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Growth of Chlorella miniata, a green microalga was investigated during this study under various temperature and light intensity values with the purpose of determining growth rate changes of the microalgae with cultivation parameters, experiments were carried out using airlift photobioreactors with a study volume of 6 L. Culturing conditions were between 66 and 385 mu mol photon m(-2) s(-1) and between 14 and 30 degrees C for light intensity and ambient temperature, respectively. Acquired data were then used to test various mathematical models for coherency with experimental results. Aiba Model for light intensity and Skewed Normal Distribution Model for temperature parameters performed superior compared to the rest of the mathematical models used during the study. Utilizing both mathematical models a novel model was deduced to express effects of both light intensity and temperature parameters in combination on algal growth. Then the developed model was used to calculate the optimum growth condition of the species. The proposed mathematical model showed good coherency with experimental data and an average relative error of 1.97% for both temperature and light intensity effects on algal growth. The theoretical optimum temperature and light intensity for the maximum specific growth rate were calculated to be 22.43 degrees C and 291.5 mu mol photon m(-2) s(-1) respectively.

International audience; An integrated screening approach was developed to assess the potential of the Botryococcus genus for the production of lipids for biofuel application (hydrocarbons and triacylglycerols). The strategy developed in this study permitted to rigorously measure mandatory parameters for the determination of strain performance – i.e. growth rate and oil content. For that purpose, mini-photobioreactors run in parallel were used together with an exhaustive lipid class analysis. The quantitative productivity measurements indicated that the ten screened strains presented very different patterns in the conditions of PBR culture, firstly run in batch, and secondly in continuous mode. Indeed, with the applied setup, only four strains presented biomass productivities close to that previously measured for the reference strain 807/1 (between 74 and 307 mg L−1 day−1 of biomass for the tested strains). HC productivity obtained under continuous light (∼14 mg L−1 day−1) was close to that measured for the strain 807/1 (∼20 mg L−1 day−1), confirming B. braunii tested strains potential for biofuel application. The analysis of the lipid chemodiversity revealed moreover that this genus should be further investigated for its polar lipids, as it suggests potential pharmaceutical applications such as production of antitumorals or immunosuppressors.

Resource competition theory predicts that the outcome of competition for two nutrients depends on the ratio at which these nutrients are supplied. Yet there is considerable debate whether nutrientratios or absolute nutrient loads determine the species composition of phytoplankton and plant communities. Here we extend the classical resource competition model for two nutrients by includinglight as additional resource. Our results suggest the nutrientload hypothesis, which predicts that nutrient ratios determine the species composition in oligotrophic environments, whereas nutrientloads are decisive in eutrophic environments. The underlying mechanism is that nutrient enrichment shifts the species interactions from competition for nutrients to competition for light, which favors the dominance of superior light competitors overshadowing all other species. Intermediate nutrient loads can generate high biodiversity through a fine-grained patchwork of two-species and three-species coexistence equilibria. Depending on the species traits, however, competition for nutrients and light may also produce multiple alternative stable states, suppressing the predictability of the species composition. The nutrient-load hypothesis offers a solution for several discrepancies between classical resource competition theory and field observations, explains why eutrophication often leads to diversity loss, and provides a simple conceptual framework for patterns of biodiversity and community structure observed in nature.

We investigate biological mechanisms that generate oscillations and chaos in multispecies competition models. For this purpose, we use a competition model concerned with competition for abiotic essential resources. Because phytoplankton and plants consume quite a number of abiotic essential resources, the model is particularly relevant for phytoplankton communities and terrestrial vegetation. We show that the predicted dynamics depend crucially on the relationship between the resource requirements and the resource consumption characteristics of the species. More specifically, the model predicts that competition generates (1) stable coexistence if species consume most of the resources for which they have high requirements, (2) oscillations and chaos if species consume most of the resources for which they have intermediate requirements, and (3) competitive exclusion with a winner that depends on the initial conditions if species consume most of the resources for which they have low requirements. The theoretical predictions are compared with available data on resource utilization patterns of phytoplankton species.

Biodiversity has both fascinated and puzzled biologists(1). In aquatic ecosystems, the biodiversity puzzle is particularly troublesome, and known as the 'paradox of the plankton'(2). Competition theory predicts that, at equilibrium, the number of coexisting species cannot exceed the number of limiting resources(3-6). For phytoplankton, only a few resources are potentially limiting: nitrogen, phosphorus, silicon, iron, light, inorganic carbon, and sometimes a few trace metals or vitamins. However, in natural waters dozens of phytoplankton species coexist(2). Here we offer a solution to the plankton paradox. First, we show that resource competition models(6-10) can generate oscillations and chaos when species compete for three or more resources. Second we show that these oscillations and chaotic fluctuations in species abundances allow the coexistence of many species on a handful of resources. This model of planktonic biodiversity may be broadly applicable to the biodiversity of many ecosystems. [KEYWORDS: Limited growth; competition; phytoplankton; communities limitation; hypothesis]