科研之友
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摘要
The common brown macroalga Sargassum hemiphyllum forms extensive beds in the intertidal zones of temperate coasts, which has important ecological roles for a healthy coastal ecosystem. Efficient production of its seedlings is in great need for both natural resource restoration and aquaculture of this species. Fouling by the diatom Cylindrotheca closterium is a main constraint for seedling cultivation of S. hemiphyllum. In this study, we inves-tigated the interactions between S. hemiphyllum and C. closterium under different nutrient conditions. The two algae were incubated together (co-culture mode) or separately (mono-culture mode). NO3- and PO43- were used as nitrogen (N) and phosphorous (P) sources, respectively, and eight N concentrations were prepared from 0 to 300 mu M with a N:P ratio of 10:1. The results showed that the growth of C. closterium was inhibited by S. hemiphyllum only when the N concentration was 5-50 mu M, whereas the growth of S. hemiphyllum was inhibited by C. closterium regardless of N concentration in the culture medium. These results indicated that the inhibitory effects of the two algae on each other are species-specific and dependent on N availability. Inhibition was most evident under the nutrient-limited condition and was alleviated by sufficient N in the culture medium. At 5-25 mu M N, co-culture decreased the tissue N and P contents and the maximal quantum yield of photosystem II (Fv/fm) of S. hemiphyllum, which resulted in N-and P-limited status and decreased growth. Meanwhile tissue N and P contents and Fv/fm of C. closterium were stimulated in co-culture mode, but its growth was still suppressed, suggesting an allelopathic effect from S. hemiphyllum. At 100-300 mu M N, the tissue N and P accumulation, Fv/fm, and growth rate of co-cultured C. closterium were higher than the respective mono-culture values, indicating that it had a nutrient competitive advantage over the co-cultured S. hemiphyllum and so had an inhibitory effect on S. hemiphyllum. The competitive and inhibitory effects of C. closterium on S. hemiphyllum were relatively lower when the N concentration was in the 5-50 mu M range. However, S. hemiphyllum grows well when N concentration is > 25 mu M and didn't suffer a N-and P-limitation. Thus, we suggest that the nutrient condition in the culture medium of S. hemiphyllum be set at 25-50 mu M N with a N:P ratio of 10 to weaken the adverse effects of the fouling C. closterium.
