Outdoor culture system The two outdoor open culture systems used for cultivation are similar the one designed by Dr. Ivan Šetlík in the 1960s (Šetlík et al., 1970). They consists of a 35m2 inclined surface (inclination 2.5°) exposed to sunlight. The suspension flows on the surface due to the gravity before falling in a tank located downstairs. The suspension is then pumped to the roof by a hydraulic pump (1000 liters.h−1) to ensure a continuous cycle. Transverse laths are placed on the inclined surface in order to increase the thickness and the mixing of the suspension. Layer thickness increases from 26mm behind the lath to 44mm in front of the next lath. The suspension volume was 4000l at the beginning of the culture. The volume on the inclined surface was 1900l while the volume in the tank varied around a value of 2100l, depending of evaporation and rain.