Does clonal fragmentation of the floating plant Eichhornia crassipes affect the growth of submerged macrophyte communities?

Abstract

Few studies have tested the effect of clonal fragmentation at the community level. Floating plants and submerged macrophytes can coexist, and the presence of floating plants may greatly restrict the growth of submerged macrophyte communities. Clones of floating plants are frequently fragmented by disturbance, but little is known about how clonal fragmentation of floating plants affects the growth of submerged macrophyte communities and whether such effect depends on the intensity (frequency) of fragmentation. We assembled experimental aquatic communities consisting of four submerged macrophytes (Hydrilla verticillata, Ceratophyllum demersum, Chara fragilis and Myriophyllum spicatum), and grew them without the floating plant Eichhornia crassipes, with an intact clone of E. crassipes, or with a clone fragmented every 5, 10 or 15 days. Clonal fragmentation, irrespective of the frequency, did not significantly affect the growth of the floating plant. Consequently, it did not significantly affect the growth of the submerged macrophyte community or that of each of the four submerge macrophytes. However, compared to the treatment without E. crassipes, the presence of E. crassipes significantly decreased the biomass of the macrophyte community because it greatly decreased the biomass of the most abundant species H. verticillata. Therefore, the presence of floating plants can influence the establishment of submerged macrophyte communities, but clonal fragmentation of floating plants may not. To restore submerged macrophyte communities, measures should be taken to restrict the spread of floating plants, and breaking clones of floating plants may not be an effective measure.