Investigation of mixotrophic,heterotrophic, and autotrophic growth of Chlorella vulgaris under agricultural waste medium

Growth of Chlorella vulgaris and its lipid production were investigated under autotrophic, heterotrophic, and mixotrophic conditions. Cheap agricultural waste molasses and corn steep liquor from industries were used as carbon and nitrogen sources, respectively. Chlorella vulgaris grew remarkably under this agricultural waste medium, which resulted in a reduction in the final cost of the biodiesel production. Maximum dry weight of 2.62 g L^?1 was obtained in mixotrophic growth with the highest lipid concentration of 0.86 g L^?1. These biomass and lipid concentrations were, respectively, 140% and 170% higher than autotrophic growth and 300% and 1200% higher than heterotrophic growth. In mixotrophic growth, independent or simultaneous occurrence of autotrophic and heterotrophic metabolisms was investigated. The growth of the microalgae was observed to take place first heterotrophically to a minimum substrate concentration with a little fraction in growth under autotrophic metabolism, and then the cells grew more autotrophically. It was found that mixotrophic growth was not a simple combination of heterotrophic and autotrophic growth.     

AUTO-, HETERO-, AND MIXOTROPHIC GROWTH OF CHLAMYDOMONAS HUMICOLA (CMLOROIMIYCKAK) ON ACETATE1

Relative growth rate, isocitrate lyase activity, chlorophyll, protein, lipid, and soluble carbohydrate contents were investigated in Chlamydomonas humicola Lucksch during auto-, mixo-, and heterotrnphic growth. Mixotrophic cells have a relative growth rate of 1.66 d ^–1as compared to 0.78 d ^–1 and 0.21 d ^–1 for hetero- and autotrophic cells, respectively. Addition of acetate to autotrophic cells resulted in an increase in cell dry weight during the first day, followed by a rapid decrease and stabilization at 40 pg·cell ^–1. Cellular yield of mixotrophu cells, on a dry weight basis, was 6.6 times that of heterotrophic cells and 21.9 limes that of autotrophic ones. After 4 d, mixotrophic cells were characterized by higher chlorophyll (3.6% dry weight [d.w.]) and protein (58.6% d.w.) contents and lower lipid (4.8% d.w.) and soluble carbohydrate (1.3% d.w.) contents than those of autotrophic (2.6% d.w. chlorophyll, 31.0% d.w. protein, 10.2% d.w. lipid, and 6.5% d.w. soluble carbohydrate) and heterotrophic (1.5% d.w. chlorophyll, 36.9% d.w. protein, 5.6% d.w. lipid, and 6.0% d.w. soluble carbohydrate) cells. The ratio of chlorophyll a/b was highest in heterotrophic cells due to lower chlorophyll b content. Isocitrate lyase activity, a key enzyme in ecetate assimitation, could not be detected in autotrophic cells. Addition of 10 mM acetate to the culture medium of hetero- and mixotrophic cells resulted in increased isocitrate lyase activity with a maximum after 24 h, followed by a decline in activity over a 7-d period. After 7 d of growth, only 0.01 mM acetate was found in the culture medium of mixotrophic cells as compared to 3.2 mM in the medium of heterotrophic ones, from an initial concentration of 10 mM.     

Variation in Heterotrophic and Autotrophic Nitrifier Populations in Relation to Nitrification in Organic Soils

The occurrence of heterotrophic and autotrophic nitrifiers in Pahokee muck and the role of these organisms in the ecosystem were assessed by surveying their population densities under different field conditions and by observing the relationship of these populations with aerobic bacteria and soil moisture. Heterotrophic nitrifier populations varied from 2.0 × 10⁵ to 3.8 × 10⁶ bacteria per cm³ of muck in surface fallow (bare) Pahokee muck during the annual cycle. This population decreased 40-fold between the surface and the 60- to 70-cm depths of soil. Similar variations were noted with autotrophic nitrifier populations. Significant correlations were found between heterotrophic nitrifiers and both soil moisture and aerobic bacteria. These relationships did not exist for the autotrophic nitrifiers. In soil that had been heated to kill the autotrophic nitrifiers, while preserving a population of the heterotrophs, and then amended with sodium acetate or ammonium sulfate or both, no nitrate or nitrite accumulated, although significant increases in heterotrophic nitrifiers were detected. In unheated control soil, nitrate plus nitrite-N increased from 14.3 to 181 μg/g of wet soil, and 48 μg of nitrite-N per g was produced. These data suggest that the autotrophic nitrifiers were the sole population responsible for nitrification in Pahokee muck.     

