Role of sediment structuring by detritus on colonization and interspecific competition of one native and one invasive submerged macrophyte.
The deposition of plant detritus changes sediment features, but little is known about how the accumulation of detritus affects the colonization of invasive and native submerged macrophytes. We tested the predictions that (i) submerged macrophyte occurrences correlate positively with the presence of detritus over sediment; (ii) the colonization of submerged macrophytes increases in the presence of detritus; (iii) the invasive macrophyte Hydrilla verticillata grows faster than the native macrophyte Egeria najas independent of the presence of detritus and (iv) E. najas is affected by competition with H. verticillata, and competition is mediated by the presence of detritus. We evaluated the co-occurrences of submerged macrophytes and detritus in situ and experimentally tested the effects of detritus on submerged macrophyte growth with and without competition. The presence of submerged macrophytes and detritus was negatively correlated in situ. Our experiments indicate that the detritus of emergent macrophytes, including invasive macrophytes, enhances nutrients after reflooding and increases the early growth of submerged macrophytes but does not influence the outcome of competition. Thus, the facilitation of invasive success at the beginning of detritus decomposition (indicated by our experiments) may be counteracted by negative effects after a long decomposition period (indicated by our field data).