changes. Over the twenty year study period, annual mean Chla showed significantly positive correlations with both annual mean TN and TP (P < 0.001), reflecting a strong phytoplankton biomass response to changes in nutrient inputs to the lake. However, phytoplankton biomass responded slowly to annual changes in TN after 2002. There was not a well-defined or significant relationship between spring TN and summertime Chla. The loss of a significant fraction of spring N loading due to denitrification likely weakened this relationship. Bioavailability of both N and P during the summer plays a key role in sustaining cyanobacterial blooms. The frequency of occurrence of bloom level Chla (>20 μg L^?1) was compared to TN and TP to determine nutrient-bloom thresholds. A decline in bloom risk is expected if TN remains below 1.0 mg L^?1 and TP below 0.08 mg L^?1.     

Evaluation of growth and phycobiliprotein composition of cyanobacteria isolates cultivated in different nitrogen sources

Phycobiliproteins, light-harvesting pigments found in cyanobacteria and in some eukaryotic algae, have numerous commercial applications in food, cosmetic, and pharmaceutical industries. Colorant production from cyanobacteria offers advantages over their production from higher plants, as cyanobacteria have fast growth rate and high photosynthetic efficiency and require less space. In this study, three cyanobacteria strains were studied for phycobiliprotein production and the influence of sodium nitrate, potassium nitrate and ammonium chloride on the growth and phycobiliprotein composition of the strains were evaluated. In the batch culture period of 12 days, Phormidium sp. and Pseudoscillatoria sp. were able to utilize all tested nitrogen sources; however, ammonium chloride was the best nitrogen source for both strains to achieve maximum growth rate μ?=?0.284?±?0.03 and μ?=?0.274?±?0.13 day^?1, chlorophyll a 16.2?±? 0.5 and 12.2?±? 0.2 mg L^?1, and phycobiliprotein contents 19.38?±?0.09 and 19.99?±?0.14% of dry weight, whereas, for Arthrospira platensis, the highest growth rate of μ?=?0.304?±?0.0 day^?1, chlorophyll a 19.1?±?0.5 mg L^?1, and phycobiliprotein content of 22.27?±?0.21% of dry weight were achieved with sodium nitrate. The phycocyanin from the lyophilized cyanobacterial biomass was extracted using calcium chloride and food grade purity (A₆₂₀/A₂₈₀ ratio >?0.7) was achieved. Furthermore, phycocyanin was purified using two-step chromatographic method and the analytical grade purity (A₆₂₀/A₂₈₀ ratio >?4) was attained. SDS-PAGE demonstrated the purity and presence of two bands corresponding to α- and β-subunits of the C-phycocyanin. The results showed that Phormidium sp. and Pseudoscillatoria sp. could be good candidates for phycocyanin production.     

Parameterization of surface irradiance and primary production in Århus Bay,SW Kattegat,Baltic Sea

The aims of the present study were to develop a parameterization of a one-year-long observed PAR time-series, apply the PAR parameterization in a primary production relation, and compare calculated and observed time-series of primary production. The PAR parameterization was applied in the generally used relation for the primary production (P _d): P _d = a(BI ₀ Z ₀) + b with observed photic depth (Z ₀) and Chl-a concentrations (B). It was tested whether the PAR parameterization in combination with this simple relation for primary production was able to describe the actual measured primary production. The study is based on a one year long time-series of PAR, CTD-casts (n = 45), and primary production measurements (n = 24) from Århus Bay (56°09′ N; 10°20′ E), south west Kattegat. Results showed a high and positive correlation between observed and calculated primary production in the bay, as based on the present PAR parameterization combined with the simple primary production relation. The developed PAR parameterization, which calculates total daily surface irradiance per day (M photons m^?2 d^?1), can be applied in any ecological application taking into account that it was developed for the latitude of 56° N.     