EFFICIENCY OF GROWTH AND NUTRIENT UPTAKE FROM WASTEWATER BY HETEROTROPHIC,AUTOTROPHIC, AND MIXOTROPHIC CULTIVATION OF CHLORELLA VULGARIS IMMOBILIZED WITH AZOSPIRILLUM BRASILENSE1

Heterotrophic growth of microalgae presents significant economic advantages over the more common autotrophic cultivation. The efficiency of growth and nitrogen, phosphorus, and glucose uptake from synthetic wastewater was compared under heterotrophic, autotrophic, and mixotrophic regimes of Chlorella vulgaris Beij. immobilized in alginate beads, either alone or with the bacterium Azospirillum brasilense. Heterotrophic cultivation of C. vulgaris growing alone was superior to autotrophic cultivation. The added bacteria enhanced growth only under autotrophic and mixotrophic cultivations. Uptake of ammonium by the culture, yield of cells per ammonium unit, and total volumetric productivity of the culture were the highest under heterotrophic conditions when the microalga grew without the bacterium. Uptake of phosphate was higher under autotrophic conditions and similar under the other two regimes. Positive influence of the addition of A. brasilense was found only when light was supplied (autotrophic and mixotrophic), where affinity to phosphate and yield per phosphate unit were the highest under heterotrophic conditions. The pH of the culture was significantly reduced in all regimes where glucose was consumed, similarly in heterotrophic and mixotrophic cultures. It was concluded that the heterotrophic regime, using glucose, is superior to autotrophic and mixotrophic regimes for the uptake of ammonium and phosphate. Addition of A. brasilense positively affects the nutrient uptake only in the two regimes supplied with light.     

Isolation and Characterization of Taiwanese Heterotrophic Microalgae: Screening of Strains for Docosahexaenoic Acid (DHA) Production

Marine heterotrophic microalgal species which are potentially rich in docosahexaenoic acid (DHA, C22:6n−3) have been found in Taiwan; however, there was a lack of detailed analysis and characterization of these indigenous algae which is needed for the development of commercial applications. Hence, the objective of this study was to screen DHA-rich heterotrophic microalgae species indigenous to Taiwan for commercial purposes. Heterotrophic microalgae from a variety of marine habitats were isolated, cultivated, and then identified according to their 18S rRNA gene sequences and morphological characteristics. A comparison was made of their fatty acid profiles, fatty acid content, and amount of biomass. For the strain with highest DHA yield, the optimal growth conditions were determined in order to establish the best fermentation conditions for scale-up. In this study, 25 heterotrophic microalgal strains were successfully isolated from marine habitats around Taiwan. All of the isolated strains showed a close phylogenic relationship with the Thraustochytriaceae family according to their 18S rRNA gene sequences. GC/MS analysis discerned seven distinctive fatty acid profiles of these strains, with the production of eicosapentaenoic acid (C20:5n−3) ranging from 0.02 to 2.61 mg L⁻¹, and DHA ranging from 0.8 to 18.0 mg L⁻¹. An Aurantiochytrium strain BL10 with high DHA production was subsequently chosen for further manipulation. Under optimal growth conditions it could produce up to 59.0 g of dry biomass per liter of culture, with dry biomass containing 73% total fatty acid and 29% DHA, revealing BL10 as an excellent source of microbial DHA.     

