Dinghui Zou’s research while affiliated with South China University of Technology and other places

Pyropia haitanensis was cultured under two CO2 (410 (LC), 1000 (HC) μL L⁻¹) concentrations and six chloramphenicol (CAP)-methanol solutions (0, 0+methanol, 10, 50, 100, 250 μg mL⁻¹) to investigate the effects of elevated CO2 and CAP on its growth, photosynthesis and biochemical characteristics. HC had no obvious effects on the growth rate (RGR) with CAP in the range of 10 to 100 μg mL⁻¹, but the decrease of RGR by HC was statistically significant with the CAP dosage at 250 μg mL⁻¹. HC had no significant effect on net photosynthetic rates (Pn) in the present of CAP (10-250 μg mL⁻¹). CAP greatly reduced net photosynthesis as well as the maximal photochemical yield (Fv/Fm) and photosynthetic efficiency (αETR). In contrast, the maximum relative electron transport rates (rETRm) were almost constant with the CAP dosage from 10 to 100 μg mL⁻¹. HC significantly increased the energy fluxes (per RC) for absorption (ABS/RC), trapping (TRo/RC) and transport fluxes (ETo/RC) with the dosage of CAP at 250 μg mL⁻¹. Principal component analysis (PCA) indicated that CAP was positively correlated with the synthesis of free amino acids (FAA), contents of umami-, sweet- and essential AA were significantly enhanced with the interaction of HC and higher CAP dosage at 100 μg mL⁻¹, which led to the variation of flavor in algae. Furthermore, phycobiliproteins and soluble protein (SP) contents were remarkably reduced by CAP. Contents of chlorophyll a (Chl a), carotenoids (Car), soluble carbohydrates (SC) and C/N ratios were almost unchanged among treatments. The study indicates that future ocean acidification has no obvious effects on the biomass productivity of P. haitanensis, maintained steady photosynthetic activities with the CAP (within 100 μg mL⁻¹) and induces better flavor. The data obtained have important theoretical relevance for in-depth understanding of algal responses to global changes and oceanic contamination.

Macroalgae provide food for microbial, meio- and macro-faunal communities in coastal ecosystems, thus mediating nutrient dynamics and functions in these ecosystems. Because of this vital role, it is important to clarify physiological information about macroalgae as it reflects their growth potential in the field. In this study, we examined the biomass, pigment content, and photosynthetic O2 evolution rate versus irradiance curves of 18 macroalgal species from the intertidal zone of the Guangdong–Hong Kong–Macao Greater Bay Area, China, and investigated their photosynthetic patterns in relation to phyla characteristics, morphology, and growth locations. The results showed that green algae had the highest maximum photosynthetic O2 evolution rate (Pmax), light utilization efficiency (α), and dark respiration (Rd) among the three macroalgal phyla; the sheet-like macroalgal species had the highest Pmax, α, and Rd among the four morphological categories. The macroalgal species in the upper intertidal zone showed higher Pmax and α and lower saturation irradiance (EK) and compensation irradiance (EC) than those species in the lower intertidal location. The PCA results showed that the biomass of sheet-like macroalgal species was positively correlated with factor PC1 (50.34%), and that of finely branched species was negatively correlated with factor PC2 (25.17%). In addition, our results indicate that the light absorption and utilization capabilities of macroalgae could determine whether they could dominate the intertidal zone and that their photosynthetic characteristics could be used as a potential indicator of their biomass distribution in the Greater Bay Area.

Seaweed farming may alleviate coastal eutrophication and acidification, and contribute to the coastal ecosystems. Sargassum fusiforme has nutritional and medicinal benefits, and its cultivation in China has expanded in recent years. However, the environmental benefits of coastal S. fusiforme farming to the surface seawater remain unclear. In this study, we compared cultured and non-cultured areas, during the culture and non-culture seasons, in the main S. fusiforme coastal growing area of China. The results showed that S. fusiforme farming slightly increased the dissolved oxygen content and pH of surface seawater but decreased the nutrient content and chemical oxygen demand. Furthermore, the eutrophication level of seawater decreased by 36% on average. In the later stage of cultivation, with large S. fusiforme biomass, the eutrophication level of the surface seawater decreased by >50%. In addition, S. fusiforme farming increased the phytoplankton biomass and diversity index, and in conjunction with environmental factors, altered the phytoplankton community structure. After the harvest of S. fusiforme, the dominant phytoplankton mostly comprised red tide microalgae, and their abundance was relatively large. Experiments and harvest evaluations showed that S. fusiforme cultivation removed 8082 t of carbon, 642 t of nitrogen, and 61 t of phosphorus from coastal China during one culture period. This study showed that large-scale cultivation of S. fusiforme can slightly improve coastal surface seawater quality by removing nutrients, alleviating eutrophication, and actively altering phytoplankton community structure. These environmental benefits may play an important role in maintaining the health of coastal ecosystems.

