The Influence Of Submerged Macrophyte On Epiphytic Algae

Epiphytic community, which can be widely observed in large and medium-sized shallow lakes, is a complex community consisting of organisms such as living algae, bacteria and fungi, covering the surfaces of large submerged plant. Epiphytic community has a specific species composition and spatial structure.At the same time, it shows closely relationship with the host plants and surrounding water environment, which plays an important role in aquatic ecosystems. Therefore, studying how different submerged macrophytes (exotic species with their native congeners) influence on native epiphytic algae, contributes to understanding the allelopathic algal inhibiting effects of aquatic plants, the interspecific competition of submerged plants and interaction mechanism between aquatic plants and epiphytic algae, which is of great importance for ecological management of lake eutrophication and ecological impact assessment of biological invasion.This study compared the difference of community composition and structure characteristics of epiphytic algae which attached to native species. Then we used two exotic submerged macrophytes compared with their native congeners to explore how different dose leaching solution influence on growth and community composition of native epiphytic algae. The further research was a comparison of chemical components in leaves leaching solution between exotic submerged macrophytes and their native species by GC-MS technology. Next, we made an exploring about different types and dose of chemical components influencing on growth status of the several kinds of common epiphytic algae, the chemical components which are secreted from all these four submerged macrophytes or secreted only from exotic species. We compared the differences how exotic submerged macrophytes and native species influence on epiphytic algae which attached to native species. The results showed that:(1) We compared the differences of community composition and structure characteristics of epiphytic algae which attached to native submerged macrophytes H. verticillata and M. spicatum.12 species of epiphytic algae which attached to H. verticillata were observed by microscopic examination, while the other epiphytic algae community was consisted of 26 species. The epiphytic algae community mainly includes Chlorophyta, Cyanophyta, Bacillariophyta, Euglenophyta and several species of Xanthophyta. M. spicatum has more complicated epiphytic algae community than H. verticillata. The species richness index and species diversity index of epiphytic algae community on M. spicatum respectively were 3.696 and 3.117, while the two indexes of epiphytic algae community on H. verticillata respectively were 2.061 and 2.028.(2) The leaves leaching solution of exotic submerged macrophyte species(E. nuttallii and M. aquaticum) and their native congeners (H. verticillata and M. spicatum) all had obvious influences on epiphytic algae which attached to the native species, it significantly decreased the total number of algal cells and made the epiphytic algae community composition tend to be more simple.The exotic species used in our study showed stronger algal inhibiting effect on epiphytic algae than native ones, and more significant in high doses.The four submerged macrophyte leaching solutions all reduced total number of native epiphytic algae, and showed the trend that low dose of leaching solution can promote the species richness and the diversity of the epiphytic algae community, while high dose showed inhibiting effect. The study also showed that exotic species had more significant negative effects. Besides, we found that fresh plant materials showed a more significant allelopathic algal inhibiting effect than dry ones.(3) This study made a comparison of chemical components in four submerged macrophyte (H. verticillata, M. spicatum, E. nuttallii and C. caroliniana) leaves leaching solution by GC-MS technology and found obvious difference between exotic species and native ones. The selected chemical components were 2-Naphthalenamine,N-phenyl- which is secreted from all of these four submerged macrophytes, 1-Propanone,1-phenyl- which is secreted only from E. nuttallii, and Benzobfuran,2,3-dihydro-which is secreted only from C. caroliniana. Our results showed that these chemical components significantly reduced the algal cell concentration and chlorophyll content of S. obliqnus and C. vulgaris, however, the inhibiting effect on S. quadricanda was weaker. In addition, 1-Propanone,1-phenyl-showed the strongest inhibiting effects, followed by Benzobfuran,2,3-dihydro-, the weakest is 2-Naphthalenamine,N-phenyl-, this means that the chemical components secreted from the exotic submerged macrophytes (E. nuttallii and C. caroliniana) have stronger allelopathic algal inhibiting effects on epiphytic algae, and the special substances from exotic plants may show stronger inhibiting effects than common substances.(4) There were significant differences in the responses of these three epiphytic growth indicators (relative growth rate, algal cell concentration and chlorophyll content) on the different chemical components doses and processing time. The lower dose of chemical components can promote the growth of epiphytic algae, while the higher dose showed inhibition effects, and the algae had obvious and steady growth curve as the processing time. This may be related to the accumulation effect of aquatic plants allelopathy, the chemical active component released by host plant often need to reach certain amount that may show the significant inhibiting effect.Through the study of submerged macrophytes influencing on the epiphytic algae, we found that exotic species show more significant inhibition on native epiphytic algae than the native ones, and the chemical components secreted only from exotic submerged macrophytes show stronger allelopathic algal inhibiting effects. The results of our study had reference value on the study of the submerged macrophyte epiphytic community, the interspecific competition of submerged plants and exotic submerged plants invasion.