Aquatic carnivorous plants fill gaps in the functional niches of macrophytes: Intra-species variability and group strategies

The inclusion of aquatic carnivorous plants (ACP) in global plant functional assessment is a key step to fully understand the functional space of macrophytes. For this purpose, we measured functional traits of ACP, focusing on the leaf economics spectrum, describing the functional space of ACP and comparing it with that of four widespread macrophyte growth forms (ceratophyllids, rooted submerged hydrophytes, nymphaeids and lemnids). Eight ACP species (Aldrovanda vesiculosa, and seven Utricularia spp.) were sampled in the Třeboňsko Biosphere Reserve and Protected Landscape Area (Czech Republic). Given the peculiar morphology of the target species, this required standardizing the selection of shoot portions for functional analysis by identifying “functional units” (fu) to be considered homologous to leaves. The analyzed ACP show wide functional variation, reflected in four different functional clusters. Aldrovanda vesiculosa differs markedly – in investment in carnivory and carbon content – from the Utricularia species, which in turn are characterized by significant differences, especially in fu size, number of traps, dry matter content, and chlorophyll-a content. Moreover, the functional space of ACP diverges significantly, with minimal overlap (∼10 %), with submerged species. All investigated ACP show traits related to rapid turnover of fu, confirming the tendency to adopt an acquisitive strategy. This, however, seems to be efficient only under conditions typical of these species (i.e. in nutrient-poor aquatic ecosystems). Our results considerably expand the available information on the functional space of aquatic macrophytes including ACP, clearly indicating the next steps for a full functional understanding of these species.