Based on the yields of cultivated seaweeds of Guangdong Province in the past 20 years, this study evaluated the values of ecosystem service functions, including carbon sink and oxygen release, removal of N and Pi nutrients, and absorption of heavy metals. The results indicated that all the ecological values of cultivated seaweeds showed a rising trend from 2000 to 2019. The total ecosystem service value increased from $2.50 million in 2000 to$10.36 million in 2019 at an average annual growth rate of 8.41%. The values of carbon sink and oxygen release, removal of N and Pi nutrients and absorption of heavy metals increased from $10.71 million,$12.98 million and $1.25 million in 2000 to$41.76 million, $56.64 million and$5.25 million in 2019 respectively. Besides, the value of carbon sink and oxygen release and removing N and Pi nutrients contributed significantly to the total ecosystem service value, accounting for 41.36% and 53.15%, while the annual average value of absorption of heavy metals only accounted for 5.49%. In addition, since the market price of Saccharina japonica, Gracilaria spp. and Eucheuma denticulaturn is low, their economic profits are less than the ecological services. They should be given ecological compensations of 1.39/kg, 1.50/kg, and $1.27/kg respectively based on the market price in China. This study illustrates clearly huge ecological values of cultivated seaweeds in carbon emission reduction and improving coastal eutrophication. On the other hand, ecological compensations can promote the healthy development of seaweed cultivation industry and maximize the ecosystem service functions of seaweeds.

Biochemical compositions and photosynthetic characteristics of three naturally cohabitated macroalgae, Ulva fasciata, Sargassum hemiphyllum and Grateloupia livida, were comparably explored in the field conditions in Daya Bay, northern South China Sea, as well as their responses to temperature rise. Chlorophyll a (Chl a) and carotenoids contents of U. fasciata were 1.00 ± 0.15 and 0.57 ± 0.08 mg g⁻¹ in fresh weight (FW), being about one- and two-fold higher than that of S. hemiphyllum and G. livida; and the carbohydrate content was 20.3 ± 0.07 mg g⁻¹ FW, being about three- and one-fold higher, respectively. Throughout the day, the maximal photochemical quantum yield (FV/FM) of Photosystem II (PS II) of these three macroalgae species decreased from morning to noon, then increased to dusk and kept steady at nighttime. Consistently, the rapid light curve-derived light utilization efficiency (α) and maximum relative electron transfer rate (rETRmax) were lower at noon than that at morning- or night-time. The FV/FM of U. fasciata (varying from 0.78 to 0.32) was 38% higher than that of G. livida throughout the day, and that of S. hemiphyllum was intermediate. The superoxide dismutase (SOD) and catalase (CAT) activities in U. fasciata were lower than that in S. hemiphyllum and G. livida. Moreover, the rises in temperature species-specifically mediated the damage (k) caused by stressful high light and the corresponding repair (r) to photosynthetic apparatus, making the r/k ratio increase with the rising temperature in U. fasciata, unchanged in S. hemiphyllum but decreased in G. livida. Our results indicate that U. fasciata may compete with S. hemiphyllum or G. livida and dominate the macroalgae community under aggravatedly warming future in the Daya Bay.

