Effect Of Iron On The Growth,distribution And Seasonal Dynamics Of Raphidiopsis Raciborskii And Staurastrum Spp.

Raphidiopsis raciborskii and Staurastrum spp.are common and dominate species in?sub?tropical reservoirs.The seasonal variation of iron supply potentially drive the seasonal succession of R.raciborskii and Staurastrum spp.Here,we carried out monoculture experiments and field investigation to evaluate the effect of iron on the growth,distribution and seasonal dynamics of them.In monoculture experiments,two strains,each from one represented species R.raciborskii and Staurastrum:R.raciborskii strain N8 and Staurastrum sp.strain FACHB-1449 were used for the culture experiment at 8 iron concentrations levels:from 0 mg/L to 1.378 mg/L.We investigated30 tropical reservoirs in Guangdong province during the wet and dry season,and analyzed the effects of iron on the distribution of R.raciborskii and Staurastrum spp.In addition,we also analyzed the effect of iron on the seasonal dynamics of biomass and relative abundance of R.raciborskii and Staurastrum spp.of a typical tropical reservoir.Combining monoculture experiments and field investigation,we try to demonstrate the effect of iron on the growth,distribution and seasonal dynamic of R.raciborskii and Staurastrum spp.The main results were summarized as follows:1.In monoculture experiments,the specific growth rate of R.raciborskii?N8?increased significantly with the increasing iron concentration,the specific growth rate was 0.03±0.01 d^-1 in the treatment without added iron,and the maximum specific growth rate was 0.17±0.01 d^-1when iron concentration was 0.689 mg/L.Siderophore were detected in all treatments of N8.The strain of Staurastrum sp.?FACHB-1449?grew well in all treatments,its specific growth rate was 0.19±0.01d^-1 in the treatment without added iron,the maximum specific growth rate was 0.23±0.01 d^-1when iron concentration was 0.0172 mg/L,and no siderophore were detected in the treatments.2.During the sampling period,Total iron concentration ranged from 0.04 mg/L to 1.16 mg/L,and dissolved concentration ranged from 0.005 mg/L to 0.107 mg/L in surface water of 30reservoirs.Total iron and dissolved concentration were higher in dry season than in wet season.There was a significant difference that iron had an effect on the distribution of R.raciborskii and Staurastrum spp.Dissolved inorganic nitrogen concentration and transparency were the significant factors for distribution of R.raciborskii.R.raciborskii were detected in reservoirs that usually transparency was less than 0.78 meter and the dissolved inorganic nitrogen concentration was less than 0.47 mg/L.When the concentration of dissolved iron was greater than 0.015 mg/L,R.raciborskii had absolute dominance?the dominance was greater than 80%?.Comparatively,temperature was explaining factor for the distribution of Staurastrum.Staurastrum were detected in reservoirs that usually temperature was higher than 28 degrees Celsius,dissolved iron concentration did not significantly explained its distribution.3.The observation of the typical reservoir?Dashahe Reservoir?showed that the factors significantly explaining the seasonal dynamic were different between R.raciborskii and Staurastrum spp.The concentration of dissolved iron concentration and dissolved inorganic nitrogen concentration were the important factors that affect the seasonal dynamics of R.raciborskii.The dissolved iron concentration was positively correlated with the biomass and dominance of R.raciborskii.The dissolved inorganic nitrogen concentration was negatively correlated with the biomass and dominance of R.raciborskii.The concentration of dissolved inorganic nitrogen concentration was the important factors that affect the seasonal dynamics of Staurastrum spp.The dissolved inorganic nitrogen concentration was negatively correlated with the biomass and dominance of Staurastrum spp.And no significant correlation was detected between seasonal dynamic of Staurastrum and dissolved iron concentration.In summary,the iron demand of R.raciborskii could be significantly higher than that of Staurastrum.The supply of dissolved iron significantly affects the distribution and seasonal dynamics of R.raciborskii,but not for the distribution and seasonal dynamics of Staurastrum.Compared with Staurastrum,the supplying of iron could be more important for competitive advantage of R.raciborskii in tropical reservoirs.