| Macroalgae are an important part of the coastal marine primary productivity. As a specie of green tides algae, it is important that the effects of environmental factors on Ulva prolifera reflect the response of photosynthetic physiological characteristics in macroalgae to the changes of marine environment. In this paper, we study the effects of the different CO2 concentrations, heavy metal copper, temperature, irradiance and modes of reproduction on Ulva species by comparing the growth, photosynthesis, fluorescence parameters and pigments contents. The main results are as follows:When Ulva linza was cultured at different CO2 concentrations, contrast to the low CO2 concentration (LC), high CO2 concentration enhanced the RGR, relative electron transport rate (rETR), NPQ, maximum electron transport rate (ETRmax) and electron transport efficiency (a). When the thalli was cultured at low irradiance, there was not significant difference between photosynthesis rate of LC and HC. However, under high irradiance, high CO2 concentration had significant inhibition effects on the photosynthesis rate at different pH value. The results showed that acid zones and internal CA constituted functional elements in the CCMs of U. linza grown in the long-term CO2 condition and acid zones was the most important tools for the thalli to acquire exogenous carbon source. Contrastingly, AZ, tris buffer and EZ all inhibited the net photosynthetic rate of thalli grown in ambient CO2 condition. This means that acid zones, external and internal CA work together in the thalli grown in natural seawater medium and the acquirement of exogenous carbon source in the thalli was attributed to the collaboration of acid zones and external CA.Copper inhibited the growth and photosynthesis of Ulva prolifera, with the decrease of electron transport rate, photosynthetic efficiency and light saturation point. Especially, the inhibition of RGR increased with the increasing copper concentrations. The enhanced CO2 concentration can reduce the toxicity on Ulva prolifera, leading to enhancing RGR, with the increasing of electron transport rate, photosynthetic efficiency, light saturation point and pigments contents. However, under the stress of high CO2 and copper concentrations, the photosynthesis, electron transport and pigment of Ulva prolifera was decreased, resulting in decreasing RGR.The main factor resulting in Ulva prolifera floating on the surface of seawater is the photosynthetic rate of thalli. Ulva prolifera is usually found in April then blooms in June or July, finally die out in August. Under the coaction of temperature and irradiance, when the photosynthesis of Ulva prolifera increased, which resulted in increasing RGR and stronger branches, the thalli can float on the sea surface by airbags. When the photosynthesis declined, leading to branches reducing and thinning, the thalli sink.We got the thalli grown from the spores (ST) and that from vegetative multiplication (VT) by using enclosure experiment in situ and then estimated the difference of photosynthetic performance between ST and VT by comparing the growth, photosynthesis and fluorescence parameters of VT and ST. Our results showed that the growth rate of ST was significantly higher than VT by 61.27% and the maximum photosynthetic rate Pmax, photosynthetic efficiency a and P/R of ST were significantly higher than those of VT by 25.33%,14.93%,134.69%, respectively. While the respiration rate and light compensation point for photosynthesis of ST were lower than those of VT by 45.7% and 52.2%, respectively. It showed that ST possessed better growth advantage compared with VT. Relative electron transport rates (rETR) and non-photochemical quenching (NPQ) of VT were significantly higher than that of ST, and had a higher non-photochemical quenching in the high light. These results implied that compared with the thalli grown from the spores, the thalli grown through vegetative multiplication had stronger high light adaptation ability. |
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