Problems in developing the biotechnology of algal biomass production

Summary The effects of environmental conditions (solar irradiance and temperature) and population density on the production of Spirulina biomass with brackish water are reported for cultures grown in outdoor ponds. Higher specific growth rates were observed at lower population densities. Lower growth rates were associated with limitation by light in dense cultures under optimum conditions in the summer. Seasonal variation in productivity was observed. In summer, light was the limiting factor, whereas in winter the low daytime temperature appeared to constitute the major limitation. The oxygen concentration in the culture can serve as a useful indicator of limiting factors and can also be used to estimate the extent of such limitations.     

Productivity and complementarity in grassland microcosms of varying diversity

Several researchers have hypothesized that, through various mechanisms, loss of species and functional group richness from a plant community will affect the magnitude and interannual variability of productivity. To test this hypothesis, I conducted a microcosm study of California grassland communities that differed in species richness. I grew cohorts of microcosms that simulated undisturbed grassland (in one year) and gopher-disturbed grassland (in two consecutive years). As the number of species per functional group decreased from 4 to 1, biomass production remained constant in all three cohorts. As species richness decreased from 16 to 1 (or 8 to 1, in either case including a drop in functional group richness), productivity declined in one of the cohorts. In this cohort, productivity of one polyculture marginally exceeded that of the most productive monoculture. Resource complementarity and a type of selection effect may have each contributed to the observed diversity-productivity relationships. Results suggest the existence of a selection effect that involves species that are highly productive in mixtures, rather than in monoculture. Over two seasons, species and functional group richness did not affect the interannual variability of biomass production. Comparisons of interannual changes in the productivity of monocultures and polycultures suggested that, in some polycultures, increased water availability might have relieved interspecific competition more than intraspecific competition. Based on results from this experiment and other manipulative experiments, I develop a framework to explain the relationship between species richness and productivity in terrestrial plant communities. The framework highlights the importance of environmental variation in shaping the diversity/productivity relationship.     

Progress on lipid extraction from wet algal biomass for biodiesel production

Lipid recovery and purification from microalgal cells continues to be a significant bottleneck in biodiesel production due to high costs involved and a high energy demand. Therefore, there is a considerable necessity to develop an extraction method which meets the essential requirements of being safe, cost‐effective, robust, efficient, selective, environmentally friendly, feasible for large‐scale production and free of product contamination. The use of wet concentrated algal biomass as a feedstock for oil extraction is especially desirable as it would avoid the requirement for further concentration and/or drying. This would save considerable costs and circumvent at least two lengthy processes during algae‐based oil production. This article provides an overview on recent progress that has been made on the extraction of lipids from wet algal biomass. The biggest contributing factors appear to be the composition of algal cell walls, pre‐treatments of biomass and the use of solvents (e.g. a solvent mixture or solvent‐free lipid extraction). We compare recently developed wet extraction processes for oleaginous microalgae and make recommendations towards future research to improve lipid extraction from wet algal biomass.     

Two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production

A two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production was studied, wherein high density heterotrophic cultures of Chlorellasorokiniana serve as seed for subsequent phototrophic growth. The data showed growth rate, cell density and productivity of heterotrophic C.sorokiniana were 3.0, 3.3 and 7.4 times higher than phototrophic counterpart, respectively. Hetero- and phototrophic algal seeds had similar biomass/lipid production and fatty acid profile when inoculated into phototrophic culture system. To expand the application, food waste and wastewater were tested as feedstock for heterotrophic growth, and supported cell growth successfully. These results demonstrated the advantages of using heterotrophic algae cells as seeds for open algae culture system. Additionally, high inoculation rate of heterotrophic algal seed can be utilized as an effective method for contamination control. This two-stage heterotrophic phototrophic process is promising to provide a more efficient way for large scale production of algal biomass and biofuels.     

Effect of the nonilluminated part of suspension on biomass production in an algal reactor

The production of algal biomass in the illuminated and nonilluminated part of the suspension in an algal reactor was analyzed with regard to the biological inertia of the algae. The calculations indicate a considerable effect of nonilluminated part of the reactor on algal biomass production. The intensity of suspension stirring affects biomass production only slightly.     

Calculation of biomass production in algal suspension layer illuminated from two sides

Equations were derived for biomass production in optically dense algal suspension under the limit conditions of low- and very high-intensity stirring. A formula was obtained for the concentration of algae which gives maximum production at a given intake of radiation energy.     