Seasonal variation in light utilisation,biomass production and nutrient removal by wastewater microalgae in a full-scale high-rate algal pond

There has been renewed interest in the combined use of high-rate algal ponds (HRAP) for wastewater treatment and biofuel production. Successful wastewater treatment requires year-round efficient nutrient removal while high microalgal biomass yields are required to make biofuel production cost-effective. This paper investigates the year-round performance of microalgae in a 5-ha demonstration HRAP system treating primary settled wastewater in Christchurch, New Zealand. Microalgal performance was measured in terms of biomass production, nutrient removal efficiency, light absorption and photosynthetic potential on seasonal timescales. Retention time-corrected microalgal biomass (chlorophyll a) varied seasonally, being lowest in autumn and winter (287 and 364 mg m^?3day^?1, respectively) and highest in summer (703 mg m^?3day^?1), while the conversion efficiency of light to biomass was greatest in winter (0.39 mg Chl- a per μmol) and lowest in early summer (0.08 mg Chl- a per μmol). The percentage of ammonium (NH₄–N) removed was highest in spring (79 %) and summer (77 %) and lowest in autumn (47 %) and winter (53 %), while the efficiency of NH₄–N removal per unit biomass was highest in autumn and summer and lowest in winter and spring. Chlorophyll-specific light absorption per unit biomass decreased as total chlorophyll increased, partially due to the package effect, particularly in summer. The proportional increase in the maximum electron transport rate from winter to summer was significantly lower than the proportional increase in the mean light intensity of the water column. We concluded that microalgal growth and nutrient assimilation was constrained in spring and summer and carbon limitation may be the likely cause.     

Potential Outdoor Cultivation of Green Microalgae Based on Response to Changing Temperatures and by Combining with Air Temperature Occurrence

In this study, our working hypothesis was to examine whether temperature alters biomass and metabolite production by microalgae according to strain. We also addressed whether it is possible to choose a strain suitable for growing in each season of a given region. A factorial experiment revealed a significant interaction between chlorophylls a and b (Chl a and Chl b), carotenoid/Chl (a?+?b) ratio, biomass and total lipid productivity of six green microalgae (four Chlorella spp., Chlorella sorokiniana and Neochloris oleoabundans) after 15 days at four temperatures. At 39/35 °C, two Chlorella sp. strains (IPR7115 and IPR7117) showed higher total carotenoids/Chl (a?+?b) (0.578 and 0.830), respectively. N. oleoabundans had the highest Chl a (8210 μg L^?1) and Chl b (1909 μg L^?1) at 19/15 °C and highest maximum dry biomass (2900 mg L^?1), specific growth rate (0.538 day^?1) and total lipids (1003 mg L^?1) at 15/8 °C. We applied a method to infer the growth of these six green microalgae in outdoor ponds, as based on their response to changing temperatures and by combining with historical data on day/night air temperature occurrence for a given region. We conclude that the use of regionalized maps based on air temperature is a good strategy for predicting microalgal cultivation in outdoor ponds based on their features and tolerance to changing temperature.     

Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay,Rio de Janeiro,Brazil)

We investigate the carbon dynamics in Guanabara Bay, an eutrophic tropical coastal embayment surrounded by the megacity of Rio de Janeiro (southeast coast of Brazil). Nine sampling campaigns were conducted for dissolved, particulate and total organic carbon (DOC, POC and TOC), dissolved inorganic carbon (DIC), partial pressure of CO₂ (pCO₂), chlorophyll a (Chl a), pheo-pigments and ancillary parameters. Highest DOC, POC and Chl a concentrations were found in confined-shallow regions of the bay during the summer period with strong pCO₂ undersaturation, and DOC reached 82 mg L^?1, POC 152 mg L^?1, and Chl a 800 μg L^?1. Spatially and temporally, POC and DOC concentrations varied positively with total pigments, and negatively with DIC. Strong linear correlations between these parameters indicate that the production of TOC translates to an equivalent uptake in DIC, with 85% of the POC and about 50% of the DOC being of phytoplanktonic origin. Despite the shallow depths of the bay, surface waters were enriched in POC and DOC relative to bottom waters in periods of high thermohaline stratification. The seasonal accumulation of phytoplankton-derived TOC in the surface waters reached about 105 g C m^?2 year^?1, representing between 8 and 40% of the net primary production. The calculated turnover time of organic carbon was 117 and 34 days during winter and summer, respectively. Our results indicate that eutrophication of coastal bays in the tropics can generate large stocks of planktonic biomass and detrital organic carbon which are permanently being produced and partially degraded and buried in sediments.     

