3.1. Simulation of S. obliquus sp. C1S biomass productivity in different ecoregions of South America
The geographical sites for simulations of microalgal potential productivity in this study were chosen to cover a broad range of mean irradiation, temperature and day length (Table 1 and Figure S2, Supporting information). This study prioritized coastal areas with potential access to seawater, considering that tropical and subtropical forests provide essential ecosystem services including natural biodiversity conservation and global climate change mitigation[27] (Figure S3, Supporting information).
The overall mean annual productivity in South America of 12 ± 4 g · m- 2 · d-1 fits very well previous estimations in other studies, regardless of differences in the strains used and culture systems. For example, extensive literature analyses performed by other researchers indicated that most commonly achieved annual productivities in raceway ponds in different regions of the world were 10 - 15 g · m- 2 ·d-1[8,9,12–15]. The model proposed by Moody and colleagues suggested an average world productivity of 9.4 g · m- 2 · d-1 forNannochloropsis cultivated in photobioreactors, and up to 15 g · m- 2 · d-1 in Brazil, Colombia and other non-South American regions [18]. Another study assessing the productivity of C. sorokiniana (DOE 1412) under climate-simulated conditions of Southern Florida indicated an average year-round biomass productivity of 15 g · m- 2· d-1 [25]. A more recent estimation of S. obliquus biomass productivity in photobiorreactors under Brazilian simulated-climate indicated a higher productivity of the Tropical Northern region of the country (Boa Vista) with an annual mean biomass productivity of 0.278 ± 0.01 g · L-1 · d-1[26].
We observed very low seasonal variability in biomass productivity in Tropical and Subtropical regions. The recent study by Siqueira and colleagues for S. obliquus biomass productivity under simulated-climate conditions of Northern Brazil indicated a low summer to winter productivity ratio of 1.3:1 [26]. This low seasonality would allow an almost year-round steady production in this vast region, surpassing NREL-DOE target of summer to winter productivity ratio of 3:1 [14]. The productivities estimated in this simulations would enable some commercial feasibility, after due optimizations and practical demonstrations on site. However, a large seasonality and low productivity in winter (i.e. 3.49 ± 0.04 g · m- 2 · d-1 in Comodoro Rivadavia) would pose a difficult-to-overcome limitation for year-round high productivity in the Southern part of the continent. Both, a similar low level accumulation of lipids [12.4 -17.0% (w/w)] and mild increase at lower temperatures in S. obliquus was also observed in a parallel study by Siqueira and colleagues [26].