Grazer biomass correlates more strongly with production than with biomass of algal turfs on a coral reef

The biomass of large herbivorous grazing fish on the shallow reef crest of Myrmidon Reef, Great Barrier Reef, is 7.0 times that on the reef slope (15 m depth), and 2.3 times that on the reef flat. Biomass of algal turfs on the crest was only 1.4 and 1.0 times that on the slope and flat, respectively. In contrast, rate of production of algal turfs on the crest was 5.3 and 2.8 times that on the slope and flat, respectively. A multiple correlation between large grazer biomass, algal turf biomass, and algal turf production across the three zones showed that only rate of algal production correlated significantly with large grazer biomass (algal production p=0.007, algal biomass p=0.418). This result suggests that large grazers may aggregate in zones of highest algal turf production. The mechanisms by which fish respond to habitat-specific differences in food production remain unclear.     

Optimizing algal biomass production in an outdoor pond: a simulation model

A deterministic simulation model was developed to predict production rates of the marine prymnesiophyteIsochrysis galbana in an outdoor algal mass culture system. The model consists of photoadapation, gross photosynthesis and respiration sections. Actual physiological and biophysical laboratory data, obtained from steady state cultures grown under a wide range of irradiance levels, were used in calculating productivity. The resulting values were used to assess optimal operational parameters to maximize algal biomass production. The model predicted a yearly averaged production rate of 9.7 g C m^?2d^?1, which compared well with field data reported in the literature. The model evaluated the effect of pond depth and chlorophyll concentration on potential production rate in various seasons. The model predicted that a yearly averaged chlorophyll areal density of 0.65 g m^?2 will yield the maximal production rate. Chlorophyll areal density should be seasonally adjusted to give maximal production. This adjustment could be done either by changing pond depth or chlorophyll concentration. The model predicted that under optimal operational conditions, the diurnal respiration losses averaged 35% of gross photosynthesis. The calculated growth rate for maximal productivity ranged between 0.15 and 0.24 d^?1, suggesting an optimal hydraulic retention time of 6.7 and 4.2 d for various seasons.     

Endophytic fungal mutualists: seed-borne Stagonospora spp. enhance reed biomass production in axenic microcosms

Fungal endophytes mainly belong to the phylum Ascomycota and colonize plants without producing symptoms. We report on the isolation of seed-borne fungal endophytes from Phragmites australis (common reed) that were ascribed to the genus Stagonospora. Nested polymerase chain reaction (PCR) assays revealed that a Stagonospora sp. regularly colonized reed as shown for a period of three years. In spring, it was only detected in roots, whereas in autumn, it could frequently be found in all organs, including seeds. Microcosm experiments revealed that seeds harbored viable propagules of the fungus that colonized the developing germling, indicating vertical transmission. Endophytic growth was confirmed by immunofluorescence microscopy, reisolation of the fungus after surface sterilization, and PCR. Aseptic microcosms were established for studying fungal contributions towards host vitality. Several Stagonospora isolates enhanced reed biomass. Seed-borne endophytic Stagonospora spp. thus can provide improved vigor to common reed, which could be most important when seed-derived germlings establish new reed stands.     

Lagged effects of experimental warming and doubled precipitation on annual and seasonal aboveground biomass production in a tallgrass prairie

Global climate change is expected to result in a greater frequency of extreme weather, which can cause lag effects on aboveground net primary production (ANPP). However, our understanding of lag effects is limited. To explore lag effects following extreme weather, we applied four treatments (control, doubled precipitation, 4 °C warming, and warming plus doubled precipitation) for 1 year in a randomized block design and monitored changes in ecosystem processes for 3 years in an old‐field tallgrass prairie in central Oklahoma. Biomass was estimated twice in the pretreatment year, and three times during the treatment and posttreatment years. Total plant biomass was increased by warming in spring of the treatment year and by doubled precipitation in summer. However, double precipitation suppressed fall production. During the following spring, biomass production was significantly suppressed in the formerly warmed plots 2 months after treatments ceased. Nine months after the end of treatments, fall production remained suppressed in double precipitation and warming plus double precipitation treatments. Also, the formerly warmed plots still had a significantly greater proportion of C₄ plants, while the warmed plus double precipitation plots retained a high proportion of C₃ plants. The lag effects of warming on biomass did not match the temporal patterns of soil nitrogen availability determined by plant root simulator probes, but coincided with warming‐induced decreases in available soil moisture in the deepest layers of soil which recovered to the pretreatment pattern approximately 10 months after the treatments ceased. Analyzing the data with an ecosystem model showed that the lagged temporal patterns of effects of warming and precipitation on biomass can be fully explained by warming‐induced differences in soil moisture. Thus, both the experimental results and modeling analysis indicate that water availability regulates lag effects of warming on biomass production.     

