Effects of shade on individual ramet growth and on clonal growth of the aquatic fern Salvinia auriculata (Salviniaceae)

Abstract

Light intensity is among the major environmental factors determining the ecological distribution of any plant. The effects of light availability on aquatic plants continue to be discussed, as some species show higher growth under full sun conditions and other species show reduced growth. The aim of this study was to test the effects of different shade levels on ramets and clonal growth of the fern Salvinia auriculata. We hypothesized that the ramets grow better under shade conditions over time as in most land ferns. We performed a greenhouse experiment, putting plants under three treatments: control (0% shade), 30% shade, and 70% shade. We monitored the growth of individual ramets as well as clonal spread for 30 days. The number of new ramets (clonal growth) increased exponentially in the three treatments, however this number was higher in shade than in full sun plots. The size of floating leaves, submerged leaves, and rhizomes was higher under shade treatments compared to individuals under sun treatment. Our results showed that S. auriculata has a high growth performance under shade environments, including both clonal growth and the size of individual ramets, similar to most land ferns. This species appears highly plastic as it also thrives under bright sun, which appears to be a consistent pattern among fern species in both terrestrial and aquatic environments. Because shade has been proposed as a treatment to control and manage aquatic plants, application of this treatment should be carefully considered depending of the species, especially when it involves aquatic fern species.