Ecophysiological determinants of plant performance under flooding: a comparative study of seven plant families

1 Plant performance of species in river floodplains is negatively affected by submergence, due to severely hampered gas exchange under water. Several individual traits have been shown to determine flooding tolerance, but the interrelationships among these traits and their effects on plant performance still remain largely unknown. 2 Here, we aim for a more coherent understanding of submergence tolerance, by investigating whether different traits are alternative strategies to enhance survival under water or whether these traits act in concert. 3 Because responses to submergence may be taxon-specific, we chose a multiple-species approach that allowed phylogenetic comparisons. The phenotypic traits investigated in the current study were constitutively different in species originating from frequently flooded habitats than in species from dry habitats: wet species were taller and had a higher specific leaf area (SLA), chlorophyll content, aerenchyma content, and longer longevity of terrestrial and 'aquatic' leaves compared with species from dry habitats. Moreover, the frequently flooded species appeared to be more plastic for these traits in response to submergence. Neither the phylogenetic component nor the light climate under water were important for the expression of the submergence-related traits. 4 Principal component analysis (PCA) showed that these traits were divided in two independent clusters structured either around the petiole (i.e. aerenchyma content and shoot length) or the leaf lamina (i.e. SLA, chlorophyll content and leaf longevity). Shoot length and aerenchyma content of the petiole were also positively correlated, albeit not significantly. A positive correlation between SLA and leaf longevity was observed under water, indicating that thinner leaves may have an increased potential for gas exchange, resulting in increased leaf longevity and plant survival. 5 Path analyses indicated significant positive effects of the two trait clusters on plant performance during full submergence. 6 Our study shows that multiple ecophysiological traits act in concert to fine tune responses to dynamic and unpredictable environments such as river floodplains.