An analysis of long-term winter data on phytoplankton and zooplankton in Neusiedler See,a shallow temperate lake,Austria

In the last 40 years, the shallow steppe lake, Neusiedler See, was ice covered between 0 and 97 days. The North Atlantic Oscillation (NAO) as well as the Mediterranean Oscillation affected the lake and its conditions during winter. Both climate indices correlated negatively with the duration of ice cover and the timing of ice-out. Average winter phytoplankton biomass increased from less than 0.2 (0.05–0.84) mg FM l^?1 in the late 1960s/beginning of 1970s to 3.1 (1.72–5.61) mg FM l^?1 in the years 2001–2004. The increase in annual winter biomass of phytoplankton was associated with a significant shift in the composition of the algal assemblage. In the winter 1997/1998, diatoms contributed between 40 and 80% to the phytoplankton biomass while in 2006/2007 cyanoprokaryotes contributed 46%. Mean chlorophyll-a concentrations during winter were significantly correlated with those of total phosphorus (P_tot). Together with cold-water species (rotifer Rhinoglena fertöensis), perennial, eurythermal ones (copepod Arctodiaptomus spinosus) contributed to the zooplankton community. High zooplankton numbers were encountered when rotifers, particularly when densities of Rhinoglena fertöensis were high (r ² = 0.928). Zooplankton abundance and biomass varied from year to year but correlated positively with Chl-a (biomass ? r ² = 0.69; numbers ? r ² = 0.536). Winter zooplankton populations were primarily influenced by winter conditions, but in early winter also by survival of autumn populations, i.e., the more adults of Arctodiaptomus spinosus survived into winter, the higher was the zooplankton biomass in early winter. Phyto- and zooplankton dynamics in shallow lakes of the temperate region seem to critically depend on the biomass in autumn and on winter conditions, specifically on ice conditions and thus are related to climate signals such as the NAO.     

Biomass and terpenoids produced by mutant strains of <Emphasis Type="Italic">Arthrospira</Emphasis> under low temperature and light conditions

The filamentous Cyanobacterium Arthrospira is commercially produced and is a functional, high-value, health food. We identified 5 low temperature and low light intensity tolerant strains of Arthrospira sp. (GMPA1, GMPA7, GMPB1, GMPC1, and GMPC3) using ethyl methanesulfonate mutagenesis and low temperature screening. The 5 Arthrospira strains grew rapidly below 14?°C, 43.75 μmol photons m^?2 s^?1 and performed breed conservation at 2.5?°C, 8.75 μmol photons m^?2 s^?1. We used morphological identification and molecular genetic analysis to identify GMPA1, GMPA7, GMPB1 and GMPC1 as Arthrospira platensis, while GMPC3 was identified as Arthrospira maxima. Growth at different culture temperatures was determined at regular intervals using dry biomass. At 16?°C and 43.75 μmol photons m^?2 s^?1, the maximum dry biomass production and the mean dry biomass productivity of GMPA1, GMPB1, and GMPC1 were 2057?±?80 mg l^?1, 68.7?±?2.5 mg l^?1 day^?1, 1839?±?44 mg l^?1, 60.6?±?1.8 mg l^?1 day^?1, and 2113?±?64 mg l^?1, 77.7?±?2.5 mg l^?1 day^?1 respectively. GMPB1 was chosen for additional low temperature tolerance studies and growth temperature preference. In winter, GMPB1 grew well at mean temperatures <10?°C, achieving 3258 mg dry biomass from a starting 68 mg. In summer, GMPB1 grew rapidly at mean temperatures more than 28?°C, achieving 1140 mg l^?1 dry biomass from a starting 240 mg. Phytonutrient analysis of GMPB1 showed high levels of C-phycocyanin and carotenoids. Arthrospira metabolism relates to terpenoids, and the methyl-d-erythritol 4-phosphate pathway is the only terpenoid biosynthetic pathway in Cyanobacteria. The 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) gene from GMPB1 was cloned and phylogenetic analysis showed that GMPB1 is closest to the Cyanobacterium Oscillatoria nigro-viridis PCC711. Low temperature tolerant Arthrospira strains could broaden the areas suitable for cultivation, extend the seasonal cultivation time, and lower production costs.     

