Ramet versus sporocarp production in the aquatic fern Salvinia auriculata (Salviniaceae): the role of shading

Abstract

Aquatic plants exposed to environmental changes exhibit plastic responses, resulting in functional adjustments to reduce stress effects. Lack of light can limit plant development and can affect biomass allocation and reproduction, stressing plants and sometimes halting their growth. Shading techniques have been used to control the excessive growth of weed plants, such as the aquatic fern Salvinia auriculata Aublet that can form dense mats on the water surface, causing problems in water use. We used shading nets in a greenhouse experiment to evaluate the effect of shade on the biomass of S. auriculata, and to determine if the fern changes its allocation of biomass to sexual (sporocarps) or asexual (buds) reproduction under different shade levels (full-sun control, 35% shade, and 70% shade). Under shade conditions, ramet biomass decreased and no sporocarps were produced, although the number of buds increased. Production of structures for sexual reproduction incurs a high energy cost, so S. auriculata invested in bud production (clonal reproduction). The differing energy requirements resulted in a significant trade-off between bud and sporocarp production. In conclusion, our study indicated that shading is not an efficient control technique for S. auriculata since it did not affect the clonal reproduction, a strategy that accelerates colonisation and facilitates rapid spread.