Atmospheric CO2 concentration is predicted to nearly double by the end of this century. There are a large number of reports on the effects of elevated atmospheric CO2 concentrations on seaweeds. However, the investigation concerning the impacts of combined effects of elevated atmospheric CO2 concentrations and incubation densities on seaweeds is very limited. The marine macroalga Pyropia haitanensis was cultured in jars containing 10 L seawater under outdoor conditions. The treatments were designated as ambient (390 μL·L⁻¹) and elevated (800 μL·L⁻¹) CO2 concentrations, and three incubation densities (1.0, 2.0, and 4.0 g FW·L⁻¹), to examine the effects of elevated CO2 on growth, nutrient uptake percentage, and photosynthesis on the algae grown at different incubation densities conditions. The results showed that elevated CO2 significantly enhanced the relative growth rate (RGR) and nutrient uptake percentage, but inhibited photosynthesis irrespective of the incubation density. The RGR and photosynthesis of P. haitanensis were decreased with increased incubation density. The RGR was even negative at high incubation density of 4.0 g FW·L⁻¹. The nutrient uptake percentage was enhanced with increasing incubation density, regardless of the CO2 concentration in culture. Our results suggested that lower density-grown P. haitanensis was more responsive to CO2 enrichment than higher density-grown algae.

In nature growing of macroalgae increases their biomass densities, which alters the surrounding environments and in turn affects their photophysiologies. Photosynthetic performances were explored for two common and widely spread macroalgae species, a branched Gracilaria lemaneiformis (Rhodophyta) and a thin, sheet-like Ulva conglobata (Chlorophyta), responding to a matrix of biomass densities (1.0, 2.0 and 4.0 g L⁻¹) and pCO2 (400 and 800 ppm). In all three biomass densities the photosynthetic capability of G. lemaneiformis was enhanced by elevated pCO2, but that of U. conglobata was reduced. The photosynthesis versus irradiance (P vs. E) curve-derived parameters [i.e., light-utilizing efficiency (α), saturating light irradiance (EK) and maximum photosynthetic rate (Pmax)] of G. lemaneiformis generally increased with increasing densities under both ambient and elevated pCO2, as did the dark respiration (Rd); but the α, EK, Pmax and Rd of U. conglobata decreased. The elevated pCO2 increased the α, EK and Pmax but decreased the Rd of G. lemaneiformis in all three densities, while the opposite effects occurred in the U. conglobata. Accordingly, the elevated pCO2 enhanced the integrated daily production of G. lemaneiformis by 62%, but reduced that of U. conglobata by 26%, indicating that rising pCO2 favors the photosynthesis of branched G. lemaneiformis but reduces that of sheet-like U. conglobata. We propose that the changes in algal density greatly mediate their physiological responses to increasing ambient CO2.

Both temperature and nutrient nitrogen are rising in worldwide aquatic ecosystems. To explore their interactive impacts on algal physiology, we measured the growth, cell components, photosynthesis, and dark respiration of a farmed green alga, Caulerpa lentillifera, under a matrix of temperatures (low, 22 °C; high, 27 °C) and nitrogen concentrations (low, 47 μmol L−1; medium, 188 μmol L−1; high, 750 μmol L−1). The relative growth rate (RGR) was less than 1.0% day−1 at low temperature, which was ~ eightfold higher at high temperature, with no significant effect of nitrogen. Pigment contents of chlorophyll a (Chl a) and carotenoids (Car) and soluble protein content increased with increasing nitrogen levels. High temperature reduced Chl a content under lower nitrogen and enhanced Car contents under higher nitrogen, but had a limited effect on proteins. Photosynthetic parameters, i.e., light-utilized efficiency (α) and maximum photosynthetic rate (Pmax), and dark respiration rate (Rd) increased with increasing nitrogen levels at low temperature. High temperature enhanced the α, Pmax, and Rd under low nitrogen, but reduced them under high nitrogen. Moreover, high temperature lowered both superoxide dismutase (SOD) and catalase (CAT) contents, indicating the beneficial effects on metabolism of C. lentillifera and thus the growth. In addition, our results indicate that the temperature-caused effects on photosynthesis and respiration of C. lentillifera are reversed by increased nitrogen levels.

Nitrate reductase (NR) is an intracellular enzyme commonly occurring in the cytoplasm. This enzyme is the rate-limiting enzyme in nitrate assimilation, and its activity is strongly related to the bioavailability of nitrate. Here a method is described to determine the in vivo NR activity by using the marine macroalga Gracilaria lemaneiformis as the experimental organism.

Dark respiration (mitochondrial respiration) occurs both in the light and in darkness. Here the principle of determination of mitochondrial respiration in the light is described. The Kok method is introduced to estimate the rate of mitochondrial respiration in the light by using a LCA-4infrared gas analyzer with Ulva lactuca thalli as an example.