The aromatic cytokinin <Emphasis Type="Italic">meta-</Emphasis>topolin promotes in vitro propagation,shoot quality and micrografting in <Emphasis Type="Italic">Corylus colurna</Emphasis> L.

The role of 4.1 or 8.2 μM meta-topolin (mT) on shoot multiplication, rooting and ex vitro acclimatization of micropropagated Corylus colurna L., a promising non-suckering rootstock for hazelnut (Corylus avellana L.), was examined in comparison to N⁶-benzyladenine (BA), the most used cytokinin in tissue culture of Corylus spp. The influence of 8.2 μM mT and BA on photosynthetic pigments content and antioxidant enzymes activity, catalase (CAT) and guaiacol peroxidase (POD), in regenerated shoots, and on the preparation of the rootstock for micrografting was also evaluated. The highest shoot multiplication was recorded on medium containing 8.2 μM mT and an overall positive effect of mT on growth and quality of micropropagated shoots was found. The highest chlorophyll a content (1.236 mg g^?1 fresh weight, FW) and chlorophyll a/b ratio (2.48), and the lowest total carotenoids content (0.292 mg g^?1 FW) and CAT activity (25.8 μmol min^?1 mg^?1 protein) were detected after 8.2 μM mT application, while no significant differences were found in chlorophyll b content and POD activity between the two cytokinins. The best rhizogenesis response (98% for 4.1 μM and 100% for 8.2 μM mT) and ex vitro acclimatization competence (higher than 78%) were exhibited from shoots multiplied on mT. Furthermore, the multiplication of rootstock on mT allowed obtaining the highest (70%) response of successful micrografting. The present findings provide the first evidence of the successful applicability of mT in C. colurna tissue culture and development of micrografted plantlets.     

Effects of light intensity and quality on phycobiliprotein accumulation in the cyanobacterium <Emphasis Type="Italic">Nostoc sphaeroides</Emphasis> Kützing

Objectives

To assess the effects of light intensity and quality on the growth and phycobiliproteins (PBP) accumulation in Nostoc sphaeroides Kützing (N. sphaeroides).

Results

Dry weights, dry matter, protein, chlorophyll and PBP contents were higher under 90 μmol m^?2 s^?1 than under other intensities (both higher and lower). Phycocyanin and allophycocyanin increased with light intensity while phycoerythrin decreased. Fresh weights, protein and PBP contents increased at the highest rates under blue light. Red light resulted in higher values of dry matter, phycocyanin and chlorophyll a.

Conclusion

White light at 90 μmol m^?2 s^?1 or blue light 30 μmol m^?2 s^?1 were optimal for the growth and phycobiliprotein accumulation in N. sphaeroides.

     

Distribution of marine viruses and their potential hosts in Prydz Bay and adjacent Southern Ocean,Antarctic

Viruses play a key role in all marine ecosystems, and yet little is known of their distribution in Antarctic waters, especially in bathypelagic waters (>1000 m). In this study, the abundance and distribution of viruses and their potential hosts from the surface to the bottom of Prydz Bay, Antarctic, was investigated using flow cytometry. Viruses and autotrophs were abundant in nearshore and continental shelf waters, while heterotrophic bacteria and picoeukaryotes were abundant in offshore waters. Virus and bacteria abundances generally decreased with increasing depth but increased slightly just above the seafloor. Within the water column, maximum virus numbers coincided with the maximum values of chlorophyll a (when greater than 0.1 μg l^?1), in the surface and subsurface (25 m). In the open ocean, however, virus abundance usually correlated with bacterial abundance at greater depths (50, 300 and 500 m) where the surface chlorophyll a concentration was lower than 0.1 μg l^?1. Viral abundance was correlated with the host cell abundance, and this was different in different pelagic zones (bacteria and autotrophs (i.e., chlorophyll a concentration) in the epipelagic waters, picoeukaryotes and bacteria in mesopelagic waters and bacteria in bathypelagic waters). Principle component analysis and Pearson correlation analysis indicated that there was a close relationship between virus abundance and chlorophyll a, bacteria and nutrients (NO₂ + NO₃, phosphate and silicate), and picoeukaryote abundance was mainly correlated with water depth and salinity.     

