As a widespread phytoplankton species, the coccolithophore Gephyrocapsaoceanica has a significant impact on the global biogeochemical cycle through calcium carbonate precipitation and photosynthesis. As global change continues, marine phytoplankton will experience alterations in multiple parameters, including temperature, pH, CO 2 , and nitrogen sources, and the interactive effects of these variables should be examined to understand how marine organisms will respond to global change. Here, we show that the specific growth rate of G. oceanica is reduced by elevated CO 2 (1000 μatm) in NO À 3-grown cells, while it is increased by high CO 2 in NH þ 4-grown ones. This difference was related to intracellular metabolic regulation, with decreased cellular particulate organic carbon and particulate organic nitrogen (PON) content in the NO À 3 and high CO 2 condition compared to the low CO 2 condition. In contrast, no significant difference was found between the high and low CO 2 levels in NH þ 4 cultures (p > 0.05). The temperature increase from 20˚C to 25˚C increased the PON production rate, and the enhancement was more prominent in NH þ 4 cultures. Enhanced or inhibited particulate inorganic carbon production rate in cells supplied with NH þ 4 relative to NO À 3 was observed, depending on the temperature and CO 2 condition. These results suggest that a greater disruption of the organic carbon pump can be expected in response to the combined effects of increased NH þ 4 /NO À 3 ratio, temperature, and CO 2 level in the oceans of the future. Additional experiments conducted under nutrient limitation conditions are needed before we can extrapolate our findings to the global oceans.

Neopyropia yezoensis is a typical intertidal seaweed and a major mariculture crops in China. The culture area of N. yezoensis has been largely increasing in the past decade. Whether large-scale cultivation of N. yezoensis has a genetic impact on wild populations remains unknown. Here, eleven polymorphic microsatellite markers were developed and applied for the genetic structure analysis of 22 N. yezoensis populations from along the coast of China. The populations were divided into 4 groups based on the Bayesian model-based structure analysis. A significant genetic structure difference was present between the cultivated populations and the wild ones. The 13 wild populations were divided into two distinct groups, with no obvious correlation between the inter-population genetic variation and geographical distance within each group. The average polymorphism of 9 cultured N. yezoensis populations was higher than that of the wild populations, and the percentage of polymorphic loci of the most cultivated populations was at a high level (P=90.91%). It indicated that the germplasm of cultivated N. yezoensis in China are diversified. The genetic differentiation between the cultivated populations and the wild populations decreased with the increasing cultivation time. But the gene flow between the cultivated populations and the wild ones was asymmetric, exhibiting a trend from wild population to cultured population. The result indicated that even if there is a genetic impact of N. yezoensis aquaculture on wild resource, it is a long-term and slow process. This research provided useful insights for future germplasm resource evaluation and genetic breeding of N. yezoensis.

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Bangia fuscopurpurea is a widespread intertidal seaweed that is commercially cultured in China. This seaweed is frequently exposed to hyposalinity stress, but little is known about the adaptation mechanisms. Ascorbate−glutathione (AsA−GSH) cycle plays important roles in many organisms under a variety of abiotic stress, including hyposaline stress. In this study, we investigated the response of key metabolites and enzymes involved in the AsA−GSH cycle of B. fuscopurpurea under hyposalinity, with the addition of exogenous GSH and Lbuthionine-sulfoximine (BSO). The quantification of BfAPX gene expression was assessed across varied treatment regimens. And the putative interaction proteins of BfAPX were screened by yeast two hybrid system. It was found that under hyposalinity (15 and/or 0 psu), the content of reduced glutathione (GSH), total glutathione (GSH+ oxidized glutathione, GSSG) and cysteine, the ratio of GSH/GSSG and ascorbic acid (AsA)/ dehydroascorbic acid (DHA), and the activity of ascorbic acid peroxidase (APX) and monodehydroascorbate reductase (MDHAR) was significantly up-regulated. The hyposality-promoted GSH/GSSG was weakened while the glutathione reductase (GR) activity was promoted by adding exogenous GSH and BSO. The hyposality-promoted AsA/DHA ratio was strengthened by exogenous GSH but weakened by BSO. The dehydroascorbate reductase (DHAR) activity had no significant changes either with or without exogenous GSH under all salinities, while DHAR activity together with DHA content was enhanced by BSO. The expression of APX gene markedly increased under hyposalinity+BSO treatment. Putative interacting proteins of APX, including glutamate dehydrogenase 1a and fructose diphosphate aldolase, were identified through screening. The results indicated that the AsA−GSH cycle was involved in response of B. fuscopurpurea to hyposalinity by means of increasing GSH/GSSG ratio (through promoting GSH biosynthesis pathway and GSH regeneration from GSSG by GR catalyzation) and AsA/DHA ratio (promoting AsA regeneration through MDHAR). These findings would contribute to improve the aquaculture of this promising economic species and unveil how intertidal seaweeds address the global climate challenges.