Optimization of Combined Submerged Macrophyte Planting Conditions for Inhibiting Algae by Response Surface Methodology

Combined planting of submerged macrophytes could be an effective way of controlling algal blooms in landscape waters. In this study, the algal inhibition of single and combined planting of Hydrilla verticillata (A) and Myriophyllum spicatum (B) were explored. The optimized combined planting conditions were investigated using the central composite design. The results showed that the combined planting had a synergistic algal-inhibiting effect. Its inhibition (I (K)) is about 10.8% higher than that of single planting with the same density. The synergism of the combined planting may be due to the different ways in which the two plants inhibit the algal growth. H. verticillata inhibited the algal biomass and M. spicatum inhibited the algal specific growth rate. When the density of H. verticillata and M. spicatum were 7.2 g/L and 6.7 g/L, the value of I (K) reached a maximum 92.2%. Although increasing planting density would improve the algal inhibition, high planting density was not beneficial for the growth of plants. Moreover, no further significant improvement was shown with the increasing planting density when the value of I(K) was higher than 90%. Therefore, the cost-effective combined macrophyte density was 11.6 g/L and the value of A/B ranged from 1.05 to 1.07, where the value of I (K) could achieve 90%. This study can provide a practical basis for using macrophytes to control algal blooms.

Higher-order interaction inhibits bacterial invasion of a phototroph-predator microbial community

In nature, the composition of an ecosystem is thought to be important for determining its resistance to invasion by new species. Studies of invasions in natural ecosystems, from plant to microbial communities, have found that more diverse communities are more resistant to invasion. It is thought that more diverse communities resist invasion by more completely consuming the resources necessary for would-be invaders. Here we show thatEscherichia colican successfully invade cultures of the algaChlamydomonas reinhardtii(phototroph) or the ciliateTetrahymena thermophila(predator), but cannot invade a community where both are present. The invasion resistance of the algae-ciliate community is due to a higher-order (3-way) interaction that is unrelated to resource consumption. We show that the mechanism of this interaction is the algal inhibition of bacterial aggregation which leaves bacteria vulnerable to ciliate predation. This mechanism of invasion resistance requires both the algae and the ciliate to be present and provides an example of invasion resistance through a trait-mediated higher-order interaction.

Inhibitory effects of Pontederia cordata on the growth of Microcystis aeruginosa

This study investigated the effect of Pontederia cordata on Microcystis aeruginosa growth in three different experimental settings: (i) co-cultivation, (ii) exposure of cyanobacteria to culture water of P. cordata, and (iii) exposure of M. aeruginosa to organic extracts of P. cordata. Results showed that the growth of M. aeruginosa was significantly inhibited by co-cultivation, with the highest inhibition rate of 61.9% within 5 days. Moreover, 95% culture water with P. cordata could markedly inhibit the growth of M. aeruginosa, with inhibition rate of 98.3% on day 6, indicating that most of the algal cells died. The organic extracts of fibrous root showed stronger inhibition effect than the leaf and stalk extracts. Acetone extract of fibrous root showed the strongest inhibitory effect on M. aeruginosa. Different components of 80% acetone extracts from fibrous root exhibited varied effects on the growth of M. aeruginosa. Ethyl acetate and water components had strong inhibition effects on M. aeruginosa. By contrast, n-butyl alcohol components had weak inhibition effects, and hexane components even promoted the growth of M. aeruginosa. Allelochemicals of P. cordata were primarily released into the water through the fibrous root. Results indicated that P. cordata can be applied in environmentally friendly algal inhibition.