Bio-optical characterization of selected cyanobacteria strains present in marine and freshwater ecosystems

The optical properties, i.e., absorption and scattering spectra of ten strains of cyanobacteria from the Baltic Sea and Pomeranian lakes (Aphanizomenon flos-aquae KAC 15, Microcystis aeruginosa CCNP 1101, Anabaena sp. CCNP 1406, Synechocystis salina CCNP 1104, Phormidium sp. CCNP 1317, Nodularia spumigena CCNP 1401, Synechococcus sp. CCNP 1108, Nostoc sp. CCNP 1411, Cyanobacterium sp. CCNP 1105, Pseudanabaena cf. galeata CCNP 1312) grown under low light conditions were investigated. Moreover, the chlorophylls, carotenoids, and phycobilin composition as well as the size structure of chosen cyanobacteria were measured. Studied species revealed high diversity both in optical properties with the absorption spectra similarity index ranging from 0.67 to 0.94 and the pigment composition. The chlorophyll-specific absorption coefficient at 440 nm a _ph *(440) varied between 0.017 and 0.065 m² mg^?1. The influence of the package effect was only observed in the case of large filamentous cyanobacteria like N. spumigena or Nostoc sp. Interestingly, the package effect factor Q _a *(675) for large-celled Anabaena sp. was 0.92. Besides chlorophyll a, only echinenone, β-carotene, and phycocyanin were present in all analyzed cyanobacteria strains. Zeaxanthin, which is widely used as a marker pigment for cyanobacteria, was absent in the toxic N. spumigena and Anabaena sp., which are the species that occur in the Baltic Sea most frequently causing summer cyanobacterial blooms. The investigation also showed that the sample preservation technique can introduce some major errors within the absorption band affected by the phycocyanin absorption.     

Seasonal variation and diet quality among Spanish people aged over 55 years

There is evidence supporting the importance of a healthy diet; however, there are few studies analyzing the seasonal variation of food intake. The present study was aimed to evaluate seasonal variation of food and energy intake in Spanish elderly also to investigate diet quality based on the Healthy Eating Index (HEI) score. From a cross-sectional study, 28 individuals (39% males) aged over 55 years volunteered for a longitudinal follow-up. Dietary assessment was evaluated through 24-h dietary recalls. Energy and nutrient intake were calculated using DIAL software. Furthermore, diet quality was measured using HEI. Data was analyzed considering the interaction of sex, age, fitness status, and body composition. Cereals intake was significantly lower in summer than in winter and autumn (both p?<?0.05); whereas, drinks intake was significantly higher in summer than in winter, spring, and autumn (all p?<?0.01). Daily energy intake was significant higher in spring than in summer, and in autumn than in summer (p?<?0.05), and energy intake from lunch was also statistically higher in spring than in summer (p?<?0.01). The HEI was classified as good; however, a negative and significant association was observed between HEI and cholesterol, alcohol, and monounsaturated fatty acids intake (p?<?0.01). Cereals and drinks intake and total daily energy intake changed according to seasons. This should be considered in nutritional studies. Diet quality seems not to be affected by these seasonal changes, and HEI did not show a good association with the majority of foods and macro- and micronutrients.     

