Compensation Of Phaeodactylum Tricornutum Under Ultraviolet Radiation And Darkness Stress

Phaeodactylum tricornutum that belongs to Bacillariophyta, Pennatae, Phaeodactylales, Phaeodactylum Bohl is the main contributor to the primary productivity in coastal waters; it is also an important algal species for aquaculture and the exploration of some valuable active substrates. Two types of experiment were conducted for Phaeodactylum tricornutum, one is the test for the stress of continuous darkness, and other one is the test of short time darkness stress under different ultraviolet radiation (UVR) condition. For the last test, three different light regimes were applied, which were normal light 4 days (L4), darkness 2 days (D2), and darkness 4 days (D4), respectively. Then each light treatment was further applied with five different UV radiations: no UVR (UVO), UVR 0.1 minutes (UV0.1), UVR 0.8 minutes (UVR0.8), UVR2 minutes (UV2), and UVR 5 minutes (UVR5). The cell density, biomass (chlorophyll a concentration), cell carbohydrate and protein contents were measured for each treatments. The results showed that: 1) Cell density, chlorophyll a concentration, and cell carbohydrate and protein contents decreased significantly in the 12 days darkness treatment. The cell density was 2.93 *10^5 cell/ml, which was only about 2.83% of the control. 2) Cell density, chlorophyll a concentration, and cell carbohydrate and protein contents of the UV0.1 and UV0.8 treatmentswere equal or above the control treatments, however, the values for UV2 and UV5 treatments were lower compared to control treatment. 3) Cell density, chlorophyll a concentration, and cell carbohydrate and protein contents of D2 treatment were equal or above the control treatment, but the D4 treatment had lower values compared to control treatment. 4) The index for all treatments reached to the maximum values right after the exponential growth phase, and it took longer time to reach as maximum value as the increase of the stress. 5) The understanding of the compensation of Phaeodactylum tricornutum under UV/darkness stress could provide the valuable information for big scale microalgae cultivation and the prevention for harmful algal blooms.