The number of extinct or urgently threatened species rapidly accelerates
and almost one-third of freshwater biodiversity face extinction.
Consequently, the need to identify means to help protect and conserve
species is paramount. Here, we explore mechanistic links between
eutrophication and species declines. Specifically, we hypothesised that
declining species within the plant genus Potamogetonaceae exhibit a low
degree of ecophysiological trait plasticity and a suboptimal trait
expression under enhanced levels of nutrients rendering these species
prone to extinction under eutrophication. Individuals of five species
including common species (S. pectinatus, P. perfoliatus and P. crispus)
and declining species (P. compressus and P. gramineus) were transplanted
into three replicate lakes along a gradient in nutrient availability.
After four weeks, ecophysiological traits were measured and the
phenotypic plasticity was assessed. We found that declining species were
unable to convert increased nutrients availability into enhanced rates
of growth. Additionally, we found that the ecophysiological plasticity
was lower both regarding nutrient acquisition and the ability to adjust
physiologically to maximise growth under the prevailing nutrient regime.
We conclude that the mechanisms behind species declines link to
inappropriate ecophysiological adjustments under nutrient enrichment
that have severe consequences for their competitive capabilities,
eventually leading to local extinction.