川中丘陵区冬水田种植模式转旱作土壤呼吸组分特征及碳平衡

冬水田-水稻是川中丘陵区传统的稻田种植模式,冬水田种植模式转变是实现多熟种植及机械化的重要途径。为探究冬水田-水稻种植模式转旱作过程中作物季及休闲期土壤呼吸速率及其组分构成,试验设置冬水田-水稻转旱作(FTD)、冬水田-水稻(FR)和冬闲田-玉米(FM)3种不同种植模式,采用根排除法和静态明箱-气相色谱法原位取样测定作物季及季后休闲期土壤呼吸及其组分,并通过测算净生态系统生产力(NEP)进而判断冬水田-水稻转旱作过程的农田系统碳汇强度。结果表明:(1)FTD显著提高了土壤总呼吸速率及其自养和异养呼吸速率,从而提高了其累积排放量(P<0.05)。与FR相比,FTD的土壤总呼吸及其自养和异养呼吸的累积排放量分别提高了13.14倍、11.32倍和15.56倍(P<0.05);与FM相比,FTD的土壤总呼吸及其自养和异养呼吸的累积排放量分别提高了70.56%、40.83%和115.47%(P<0.05)。(2)与FR和FM相比,FTD均降低了土壤呼吸及其组分的温度敏感性(Q₁₀),且土壤总呼吸的温度敏感性介于异养呼吸和自养呼吸之间。(3)FR,FM和FTD的净生态系统生产力(NEP)均为正值,其数值分别为7911.66 kg/hm²,5667.89 kg/hm²和1583.46 kg/hm²,均表现为大气CO₂的碳汇,但与FR与FM相比,FTD显著降低了其净生态系统生产力,呈现出较弱的碳汇。     

Glycollate production and excretion byAlcaligenes eutrophus

Autotrophic cultures of the facultative chemolithotrophAlcaligenes eutrophus have been found to excrete glycollate. This excretion was greatly stimulated by the incorporation of up to 20% (v/v) oxygen in the hydrogen used for gassing. The stimulatory effect of oxygen was prevented by the addition of 10% (v/v) CO₂ to the gassing mixture. Glycollate excretion only in the presence of oxygen was increased by the addition of 2-pyridyl-hydroxymethane sulphonic acid (HPMS), an inhibitor of glycollate oxidation, indicating that glycollate formation itself was stimulated by oxygen. No glycollate excretion by cultures grown heterotrophically on pyruvate was detected, either in the absence or presence of HPMS, under heterotrophic or autotrophic conditions.Extracts from autotrophic cells showed phosphoglycollate phosphatase and glycollate oxidoreductase activities, which were considerably lower in extracts prepared from pyruvate- or fructose-grown (heterotrophic) cells. The increase in activity of both enzymes upon cell transfer from heterotrophic to autotrophic growth was prevented by chloramphenicol and resembled the induction ofd0ribulose 1,5-diphosphate carboxylase under the same conditions.Abbreviations DTE dithioerythritol - EDTA ethylenediamine tetraacetate - HPMS 2-pyridyl-hydroxymethane sulphonie acid - RuDP d-ribulose 1,5-diphosphate     

Effect of cytokinins on <Emphasis Type="BoldItalic">in vitro</Emphasis> development of autotrophism and acclimatization of <Emphasis Type="Italic">Annona glabra</Emphasis> L.

The role of cytokinins in the differentiation of the photosynthetic apparatus in micropropagated plants and their effect on the plant’s ability to transition from a heterotrophic to an autotrophic condition during acclimatization was investigated. Annona glabra L. shoots were cultured on woody plant medium supplemented with sucrose and different cytokinins to evaluate leaf tissue for chloroplast development, chloroplast numbers, photosynthetic pigmentation, total photosynthetic potential, and soluble sugar content. Plants were transferred to the rooting medium in the presence or absence of sucrose and then acclimatized. Kinetin and benzyladenine (BAP) stimulated chloroplast differentiation. Inclusion of zeatin in the medium induced the formation of greater numbers of chloroplasts in the leaves, while plants cultivated in the presence of only kinetin and BAP demonstrated greater chlorophyll a and carotenoid content. The use of kinetin and BAP during in vitro culture promoted accumulation of dry matter during the acclimatization phase, especially in plants rooted under autotrophic conditions (without sucrose). Kinetin and BAP promoted development of more leaf area and greater plant survival rates in plant acclimatization on both autotrophic and heterotrophic media. The inhibitory effects of thidiazuron on the differentiation of chloroplasts, accumulation of chlorophyll a, and photosynthetic potential were examined.     

