Photosynthetic comparison between economic seaweed Sargassum fusiforme and epiphytic Ulva lactuca under high CO2 concentration
To understand the effects of elevated atmospheric CO2 concentration and competition of epiphytic algae on the growth and photosynthesis of Sargassum fusiforme,S.fusiforme and its main epiphytic macroalgae Ulva lactuca were used to compare their photosynthetic characteristics after monoculture and bi-culture treatments.The results showed that,in monoculture,high CO2 concentration increased the maximum electron transfer rate(rETRm)of 5.fusiforme,but decreased its dark respiration rate(Rd)and ratio of dark respiration rate to total photosynthetic rate(Pg),whereas the Rd and Rd/Pg ratio of U.lactuca was not significantly affected.Additionally,the inhibitory effect of transient high temperature(25 ℃)on the maximum quantum yield(Fv/Fm)and rETRm of photosystem Ⅱ(PS Ⅱ)of S.fusiforme was significantly higher than that of U.lactuca.In bi-culture,the photosynthetic activity of S.fusiforme was inhibited and significantly lower than that of U.lactuca,and the rETRm of U.lactuca was not significantly affected.Moreover,when the transient temperature was 25 ℃,S.fusiforme grown in bi-culture condition had the lowest values of rETRm,Fv/Fm and net photosynthetic rate(Pn)and the highest values of Rd.Moreover,the Q10 value of Rd of S.fusiforme was higher than that of U.lactuca.In bi-culture,the change of transient temperature exhibited no significant effect on the rETRm of U.lactuca.This study showed that high CO2 concentration improved the photosynthetic capacity of S.fusiforme but had no significant effect on the photosynthetic capacity of U.lactuca.The photosynthesis and respiration of S.fusiforme were sensitive to temperature changes,while U.lactuca had ability to adapt to temperature rising,showing interspecific competitive advantage under bi-culture condition.
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