|  |
Program |
 |
| |
 |
Special Session 1: Ecosystem under multiple stressors |
| |
|
|
Effect of UV radiation and phosphate supply on Trichodesmium
SS1-12-S
Wing Kwan Mak* , The Hong Kong University of Science and Technology
Pingping Qu, The University of Southern California
Zhu Zhu, Institute of Oceanology, Shanghai Jiao Tong University
David Allen Hutchins, The University of Southern California
Kunshan Gao, Xiamen University
Feixue Fu, The University of Southern California
Presenter Email: wkmakab@connect.ust.hk
|
| We examined the effect of ultraviolet A radiation (UVA, 320-400 nm) and inorganic phosphate (Pi) availability on two culture isolates of the N2 fixing cyanobacterium Trichodesmium, IMS101 and 2175. We measured the growth, nitrogen fixation and stoichiometric ratios following two weeks of incubation in treatments mimicking the natural intensity of UVA at 40m depth in the open ocean, versus controls without UVA. Both UVA treatments were maintained exponentially under both P-replete (Pi =10uM) and P-limited (P=0.5uM) conditions. We also studied the effects of UVB (280-320 nm) on the strains in a 6-day incubation. Our results show that 2175 has a higher tolerance to UVA irradiance and P-limitation. While the growth and nitrogen fixation rates of IMS101 were inhibited by UVA irradiance, those of 2175 did not show a significant change. Differing adaptations to P-limitation may be beneficial in tolerating UVA. Filaments were lengthened in IMS101, while shortened in 2175 under P-limitation. N:P and C:P of IMS101 increased, implying biochemical composition changes occurred, but the stoichiometric ratio of 2175 did not change. When phosphate was limiting, applying UVA irradiance did not further inhibit growth and nitrogen fixation of IMS101, but it further reduced the growth of 2175. This suggests the structural changes in IMS101 (e.g. longer filaments, biochemical changes) but not 2175 may be beneficial in tolerating UVA. For UVB experiments, both strains maintained growth in the first three days, while growth was inhibited from the fourth days onwards. Nitrogen fixation rates of both IMS101 and 2175 were significantly lower on Day 6, showing UVA and UVB caused different inhibitory effects on Trichodesmium. Our results suggest that natural UV radiation may have a significant negative impact on N2 fixation in the oligotrophic ocean, but also imply that there may be substantial variability in the sensitivity of different strains to UV inhibition. |
|
|
|
|