Biomass and lipid productivities of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> under autotrophic,heterotrophic and mixotrophic growth conditions

Biomass and lipid productivities of Chlorella vulgaris under different growth conditions were investigated. While autotrophic growth did provide higher cellular lipid content (38%), the lipid productivity was much lower compared with those from heterotrophic growth with acetate, glucose, or glycerol. Optimal cell growth (2 g l⁻¹) and lipid productivity (54 mg l⁻¹ day⁻¹) were attained using glucose at 1% (w/v) whereas higher concentrations were inhibitory. Growth of C. vulgaris on glycerol had a similar dose effects as those from glucose. Overall, C. vulgaris is mixotrophic.     

Carbon assimilation pathways in sulfate-reducing bacteria II. Enzymes of a reductive citric acid cycle in the autotrophic Desulfobacter hydrogenophilus

The strict anaerobe Desulfobacter hydrogenophilus is able to grow autotrophically with CO₂, H₂, and sulfate as sole carbon and energy sources. The generation time at 30°C under autotrophic conditions in a pure mineral medium was 15 h, the growth yield was 8 g cell dry mass per mol sulfate reduced to H₂S. Enzymes of the autotrophic CO₂ assimilation pathway were investigated. Key enzymes of the Calvin cycle and of the acetyl CoA pathway could not be found. All enzymes of a reductive citric acid cycle were present at specific activities sufficient to account for the observed growth rate. Notably, an ATP-citrate lyase (1.3 mol · min^-1 · mg cell protein^-1) was present both in autotrophically and in heterotrophically grown cells, which was rapidly inactivated in the absence of ATP. The data indicate that in D. hydrogenophilus a reductive citric acid cycle is operating in autotrophic CO₂ fixation. Since other autotrophic sulfate reducers possess an acetyl CoA pathway for CO₂ fixation, two different autotrophic pathways occur in the same physiological group.Dedicated to Prof. H. G. Wood on the occasion of his 80th birthday     

Reduced inorganic sulfur oxidation supports autotrophic and mixotrophic growth of Magnetospirillum strain J10 and Magnetospirillum gryphiswaldense

Magnetotactic bacteria are present at the oxic–anoxic transition zone where opposing gradients of oxygen and reduced sulfur and iron exist. Growth of non‐magnetotactic lithoautotrophic Magnetospirillum strain J10 and its close relative magnetotactic Magnetospirillum gryphiswaldense was characterized in microaerobic continuous culture. Both strains were able to grow in mixotrophic (acetate + sulfide) and autotrophic (sulfide or thiosulfate) conditions. Autotrophically growing cells completely converted sulfide or thiosulfate to sulfate and produced 7.5 g dry weight per mol substrate at a maximum observed growth rate of 0.09 h^?1 for strain J10 and 0.07 h^?1 for M. gryphiswaldense. The respiratory activity for acetate was repressed in autotrophic and also in mixotrophic cultures, suggesting acetate was used as C‐source in the latter. We have estimated the proportions of substrate used for assimilatory processes and evaluated the biomass yields per mol dissimilated substrate. The yield for lithoheterotrophic growth using acetate as the C‐source was approximately twice the autotrophic growth yield and very similar to the heterotrophic yield, showing the importance of reduced sulfur compounds for growth. In the draft genome sequence of M. gryphiswaldense homologues of genes encoding a partial sulfur‐oxidizing (Sox) enzyme system and reverse dissimilatory sulfite reductase (Dsr) were identified, which may be involved in the oxidation of sulfide and thiosulfate. Magnetospirillum gryphiswaldense is the first freshwater magnetotactic species for which autotrophic growth is shown.     

Identification of sterols and alcohols produced by green algae of the generaChlorella andScenedesmus by means of gas chromatography—mass spectrometry

Sterols and alcohols isolated from a collection of industrially important fresh-water green algaeChlorella kessleri, Scenedesmus acuminatus, S. acutus andS. acutus var.Tomasclli cultivated heterotrophically or autotrophically under pilot plant conditions, were identified and quantified by gas chromatography — mass spectrometry. Previsously demonstrated sterols with double bonds in position 5 and 7 were detected. In addition, cholesta-5,7,22-trien-3 β-oI that had not yet been described in green algae was found inS. acutus. Alcohols were found only inC. kessleri cultivated under heterotrophic conditions. Some saturated and unsaturated alcohols were detected for the first time in green algae.     