Positive effect of shredders on microbial biomass and decomposition in stream microcosms

1. Animals play a major role in nutrient cycling via excretory processes. Although the positive indirect effects of grazers on periphytic algae are well understood, little is known about top‐down effects on decomposers of shredders living on leaf litter. 2. Nutrient cycling by shredders in oligotrophic forest streams may be important for the microbial‐detritus compartment at very small spatial scales (i.e. within the leaf packs in which shredders feed). We hypothesised that insect excretion may cause local nutrient enrichment, so that microorganism growth on leaves is stimulated. 3. We first tested the effect of increasing concentration of ammonium (+10, +20 and +40 μg NH₄⁺ L^?1) on fungal and bacterial biomass on leaf litter in a laboratory experiment. Then we performed two experiments to test the effect of the presence and feeding activity of shredder larvae. We used two species belonging to the trichopteran family Sericostomatidae: the Palaearctic Sericostoma vittatum and the Neotropical Myothrichia murina, to test the effect of these shredders on fungal and bacterial biomass and decomposition on leaves of Quercus robur and Nothofagus pumilio, respectively. All experiments were run in water with low ammonium concentrations (2.4 ± 0.34 to 14.47 ± 0.95 μg NH₄⁺ L^?1). 4. After 5 days of incubation, NH₄ concentrations were reduced to near‐ambient streamwater concentrations in all treatments with leaves. Fungal biomass was positively affected by increased ammonium concentration. On the other hand, bacteria abundance was similar in all treatments, both in terms of abundance (bacteria cells mg^?1 leaf DW) and biomass. However, there was a tendency towards larger mean cell size in treatments with 20 μg NH₄ L^?1. 5. In the experiment with S. vittatum, fungal biomass in the treatment with insects was more than twice that in the control after 15 days. Bacteria were not detected in treatments with insects, where hyphae were abundant, but they were abundant in treatments without larvae. In the decomposition experiment run with M. murina, leaf‐mass loss was significantly higher in treatments with larvae than in controls. 6. Our hypothesis of a positive effect of shredders on fungal biomass and decomposition was demonstrated. Insect excretion caused ammonium concentration to increase in the microcosms, contributing to microbial N uptake in leaf substrata, which resulted in structural and functional changes in community attributes. The positive effect of detritivores on microbes has been mostly neglected in stream nutrient‐cycling models; our findings suggest that this phenomenon may be of greater importance than expected in stream nutrient budgets.     

The role of complementarity and selection effects in P acquisition of intercropping systems

Plant and Soil - How nitrogen deposition and increasing precipitation would affect leaf nutrient concentration and internal nutrient cycling of desert plants is still unclear. The aim of our study...     

Grazing and nutrient influences of Daphnia and Eudiaptomus on phytoplankton in laboratory microcosms

In two experiments, top-down and bottom-up influences of theherbivorous crustaceans Daphnia pulicaria and Eudiaptomus grac$$$loideson phytoplankton were compared in laboratory microcosms. Ina long-term experiment (63 days), both grazers were able toestablish populations. The Daphnia population exerted strongergrazing pressure, whereas Eudiaptomus fed more selectively.Daphnia retained relatively more phosphorus (P) and thus causedalgal P limitation; with Eudiaptomus as a grazer, both nitrogen(N) and P remained limiting. In a short-term experiment (1 day),N and P release rates and algal-specific grazing rates by bothconsumers were measured. In this experiment, the increase inconcentrations of soluble mineral nutrients (     

The effect of temperature and algal biomass on bacterial production and specific growth rate in freshwater and marine habitats

We analyzed heterotrophic, pelagic bacterial production and specific growth rate data from 57 studies conducted in fresh, marine and estuarine/coastal waters. Strong positive relationships were identified between 1) bacterial production and bacterial abundance and 2) bacterial production and algal biomass. The relationship between bacterial production and bacterial abundance was improved by also considering water temperature. The analysis of covariance model revealed consistent differences between fresh, marine and estuarine/coastal waters, with production consistently high in estuarine/coastal environments. The log-linear regression coefficient of abundance was not significantly different from 1.00, and this linear relationship permitted the use of specific growth rate (SGR in day⁻¹) as a dependent variable. A strong relationship was identified between specific growth rate and temperature. This relationship differed slightly across the three habitats. A substantial portion of the residual variation from this relationship was accounted for by algal biomass, including the difference between marine and estuarine/coastal habitats. A small but significant difference between the fresh- and saltwater habitats remained. No significant difference between the chlorophyll effect in different habitats was identified. The model of SGR against temperature and chlorophyll was much weaker for freshwater than for marine environments. For a small subset of the data set, mean cell volume accounted for some of the residual variation in SGR. Pronounced seasonality, fluctuations in nutrient quality, and variation of the grazing environment may contribute to the unexplained variation in specific growth.     