Parasitism Rate of <Emphasis Type="Italic">Habrobracon hebetor</Emphasis> to <Emphasis Type="Italic">Ephestia kuehniella</Emphasis> Larvae: Residual Effect of Deltamethrin,Fenvalerate and Azadirachtin

Sublethal concentrations of chemical insecticides may cause changes in some behavioral characteristics of natural enemies such as functional responses. The residual effect of three synthetic insecticides including deltamethrin, fenvalerate and azadirachtin were studied on functional response of Habrobracon hebetor Say to Ephestia kuehniella Zeller larvae. Seven host densities (2, 4, 8, 16, 32, 64 and 96) were used during a 24 h period. The resulting data were appropriately fit to Type II functional response models in all treatments: (1) control (0.0916 h^?1; and T _h  = 0.2011 h); (2) deltamethrin (a = 0.0839 h^?1; and T _h  = 0.3560 h); (3) fenvalerate (a = 0.0808 h^?1 and T _h  = 0.3623 h); and (4) azadirachtin (a = 0.0900 h^?1 and T _h  = 0.2042 h). Maximum theoretical parasitism rate (T/T _h ) was 119.34 estimated for control wasps. There was no significant difference between the values of attack rates (a and a + D _a ) in all treatments while the handling time was statistically affected in female wasps treated with fenvalerate. Our findings will be useful in safe application of these insecticides in pest management programmes.     

Comparative study of daytime and nighttime sap flow of <Emphasis Type="Italic">Populus euphratica</Emphasis>

In order to quantify and characterize the variance in desert riparian forest tree sap flow, we measured the sap flow from Populus euphratica and compared the daytime and nighttime patterns and responses to environmental variables. Results showed that daytime sap flow velocity was significantly higher (P?<?0.05). Daytime and nighttime mean sap flow velocities were 7.65 and 4.01 cm h^?1 in spring, 21.38 and 9.60 cm h^?1 in summer, and 11.04 and 5.21 cm h^?1 in autumn, respectively. Moreover, results indicated that the stoma remained partially open (15% minimum) throughout the night, providing sufficient evidence for the existance of nighttime transpiration. The vapor pressure deficit (VPD), stomatal conductance (Cs), photosynthetically active radiation (PAR), air temperature (Ta), wind speed (WS), and soil moisture (θ) all had significant positive effects on P. euphratica sap flow velocity (P?<?0.05). Furthermore, the relationship between daytime sap flow velocity and VPD showed clockwise hysteresis, while the relationship between nighttime sap flow velocity and VPD showed counter-clockwise hysteresis. It was evident that PAR and VPD were the key factors impacting daytime sap flow velocity, while Cs and θ were the key factors impacting nighttime sap flow velocity. Furthermore, linear regression results showed that daytime sap flow had a significant positive effect on nighttime sap flow throughout the growing season (P?<?0.05).     

Effect of Some Honeybee Diseases on Seasonal Mortality of <Emphasis Type="Italic">Apis mellifera intermissa</Emphasis> in Algeria Apiaries

With a view to identify the pathogens and to establish the role of these pathogens in regulation of the density of honey bee population occurring in the apiaries of the area concerned samples of honeybee were collected from the beekeepers in some parts of central Algeria It is revealed that Nosema sp., Varroa destrutor, Peanibacillus larvae are associated with the disease manifestation in honey bees. The presence of Nosema sp., Varroa destrutor, Peanibacillus larvae was analyzed using standard OIE methods. Spores of Paenibacillus larvae were detected in 56.6 % in winter 52.32 % in spring. 29.33 % in autumn and 11.25 % in summer. Nosema infestation was recorded in 47.91 % bee individuals during spring. Varroa infestation rate was maximum 12.57 % in summer and lowest 3.44 % in spring. Analysis of data indicates that Boumerdes and Tipaza, diseases induced mortality exceeds 10 % in honeybee. There exists a significant correlation between Nosema disease and mortalities in honeybees. Seasons play significant role, irrespective of pathogens, in disease manifestation.     