Hydrogen sulfide removal by immobilized autotrophic and heterotrophic bacteria in the bioreactors

Summary Autotrophic Thiobacillus sp. CH11 and heterotrophic Pseudomonas putida CH11 were isolated from piggery waste water. Extensive tests, including removal action, removal efficiency, removal capacity, and adaptability to perturbed conditions were conducted on autotrophic and heterotrophic biofilters. The results clearly demonstrate the application potential of autotrophic and heterotrophic biofilters for the continuous H₂S removal under different perturbed conditions.     

Growth characteristics of the cyanobacterium Nostoc flagelliforme in photoautotrophic, mixotrophic and heterotrophic cultivation

Nostoc flagelliforme is a terrestrial cyanobacterium with high economic value. Dissociated cells separated from a natural colony of N. flagelliforme were cultivated for 7 days under either phototrophic, mixotrophic or heterotrophic culture conditions. The highest biomass, 1.67 g L⁻¹ cell concentration, was obtained under mixotrophic culture, representing 4.98 and 2.28 times the biomass obtained in phototrophic and heterotrophic cultures, respectively. The biomass in mixotrophic culture was not the sum as that in photoautotrophic and heterotrophic cultures. During the first 4 days of culture, the cell concentration in mixotrophic culture was lower than the sum of those in photoautotrophic and heterotrophic cultures. However, from the 5th day, the cell concentration in mixotrophic culture surpassed the sum of those obtained from the other two trophic modes. Although the inhibitor of photosynthetic electron transport DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] efficiently inhibited autotrophic growth of N. flagelliforme cells, under mixotrophic culture they could grow by using glucose. The addition of glucose changed the response of N.flagelliforme cells to light. The maximal photosynthetic rate, dark respiration rate and light compensation point in mixotrophic culture were higher than those in photoautotrophic cultures. These results suggest that photoautotrophic (photosynthesis) and heterotrophic (oxidative metabolism of glucose) growth interact in mixotrophic growth of N. flagelliforme cells.     

Effects of irradiance on diel and seasonal patterns of nutrient uptake by stream periphyton

1. Irradiance strongly affects the abundance of stream periphyton communities that in turn influence patterns of instream nutrient uptake. We examined relationships between irradiance and periphyton nutrient uptake taking into account diel and seasonal variation in ambient irradiance. 2. Uptake of dissolved N, P and C by periphyton as areal uptake (U) and demand (V_f) was determined under 11 irradiance levels (0–100% of ambient conditions) using shallow stream‐side experimental channels. Experiments were conducted once per season over one annual cycle with both day and night uptake rates assessed, together with periphyton biomass and autotrophic production rates. 3. No consistent diel variation in areal uptake or demand was detected for the predominant inorganic or total dissolved nutrients even at the highest irradiances. Lack of variation may indicate nutrient limitation, with photosynthetic sequestration and storage of C during the day for subsequent utilisation at night. Alternatively, oxygen consumption by photoautotrophs at night may stimulate compensatory heterotrophic uptake (e.g. denitrification). 4. In all seasons, release of dissolved organic N was detected during the day but to a lesser extent at night. This was not directly related to irradiance levels, indicating that heterotrophic metabolism (e.g. microbial decomposition) contributes to this phenomenon. 5. Areal uptake and demand for the predominant inorganic and total dissolved nutrients increased in response to increasing irradiance in some or all seasons, but rates were typically higher during the spring and summer. Saturation of areal uptake and demand at elevated irradiances was evident during the spring. demand was also saturated at higher irradiances in the summer and autumn. Maximum demand was comparable during spring and summer, but saturation occurred at lower irradiance in summer (24 h average 135–145 μmol m^?2 s^?1) relative to spring (312–424 μmol m^?2 s^?1), indicating more efficient nutrient uptake in summer. Higher total periphyton biomass in summer, but comparable autotrophic biomass (chlorophyll a), implies that heterotrophic metabolism may contribute to this greater efficiency. In spring, autotrophic biomass peaked at an irradiance level of 225 μmol m^?2 s^?1, also suggesting a role for heterotrophic metabolism in demand at higher irradiances. 6. The results of this study show that irradiance levels exert a strong influence on the nature and quantity of instream nutrient uptake with N demand saturated at elevated irradiance levels during the spring, summer and autumn. Our results also suggest that heterotrophic metabolism makes a measurable contribution to instream nutrient uptake even under higher irradiances that favour autotrophic activity.     

