Effects of leaf extracts of three terrestrial plants on the growth 

and photosynthetic physiology of Prorocentrum donghaiense

XIANG Shu, CHEN Wenwen, SHEN Anglyu

(College of Marine Ecology and Environment, Shanghai Ocean University, Shanghai201306, China)

Abstract: Harmful algal bloom is an increasingly serious marine environmental problem for aquaculture, fisheries and public health in many coastal areas throughout the world. The dinoflagellate Prorocentrum donghaiense has been a major bloom species in the Yangtze River Estuary and adjacent coastal waters of the East China Sea during the annual blooms that occur in late April and May since 2000. Therefore, the control of P. donghaiense bloom gradually becomes one of research hotspots, and plant allelopathy is one of the important means of biological control of algal blooms due to its advantages such as simple operation, low environmental pressure, no secondary pollution and economic applicability. However, there are few studies on the effective control of P. donghaiense bloom in the East China Sea, especially in the cage culture area where blooms are easy to occur in the offshore area. Moreover, it has been found that the allelochemicals extracted from terrestrial woody plants have a good inhibitory effect on marine algae, however, there are only a few reports describing the inhibition effect of terrestrial plant extracts on bloomforming species, especially for P. donghaiense. We hypothesized that leaf powder of terrestrial plants could build a bloom isolation zone in the cage aquaculture area learned from the principle of forest fire prevention isolation zone. Therefore, in this study, leaves of three common terrestrial plants, Cinnamomum camphora, Nerium indicum and Ginkgo biloba, were selected as algae inhibition materials, and the effects of seawater extracts from these three plant leaves on the growth inhibition effect were studied. Furthermore, the effects of leaf extracts of the three plants on the actual photochemical quantum efficiency (Fv′/Fm′), photosynthesis efficiency (α), relative maximal electron transport rates (rETRmax), and light saturation coefficient (Ik) of P. donghaiense were as well carried out to comprehensively evaluate the regulatory effects of leaf extracts of the three plants on the photosystem PS Ⅱ of algae to provide basis for biological control of P. donghaiense bloom. Results showed that low concentration of the extracts (< 1.0 g·L-1) from the leaves of C. camphora and N. indicum had no obvious inhibitory effect on P. donghaiense during the experiment period, 0.5 g·L-1 and 1.0 g·L-1 G. biloba extracts could slightly stimulate the growth of algae cells when treated for 72 h. However, the three extracts had a significant inhibitory effect on the algae density of P. donghaiense at 48 h (P<0.05) with the increase of extract concentration(> 1.0 g·L-1), and the cell growth inhibition rate of P. donghaiense treated by C. camphora and N. indicum extracts was 100.0% under 3.0 g·L-1 at 96 h, higher concentrations of G. biloba extract (3.0 and 5.0 g·L-1) had a significant effect on the growth of P. donghaiense (P<0.05) as well and the cell growth inhibition rate was 74.9% and 88.7% at 96 h. The 96 h EC50 of P. donghaiense cell growth under C. camphora, N. indicum and G. biloba extracts was 0.84 g·L-1, 1.30 g·L-1 and 1.74 g·L-1, respectively. In addition, there was no significant difference of Fv′/Fm′ values in P. donghaiense under low concentration of extracts (0.1 g·L-1 for C. camphora and N. indicum, and ≤ 1.0 g·L-1 for G. biloba) compared to that of the control group. The algal inhibition ratio of Fv′/Fm′ under 0.5 g·L-1, 1.0 g·L-1 and 3.0 g·L-1 C. camphora extracts was 19.4%, 29.9% and 100.0% after 96 h treatment, respectively. The algal inhibition ratios of Fv′/Fm′ under 0.5 g·L-1, 1.0 g·L-1, 3.0 g·L-1 and 5.0 g·L-1 N. indicum extracts were 11.9%, 19.4%, 97.0% and 100.0% after 96 h treatment, respectively. The algal inhibition ratios of Fv′/Fm′ under 3.0 g·L-1 and 5.0 g·L-1 G. biloba extracts were 88.9% and 100.0% after 96 h treatment, respectively. By analyzing the relativeelectron transfer efficiency (rETR) and fast light response curve, it was found that values of α, rETRmax, and Ik decreased in different degrees with the increase of leaf extracts concentration and treatment time. For example, there was no significant difference of α, rETRmax, and Ik values in P. donghaiense under low concentration of three extracts (< 1.0 g·L-1) compared to that of the control group after 24 h treatment, and values of α, rETRmax, and Ik in P. donghaiense under high concentration of three extracts (≥ 3.0 g·L-1) were significant lower than that in the control group at the end of the experiment (P<0.05). Furthermore, the algal inhibition ratio of α, rETRmax, and Ik under 3.0 g·L-1 C. camphora extract treatment was 100.0%, the algal inhibition ratio of these parameters under 3.0 g·L-1 N. indicum extract treatment was 57.4%, 94.0% and 70.1%, and the algal inhibition ratio of these parameters under 5.0 g·L-1 G. biloba extract was 88.9%, 96.1% and 62.2% after 96 h culture. These results indicated that the photosynthesis of P. donghaiense was inhibited significantly by these extracts. In summary, the leaf extracts of C. camphora, N. indicum and G. biloba have different inhibitory effects on the growth of P. donghaiense. By comprehensively analyzing the changes of P. donghaiense cell density and values of 96 h EC50, it can be found that C. camphora has the best inhibitory effect, N. indicum takes the second place, and G. biloba leaf extract has the lowest inhibitory effect. The difference in algal inhibition efficiency may be due to the different types and contents of allelochemicals contained in the three plants. The photosynthetic parameters of P. donghaiense significantly reduced when treated by high concentration extracts (≥ 3.0 g·L-1) of C. camphora, N. indicum and G. biloba leaves, so they have a significant inhibitory effect on the photosynthesis of P. donghaiense, and future research can focus on the changes of photosynthetic pathways in algae through transcriptomic analysis. The results of this study provide a basis for screening effective algae inhibiting plants for controlling P. donghaiense bloom through allelopathy, especially in the offshore cage culture area.

Keywords: Prorocentrum donghaiense; common terrestrial plants;allelopathy of plants; growth restriction; photosynthetic system