Effects of macrophyte leachate on <Emphasis Type="Italic">Anabaena</Emphasis> sp. and <Emphasis Type="Italic">Chlamydomonas moewusii</Emphasis> growth in freshwater tropical ecosystems

This study reports on the effects of dissolved organic matter (DOM) derived from the aquatic macrophyte Pistia stratiotes (collected from a tropical reservoir) on the mixotrophic growth of two phytoplankton species (Chlamydomonas moewusii and Anabaena sp.). The DOM from P. stratiotes had a mainly aliphatic structure, low molecular weight, low cellulose and lignin content and high carbon content. The addition of DOM (5% v/v) significantly decreased the growth rate of Anabaena sp. but increased the chlorophyll a concentration of C. moewusii. Higher light intensity (100 versus 30 µmol m^?2 s^?1) was important for Anabaena sp., increasing its growth rate and chlorophyll content. The use of DOM from P. stratiotes to mitigate cyanobacterial blooms should be further explored in future studies.     

Abscisic Acid-Induced Starch Accumulation in Bioenergy Crop Duckweed <Emphasis Type="Italic">Spirodela polyrrhiza</Emphasis>

Spirodela polyrrhiza, a fast-growing duckweed with high starch and low lignin content, shows promise as a feedstock for bioenergy. Abscisic acid (ABA) is a biological hormone that controls plant growth and stress response. The effects of different ABA concentrations (0, 1.0 × 10^?5, 1.0 × 10^?4, 1.0 × 10^?3, 1.0 × 10^?2, and 1.0 × 10^?1 mg/L) on duckweed biomass growth, carbon dioxide fixation, formation of photosynthetic pigments (Chlorophyll a (Chla), Chlorophyll b (Chlb), and carotenoids), the activities of soluble starch synthase (SSS) and starch branching enzyme (SBE), and the starch content of biomass were investigated in this study. ABA at concentrations lower than 1.0 × 10^?3 mg/L promoted carbon dioxide fixation, whereas it inhibited carbon dioxide fixation at concentrations over 1.0 × 10^?3 mg/L. ABA enhanced SSS and SBE activities at concentrations lower than 1.0 × 10^?2 mg/L. ABA treatment increased the content of Chla, Chlb, and carotenoids and resulted in the enhancement of starch content. Chla content gradually increased with the increasing concentration of ABA (1.0 × 10^?5 to 1.0 × 10^?2 mg/L). After culturing for 10 days, starch content in 1.0 × 10^?2 mg/L ABA medium reached 35.3% of dry weight (DW), which was the highest level in this study. This suggests that there is a great potential to develop a technology to increase starch accumulation in duckweed which can be used as an alternative to corn, sugarcane, or other food crops as a starch source.     

Primary production of aquatic macrophytes and their epiphytes in two shallow lakes (Peipsi and Võrtsjärv) in Estonia

In shallow lakes with large littoral zones, epiphytes and submerged macrophytes can make an important contribution to the total annual primary production. We investigated the primary production (PP) of phytoplankton, submerged macrophytes, and their epiphytes, from June to August 2005, in two large shallow lakes. The production of pelagic and littoral phytoplankton and of the dominant submerged macrophytes in the littoral zone (Potamogeton perfoliatus in Lake Peipsi and P. perfoliatus and Myriopyllum spicatum in Lake Võrtsjärv) and of their epiphytes was measured using a modified ¹⁴C method. The total PP of the submerged macrophyte area was similar in both lakes: 12.4 g C m^?2 day^?1 in Peipsi and 12.0 g C m^?2 day^?1 in Võrtsjärv. In Peipsi, 84.2% of this production was accounted for by macrophytes, while the shares of phytoplankton and epiphytes were low (15.6 and 0.16%, respectively). In Võrtsjärv, macrophytes contributed 58%, phytoplankton 41.9% and epiphytes 0.1% of the PP in the submerged macrophyte area. Epiphyte production in both lakes was very low in comparison with that of phytoplankton and macrophytes: 0.01, 5.04, and 6.97 g C m^?2 day^?1, respectively, in Võrtsjärv, and 0.02, 1.93, and 10.5 g C m^?2 day^?1, respectively, in Peipsi. The PP of the littoral area contributed 10% of the total summer PP of Lake Peipsi sensu stricto and 35.5% of the total summer PP of Lake Võrtsjärv.