Comparison of biomass production and total lipid content of freshwater green microalgae cultivated under various culture conditions

The growth and total lipid content of four green microalgae (Chlorella sp., Chlorella vulgaris CCAP211/11B, Botryococcus braunii FC124 and Scenedesmus obliquus R8) were investigated under different culture conditions. Among the various carbon sources tested, glucose produced the largest biomass or microalgae grown heterotrophically. It was found that 1 % (w/v) glucose was actively utilized by Chlorella sp., C. vulgaris CCAP211/11B and B. braunii FC124, whereas S. obliquus R8 preferred 2 % (w/v) glucose. No significant difference in biomass production was noted between heterotrophic and mixotrophic (heterotrophic with light illumination/exposure) growth conditions, however, less production was observed for autotrophic cultivation. Total lipid content in cells increased by approximately two-fold under mixotrophic cultivation with respect to heterotrophic and autotrophic cultivation. In addition, light intensity had an impact on microalgal growth and total lipid content. The highest total lipid content was observed at 100 μmol m^?2s^?1 for Chlorella sp. (22.5 %) and S. obliquus R8 (23.7 %) and 80 μmol m^?2s^?1 for C. vulgaris CCAP211/11B (20.1 %) and B. braunii FC124 (34.9 %).     

Sequential heterotrophic/autotrophic cultivation – An efficient method of producing Chlorella biomass for health food and animal feed

Sequential heterotrophic/autotrophic cultivation method was investigated for production of high concentration of Chlorella biomass with high cellular protein and chlorophyll contents. By using autotrophic growth medium, which contains glucose as organic carbon source, for heterotrophic culture, the protein and chlorophyll contents of the cells could be increased by simply illuminating the culture broth and aerating with CO₂-enriched air at the end of the heterotrophic culture. A system was then constructed for continuous sequential heterotrophic/autotrophic production of algal biomass. The system was composed of the conventional mini-jar fermentor for the heterotrophic phase and a tubular photobioreactor for the autotrophic phase. The exhaust gas from the heterotrophic phase was used for aeration of the autotrophic phase in order to reduce the CO₂ emission into the atmosphere. With this system, it was possible to produce high Chlorella biomass concentration (14 g L-¹) containing 60.1% protein and 3.6% chlorophyll continuously for more than 640 h. During the steady state, about 27% of the CO₂ produced in the heterotrophic phase was re-utilized in the autotrophic phase. When the tubular photobioreactor was replaced with a 3.5-L internally illuminated photobioreactor, the productivity increased from 2 g L-¹ d-¹ to 4 g L-¹ d-¹. However, the chlorophyll content of the cells was lower due to the lower light supply coefficient of the photobioreactor. This revised version was published online in August 2006 with corrections to the Cover Date.     

寒温带岛状林沼泽土壤呼吸速率和季节变化

2011年生长季内利用静态箱-气相色谱法,研究了寒温带典型湿地白桦(Betula platyphylla)岛状林沼泽、兴安落叶松(Larix gmelinii)岛状林沼泽土壤呼吸速率的季节动态及其主要环境因子,利用壕沟隔断法对土壤呼吸各组分间的差异进行研究。结果表明:生长季白桦和兴安落叶松岛状林沼泽土壤呼吸速率具有明显的季节性规律,土壤呼吸总速率分别为368.60和312.46 mg m-2h-1,异养呼吸速率分别为300.57和215.70 mg m-2h-1,占土壤呼吸总速率的81.5%和69.0%;自养呼吸速率为68.03和96.76 mg m-2h-1,占土壤呼吸总速率的18.5%和31.0%。不同处理条件下的土壤呼吸在季节变化上表现基本一致,高峰期都发生在夏季;土壤呼吸与温度呈极显著相关性,但与土壤湿度的相关性较差。生长季白桦和兴安落叶松岛状林沼泽土壤呼吸总量分别为12.64和10.61 t/hm2。     

