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].