Rice biomass production and carbon cycling in 13CO2 pulse-labeled microcosms with different soils under submerged conditions

Aims

Rice fields are an important source for the greenhouse gas methane. Plants play an essential role in carbon supply for soil microbiota, but the influence of the microbial community on carbon cycling is not well understood.

Methods

Microcosms were prepared using sand-vermiculite amended with different soils and sediments, and planted with rice. The microcosms at different growth stages were pulse-labeled with ¹³CO₂ followed by tracing ¹³C in plant, soil and atmospheric carbon pools and quantifying the abundance of methanogenic archaea in rhizosphere soil.

Results

Overall,?>85 % of the freshly assimilated carbon was allocated in aboveground plant biomass, approximately 10 % was translocated into the roots and?4, but emission of ¹³C-labeled CH₄ started immediately and ¹³C enrichment revealed that plant-derived carbon was an important source for methanogenesis. The results further demonstrated that carbon assimilation and translocation processes, microbial abundance and gas emission were not only affected by the plant growth stage, but also by the content and type of soil in which the rice plants grew.

Conclusions

The study illustrates the close ties between plant physiology, soil properties and microbial communities for carbon turnover and ecosystem functioning.     

Phycoremediation coupled production of algal biomass,harvesting and anaerobic digestion: Possibilities and challenges

Biogas produced from anaerobic digestion is a versatile and environment friendly fuel which traditionally utilizes cattle dung as the substrate. In the recent years, owing to its high content of biodegradable compounds, algal biomass has emerged as a potential feedstock for biogas production. Moreover, the ability of algae to treat wastewater and fix CO₂ from waste gas streams makes it an environmental friendly and economically feasible feedstock. The present review focuses on the possibility of utilizing wastewater as the nutrient and waste gases as the CO₂ source for algal biomass production and subsequent biogas generation. Studies describing the various harvesting methods of algal biomass as well as its anaerobic digestion have been compiled and discussed. Studies targeting the most recent advancements on biogas enrichment by algae have been discussed. Apart from highlighting the various advantages of utilizing algal biomass for biogas production, limitations of the process such as cell wall resistivity towards digestion and inhibitions caused due to ammonia toxicity and the possible strategies for overcoming the same have been reviewed. The studies compiled in the present review indicate that if the challenges posed in translating the lab scale studies on phycoremediation and biogas production to pilot scale are overcome, algal biogas could become the sustainable and economically feasible source of renewable energy.     

Effects of algal diversity on the production of biomass in homogeneous and heterogeneous nutrient environments: a microcosm experiment

Background

One of the most common questions addressed by ecologists over the past decade has been-how does species richness impact the production of community biomass? Recent summaries of experiments have shown that species richness tends to enhance the production of biomass across a wide range of trophic groups and ecosystems; however, the biomass of diverse polycultures only rarely exceeds that of the single most productive species in a community (a phenomenon called ‘transgressive overyielding’). Some have hypothesized that the lack of transgressive overyielding is because experiments have generally been performed in overly-simplified, homogeneous environments where species have little opportunity to express the niche differences that lead to ‘complementary’ use of resources that can enhance biomass production. We tested this hypothesis in a laboratory experiment where we manipulated the richness of freshwater algae in homogeneous and heterogeneous nutrient environments.

Methodology/Principal Findings

Experimental units were comprised of patches containing either homogeneous nutrient ratios (16∶1 nitrogen to phosphorus (N∶P) in all patches) or heterogeneous nutrient ratios (ranging from 4∶1 to 64∶1 N∶P across patches). After allowing 6–10 generations of algal growth, we found that algal species richness had similar impacts on biomass production in both homo- and heterogeneous environments. Although four of the five algal species showed a strong response to nutrient heterogeneity, a single species dominated algal communities in both types of environments. As a result, a ‘selection effect’–where diversity maximizes the chance that a competitively superior species will be included in, and dominate the biomass of a community–was the primary mechanism by which richness influenced biomass in both homo- and heterogeneous environments.

Conclusions/Significance

Our study suggests that spatial heterogeneity, by itself, is not sufficient to generate strong effects of biodiversity on productivity. Rather, heterogeneity must be coupled with variation in the relative fitness of species across patches in order for spatial niche differentiation to generate complementary resource use.