Recovery limitation of endangered Ottelia acuminata by allelopathic interaction with cyanobacteria

Abstract

Recovery of rare aquatic plant species in eutrophic lakes often fails, and mutual allelopathic effects between cyanobacteria and submerged macrophytes are one potential reason. In this study, we investigated allelopathic interactions between cyanobacteria and Ottelia acuminata, an endangered submerged macrophyte species in China. We tested effects of Microcystis aeruginosa on germination and seedling growth of two varieties of O. acuminata (O. acuminata var. crispa, OAC; and O. acuminata var. songmingensis, OAS) and vice versa effects of culture water of young seedlings and mature macrophytes on the growth of M. aeruginosa. We found that: (1) The culture water of mature O. acuminata (both OAC and OAS) allelopathically promoted M. aeruginosa growth, while seedlings had no effect. (2) M. aeruginosa exudates and extracts significantly promoted or inhibited seed germination of O. acuminata; (3) both exudates and extracts significantly decreased the seedling vitality of OAC and OAS. (4) M. aeruginosa exudates and extracts inhibited seedlings growth of O. acuminata, especially growth of roots and the second true leaf. (5) Allelopathic effects of M. aeruginosa exudates were stronger than those of extracts, and OAC showed stronger resistance to cyanobacteria than OAS. Our results indicate that cyanobacteria can allelopathically inhibit O. acuminata mainly by their exudates, while mature O. acuminata stimulate cyanobacteria growth. Such negative effects of cyanobacteria may contribute to the disappearance of O. acuminata and also slow down their recovery in eutrophic lakes.