2.1. Simulation of S. obliquus sp. C1S biomass productivity in different ecoregions of South America
Previous studies suggested that the average algal productivity in summer (high productivity season) and winter (low productivity season) could be a good estimator of average annual productivity in any region[14,25]. To further confirm the appropriateness of this simplification, we calculated the S. obliquus average productivity of biomass, lipids or carbohydrates in the four seasons in Buenos Aires, La Quiaca, Posadas (Argentina) and Fortaleza (Brazil) and compared them against the average values considering only summer and winter (Figure S1, Supporting information). Strong positive correlations (r = 0.86; 0.87; or 0.96; P <0.0001, for biomass, carbohydrates or lipids, respectively) suggested that a simplified model based on summer and winter productivities would provide a good estimation for mean annual productivities across a broad range of simulated-climates.
Figure 1 shows the average summer and winter biomass productivity in 20-cm deep simulated ponds of cultures supplemented with CO2. The calculated mean annual productivities were 16.76 ± 1.88; 13.72 ± 3.11; 13.03 ± 1.39; 10.61 ± 2.43; 10.56 ± 3.70; and 7.36 ± 4.48 g · m- 2 · d-1 in Fortaleza (Brazil), Paita (Peru), Caracas (Venezuela), Posadas, Buenos Aires, and Comodoro Rivadavia (Argentina), respectively. The overall mean annual productivity in South America was 12 ± 4 g · m- 2 · d-1 (n=24 ).
Seasonal variability between summer and winter was lower in Tropical and Subtropical regions for summer to winter productivity ratios of 1.2:1; 1.4:1; 1.2:1; 1.5:1 in Fortaleza, Paita, Caracas, Posadas, respectively.
Our simulations suggest potential biomass productivities in summer, from 18.25 ± 0.54 g · m- 2 · d-1 to 11.24 ± 0.2 g · m- 2 · d-1 in Fortaleza (the highest in this study) and Comodoro Rivadavia (the lowest in this study), respectively and a large seasonality and low productivity in winter in Comodoro Rivadavia (3.49 ± 0.04 g · m- 2 · d-1).
Under nutrient-sufficient and short-cycle cultivation conditions,S. obliquus only presented low levels of lipids at 13.4 ± 2.9% (w/w) across these simulations. Only a minor increase in lipids accumulation was observed in the coldest condition analyze, which corresponded to Comodoro Rivadavia winter simulated-climate, at 22.57 ± 0.23% (w/w). Carbohydrates also remained at low levels across the study at about 29.3 ± 13.1% (w/w) and a mild tendency to increase in warmer conditions at 32.1 ± 2.7% and 34.4 ± 4.4%, in the summer simulated- climate of Paita and Fortaleza, respectively (Table S1, Supporting information).