Differential growth and biochemical composition of photoautotrophic and heterotrophic <Emphasis Type="Italic">Isochrysis maritima</Emphasis>: evaluation for use as aquaculture feed

The growth and biochemical composition of photoautotrophic and heterotrophic Isochrysis maritima in 50 L of Walne’s medium were compared. Heterotrophic I. maritima fed with 0.02 M glucose had a 4.6-fold higher maximum cell density (38.17 ± 0.23 × 10⁶ cells mL^?1) than photoautotrophic cells (8.29 ± 0.70 × 10⁶ cells mL^?1). The carbohydrate content was slightly higher in heterotrophic cells at all growth stages (mid-exponential, 40.8%; early stationary, 48.3%; and late stationary, 47.6%), but there was no significant effect on the protein content under either trophic condition. The total saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) were higher under heterotrophic conditions than those under photoautotrophic conditions. However, because omega-3 PUFAs are the most essential element in feed nutrition, low results for eicosapentaenoic acid (EPA) (0.28 ± 0.06%) and docosahexaenoic acid (DHA) (3.22 ± 0.26%) in the heterotrophic cells compared to the photoautotrophic cells (EPA: 0.44 ± 0.11%; DHA: 8.58 ± 0.73%) plus a low omega-3/6 PUFAs ratio (heterotrophic: 0.16–0.47; photoautotrophic: 2.60–2.88) and high value of (SFA + MUFA)/PUFA (heterotrophic: 5.50–6.81; photoautotrophic: 2.64–3.60) showed that this species is not suitable for aquaculture feed when cultivated under heterotrophic conditions.     

RESPONSE TO PHOTOPERIOD AND TEMPERATURE BY SPARTINA ALTERNIFLORA (POACEAE) FROM NORTH CAROLINA AND SPARTINA FOLIOSA FROM CALIFORNIA

Seedlings of Spartina alterniflora Loisel. from Oregon Inlet, North Carolina were generally taller and produced significantly more culms and total dry weight than those of S. foliosa Trin. from two California populations (Alameda Beach and Marin County) in eight photoperiod-temperature treatments over a 17-wk period. Seedlings of S. alterniflora produced maximal biomass in 30–26 C whereas those of S. foliosa produced maximal biomass in 22–18 C, both under long-day conditions. The average photosynthesis rate for S. alterniflora (3.0 mg C g dry wt^−- hr^−-1) was 1.6 times higher than that for S. foliosa (1.9 mg C g dry wt^−-1 hr^−-1), but the dark respiration rates (0.3 and 0.4 mg C g dry wt^−-1 hr^−-1, respectively) were not significantly different. The proportion of rhizomes was greater under short than long-day conditions for both species in most temperature regimes. The average shoot soluble carbohydrate and starch concentrations were higher for S. foliosa (8.4 and 0.9%, respectively) than those for S. alterniflora (6.0 and 0.4%, respectively). The average rhizome soluble carbohydrate concentration (18%) for S. alterniflora under long-day conditions was significantly lower than that under short-day conditions (28%) and also lower than those for S. foliosa under both long (26%) and short-day (25%) conditions. Rhizome starch concentrations of S. alterniflora were significantly higher in the short than in most long-day temperatures and were generally higher for S. alterniflora than for S. foliosa under short-day conditions. The root starch concentration of S. alterniflora under short-day conditions (1.3%) was higher than that under long-day conditions (0.2%) and also higher than those of S. foliosa under both long (0.2%) and short-day (0.7%) conditions. The two species exhibited similar patterns of carbohydrate storage in belowground organs, similar flower initiation processes not under strict photoperiod control, and similar respiration rates, but significantly different photosynthetic rates and growth responses with S. alterniflora having the potential to be the more productive species.